1.
Isocyanide
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An isocyanide is an organic compound with the functional group -N≡C. It is the isomer of the cyanide, hence the prefix iso. The organic fragment is connected to the group via the nitrogen atom. They are used as building blocks for the synthesis of other compounds, the C-N distance in isocyanides is very short,1.158 Å in methyl isocyanide. The C-N-C angles are near 180°, akin to carbon monoxide, isocyanides are described by two resonance structures, one with a triple bond between the nitrogen and the carbon and one with a double bond between. Surprisingly, the one, with a carbenic character is the more important. Nevertheless, the π lone pair of the nitrogen, responsible of the zwitterionic structure, isocyanides are best shown as a mixture of both resonance structures. 5 Hz for the isocyanide 13C nucleus and 5–14 Hz for the 13C nucleus which the group is attached to. To quote from Lieke, Es besitzt einen penetranten, höchst unangenehmen Geruch, das Oeffnen eines Gefässes mit Cyanallyl reicht hin, note that in Liekes day, the difference between isocyanide and nitrile was not fully appreciated. Ivar Karl Ugi states that The development of the chemistry of isocyanides has probably suffered, through the characteristic odor of volatile isonitriles, which has been described by Hofmann and Gautier as highly specific, almost overpowering, horrible, and extremely distressing. It is true that many workers in this field have been turned away by the odour. Isocyanides have been investigated as potential non-lethal weapons, some isocyanides convey less offensive odours such as malt, natural rubber, creosote, mild cherry or old wood. Non-volatile derivatives such as tosylmethyl isocyanide do not have objectionable odors, while some isocyanides are toxic, others exhibit no appreciable toxicity for mammals. Referring to ethyl isocyanide, toxicological studies in the 1960s at Bayer showed that oral, the first isocyanide, allyl isocyanide, was reported in 1859 by the chemist Lieke from the reaction of allyl iodide and silver cyanide. Normally the alkylation of a metal cyanide gives a nitrile. Commonly, isocyanides are synthesized by dehydration of a formamide, the formamide can be dehydrated with phosphorus oxychloride, phosgene, diphosgene, or the Burgess Reagent. RNHCH + POCl3 → RNC + PO2Cl +2 HCl In the carbylamine reaction potassium hydroxide reacts with chloroform to produce dichlorocarbene and this then converts primary amines to isocyanides. As it is effective for primary amines it is used as a chemical test for their presence
2.
Functional group
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In organic chemistry, functional groups are specific groups of atoms or bonds within molecules that are responsible for the characteristic chemical reactions of those molecules. The same functional group will undergo the same or similar chemical reaction regardless of the size of the molecule it is a part of, however, its relative reactivity can be modified by other functional groups nearby. The atoms of functional groups are linked to other and to the rest of the molecule by covalent bonds. Any subgroup of atoms of a compound also may be called a radical, and if a covalent bond is broken homolytically, Functional groups can also be charged, e. g. in carboxylate salts, which turns the molecule into a polyatomic ion or a complex ion. Complexation and solvation is also caused by interactions of functional groups. In the common rule of thumb like dissolves like, it is the shared or mutually well-interacting functional groups give rise to solubility. For example, sugar dissolves in water because both share the functional group and hydroxyls interact strongly with each other. Combining the names of groups with the names of the parent alkanes generates what is termed a systematic nomenclature for naming organic compounds. In traditional nomenclature, the first carbon atom after the carbon that attaches to the group is called the alpha carbon, the second, beta carbon. IUPAC conventions call for numeric labeling of the position, e. g. 4-aminobutanoic acid, in traditional names various qualifiers are used to label isomers, for example isopropanol is an isomer is n-propanol. The following is a list of functional groups. In the formulas, the symbols R and R usually denote an attached hydrogen, or a side chain of any length. Functional groups, called hydrocarbyl, that only carbon and hydrogen. Each one differs in type of reactivity, there are also a large number of branched or ring alkanes that have specific names, e. g. tert-butyl, bornyl, cyclohexyl, etc. Hydrocarbons may form charged structures, positively charged carbocations or negative carbanions, examples are tropylium and triphenylmethyl cations and the cyclopentadienyl anion. Haloalkanes are a class of molecule that is defined by a carbon–halogen bond and this bond can be relatively weak or quite stable. In general, with the exception of fluorinated compounds, haloalkanes readily undergo nucleophilic substitution reactions or elimination reactions, the substitution on the carbon, the acidity of an adjacent proton, the solvent conditions, etc. all can influence the outcome of the reactivity. Compounds that contain nitrogen in this category may contain C-O bonds, compounds that contain sulfur exhibit unique chemistry due to their ability to form more bonds than oxygen, their lighter analogue on the periodic table
3.
Organic compound
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An organic compound is virtually any chemical compound that contains carbon, although a consensus definition remains elusive and likely arbitrary. Organic compounds are rare terrestrially, but of importance because all known life is based on organic compounds. The most basic petrochemicals are considered the building blocks of organic chemistry, for historical reasons discussed below, a few types of carbon-containing compounds, such as carbides, carbonates, simple oxides of carbon, and cyanides are considered inorganic. The distinction between organic and inorganic compounds, while useful in organizing the vast subject of chemistry. Organic chemistry is the science concerned with all aspects of organic compounds, Organic synthesis is the methodology of their preparation. The word organic is historical, dating to the 1st century, for many centuries, Western alchemists believed in vitalism. This is the theory that certain compounds could be synthesized only from their classical elements—earth, water, air, vitalism taught that these organic compounds were fundamentally different from the inorganic compounds that could be obtained from the elements by chemical manipulation. Vitalism survived for a while even after the rise of modern atomic theory and it first came under question in 1824, when Friedrich Wöhler synthesized oxalic acid, a compound known to occur only in living organisms, from cyanogen. A more decisive experiment was Wöhlers 1828 synthesis of urea from the inorganic salts potassium cyanate, urea had long been considered an organic compound, as it was known to occur only in the urine of living organisms. Wöhlers experiments were followed by others, in which increasingly complex organic substances were produced from inorganic ones without the involvement of any living organism. Even though vitalism has been discredited, scientific nomenclature retains the distinction between organic and inorganic compounds, still, even the broadest definition requires excluding alloys that contain carbon, including steel. The C-H definition excludes compounds that are considered organic, neither urea nor oxalic acid is organic by this definition, yet they were two key compounds in the vitalism debate. The IUPAC Blue Book on organic nomenclature specifically mentions urea and oxalic acid, other compounds lacking C-H bonds but traditionally considered organic include benzenehexol, mesoxalic acid, and carbon tetrachloride. Mellitic acid, which contains no C-H bonds, is considered an organic substance in Martian soil. The C-H bond-only rule also leads to somewhat arbitrary divisions in sets of carbon-fluorine compounds, for example, CF4 would be considered by this rule to be inorganic, whereas CF3H would be organic. Organic compounds may be classified in a variety of ways, one major distinction is between natural and synthetic compounds. Another distinction, based on the size of organic compounds, distinguishes between small molecules and polymers, natural compounds refer to those that are produced by plants or animals. Many of these are extracted from natural sources because they would be more expensive to produce artificially
4.
Polyol
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A polyol is an alcohol containing multiple hydroxyl groups. In two different technological disciplines the term polyol has a meaning, food science and polymer chemistry. They are also added to chewing gum because they are not broken down by bacteria in the mouth or metabolized to acids, maltitol, sorbitol, xylitol, erythritol, and isomalt are some of the more common types. Sugar alcohols may be formed under reducing conditions from their analogue sugars. In polymer chemistry, polyols are compounds with multiple functional groups available for organic reactions. A molecule with two groups is a diol, one with three is a triol, one with four is a tetrol and so on. Monomeric polyols such as glycerin, pentaerythritol, ethylene glycol and sucrose often serve as the point for polymeric polyols. These materials are referred to as the initiators and reacted with propylene oxide or ethylene oxide to produce polymeric polyols. However, they should not be confused with radical initiators used to promote other polymerization reactions. The functional group used as the point for a polymeric polyol need not be a hydroxyl group. A primary amino group often functions as the point for two polymeric chains, especially in the case of polyether polyols. Polymeric polyols are used to produce other polymers. They are reacted with isocyanates to make polyurethanes used to make mattresses, foam insulation for appliances, home and automotive seats, elastomeric shoe soles, fibers, polymeric polyols are usually polyethers or polyesters. Common polyether diols are polyethylene glycol, polypropylene glycol, and poly glycol, the examples shown below are fairly low molecular weight triols based on glycerin being reacted with propylene oxide, ethylene oxide or a combination of the two. In reality, the chains would not be of length in any one molecule. Polyether polyols account for about 90% of the polymeric polyols used industrially, another class of polymeric polyols is the polyesters. Polyesters are formed by condensation or step-growth polymerization of diols and dicarboxylic acids, alternatively, the hydroxyl group and the carboxylic acid may be within the same molecule, as in the case of caprolactone. The example below is a structure that could be obtained by reacting pentaerythritol with gamma-butyrolactone
5.
