In chemistry, an alcohol is any organic compound in which the hydroxyl functional group is bound to a carbon. The term alcohol referred to the primary alcohol ethanol, used as a drug and is the main alcohol present in alcoholic beverages. An important class of alcohols, of which methanol and ethanol are the simplest members, includes all compounds for which the general formula is CnH2n+1OH, it is these simple monoalcohols. The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; when a higher priority group is present in the compound, the prefix hydroxy- is used in its IUPAC name. The suffix -ol in non-IUPAC names typically indicates that the substance is an alcohol. However, many substances that contain hydroxyl functional groups have names which include neither the suffix -ol, nor the prefix hydroxy-. Alcohol distillation originated in India. During 2000 BCE, people of India used. Alcohol distillation was known to Islamic chemists as early as the eighth century.
The Arab chemist, al-Kindi, unambiguously described the distillation of wine in a treatise titled as "The Book of the chemistry of Perfume and Distillations". The Persian physician, alchemist and philosopher Rhazes is credited with the discovery of ethanol; the word "alcohol" is from a powder used as an eyeliner. Al- is the Arabic definite article, equivalent to the in English. Alcohol was used for the fine powder produced by the sublimation of the natural mineral stibnite to form antimony trisulfide Sb2S3, it was considered to be the essence or "spirit" of this mineral. It was used as an antiseptic and cosmetic; the meaning of alcohol was extended to distilled substances in general, narrowed to ethanol, when "spirits" was a synonym for hard liquor. Bartholomew Traheron, in his 1543 translation of John of Vigo, introduces the word as a term used by "barbarous" authors for "fine powder." 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 word's 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, combining the word ethane with the "-ol" ending of "alcohol". IUPAC nomenclature is used in scientific publications and where precise identification of the substance is important in cases where the relative complexity of the molecule does not make such a systematic name unwieldy. In naming simple alcohols, the name of the alkane chain loses the terminal e and adds the suffix -ol, e.g. as in "ethanol" from the alkane chain name "ethane".
When necessary, the position of the hydroxyl group is indicated by a number between the alkane name and the -ol: propan-1-ol for CH3CH2CH2OH, propan-2-ol for CH3CHCH3. If a higher priority group is present the prefix hydroxy-is used, e.g. as in 1-hydroxy-2-propanone. In cases where the OH functional group is bonded to an sp2 carbon on an aromatic ring the molecule is known as a phenol, is named using the IUPAC rules for naming phenols. In other less formal contexts, an alcohol is 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 hydroxyl 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, the alcohol moiety is indicated using the "hydroxy-" prefix. Alcohols are classified into primary 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, the next is ethanol, for which R=CH3, the methyl group. Secondary alcohols are those of the form RR'CHOH, the simplest of, 2-propanol. For the tertiary alcohols the general form is RR'R"COH; the simplest example is tert-butanol, for which each of R, R', R" is CH3. In these shorthands, R, R', R" represent substituents, alkyl or other attached organic groups. In archaic nomenclature, alcohols can be named as derivatives of methanol using "-carbinol" as the ending. For instance, 3COH can be named trimethylcarbinol. Alcohols have a long history of myriad uses. For simple mono-alcohols, the focus on this article, the following are most important industrial alcohols: methanol for the production of formaldehyde and as a fuel additive ethanol for alcoholic beverages, fuel additive, solvent 1-propanol, 1-butanol, isobutyl alcohol for use as a solvent a
An aminal or aminoacetal is a functional group or type of organic compound that has two amine groups attached to the same carbon atom: -C-.. The aminal and the hemiaminal groups are analogous to hemiacetals and acetals with nitrogen replaced by oxygen. Aminals are encountered for instance, the Fischer indole synthesis. Cyclic aminals are well known, being derived by the condensation of a diamine and an aldehyde. An example is hexamethylenetetramine derived from formaldehyde. Hemiaminal ethers are sometimes called aminals although it is discouraged by the IUPAC; the ethers have the following structure: R‴-C-R⁗. The glycosylamines are examples of cyclic hemiaminal ethers. Acetal Hemiaminal
In chemistry, azeotropic distillation is any of a range of techniques used to break an azeotrope in distillation. In chemical engineering, azeotropic distillation refers to the specific technique of adding another component to generate a new, lower-boiling azeotrope, heterogeneous, such as the example below with the addition of benzene to water and ethanol; this practice of adding an entrainer which forms a separate phase is a specific sub-set of azeotropic distillation methods, or combination thereof. In some senses, adding an entrainer is similar to extractive distillation; the addition of a material separation agent, such as benzene to an ethanol/water mixture, changes the molecular interactions and eliminates the azeotrope. Added in the liquid phase, the new component can alter the activity coefficient of various compounds in different ways thus altering a mixture's relative volatility. Greater deviations from Raoult's law make it easier to achieve significant changes in relative volatility with the addition of another component.