Polyurethane
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Polyurethane is a polymer composed of organic units joined by carbamate links. While most polyurethanes are thermosetting polymers that do not melt when heated, polyurethane polymers are traditionally and most commonly formed by reacting a di- or polyisocyanate with a polyol. Both the isocyanates and polyols used to make polyurethanes contain, on average, some noteworthy recent efforts have been dedicated to minimizing the use of isocyanates to synthesize polyurethanes, because the isocyanates raise severe toxicity issues. Non-isocyanate based polyurethanes have recently developed as a new class of polyurethane polymers to mitigate health. Polyurethane products often are simply called “urethanes”, but should not be confused with ethyl carbamate, polyurethanes neither contain nor are produced from ethyl carbamate. Otto Bayer and his coworkers at IG Farben in Leverkusen, Germany, the new polymers had some advantages over existing plastics that were made by polymerizing olefins or by polycondensation, and were not covered by patents obtained by Wallace Carothers on polyesters. Early work focused on the production of fibres and flexible foams, polyisocyanates became commercially available in 1952, and production of flexible polyurethane foam began in 1954 using toluene diisocyanate and polyester polyols. These materials were used to produce rigid foams, gum rubber. Linear fibers were produced from hexamethylene diisocyanate and 1, 4-butanediol, in 1956 DuPont introduced polyether polyols, specifically poly glycol, and BASF and Dow Chemical started selling polyalkylene glycols in 1957. Polyether polyols were cheaper, easier to handle and more water-resistant than polyester polyols, union Carbide and Mobay, a U. S. Monsanto/Bayer joint venture, also began making polyurethane chemicals. In 1960 more than 45,000 metric tons of flexible polyurethane foams were produced, in 1967, urethane-modified polyisocyanurate rigid foams were introduced, offering even better thermal stability and flammability resistance. During the 1960s, automotive interior safety components, such as instrument, in 1969, Bayer exhibited an all-plastic car in Düsseldorf, Germany. Further increases in stiffness were obtained by incorporating pre-placed glass mats into the RIM mold cavity, also known broadly as resin injection molding, polyurethane foams are now used in high-temperature oil filter applications. Polyurethane foam is made using small amounts of blowing agents to give less dense foam. In the early 1990s, because of their impact on ozone depletion, polyurethanes are in the class of compounds called reaction polymers, which include epoxies, unsaturated polyesters, and phenolics. The properties of a polyurethane are greatly influenced by the types of isocyanates, long, flexible segments, contributed by the polyol, give soft, elastic polymer. High amounts of crosslinking give tough or rigid polymers, the crosslinking present in polyurethanes means that the polymer consists of a three-dimensional network and molecular weight is very high. In some respects a piece of polyurethane can be regarded as one giant molecule, one consequence of this is that typical polyurethanes do not soften or melt when they are heated, they are thermosetting polymers
6.
Polymer
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A polymer is a large molecule, or macromolecule, composed of many repeated subunits. Because of their range of properties, both synthetic and natural polymers play an essential and ubiquitous role in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure, Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. The units composing polymers derive, actually or conceptually, from molecules of low molecular mass. The term was coined in 1833 by Jöns Jacob Berzelius, though with a distinct from the modern IUPAC definition. The modern concept of polymers as covalently bonded macromolecular structures was proposed in 1920 by Hermann Staudinger, Polymers are studied in the fields of biophysics and macromolecular science, and polymer science. Polyisoprene of latex rubber is an example of a polymer. In biological contexts, essentially all biological macromolecules—i. e, proteins, nucleic acids, and polysaccharides—are purely polymeric, or are composed in large part of polymeric components—e. g. Isoprenylated/lipid-modified glycoproteins, where small molecules and oligosaccharide modifications occur on the polyamide backbone of the protein. The simplest theoretical models for polymers are ideal chains, Polymers are of two types, Natural polymeric materials such as shellac, amber, wool, silk and natural rubber have been used for centuries. A variety of natural polymers exist, such as cellulose. Most commonly, the continuously linked backbone of a used for the preparation of plastics consists mainly of carbon atoms. A simple example is polyethylene, whose repeating unit is based on ethylene monomer, however, other structures do exist, for example, elements such as silicon form familiar materials such as silicones, examples being Silly Putty and waterproof plumbing sealant. Oxygen is also present in polymer backbones, such as those of polyethylene glycol, polysaccharides. Polymerization is the process of combining many small molecules known as monomers into a covalently bonded chain or network, during the polymerization process, some chemical groups may be lost from each monomer. This is the case, for example, in the polymerization of PET polyester, the distinct piece of each monomer that is incorporated into the polymer is known as a repeat unit or monomer residue. Laboratory synthetic methods are divided into two categories, step-growth polymerization and chain-growth polymerization. However, some methods such as plasma polymerization do not fit neatly into either category
7.
Cyanate
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The cyanate ion is an anion with the chemical formula written as − or −. In aqueous solution it acts as a base, forming isocyanic acid, the cyanate ion is an ambidentate ligand, forming complexes with a metal ion in which either the nitrogen or oxygen atom may be the electron-pair donor. It can also act as a bridging ligand, organic cyanates are called isocyanates when there is a C−NCO bond and cyanates when there is a C−OCN bond. The three atoms in a cyanate ion lie on a line, giving the ion a linear structure. The electronic structure is described most simply as, Ö̤−C≡N, with a single C−O bond, the infrared spectrum of a cyanate salt has a band at ca.2096 cm−1, such a high frequency is characteristic of a triple bond. The cyanate ion is a Lewis base, both the oxygen and nitrogen atoms carry a lone pair of electrons and either one or the other, or both can be donated to Lewis acid acceptors. It can be described as an ambidentate ligand, isocyanic acid, HNCO, is produced when a cyanate salt is acidified. In valence bond theory the canonical form HN+≡C-O− is the contributor to the resonance hybrid. The pure compound has a point of −86.8 °C. In aqueous solution it is a weak acid, HNCO ⇌ H+ + NCO−, pKa ≈3.7. On heating isocyanic acid is converted to the cyanuric acid. In the reverse of the synthesis of urea by Friedrich Wöhler, OC2 → HNCO + NH3 isocyanic acid is produced. The vibrational spectrum is indicative of the presence of a bond between the nitrogen and carbon atoms. Sodium cyanate is isostructural with sodium fulminate, confirming the structure of the cyanate ion. It is made industrially by heating a mixture of sodium carbonate, na2CO3 +2 OC2 →2 NaNCO + CO2 +2 NH3 + H2O A similar reaction is used to make potassium cyanate. Cyanates are produced when cyanides are oxidized, use of this fact is made in cyanide decontamination processes where oxidants such as permanganate and hydrogen peroxide are used to convert toxic cyanide to safer cyanate. Cyanate is a ligand which can donate the pair of electrons on the nitrogen atom or the oxygen atom. Structurally the isomers can be distinguished by the geometry of the complex, in N-bonded cyanate complexes the M−NCO unit has a linear structure, but with O-bonded cyanate the M−O−C unit is bent
8.
Amine
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In organic chemistry, amines are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group, important amines include amino acids, biogenic amines, trimethylamine, and aniline, see Category, Amines for a list of amines. Inorganic derivatives of ammonia are also called amines, such as chloramine, see Category, compounds with a nitrogen atom attached to a carbonyl group, thus having the structure R–CO–NR′R″, are called amides and have different chemical properties from amines. An aliphatic amine has no aromatic ring attached directly to the nitrogen atom, aromatic amines have the nitrogen atom connected to an aromatic ring as in the various anilines. The aromatic ring decreases the alkalinity of the amine, depending on its substituents, the presence of an amine group strongly increases the reactivity of the aromatic ring, due to an electron-donating effect. Amines are organized into four subcategories, Primary amines — Primary amines arise when one of three atoms in ammonia is replaced by an alkyl or aromatic. Important primary alkyl amines include, methylamine, most amino acids, Secondary amines — Secondary amines have two organic substituents bound to the nitrogen together with one hydrogen. Important representatives include dimethylamine, while an example of an aromatic amine would be diphenylamine, tertiary amines — In tertiary amines, nitrogen has three organic substituents. Examples include trimethylamine, which has a fishy smell. Cyclic amines — Cyclic amines are either secondary or tertiary amines, examples of cyclic amines include the 3-membered ring aziridine and the six-membered ring piperidine. N-methylpiperidine and N-phenylpiperidine are examples of tertiary amines. It is also possible to have four organic substituents on the nitrogen and these species are not amines but are quaternary ammonium cations and have a charged nitrogen center. Quaternary ammonium salts exist with many kinds of anions, Amines are named in several ways. Typically, the compound is given the prefix amino- or the suffix, the prefix N- shows substitution on the nitrogen atom. An organic compound with multiple amino groups is called a diamine, triamine, tetraamine, systematic names for some common amines, Hydrogen bonding significantly influences the properties of primary and secondary amines. Thus the melting point and boiling point of amines is higher than those of the corresponding phosphines, for example, methyl and ethyl amines are gases under standard conditions, whereas the corresponding methyl and ethyl alcohols are liquids. Amines possess a characteristic smell, liquid amines have a distinctive fishy smell. The nitrogen atom features a lone pair that can bind H+ to form an ammonium ion R3NH+
9.
Phosgene
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Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a weapon during World War I where it was responsible for about 85% of the 100,000 deaths caused by chemical weapons. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals, in low concentrations, its odor resembles freshly cut hay or grass. In addition to its production, small amounts occur from the breakdown. The chemical was named by combining the Greek words phos and genesis, Phosgene is a planar molecule as predicted by VSEPR theory. The C=O distance is 1.18 Å, the C−Cl distance is 1.74 Å and it is one of the simplest acid chlorides, being formally derived from carbonic acid. Typically, the reaction is conducted between 50 and 150 °C, above 200 °C, phosgene reverts to carbon monoxide and chlorine, Keq =0.05. World production of this compound was estimated to be 2.74 million tonnes in 1989, because of safety issues, phosgene is often produced and consumed within the same plant, and extraordinary measures are made to contain this toxic gas. It is listed on schedule 3 of the Chemical Weapons Convention, upon ultraviolet radiation in the presence of oxygen, chloroform slowly converts into phosgene by a radical reaction. To suppress this photodegradation, chloroform is often stored in brown-tinted glass containers, chlorinated compounds used to remove oil from metals, such as automotive brake cleaners, are converted to phosgene by the UV rays of arc welding processes. Phosgene may also be produced during testing for leaks of older-style refrigerant gases, chloromethanes were formerly leak-tested in situ by employing a small gas torch with a sniffer tube and a copper reaction plate in the flame nozzle of the torch. If any refrigerant gas was leaking from a pipe or joint, in the process, phosgene gas would be created due to the thermal reaction. Electronic sensing of refrigerant gases phased out the use of testing for leaks in the 1980s. Phosgene can be released during building fires, in one instance, a deputy fire chief was killed ten days after inhaling fumes that wafted down outside a burning restaurant. After a two-day hospitalization he had appeared to recover, but ultimately suffered cardiac arrest at home following from tracheobronchial inflammation, alveolar hemorrhage, the phosgene was produced by decomposing freon-22 after flames ducted up from a grease fire heated an air-conditioning unit on the roof and ruptured a hose. The great majority of phosgene is used in the production of isocyanates and these two isocyanates are precursors to polyurethanes. In the research laboratory phosgene still finds limited use in organic synthesis, a variety of substitutes have been developed, notably trichloromethyl chloroformate, a liquid at room temperature, and bis carbonate, a crystalline substance. Thionyl chloride is commonly and more safely employed for this application
10.
Electrophile
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In chemistry, an electrophile is a reagent attracted to electrons. Electrophiles are positively charged or neutral species having vacant orbitals that are attracted to a rich centre. It participates in a reaction by accepting an electron pair in order to bond to a nucleophile. Because electrophiles accept electrons, they are Lewis acids, most electrophiles are positively charged, have an atom that carries a partial positive charge, or have an atom that does not have an octet of electrons. The electrophiles are attacked by the most electron-populated part of one nucleophile and these occur between alkenes and electrophiles, often halogens as in halogen addition reactions. Common reactions include use of water to titrate against a sample to deduce the number of double bonds present. Forming of a bromonium ion The alkene is working as an electron donor. The three-membered bromonium ion 2 consisted with two atoms and a bromine atom forms with a release of Br−. Attacking of bromide ion The bromonium ion is opened by the attack of Br− from the back side and this yields the vicinal dibromide with an antiperiplanar configuration. When other nucleophiles such as water or alcohol are existing, these may attack 2 to give an alcohol or an ether and this process is called AdE2 mechanism. Iodine, chlorine, sulfenyl ion, mercury cation, and dichlorocarbene also react through similar pathways, the direct conversion of 1 to 3 will appear when the Br− is large excess in the reaction medium. A β-bromo carbenium ion intermediate may be predominant instead of 3 if the alkene has a cation-stabilizing substituent like phenyl group, there is an example of the isolation of the bromonium ion 2. Hydrogen halides such as hydrogen chloride adds to alkenes to give alkyl halides in hydrohalogenation, for example, the reaction of Hcl with ethylene furnishes chloroethane. The reaction proceeds with an intermediate, being different from the above halogen addition. An example is shown below, Proton adds to one of the atoms on the alkene to form cation 1. Chloride ion combines with the cation 1 to form the adducts 2 and 3, in this manner, the stereoselectivity of the product, that is, from which side Cl− will attack relies on the types of alkenes applied and conditions of the reaction. At least, which of the two carbon atoms will be attacked by H+ is usually decided by Markovnikovs rule, thus, H+ attacks the carbon atom that carries fewer substituents so as the more stabilized carbocation will form. This process is called A-SE2 mechanism, hydrogen fluoride and hydrogen iodide react with alkenes in a similar manner, and Markovnikov-type products will be given
11.
Nucleophile
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A nucleophile is a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction. All molecules or ions with a pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they are by definition Lewis bases, Nucleophilic describes the affinity of a nucleophile to the nuclei. Nucleophilicity, sometimes referred to as strength, refers to a substances nucleophilic character and is often used to compare the affinity of atoms. Neutral nucleophilic reactions with solvents such as alcohols and water are named solvolysis, nucleophiles may take part in nucleophilic substitution, whereby a nucleophile becomes attracted to a full or partial positive charge. The terms nucleophile and electrophile were introduced by Christopher Kelk Ingold in 1933, the word nucleophile is derived from nucleus and the Greek word φιλος, philos for love. In general, in a row across the table, the more basic the ion the more reactive it is as a nucleophile. g. The iodide ion is more nucleophilic than the fluoride ion, many schemes attempting to quantify relative nucleophilic strength have been devised. The following empirical data have been obtained by measuring reaction rates for a number of reactions involving a large number of nucleophiles and electrophiles. Nucleophiles displaying the so-called alpha effect are usually omitted in this type of treatment. This treatment results in the values for typical nucleophilic anions, acetate 2.7, chloride 3.0, azide 4.0, hydroxide 4.2, aniline 4.5, iodide 5.0. Typical substrate constants are 0.66 for ethyl tosylate,0.77 for β-propiolactone,1.00 for 2, 3-epoxypropanol,0.87 for benzyl chloride, and 1.43 for benzoyl chloride. The equation predicts that, in a nucleophilic displacement on benzyl chloride, the Ritchie equation, derived in 1972, is another free-energy relationship, log 10 = N + where N+ is the nucleophile dependent parameter and k0 the reaction rate constant for water. In this equation, a substrate-dependent parameter like s in the Swain–Scott equation is absent, the equation states that two nucleophiles react with the same relative reactivity regardless of the nature of the electrophile, which is in violation of the Reactivity–selectivity principle. For this reason this equation is called the constant selectivity relationship. Many other reaction types have since been described. Typical Ritchie N+ values are,0.5 for methanol,5.9 for the anion,7.5 for the methoxide anion,8.5 for the azide anion. The values for the relative cation reactivities are -0.4 for the malachite green cation, +2.6 for the benzenediazonium cation, the constant s is defined as 1 with 2-methyl-1-pentene as the nucleophile
12.
Alcohol
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In chemistry, an alcohol is any organic compound in which the hydroxyl functional group is bound to a saturated carbon atom. The term alcohol originally referred to the alcohol ethanol, the predominant alcohol in alcoholic beverages. The suffix -ol in non-systematic names also typically indicates that the substance includes a functional group and, so. But many substances, particularly sugars contain hydroxyl functional groups without using the suffix, an important class of alcohols, of which methanol and ethanol are the simplest members is the saturated straight chain alcohols, the general formula for which is CnH2n+1OH. The word alcohol is from the Arabic kohl, a used as an eyeliner. Al- is the Arabic definite article, equivalent to the in English, alcohol was originally used for the very fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide Sb 2S3, hence the essence or spirit of this substance. It was used as an antiseptic, eyeliner, and cosmetic, the meaning of alcohol was extended to distilled substances in general, and then narrowed to ethanol, when spirits as a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, Vigo wrote, the barbarous auctours use alcohol, or alcofoll, for moost fine poudre. The 1657 Lexicon Chymicum, by William Johnson glosses the word as antimonium sive stibium, by extension, the word came to refer to any fluid obtained by distillation, including alcohol of wine, the distilled essence of wine. Libavius in Alchymia refers to vini alcohol vel vinum alcalisatum, Johnson glosses alcohol vini as quando omnis superfluitas vini a vino separatur, ita ut accensum ardeat donec totum consumatur, nihilque fæcum aut phlegmatis in fundo remaneat. The words meaning became restricted to spirit of wine in the 18th century and was extended to the class of substances so-called as alcohols in modern chemistry after 1850, the term ethanol was invented 1892, based on combining the word ethane with ol the last part of alcohol. In the IUPAC system, in naming simple alcohols, the name of the alkane chain loses the terminal e and adds ol, e. g. as in methanol and ethanol. When necessary, the position of the group is indicated by a number between the alkane name and the ol, propan-1-ol for CH 3CH 2CH 2OH, propan-2-ol for CH 3CHCH3. If a higher priority group is present, then the prefix hydroxy is used, in other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word alcohol, e. g. methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, Alcohols are then classified into primary, secondary, and tertiary, based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. The primary alcohols have general formulas RCH2OH, the simplest primary alcohol is methanol, for which R=H, and the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RRCHOH, the simplest of which is 2-propanol, for the tertiary alcohols the general form is RRRCOH
13.
Carbamate
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A carbamate is an organic compound derived from carbamic acid. A carbamate group, carbamate ester, and carbamic acids are functional groups that are inter-related structurally, carbamate esters are also called urethanes. Carbamic acids are derived from amines, R2NH + CO2 → R2NCO2H Carbamic acid is about as acidic as acetic acid, n-terminal amino groups of valine residues in the α- and β-chains of deoxyhemoglobin exist as carbamates. They help to stabilise the protein, when it becomes deoxyhemoglobin and this stabilizing effect should not be confused with the Bohr effect. The ε-amino groups of the residues in urease and phosphotriesterase also feature carbamate. The carbamate derived from aminoimidazole is an intermediate in the biosynthesis of inosine, carbamoyl phosphate is generated from carboxyphosphate rather than CO2. Perhaps the most important carbamate is the one involved in the capture of CO2 by plants since this process is necessary for their growth, the enzyme ribulose 1, 5-bisphosphate carboxylase/oxygenase fixes a molecule of carbon dioxide as phosphoglycerate in the Calvin cycle. At the active site of the enzyme, a Mg2+ ion is bound to glutamate and aspartate residues as well as a lysine carbamate. The carbamate is formed when an uncharged lysine side chain near the ion reacts with a carbon dioxide molecule from the air, which renders it charged. The so-called carbamate insecticides feature the carbamate ester functional group, included in this group are aldicarb, carbofuran, carbaryl, ethienocarb, fenobucarb, oxamyl, and methomyl. These insecticides kill insects by reversibly inactivating the enzyme acetylcholinesterase, the organophosphate pesticides also inhibit this enzyme, although irreversibly, and cause a more severe form of cholinergic poisoning. Fenoxycarb has a group but acts as a juvenile hormone mimic. The insect repellent icaridin is a substituted carbamate, polyurethanes contain multiple carbamate groups as part of their structure. The urethane in the name refers to these carbamate groups. In contrast, the commonly called urethane, ethyl carbamate, is neither a component of polyurethanes. Urethanes are usually formed by reaction of an alcohol with an isocyanate, commonly, urethanes made by a non-isocyanate route are called carbamates. Polyurethane polymers have a range of properties and are commercially available as foams, elastomers. Typically, polyurethane polymers are made by combining diisocyanates, e. g. Urethane was once produced commercially in the United States as an antineoplastic agent and it was found to be toxic and largely ineffective
14.