In azeotropic distillation the volatility of the added component is the same as the mixture, a new azeotrope is formed with one or more of the components based on differences in polarity. If the material separation agent is selected to form azeotropes with more than one component in the feed it is referred to as an entrainer; the added entrainer should be recovered by distillation, decantation, or another separation method and returned near the top of the original column. A common historical example of azeotropic distillation is its use in dehydrating ethanol and water mixtures. For this, a near azeotropic mixture is sent to the final column where azeotropic distillation takes place. Several entrainers can be used for this specific process: benzene, cyclohexane, heptane, isooctane and diethyl ether are all options as the mixture. Of these benzene and cyclohexane have been used the most extensively. However, because benzene has been discovered to be a carcinogenic compound, its use has declined.
While this method was the standard for dehydrating ethanol in the past, it has lost favor due to the high capital and energy costs associated with it. Another favorable method and less toxic than using benzene to break the azeotrope of the ethanol-water system is to use toluene instead. Another method, pressure-swing distillation, relies on the fact that an azeotrope is pressure dependent. An azeotrope is not a range of concentrations that cannot be distilled, but the point at which the activity coefficients of the distillates are crossing one another. If the azeotrope can be "jumped over", distillation can continue, although because the activity coefficients have crossed, the water will boil out of the remaining ethanol, rather than the ethanol out of the water as at lower concentrations. To "jump" the azeotrope, the azeotrope can be moved by altering the pressure. Pressure will be set such that the azeotrope will differ from the azeotrope at ambient pressure by some percent in either direction.
For an ethanol-water mixture, that may be at 93.9% for 20bar overpressure, instead of 95.3% at ambient pressure. The distillation works in the opposite direction, with the ethanol emerging in the bottoms and the water in the distillate. While in the low pressure column, ethanol is enriched on the way to the top end of the column, the high pressure column enriches ethanol on the bottom end, as ethanol is now the highboiler; the top product is again fed to the low pressure column, where the normal distillation is done. The bottom product of the low pressure column consists of water, while the bottom stream of the high pressure column is nearly pure ethanol at concentrations of 99% or higher. Pressure swing distillation inverts the K-values and subsequently inverts which end of the column each component comes out when compared to standard low pressure distillation. Overall the pressure-swing distillation is a robust and not so sophisticated method compared to multi component distillation or membrane processes, but the energy demand is in general higher.