Alkyl
–
In organic chemistry, an alkyl substituent is an alkane missing one hydrogen. The term alkyl is intentionally unspecific to include many possible substitutions, an acyclic alkyl has the general formula CnH2n+1. A cycloalkyl is derived from a cycloalkane by removal of an atom from a ring and has the general formula CnH2n-1. Typically an alkyl is a part of a larger molecule, in structural formula, the symbol R is used to designate a generic alkyl group. The smallest alkyl group is methyl, with the formula CH3−, the word root alkyl is encountered in several contexts. Alkylation is an important operation in refineries, for example in the production of high-octane gasoline, alkylating antineoplastic agents refer to a class of compounds that are used to treat cancer. In such case, the alkyl is used loosely. For example, nitrogen mustards are well-known alkylating agents, but they are more complex than a mere hydrocarbon, in chemistry, alkyl refers to a group, a substituent, that is attached to other molecular fragments. For example, alkyl lithium reagents have the empirical formula Li, a dialkyl ether is an ether with two alkyl groups, e. g. diethyl ether. In medicinal chemistry, the incorporation of alkyl chains into some chemical compounds increases their lipophilicity and this strategy has been used to increase the antimicrobial activity of flavanones and chalcones. Usually alkyl groups are attached to atoms or groups of atoms. Free alkyls occur as neutral compounds, as anions, or as cations, the neutral alkyl free radicals have no special name. Such species are encountered only as transient intermediates, but some are quite stable. Typically alkyl cations are generated using super acids, alkyl anions are observed in the presence of strong bases, alkyls are commonly observed in mass spectrometry of organic compounds. The simplest series have the general formula CnH2n+1, alkyls include methyl, CH3·, ethyl, propyl, butyl, pentyl, and so on. Alkyl groups that one ring have the formula CnH2n−1, e. g. cyclopropyl and cyclohexyl. First, five atoms comprise the longest straight chain of carbon centers, the parent five-carbon compound is named pentane. The methyl substituent or group is highlighted red, according to the usual rules of nomenclature, alkyl groups are included in the name of the molecule before the root, as in methylpentane
15.
Aryl
–
In the context of organic molecules, aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, be it phenyl, naphthyl, thienyl, indolyl, etc. Aryl is used for the sake of abbreviation or generalization, a simple aryl group is phenyl, C6H5, it is derived from benzene. The tolyl group, CH3C6H4, is derived from toluene, the xylyl group, 2C6H3, is derived from xylene, while the naphthyl group, C10H7, is derived from naphthalene. Arylation is a process in which an aryl group is attached to a substituent. Alkyl Aryl hydrocarbon receptor, a target for dioxins Arene compound
16.
Diol
–
A diol is a chemical compound containing two hydroxyl groups. This pairing of groups is pervasive, and many subcategories have been identified. The most common industrial diol is ethylene glycol, a geminal diol has two hydroxyl groups bonded to the same atom. These species arise by hydration of the carbonyl compounds, the hydration is usually unfavorable, but a notable exception is formaldehyde which, in water, exists in equilibrium with methanediol H2C2. Another example is 2C2, the form of hexafluoroacetone, in this case the hydration is made favorable by the electron-withdrawing trifluoromethyl groups. In a vicinal diol, the two hydroxyl groups occupy vicinal positions, that is, they are attached to adjacent atoms, examples include 1, 2-ethanediol or ethylene glycol HO−2−OH, a common ingredient of antifreeze products. Another example is propane-1, 2-diol, or alpha propylene glycol, HO−CH2−CH−CH3, used in the food and medicine industry, on commercial scales, the main route to vicinal diols is the hydrolysis of epoxides. The epoxides are prepared by oxidation with hydrogen peroxide of the alkene, using alkaline potassium manganate produces a colour change from clear deep purple to clear green, acidic potassium manganate turns clear colourless. Osmium tetroxide can similarly be used to oxidize alkenes to vicinal diols, the chemical reaction called Sharpless asymmetric dihydroxylation can be used to produce chiral diols from alkenes using an osmate reagent and a chiral catalyst. Another method is the Woodward cis-hydroxylation and the related Prévost reaction, depicted below,1, 3-Diols are often prepared industrially by aldol condensation of ketones with formaldehyde. Examples include 2-methyl-2-propyl-1, 3-propanediol and neopentyl glycol,1, 3-Diols can be prepared by hydration of α, β-unsaturated ketones and aldehydes. Another route involves the hydroformylation of epoxides followed by hydrogenation of the aldehyde and this method has been used for 1, 3-propanediol from ethylene oxide. More specialized routes to 1, 3-diols involves the reaction between an alkene and formaldehyde, the Prins reaction,1, 3-diols can be produced diastereoselectively from the corresponding β-hydroxy ketones using the Evans–Saksena, Narasaka–Prasad or Evans–Tishchenko reduction protocols. Diols where the groups are separated by several carbon centers are generally prepared by hydrogenation of diesters of the corresponding dicarboxylic acids. 1, 4-butanediol and 1, 5-pentanediol are important precursors to polyurethanes, n2 +4 H2 → n2 +2 H2O Bisphenol A is an important compound that contains two phenol groups. It is a block in the production of polycarbonate plastics. It is produced by condensation of phenol and acetone, from the industrial perspective, the dominant reactions of the diols is in the production of polyurethanes and alkyd resins. Diols react as alcohols, by esterification and ether formation, diols such as ethylene glycol are used as co-monomers in polymerization reactions forming polymers including some polyesters and polyurethanes
17.
Urea
–
Urea, also known as carbamide, is an organic compound with the chemical formula CO2. This amide has two groups joined by a carbonyl functional group. Urea serves an important role in the metabolism of nitrogen-containing compounds by animals and is the main nitrogen-containing substance in the urine of mammals and it is a colorless, odorless solid, highly soluble in water, and practically non-toxic. Dissolved in water, it is neither acidic nor alkaline, the body uses it in many processes, most notably nitrogen excretion. The liver forms it by combining two molecules with a carbon dioxide molecule in the urea cycle. Urea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry, Friedrich Wöhlers discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in chemistry. More than 90% of world production of urea is destined for use as a nitrogen-release fertilizer. Urea has the highest nitrogen content of all solid nitrogenous fertilizers in common use, therefore, it has the lowest transportation costs per unit of nitrogen nutrient. The standard crop-nutrient rating of urea is 46-0-0, many soil bacteria possess the enzyme urease, which catalyzes conversion of urea to ammonia or ammonium ion and bicarbonate ion. Thus urea fertilizers rapidly transform to the form in soils. Ammonium and nitrate are readily absorbed by plants, and are the dominant sources of nitrogen for plant growth, Urea is also used in many multi-component solid fertilizer formulations. Urea is highly soluble in water and is also very suitable for use in fertilizer solutions. For fertilizer use, granules are preferred over prills because of their particle size distribution. The most common impurity of synthetic urea is biuret, which impairs plant growth, Urea is usually spread at rates of between 40 and 300 kg/ha but rates vary. Smaller applications incur lower losses due to leaching, during summer, urea is often spread just before or during rain to minimize losses from volatilization. Because of the nitrogen concentration in urea, it is very important to achieve an even spread. The application equipment must be calibrated and properly used. Drilling must not occur on contact with or close to seed, Urea dissolves in water for application as a spray or through irrigation systems
18.
Polyurea
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Polyurea is a type of elastomer that is derived from the reaction product of an isocyanate component and a synthetic resin blend component through step-growth polymerization. The isocyanate can be aromatic or aliphatic in nature and it can be monomer, polymer, or any variant reaction of isocyanates, quasi-prepolymer or a prepolymer. The prepolymer, or quasi-prepolymer, can be made of a polymer resin. The resin blend may be made up of amine-terminated polymer resins, the amine-terminated polymer resins will not have any intentional hydroxyl moieties. Any hydroxyls are the result of conversion to the amine-terminated polymer resins. The resin blend may contain additives, or non-primary components. These additives may contain hydroxyls, such as pre-dispersed pigments in a polyol carrier, normally, the resin blend will not contain a catalyst. The word polyurea is derived from the Greek words πολυ- - poly- meaning many, the latter term refers to the substance urea, found in urine, rather than urine itself. Urea or carbamide is a compound with the chemical formula 2CO. The molecule has two groups joined by a carbonyl functional group. In a polyurea, alternating monomer units of isocyanates and amines react with other to form urea linkages. Ureas can also be formed from the reaction of isocyanates and water which forms a carbamic acid intermediate and this acid quickly decomposes by splitting off carbon dioxide and leaving behind an amine. This amine then reacts with another group to form the polyurea linkage. This two step reaction is used in what is commonly but improperly called polyurethane foams, the carbon dioxide that is liberated in this reaction is the primary blowing agent especially in many polyurethane foams which more precisely should be called polyurethane/urea foams. Polyurea and polyurethane are copolymers used in the manufacture of spandex, excellent adhesion to concrete and steel is obtained with the proper primer and surface treatment. They can also be used for molding and armor. Some polyureas reach strengths of 6000psi tensile and over 500% elongation making it a tough coating, the quick cure time allows many coats to be built up quickly. In 2014 a polyurea elastomer-based material was shown to be self-healing, melding together after being cut in half, the material also includes inexpensive commercially available compounds
19.
Aliphatic compound
–
In organic chemistry, hydrocarbons are divided into two classes, aromatic compounds and aliphatic compounds also known as non-aromatic compounds. Aliphatics can be cyclic, but only aromatic compounds contain an especially stable ring of atoms, aliphatic compounds can be saturated, like Hexane, or unsaturated, like Hexene and Hexyne. Open-chain compounds contain no rings of any type, and are thus aliphatic, aliphatic compounds can be saturated, joined by single bonds, or unsaturated, with double bonds or triple bonds. Besides hydrogen, other elements can be bound to the chain, the most common being oxygen, nitrogen, sulfur. The least complex aliphatic compound is methane, most aliphatic compounds are flammable, allowing the use of hydrocarbons as fuel, such as methane in Bunsen burners and as liquefied natural gas, and acetylene in welding. The most important aliphatic compounds are, n-, iso- and cyclo-alkanes n-, iso- and cyclo-alkenes and -alkynes
20.
Trimer (chemistry)
–
In chemistry, a trimer is an oligomer derived from three identical precursors. An example is the procedure of production of polymers, at first, a monomer is made. By combining two monomers, a dimer is produced, with further additions, a trimer and eventually a polymer is made. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids, in 1866, Marcellin Berthelot reported the first example of cyclotrimerization leading to aromatic products, the cyclization of acetylene to benzene. In the Reppe synthesis, the trimerization of acetylene gives benzene, Symmetrical 1,3, the conversion commences at approximately 175 °C,3 H2N-CO-NH2 →3 +3 NH3 The endothermic synthesis of melamine can be understood in two steps. 3 HOCN →33 +3 NH3 → C3H6N6 +3 H2O This water then reacts with cyanic acid present, which helps drive the trimerization reaction, generating carbon dioxide and ammonia. 3 HOCN +3 H2O →3 CO2 + 3NH3 In total, cyclotrimerization of formaldehyde affords 1,3, 5-Trioxane,1,3, 5-Trithiane is the cyclic trimer of the otherwise unstable species thioformaldehyde. This heterocycle consists of a ring with alternating methylene bridges. It is prepared by treatment of formaldehyde with hydrogen sulfide, three molecules of acetaldehyde condense to form “paraldehyde, ” a cyclic trimer containing C-O single bonds
21.
Cyanuric acid
–
Cyanuric acid or 1,3, 5-triazine-2,4, 6-triol is a chemical compound with the formula 3. Like many industrially useful chemicals, this triazine has many synonyms and this white, odorless solid finds use as a precursor or a component of bleaches, disinfectants, and herbicides. In 1997, worldwide production was 160 million kilograms, cyanuric acid is the cyclic trimer of the elusive species cyanic acid, HOCN. The two structures shown in the infobox readily interconvert, that is, they are tautomers, however, mixture with melamine forms melamine cyanurate, which locks cyanuric acid in the tri-keto tautomer and makes melamine cyanurate insoluble in water. The triol tautomer, which may have aromatic character, predominates in solution, the hydroxyl groups assume phenolic character. The current industrial route to CYA entails the thermal decomposition of urea, the conversion commences at approximately 175 °C,3 H2N-CO-NH2 →3 +3 NH3 CYA crystallizes from water as the dihydrate. Cyanuric acid can be produced by hydrolysis of crude or waste melamine followed by crystallization, acid waste streams from plants producing these materials contain cyanuric acid and on occasion, dissolved amino-substituted triazines, namely, ammeline, ammelide, and melamine. Melamine,3, formation occurs between 325 and 350 °C and only in small quantities. Cyanuric acid is used as a stabilizer in swimming pools. It binds to free chlorine and releases it slowly, extending the time needed to deplete each dose of sanitizer, the antineoplastic alkylating agent, teroxirone, is formed by reacting cyanuric acid with 3 equivalents of epichlorohydrin. Cyanuric acid is used as a precursor to N-chlorinated cyanurates. The dichloro derivative is prepared by chlorination,3 +2 Cl2 +2 NaOH →2 This species is typically converted to its sodium salt. Further chlorination gives trichloroisocyanuric acid,3 and these N-chloro compounds serve as disinfectants and algicides for swimming pool water. It stabilizes the chlorine in the pool and prevents the chlorine from being consumed by sunlight. Because of its trifunctionality, CYA is a precursor to crosslinking agents, testing for cyanuric acid concentration is commonly done with a turbidometric test, which uses a reagent, melamine, to precipitate the cyanuric acid. The relative turbidity of the reacted sample quantifies the CYA concentration, more recently, a sensitive method has been developed for analysis of cyanuric acid in urine. FDA permits a certain amount of acid to be present in some non-protein nitrogen additives used in animal feed. Cyanuric acid has been used as NPN, for example, Archer Daniels Midland manufactures an NPN supplement for cattle, which contains biuret, triuret, cyanuric acid and urea
22.
Hydrolysis
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Hydrolysis usually means the cleavage of chemical bonds by the addition of water. When a carbohydrate is broken into its component sugar molecules by hydrolysis, generally, hydrolysis or saccharification is a step in the degradation of a substance. Hydrolysis can be the reverse of a reaction in which two molecules join together into a larger one and eject a water molecule. Thus hydrolysis adds water to break down, whereas condensation builds up by removing water, usually hydrolysis is a chemical process in which a molecule of water is added to a substance. Sometimes this addition causes both substance and water molecule to split into two parts, in such reactions, one fragment of the target molecule gains a hydrogen ion. A common kind of hydrolysis occurs when a salt of an acid or weak base is dissolved in water. Water spontaneously ionizes into hydroxide anions and hydronium cations, the salt also dissociates into its constituent anions and cations. For example, sodium acetate dissociates in water into sodium and acetate ions, sodium ions react very little with the hydroxide ions whereas the acetate ions combine with hydronium ions to produce acetic acid. In this case the net result is an excess of hydroxide ions. For example, dissolving sulfuric acid in water is accompanied by hydrolysis to give hydronium and bisulfate, for a more technical discussion of what occurs during such a hydrolysis, see Brønsted–Lowry acid–base theory. Acid–base-catalysed hydrolyses are very common, one example is the hydrolysis of amides or esters and their hydrolysis occurs when the nucleophile attacks the carbon of the carbonyl group of the ester or amide. In an aqueous base, hydroxyl ions are better nucleophiles than polar molecules such as water, in acids, the carbonyl group becomes protonated, and this leads to a much easier nucleophilic attack. The products for both hydrolyses are compounds with carboxylic acid groups, perhaps the oldest commercially practiced example of ester hydrolysis is saponification. It is the hydrolysis of a triglyceride with a base such as sodium hydroxide. During the process, glycerol is formed, and the fatty acids react with the base and these salts are called soaps, commonly used in households. In addition, in living systems, most biochemical reactions take place during the catalysis of enzymes, the catalytic action of enzymes allows the hydrolysis of proteins, fats, oils, and carbohydrates. As an example, one may consider proteases and they catalyse the hydrolysis of interior peptide bonds in peptide chains, as opposed to exopeptidases. However, proteases do not catalyse the hydrolysis of all kinds of proteins and their action is stereo-selective, Only proteins with a certain tertiary structure are targeted as some kind of orienting force is needed to place the amide group in the proper position for catalysis
23.
Hofmann rearrangement
–
The Hofmann rearrangement is the organic reaction of a primary amide to a primary amine with one fewer carbon atom. The reaction is named after its discoverer - August Wilhelm von Hofmann and this reaction is also sometimes called the Hofmann degradation or the Harmon Process, and should not be confused with the Hofmann elimination. The reaction of bromine with sodium hydroxide forms sodium hypobromite in situ, the formation of an intermediate nitrene is not possible because it implies also the formation of an hydroxamic acid as a byproduct, which has never been observed. The intermediate isocyanate is hydrolyzed to an amine, giving off carbon dioxide. Base abstracts an acidic N-H proton, yielding an anion, the anion reacts with bromine in an α-substitution reaction to give an N-bromoamide. Base abstraction of the remaining amide proton gives a bromoamide anion, the bromoamide anion rearranges as the R group attached to the carbonyl carbon migrates to nitrogen at the same time the bromide ion leaves, giving an isocyanate. The isocyanate adds water in an addition step to yield a carbamic acid. The carbamic acid spontaneously loses CO2, yielding the amine product, several reagents can substitute for bromine. Sodium hypochlorite, Lead tetraacetate, N-bromosuccinimide, benzene, and 1, in the following example, the intermediate isocyanate is trapped by methanol, forming a carbamate. In a similar fashion, the intermediate isocyanate can be trapped by tert-butyl alcohol, the Hofmann Rearrangement also can be used to yield carbamates from α, β-unsaturated or α-hydroxy amides or nitriles from α, β-Acetylenic amides in good yields. For Amiloride, hypobromous acid was used to effect Hofmann rearrangement, gabapentin from mono-amidation 1, 1-cyclohexane diacetic acid anhydride with ammonia to 1, 1-cyclohexane diacetic acid mono-amide, followed by ‘Hoffmann’ rearrangement, U. S. Patent 20,080,103,334 Beckmann rearrangement Curtius rearrangement Iodoform reaction Lossen rearrangement Schmidt reaction Weerman degradation Clayden, oxford University Press Inc. p.1073. Reinhold Publishing Corporation, Chapman & Hall, Ltd. pp. 499–501
24.
Amide
–
An amide, also known as an acid amide, is a compound with the functional group RnExNR′2. Most common are carboxamides, but many other important types of amides are known, the term amide refers both to classes of compounds and to the functional group within those compounds. Amide can also refer to the base of ammonia or of an organic amine. For discussion of these anionic amides, see Alkali metal amides, the remainder of this article is about the carbonyl–nitrogen sense of amide. The simplest amides are derivatives of ammonia wherein one hydrogen atom has replaced by an acyl group. The ensemble is represented as RCNH2 and is described as a primary amide. Closely related and even more numerous are secondary amides which can be derived from amines and have the formula RCNHR′. Tertiary amides are commonly derived from amines and have the general structure RCNR′R″. Amides are usually regarded as derivatives of carboxylic acids in which the group has been replaced by an amine or ammonia. The lone pair of electrons on the nitrogen is delocalized into the carbonyl, consequently, the nitrogen in amides is not pyramidal. It is estimated that acetamide is described by resonance structure A for 62%, in the usual nomenclature, one adds the term amide to the stem of the parent acids name. For instance, the derived from acetic acid is named acetamide. IUPAC recommends ethanamide, but this and related names are rarely encountered. When the amide is derived from a primary or secondary amine, thus, the amide formed from dimethylamine and acetic acid is N, N-dimethylacetamide. Usually even this name is simplified to dimethylacetamide, cyclic amides are called lactams, they are necessarily secondary or tertiary amides. Functional groups consisting of –PNR2 and –SO2NR2 are phosphonamides and sulfonamides, some chemists make a pronunciation distinction between the two, saying /əˈmiːd/ for the carbonyl–nitrogen compound and /ˈeɪmaɪd/ for the anion. Others replace one of these with /ˈæmᵻd/, while others pronounce both /ˈæmᵻd/, making them homonyms. Compared to amines, amides are very weak bases, while the conjugate acid of an amine has a pKa of about 9.5, the conjugate acid of an amide has a pKa around −0.5
25.