The investment cost of the distillation columns is higher, due to the pressure inside the vessels. For low boiling azeotropes, the volatile component cannot be purified by distillation. To obtain the pure material one must "break the azeotrope", which involves a separation method that does not rely on distillation. A common approach involves the use of molecular sieves. Treatment of 96% ethanol with molecular sieves gives the anhydrous alcohol, the sieves having adsorbed water from the mixture; the sieves can be subsequently regenerated by dehydration using a vacuum oven. In organic chemistry, some dehydration reactions are subject to fast equilibria. One example is the formation of dioxolanes from aldehydes: RCHO + 2 ← → RCH2 + H2OSuch unfavorable reactions proceed when water is removed by azeotropic distillation. Azeotrope Theoretical plate Azeotrope Residue curve
A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring. Heterocyclic chemistry is the branch of organic chemistry dealing with the synthesis and applications of these heterocycles. Examples of heterocyclic compounds include all of the nucleic acids, the majority of drugs, most biomass, many natural and synthetic dyes. Although heterocyclic chemical compounds may be inorganic compounds or organic compounds, most contain at least one carbon. While atoms that are neither carbon nor hydrogen are referred to in organic chemistry as heteroatoms, this is in comparison to the all-carbon backbone, but this does not prevent a compound such as borazine from being labelled "heterocyclic". IUPAC recommends the Hantzsch-Widman nomenclature for naming heterocyclic compounds. Heterocyclic compounds can be usefully classified based on their electronic structure; the saturated heterocycles behave like the acyclic derivatives. Thus and tetrahydrofuran are conventional amines and ethers, with modified steric profiles.
Therefore, the study of heterocyclic chemistry focuses on unsaturated derivatives, the preponderance of work and applications involves unstrained 5- and 6-membered rings. Included are pyridine, thiophene and furan. Another large class of heterocycles are fused to benzene rings, which for pyridine, thiophene and furan are quinoline, benzothiophene and benzofuran, respectively. Fusion of two benzene rings gives rise to a third large family of compounds the acridine, dibenzothiophene and dibenzofuran; the unsaturated rings can be classified according to the participation of the heteroatom in the conjugated system, pi system. Heterocycles with three atoms in the ring are more reactive because of ring strain; those containing one heteroatom are, in general, stable. Those with two heteroatoms are more to occur as reactive intermediates. Common 3-membered heterocycles with one heteroatom are: Those with two heteroatoms include: Compounds with one heteroatom: Compounds with two heteroatoms: With heterocycles containing five atoms, the unsaturated compounds are more stable because of aromaticity.
The 5-membered ring compounds containing two heteroatoms, at least one of, nitrogen, are collectively called the azoles. Thiazoles and isothiazoles contain a nitrogen atom in the ring. Dithiolanes have two sulfur atoms. A large group of 5-membered ring compounds with three heteroatoms exists. One example is dithiazoles that contain a nitrogen atom. Six-membered rings with a single heteroatom: With two heteroatoms: With three heteroatoms: With four heteroatoms: With five heteroatoms: The hypothetical compound with six nitrogen heteroatoms would be hexazine. With 7-membered rings, the heteroatom must be able to provide an empty pi orbital for "normal" aromatic stabilization to be available. Compounds with one heteroatom include: Those with two heteroatoms include: Names in italics are retained by IUPAC and they do not follow the Hantzsch-Widman nomenclature Heterocyclic rings systems that are formally derived by fusion with other rings, either carbocyclic or heterocyclic, have a variety of common and systematic names.
For example, with the benzo-fused unsaturated nitrogen heterocycles, pyrrole provides indole or isoindole depending on the orientation. The pyridine analog is isoquinoline. For azepine, benzazepine is the preferred name; the compounds with two benzene rings fused to the central heterocycle are carbazole and dibenzoazepine. Thienothiophene are the fusion of two thiophene rings. Phosphaphenalenes are a tricyclic phosphorus-containing heterocyclic system derived from the carbocycle phenalene; the history of heterocyclic chemistry began in the 1800s, in step with the development of organic chemistry. Some noteworthy developments: 1818: Brugnatelli isolates alloxan from uric acid 1832: Dobereiner produces furfural by treating starch with sulfuric acid 1834: Runge obtains pyrrole by dry distillation of bones 1906: Friedlander synthesizes indigo dye, allowing synthetic chemistry to displace a large agricultural industry 1936: Treibs isolates chlorophyl derivatives from crude oil, explaining the biological origin of petroleum.