Oxidizing agent
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In chemistry, an oxidizing agent is a substance that has the ability to oxidize other substances. Common oxidizing agents are oxygen, hydrogen peroxide and halogens, in one sense, an oxidizing agent is a chemical species that undergoes a chemical reaction that removes one or more electrons from another atom. In that sense, it is one component in an oxidation–reduction reaction, in the second sense, an oxidizing agent is a chemical species that transfers electronegative atoms, usually oxygen, to a substrate. Combustion, many explosives, and organic redox reactions involve atom-transfer reactions, electron acceptors participate in electron-transfer reactions. In this context, the agent is called an electron acceptor. A classic oxidizing agent is the ferrocenium ion Fe+2, which accepts an electron to form Fe2, one of the strongest acceptors commercially available is Magic blue, the radical cation derived from N3. Extensive tabulations of ranking the electron accepting properties of various reagents are available, in more common usage, an oxidising agent transfers oxygen atoms to a substrate. In this context, the agent can be called an oxygenation reagent or oxygen-atom transfer agent. Examples include MnO−4, CrO2−4, OsO4, and especially ClO−4, notice that these species are all oxides. In some cases, these oxides can also serve as electron acceptors, as illustrated by the conversion of MnO−4 to MnO2−4, by this definition some materials that are classified as oxidising agents by analytical chemists are not classified as oxidising agents in a dangerous materials sense. An example is potassium dichromate, which does not pass the dangerous goods test of an oxidising agent, the U. S. Department of Transportation defines oxidizing agents specifically. There are two definitions for oxidizing agents governed under DOT regulations and these two are Class 5, Division 5.1 and Class 5, Division 5.2. Division 5.1 means a material that may, generally by yielding oxygen, combustion Dye Electrosynthesis Organic oxidation Organic redox reaction Reducing agent
26.
Hypobromite
–
The hypobromite ion, also called alkaline bromine water, is BrO−. Bromine is in the +1 oxidation state, hypobromite is the bromine compound analogous to hypochlorites found in common bleaches, and in immune cells. In many ways, hypobromite functions in the manner as hypochlorite. Hypobromite salts form upon treating bromine with aqueous alkali, such as sodium or potassium hydroxide, at 20 °C the reaction is rapid. Br2 +2 OH− → Br− + BrO− + H2O In this reaction the bromine disproportionates from oxidation state 0 to oxidation state −1, sodium hypobromite can be isolated as an orange solid. Hypobromite is not thermodynamically stable at any pH, but it is kinetically locked toward a further disproportion into bromate and these reactions of bromine are analogous to those of chlorine forming hypochlorite and chlorate. The corresponding chlorine reaction 1 is fast at 20 °C and reaction 2 is slow at 20 °C, a hypobromite is a compound that contains this anion. Examples include sodium hypobromite and potassium hypobromite, bromide from the diet, naturally present in the blood, is used by eosinophils, white blood cells of the granulocyte class, specialized for dealing with multi-cellular parasites. These cells react the bromide with peroxide to generate hypobromite by the action of eosinophil peroxidase, hypobromite has been proposed to be a reactive intermediate in the Hofmann rearrangement. Bromide, Br− Bromite, BrO−2 Bromate, BrO−3 Perbromate, BrO−4
27.
Lead tetraacetate
–
Lead acetate or lead tetraacetate is a chemical compound with chemical formula Pb4 and is a lead salt of acetic acid. It is commercially available often stabilized with acetic acid, in the solid state the lead atoms are surrounded by four acetate ions which are bidentate, each coordinating via two oxygen atoms. The lead atom is 8 coordinate and the O atoms form a flattened trigonal dodecahedron and it can be prepared by reaction of red lead with acetic acid. The other main lead acetate is lead acetate, lead tetraacetate is a strong oxidizing agent, a source of acetyloxy groups and a general reagent for the introduction of lead into organolead compounds. Reaction with alkenes to form γ-lactones oxidation of alcohols carrying a δ-proton to cyclic ethers and it causes irritation to skin, eyes, and respiratory tract. It affects the gum tissue, central nervous system, kidneys, blood and its oxidising nature can indirectly lead to many diseases, even cancer, by free radical mechanism
28.
Schmidt reaction
–
The Schmidt reaction is an organic reaction in which an azide reacts with a carbonyl group to give an amine or amide, with expulsion of nitrogen. It is named after Karl Friedrich Schmidt, who first reported it in 1924 by successfully converting benzophenone, reaction with hydrazoic acid forms the protonated azido ketone 2, which goes through a rearrangement reaction with the alkyl group R, migrating over the C-N bond with expulsion of nitrogen. The protonated isocyanate is attacked by water forming carbamate 4, which after deprotonation loses carbon dioxide to the amine, the reaction is related to the Curtius rearrangement except that in this reaction the azide is protonated and hence with different intermediates. A similar migration is found in the Beckmann rearrangement, attack by water and proton loss converts 5 to 7, which is a tautomer of the final amide. The scope of this reaction has been extended to reactions of carbonyls with alkyl azides R-N3 and these are annulation reactions and have some utility in the synthesis of natural products, such as lactams and alkaloids. Curtius rearrangement Hofmann rearrangement Lossen rearrangement
29.
Carboxylic acid
–
A carboxylic acid /ˌkɑːrbɒkˈsɪlɪk/ is an organic compound that contains a carboxyl group. The general formula of an acid is R–COOH, with R referring to the rest of the molecule. Carboxylic acids occur widely and include the amino acids and acetic acid, salts and esters of carboxylic acids are called carboxylates. When a carboxyl group is deprotonated, its conjugate base forms a carboxylate anion, carboxylate ions are resonance-stabilized, and this increased stability makes carboxylic acids more acidic than alcohols. Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide, carboxylic acids are commonly identified using their trivial names, and usually have the suffix -ic acid. IUPAC-recommended names also exist, in system, carboxylic acids have an -oic acid suffix. For example, butyric acid is butanoic acid by IUPAC guidelines, the -oic acid nomenclature detail is based on the name of the previously-known chemical benzoic acid. Alternately, it can be named as a carboxy or carboxylic acid substituent on another parent structure, for example, 2-carboxyfuran. The carboxylate anion of an acid is usually named with the suffix -ate, in keeping with the general pattern of -ic acid and -ate for a conjugate acid and its conjugate base. For example, the base of acetic acid is acetate. The radical •COOH has only a fleeting existence. The acid dissociation constant of •COOH has been measured using electron paramagnetic resonance spectroscopy, the carboxyl group tends to dimerise to form oxalic acid. Because they are both hydrogen-bond acceptors and hydrogen-bond donors, they participate in hydrogen bonding. Together the hydroxyl and carbonyl group forms the functional group carboxyl, carboxylic acids usually exist as dimeric pairs in nonpolar media due to their tendency to self-associate. Smaller carboxylic acids are soluble in water, whereas higher carboxylic acids are less due to the increasing hydrophobic nature of the alkyl chain. These longer chain acids tend to be soluble in less-polar solvents such as ethers. Carboxylic acids tend to have higher boiling points than water, not only because of their surface area. Carboxylic acids tend to evaporate or boil as these dimers, for boiling to occur, either the dimer bonds must be broken or the entire dimer arrangement must be vaporised, both of which increase the enthalpy of vaporization requirements significantly
30.
Hydrazoic acid
–
Hydrazoic acid, also known as hydrogen azide or azoimide, is a compound with the chemical formula HN3. It is a colorless, volatile, and explosive liquid at room temperature and pressure and it is a compound of nitrogen and hydrogen, and is therefore a pnictogen hydride. It was first isolated in 1890 by Theodor Curtius, the acid has few applications, but its conjugate base, the azide ion, is useful in specialized processes. Hydrazoic acid is soluble in water, undiluted hydrazoic acid is dangerously explosive with a standard enthalpy of formation ΔfHo = +264 kJmol−1). When dilute, the gas and aqueous solutions can be safely handled, the acid is usually formed by acidification of an azide salt like sodium azide. The pure acid may be obtained by fractional distillation as an extremely explosive colorless liquid with an unpleasant smell. NaN3 + HCl → HN3 + NaCl Its aqueous solution can also be prepared by treatment of barium azide solution with dilute sulfuric acid and it was originally prepared by the reaction of aqueous hydrazine with nitrous acid. N2H5+ + HNO2 → HN3 + H+ +2 H2O Other oxidizing agents, such as hydrogen peroxide, NOCl, NCl3 or nitric acid, in its properties hydrazoic acid shows some analogy to the halogen acids, since it forms poorly soluble lead, silver and mercury salts. The metallic salts all crystallize in the form and decompose on heating, leaving a residue of the pure metal. It is a weak acid Its heavy metal salts are explosive, azides of heavier alkali metals or alkaline earth metals are not explosive, but decompose in a more controlled way upon heating, releasing spectroscopically-pure N2 gas. Solutions of hydrazoic acid dissolve many metals with liberation of hydrogen and formation of salts, dissolution in the strongest acids produces explosive salts containing the H 2N=N=N+ ion, for example, HN=N=N + HSbCl 6 → +− The ion H 2N=N=N+ is isoelectronic to diazomethane. The decomposition of hydrazoic acid, triggered by shock, friction, spark, etc. goes as follows, 2HN3 → H2 + 3N2 Hydrazoic acid is volatile and it has a pungent smell and its vapor can cause violent headaches. The compound acts as a non-cumulative poison
31.