1951: Chargaff's rules are described, highlighting the role of heterocyclic compounds in the genetic code. Heterocyclic compounds are pervasive in many areas of technology. Many drugs are heterocyclic compounds. Hantzsch-Widman nomenclature, IUPAC Heterocyclic amines in cooked meat, US CDC List of known and probable carcinogens, American Cancer Society List of known carcinogens by the State of California, Proposition 65
A molecular sieve is a material with pores of uniform size. These pore diameters are similar in size to small molecules, thus large molecules cannot enter or be adsorbed, while smaller molecules can; as a mixture of molecules migrate through the stationary bed of porous, semi-solid substance referred to as a sieve, the components of highest molecular weight leave the bed first, followed by successively smaller molecules. Some molecular sieves are used in chromatography, a separation technique that sorts molecules based on their size. Other molecular sieves are used as desiccants; the diameter of a molecular sieve is measured in nanometres. According to IUPAC notation, microporous materials have pore diameters of less than 2 nm and macroporous materials have pore diameters of greater than 50 nm. Molecular sieves can be mesoporous, or macroporous material. Zeolites Zeolite LTA: 3–4 Å Porous glass: 10 Å, up Active carbon: 0–20 Å, up Clays Montmorillonite intermixes Halloysite: Two common forms are found, when hydrated the clay exhibits a 1 nm spacing of the layers and when dehydrated the spacing is 0.7 nm.
Halloysite occurs as small cylinders which average 30 nm in diameter with lengths between 0.5 and 10 micrometres. Silicon dioxide: 24 Å Mesoporous silica, 200–1000 Å Molecular sieves are utilized in the petroleum industry for drying gas streams. For example, in the liquid natural gas industry, the water content of the gas needs to be reduced to less than 1 ppmv to prevent blockages caused by ice. In the laboratory, molecular sieves are used to dry solvent. "Sieves" have proven to be superior to traditional drying techniques, which employ aggressive desiccants. Under the term zeolites, molecular sieves are used for a wide range of catalytic applications, they catalyze isomerisation and epoxidation, are used in large scale industrial processes, including hydrocracking and fluid catalytic cracking. They are used in the filtration of air supplies for breathing apparatus, for example those used by scuba divers and firefighters. In such applications, air is supplied by an air compressor and is passed through a cartridge filter which, depending on the application, is filled with molecular sieve and/or activated carbon being used to charge breathing air tanks.
Such filtration can remove particulates and compressor exhaust products from the breathing air supply. The U. S. FDA has as of April 1, 2012 approved sodium aluminosilicate for direct contact with consumable items under 21 CFR 182.2727. Prior to this approval Europe had used molecular sieves with pharmaceuticals and independent testing suggested that molecular sieves meet all government requirements but the industry had been unwilling to fund the expensive testing required for government approval. Methods for regeneration of molecular sieves include pressure change and purging with a carrier gas, or heating under high vacuum. Regeneration temperatures range from 175 °C to 315 °C depending on molecular sieve type. In contrast, silica gel can be regenerated by heating it in a regular oven to 120 °C for two hours. However, some types of silica gel will "pop"; this is caused by breakage of the silica spheres. Approximate chemical formula: 2/3K2O•1/3Na2O•Al2O3• 2 SiO2 • 9/2 H2O Silica-alumina ratio: SiO2/ Al2O3≈23Å molecular sieves do not adsorb molecules whose diameters are larger than 3 Å.
The characteristics of these molecular sieves include fast adsorption speed, frequent regeneration ability, good crushing resistance and pollution resistance. These features can improve both the lifetime of the sieve. 3Å molecular sieves are the necessary desiccant in petroleum and chemical industries for refining oil and chemical gas-liquid depth drying. 3Å molecular sieves are used to dry a range of materials, such as ethanol, refrigerants, natural gas and unsaturated hydrocarbons. The latter include cracking gas, ethylene and butadiene. 3Å molecular sieve is utilized to remove water from ethanol, which can be used directly as a bio-fuel or indirectly to produce various products such as chemicals, foods and more. Since normal distillation cannot remove all the water from ethanol process streams due to the formation of an azeotrope at around 95 percent concentration, molecular sieve beads are used to separate ethanol and water on a molecular level by adsorbing the water into the beads and allowing the ethanol to pass freely.