Curtius rearrangement
–
The Curtius rearrangement, first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of such as water, alcohols and amines, to yield a primary amine. The acyl azide is usually made from the reaction of acid chlorides or anydrides with sodium azide or trimethylsilyl azide, acyl azides are also obtained from treating acylhydrazines with nitrous acid. Alternatively, the acyl azide can be formed by the reaction of a carboxylic acid with diphenylphosphoryl azide. It was originally believed that the Curtius rearrangement was a process, with the loss of nitrogen gas forming an acyl nitrene. Thermodynamic calculations also support a concerted mechanism, the migration occurs with full retention of configuration at the R-group. The migratory aptitude of the R-group is roughly tertiary > secondary ~ aryl > primary, the isocyanate formed can then be hydrolyzed to give a primary amine, or undergo nucleophilic attack with alcohols and amines to form carbamates and urea derivatives respectively. Research has shown that the Curtius rearrangement is catalyzed by both Brønsted and Lewis acids, via the protonation of, or coordination to the oxygen atom respectively. Photochemical decomposition of the azide is also possible. However, photochemical rearrangement is not concerted and instead occurs by an intermediate, formed by the cleavage of the weak N–N bond. The highly reactive nitrene can undergo a variety of reactions, such as nitrene insertion and addition. In the example below the nitrene formed inserts into the solvent to form N-cyclohexylbenzamide as a side product. In one variation called the Darapsky degradation, or Darapsky synthesis, hydrazine is used to convert the ester to an acylhydrazine, which is reacted with nitrous acid to give the acyl azide. Heating the azide in ethanol yields the ethyl carbamate via the Curtius rearrangement, acid hydrolysis yields the amine from the carbamate and the carboxylic acid from the nitrile simultaneously, giving the product amino acid. The photochemical Curtius-like migration and rearrangement of a phosphinic azide forms a metaphosphonimidate in what is known as the Harger reaction. This is followed by hydrolysis, in the example below with methanol, unlike the Curtius rearrangement, there is a choice of R-groups on the phosphinic azide which can migrate. Harger has found that the alkyl groups migrate preferentially to aryl groups, and this is probably due to steric and conformational factors, as the bulkier the R-group, the less favorable the conformation for phenyl migration. For example, when carried out in the presence of tert-butanol, likewise, when the Curtius reaction is performed in the presence of benzyl alcohol, Cbz-protected amines are formed
32.
Acyl azide
–
Acyl azides are carboxylic acid derivatives with the general formula RCON3. Alkyl or aryl acyl chlorides react with sodium azide to give acyl azides and they can also be synthesized from various carboxylic acids and sodium azide in presence of triphenylphosphine and trichloroacetonitrile catalysts in excellent yields at mild conditions. Another route starts with aliphatic and aromatic aldehydes reacting with iodine azide which is formed from sodium azide, acyl azides are used as chemical reagents. On Curtius rearrangement acyl azides yield isocyanates, acyl azides are also formed in Darapsky degradation
33.
Nitrogen gas
–
Nitrogen is a chemical element with symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772, although Carl Wilhelm Scheele and Henry Cavendish had independently done so at about the same time, Rutherford is generally accorded the credit because his work was published first. Nitrogen is the lightest member of group 15 of the periodic table, the name comes from the Greek πνίγειν to choke, directly referencing nitrogens asphyxiating properties. It is an element in the universe, estimated at about seventh in total abundance in the Milky Way. At standard temperature and pressure, two atoms of the element bind to form dinitrogen, a colourless and odorless diatomic gas with the formula N2, dinitrogen forms about 78% of Earths atmosphere, making it the most abundant uncombined element. Nitrogen occurs in all organisms, primarily in amino acids, in the nucleic acids, the human body contains about 3% nitrogen by mass, the fourth most abundant element in the body after oxygen, carbon, and hydrogen. The nitrogen cycle describes movement of the element from the air, into the biosphere and organic compounds, many industrially important compounds, such as ammonia, nitric acid, organic nitrates, and cyanides, contain nitrogen. The extremely strong bond in elemental nitrogen, the second strongest bond in any diatomic molecule. Synthetically produced ammonia and nitrates are key industrial fertilisers, and fertiliser nitrates are key pollutants in the eutrophication of water systems. Apart from its use in fertilisers and energy-stores, nitrogen is a constituent of organic compounds as diverse as Kevlar used in high-strength fabric, Nitrogen is a constituent of every major pharmacological drug class, including antibiotics. Many notable nitrogen-containing drugs, such as the caffeine and morphine or the synthetic amphetamines. Nitrogen compounds have a long history, ammonium chloride having been known to Herodotus. They were well known by the Middle Ages, alchemists knew nitric acid as aqua fortis, as well as other nitrogen compounds such as ammonium salts and nitrate salts. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold, the discovery of nitrogen is attributed to the Scottish physician Daniel Rutherford in 1772, who called it noxious air. Though he did not recognise it as a different chemical substance, he clearly distinguished it from Joseph Blacks fixed air. The fact that there was a component of air that does not support combustion was clear to Rutherford, Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as air or azote, from the Greek word άζωτικός. In an atmosphere of nitrogen, animals died and flames were extinguished
34.
Lossen rearrangement
–
Here, 4-toluenesulfonyl chloride is used to form a sulfonyl Ortho-derivative of hydroxamic acid. The isocyanate can be used further to generate ureas in the presence of amines or generate amines in the presence of H2O. The mechanism below begins with an O-acylated hydroxamic acid derivative that is treated with base to form an isocyanate that generates an amine, the hydroxamic acid acid derivative is first converted to its conjugate base by abstraction of a hydrogen by a base. Spontaneous rearrangement kicks off a carboxylate anion to produce the isocyanate intermediate, the isocyanate in the presence H2O hydrolyzes and then decarboxylation via abstraction of a hydrogen by a base generates an amine and CO2 gas. Hydroxamic acids are synthesized from their corresponding esters. Curtius rearrangement Hofmann rearrangement Schmidt reaction Gabapentin Mechanism in Motion, Lossen rearrangement
35.
Hydroxamic acid
–
A hydroxamic acid is a class of organic compounds bearing the functional group RCNR, with R and R as organic residues and CO as a carbonyl group. They are amides wherein the NH center has an OH substitution and they are often used as metal chelators. Hydroxamic acids are prepared from either esters or acid chlorides by a reaction with hydroxylamine salts. For the synthesis of benzohydroxamic acid, the equations is. A well-known hydroxamic acid reaction is the Lossen rearrangement, sample gallery In the area of coordination chemistry, hydroxamic acids are excellent ligands. They deprotonate to give hydroxamates, which bind to metals ions as bidentate ligands, so high is the affinity of hydroxamates for ferric ions that nature has evolved families of hydroxamic acids to function as iron-binding compounds in bacteria. The resulting complexes are transported into the cell, where the iron is extracted and utilized metabolically, Hydroxamic acids are used extensively in flotation of rare earth minerals during the concentration and extraction of ores to be subjected to further processing. Some hydroxamic acids are HDAC inhibitors with anti-cancer properties, fosmidomycin is a natural hydroxamic acid inhibitor of 1-deoxy-D-xylulose-5-phosphate reductoisomerase. Hydroxamic acids have also investigated for reprocessing of irradiated fuel. Fouché, K. F. H. J. le Roux, complex formation of Zr and Hf with hydroxamic acids in acidic solutions. Journal of Inorganic and Nuclear Chemistry, barocas, A. F. Baroncelli, G. B. Journal of Inorganic and Nuclear Chemistry, journal of Inorganic and Nuclear Chemistry. Al-Jarrah, R. H. A. R. Al-Karaghouli, S. A. Al-Assaf, solvent extraction of uranium and some other metal ions with 2-N-butyl-2-ethyl octanohydroxamic acid. Journal of Inorganic and Nuclear Chemistry, Gopalan, Aravamudan S. Vincent J. Huber, Orhan Zincircioglu, Paul H. Smith. Novel tetrahydroxamate chelators for actinide complexation, synthesis and binding studies, journal of the Chemical Society, Chemical Communications, 1266–1268. Koshti, Nirmal, Vincent Huber, Paul Smith, Aravamudan S. Gopalan, design and synthesis of actinide specific chelators, Synthesis of new cyclam tetrahydroxamate and cyclam tetraacetonylacetone chelators
36.
Acyl group
–
An acyl group is a moiety derived by the removal of one or more hydroxyl groups from an oxoacid, including inorganic acids. It contains a double bonded oxygen atom and an alkyl group, in organic chemistry, the acyl group is usually derived from a carboxylic acid. Therefore, it has the formula RCO–, where R represents a group that is linked to the carbon atom of the group by a single bond. Although the term is almost always applied to compounds, acyl groups can in principle be derived from other types of acids such as sulfonic acids. In the most common arrangement, acyl groups are attached to a molecular fragment, in which case the carbon. Well-known acyl compounds are the acyl chlorides, such as acetyl chloride and these compounds, which are treated as sources of acylium cations, are good reagents for attaching acyl groups to various substrates. Amides and esters are classes of compounds, as are ketones and aldehydes. Acylium ions are cations of the formula RCO+, such species are common reactive intermediates, for example, in the Friedel–Crafts acylations also in many other organic reactions such as the Hayashi rearrangement. Acylium cations are characteristic fragments observed in EI-mass spectra of ketones, acyl radicals are readily generated from aldehydes by H-atom abstraction. However, they undergo rapid decarbonylation to afford the alkyl radical, acyl anions are almost always unstable, usually too unstable to be exploited synthetically. Hence synthetic chemists have developed various acyl anion equivalents as surrogates, in biochemistry there are many instances of acyl groups, in all major categories of biochemical molecules. Acyl-CoAs are acyl derivatives formed via fatty acid metabolism, acetyl-CoA, the most common derivative, serves as an acyl donor in many biosynthetic transformations. Names of acyl groups of amino acids are formed by the replacement of the ending -ine by the ending -yl, for example, the acyl group of glycine is glycyl, and of lysine is lysyl. Names of acyl groups of ribonucleoside monophosphates such as AMP, GMP, CMP, and UMP are adenylyl, guanylyl, cytidylyl, in phospholipids, the acyl group of phosphatidic acid is called phosphatidyl-. Acyl ligands are intermediates in many reactions, which are important in some catalytic reactions. Metal acyls arise usually via insertion of carbon monoxide into metal–alkyl bonds, metal acyls also arise from reactions involving acyl chlorides with low-valence metal complexes or by the reaction of organolithium compounds with metal carbonyls. Metal acyls are often described by two structures, one of which emphasizes the basicity of the oxygen center. O-alkylation of metal acyls gives Fischer carbene complexes, the names of acyl groups are derived typically from the corresponding acid by substituting the acid ending -ic with the ending -yl as shown in the table below
37.
Phosphine oxide
–
Phosphine oxides are phosphorus compounds with the formula OPX3. When X = alkyl or aryl, these are organophosphine oxides, an inorganic phosphine oxide is phosphoryl chloride. Such compounds are stable, decomposing only above 450 °C. Phosphoryl refers to a group drawn with a phosphorus-oxygen double bond. Phosphine oxides feature tetrahedral phosphorus centers, the P-O bond is short and polar. The nature of the P−O bond was once hotly debated, some discussions invoked a role for phosphorus-centered d-orbitals in bonding, but this analysis is not supported by computational analyses. In terms of simple Lewis structure, the bond is more accurately represented as a dative bond, deoxygenation proceeds with retention or inversion of configuration, depending on conditions. Inversion is favored by a combination of trichlorosilane and triethylamine, in the absence of the base, the reaction proceeds with retention. The stereochemical course is explained mechanistically by complexation followed by hydride transfer. Based on these observations, it is thought that complexation of OPR3 by trichlorosilane occurs with retention of configuration, instead of HSiCl3, other perchloropolysilanes, e. g. hexachlorodisilane, can also be used to deoxygenate phosphine oxides. In comparison, using the reaction of the corresponding phosphine oxides with perchloropolysilanes such as Si2Cl6 or Si3Cl8 in benzene or chloroform, to counter this problem Ph3P or 3P along with trichlorosilane can be used. Phosphine oxides are ligands in various applications of homogeneous catalysis, in coordination chemistry, they are known to have labilizing effects to CO ligands cis to it in organometallic reactions. The cis effect describes this process, phosphine oxides are typically viewed as useless by-products in the Wittig reaction. They can, however, be usable in certain Wittig-like reactions, thus, benzaldehyde has been converted to β-methoxystyrene using methoxymethyl diphenylphosphine oxide in a two step procedure. In step one the oxide is deprotonated at −90 °C in THF/ether with lithium diisopropylamide. After aqueous workup, adducts are isolated, with potassium-t-butoxide the adducts are, at room temperature, converted to the styrenes. As the adducts exist as a mixture of D/L compounds. The parent compound phosphine oxide is unstable and it has also been reported relatively stable in a water-ethanol solution by electrochemical oxidation of white phosphorus, where it slowly disproportionates into phosphine and hypophosphorous acid
38.
Methylene diphenyl diisocyanate
–
Methylene diphenyl diisocyanate, most often abbreviated as MDI, is an aromatic diisocyanate. Three isomers are common, varying by the positions of the groups around the rings,2, 2-MDI,2, 4-MDI. The 4,4 isomer is most widely used, and is known as 4. This isomer is known as Pure MDI. MDI reacts with polyols in the manufacture of polyurethane and it is the most produced diisocyanate, accounting for 61. 3% of the global market in the year 2000. Total world production of MDI and polymeric MDI is over 5 million tonnes per year, the largest producer is Covestro followed closely by Yantai Wanhua. Other major producers are BASF, BorsodChem, Dow, Huntsman, Nippon Polyurethane Industry, all major producers of MDI are members of the International Isocyanate Institute, whose aim is the promotion of the safe handling of MDI and TDI in the workplace, community and environment. The isomer ratio is determined by the composition of the diamine. Distillation of the MDI mixture gives polymeric MDI and an MDI isomer mixture which has a low 2,4 isomer content, further purification entails fractionation of the MDI isomer mixture. The positions of the groups influences their reactivity. In 4, 4-MDI, the two groups are equivalent but in 2, 4-MDI the two groups display highly differing reactivities. The group at the 4-position is approximately four times more reactive than the group at the 2-position due to steric hindrance, the major application of 4, 4-MDI is the production of rigid polyurethane. Typically, one tonne of polyurethane foam needs 0.616 tonne of MDI and 0.386 tonne of polyol and these rigid polyurethane foams are good thermal insulators and used in nearly all freezers and refrigerators worldwide, as well as buildings. Typical polyols used are polyethylene adipate and poly glycol,4, 4-MDI is also used as an industrial strength adhesive, which is available to end consumers as various high-strength bottled glue preparations. MDI is the least hazardous of the commonly available isocyanates but is not benign and its very low vapour pressure reduces its hazards during handling compared to the other major isocyanates. However, it, like the other isocyanates, is an allergen, persons developing sensitivity to isocyanates may have dangerous systemic reactions to extremely small exposures, including respiratory failure. Handling MDI requires strict engineering controls and personal protective equipment, compared to other organic cyanates, MDI has a relatively low human toxicity. It is a potentially violently reactive material towards water and other nucleophiles
39.
Toluene diisocyanate
–
Toluene diisocyanate is an organic compound with the formula CH3C6H32. Two of the six isomers are commercially important,2, 4-TDI and 2. 2, 4-TDI is produced in the state, but TDI is often marketed as 80/20. It is produced on a scale, accounting for 34. 1% of the global isocyanate market in 2000. Approximately 1.4 billion kilograms were produced in 2000,2, 4-TDI is prepared in three steps from toluene via dinitrotoluene and 2, 4-diaminotoluene. Finally, the TDA is subjected to phosgenation, i. e. treatment with phosgene to form TDI and this final step produces HCl as a byproduct and is a major source of industrial hydrochloric acid. Distillation of the crude TDI mixture produces an 80,20 mixture of 2, 4-TDI and 2, 6-TDI, known as TDI. Differentiation or separation of the TDI can be used to produce pure 2, 4-TDI, the isocyanate functional groups in TDI react with hydroxyl groups to form carbamate links. The two isocyanate groups in TDI react at different rates, The 4-position is approximately four times more reactive than the 2-position,2, 6-TDI is a symmetrical molecule and thus has two isocyanate groups of similar reactivity, similar to the 2-position on 2, 4-TDI. However, since both groups are attached to the same aromatic ring, reaction of one isocyanate group will cause a change in the reactivity of the second isocyanate group. It is used in the production of polyurethane foams The LD50 for TDI is 5800 mg/kg for oral contact. Despite the indicated low toxicity, TDI is classified as “very toxic” by the European Community, in the United States, the Occupational Safety and Health Administration has set a permissible exposure limit with a ceiling at 0. This chemical was one of many that two massive explosions in a chemical warehouse stationed in Tianjin, China on August 13,2015. All major producers of TDI are members of the International Isocyanate Institute, whose aim is the promotion of the handling of TDI in the workplace, community
40.
Hexamethylene diisocyanate
–
Hexamethylene diisocyanate is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate and it is produced in relatively small quantities, accounting for only 3. 4% of the global diisocyanate market in the year 2000. Aliphatic diisocyanates are used in applications, such as enamel coatings which are resistant to abrasion and degradation from ultraviolet light. These properties are desirable in, for instance, the exterior paint applied to aircraft
41.
Isophorone diisocyanate
–
Isophorone diisocyanate is an organic compound in the class known as isocyanates. More specifically, it is an aliphatic diisocyanate and it is produced in relatively small quantities, accounting for only 3. 4% of the global diisocyanate market in the year 2000. These properties are desirable in, for instance, the exterior paint applied to aircraft. Each stereoisomer is a molecule, and thus has isocyanate groups with different reactivities. The primary isocyanate group is more reactive than the secondary isocyanate group
42.
Methyl isocyanate
–
Methyl isocyanate is an organic compound with the molecular formula CH3NCO. Synonyms are isocyanatomethane, methyl carbylamine, and MIC, Methyl isocyanate is an intermediate chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives. As a highly toxic and irritating material, it is hazardous to human health. It was the principal toxicant involved in the Bhopal disaster, which killed nearly 2,259 people initially and officially 3,787 people in total, Methyl isocyanate is a colorless, lachrymatory, flammable liquid. It is soluble in water to 6–10 parts per 100 parts, Methyl isocyanate is usually manufactured by the reaction of monomethylamine and phosgene. For large scale production, it is advantageous to combine these reactants at higher temperature in the gas phase. A mixture of methyl isocyanate and two moles of hydrogen chloride is formed, but N-methylcarbamoyl chloride forms as the mixture is condensed, leaving one mole of hydrogen chloride as a gas. The methyl isocyanate is obtained by treating the MCC with an amine, such as N, N-dimethylaniline. Methyl isocyanate is also manufactured from N-methylformamide and air, in the latter process, it is immediately consumed in a closed-loop process to make methomyl. Other manufacturing methods have been reported, Methyl isocyanate reacts readily with many substances that contain N-H or O-H groups. If MIC is in excess,1,3, 5-trimethylbiuret is formed along with carbon dioxide, alcohols and phenols, which contain an O-H group, react slowly with MIC, but the reaction can be catalyzed by trialkylamines or dialkyltin dicarboxylate. Oximes, hydroxylamines, and enols also react with MIC to form methylcarbamates and these reactions produce the products described below. Ammonia, primary, and secondary amines rapidly react with MIC to form substituted ureas, other N-H compounds, such as amides and ureas, react much more slowly with MIC. It also reacts with itself to form a trimer or higher molecular weight polymers, since the formation of the MIC trimer is exothermic, the reaction can lead to violent boiling of the MIC. The high-molecular-weight polymer hydrolyzes in hot water to form the trimethyl isocyanurate, since catalytic metal salts can be formed from impurities in commercial grade MIC and steel, this product must not be stored in steel drums or tanks. Methyl isocyanate is a chemical in the production of carbamate pesticides. It has also used in the production of rubbers and adhesives