Once the beads are full of water, temperature or pressure can be manipulated, allowing the water to be released from the molecular sieve beads.3Å molecular sieves are stored at room temperature, with a relative humidity not more than 90%. They are sealed under reduced pressure, being kept away from water and alkalis. Chemical formula: Na2O•Al2O3•2SiO2•9/2H2O Silica-alumina ratio: SiO2/ Al2O3≈24Å molecular sieves are used to dry laboratory solvents, they can absorb water and other molecules with a critical diameter less than 4 Å such as NH3, H2S, SO2, CO2, C2H5OH, C2H6, C2H4. It is used in the drying and purification of liquids and gases; these molecular sieves are used t
A hemiaminal is a functional group or type of chemical compound that has a hydroxyl group and an amine attached to the same carbon atom: -C-. R can be an alkyl group. Hemiaminals are intermediates in imine formation from an amine and a carbonyl by alkylimino-de-oxo-bisubstitution. A hemiaminal is the first step in the reaction of an ketone with an amine. Being one of the most reactive carbonyls, formaldehyde is well known to give carbinolamines. Illustrative is the reaction of the weakly basic secondary amine carbazole with formaldehyde; as is typical with a secondary amine derivative, this carbinol converts to the methylene-linked bis. Ammonia adds to hexafluoroacetone to give a stable hemiaminal, 2CNH2; those generated from primary amines and ammonia are unstable to the extent that they have never been isolated and rarely been observed directly. A hemiaminal trapped in the cavity of a host–guest complex exhibited chemical half-life of 30 minutes; because both amine and carbonyl group are isolated in a cavity, hemiaminal formation is favored due to a high forward reaction rate comparable to an intramolecular reaction and due to restricted access of external base to the same cavity which would favor elimination of water to the imine.
Hemiaminal formation is a key step in an asymmetric total synthesis of saxitoxin: In this reaction step the alkene group is first oxidized to an intermediate acyloin by action of osmium chloride and sodium carbonate. The adducts formed by the addition of ammonia to aldehydes have long been studied; this class of compounds contain both a primary amino group and a hydroxyl group bonded to the same carbon atom. These species have been detected, much less isolated in bulk, they are invoked as intermediates in the formation of Schiff bases and related imines from the reaction of ammonia and aldehydes and ketones. Aminal Alkanolamine Hemiacetal
An elimination reaction is a type of organic reaction in which two substituents are removed from a molecule in either a one or two-step mechanism. The one-step mechanism is known as the E2 reaction, the two-step mechanism is known as the E1 reaction; the numbers do not have to do with the number of steps in the mechanism, but rather the kinetics of the reaction and unimolecular respectively. In cases where the molecule is able to stabilize an anion but possesses a poor leaving group, a third type of reaction, E1CB, exists; the pyrolysis of xanthate and acetate esters proceed through an "internal" elimination mechanism, the Ei mechanism. In most organic elimination reactions, at least one hydrogen is lost to form the double bond: the unsaturation of the molecule increases, it is possible that a molecule undergoes reductive elimination, by which the valence of an atom in the molecule decreases by two, though this is more common in inorganic chemistry. An important class of elimination reactions is those involving alkyl halides, with good leaving groups, reacting with a Lewis base to form an alkene.
Elimination may be considered the reverse of an addition reaction. When the substrate is asymmetric, regioselectivity is determined by Zaitsev's rule or through Hofmann elimination if the carbon with the most substituted hydrogen is inaccessible. During the 1920s, Sir Christopher Ingold proposed a model to explain a peculiar type of chemical reaction: the E2 mechanism. E2 stands for bimolecular elimination; the reaction involves a one-step mechanism in which carbon-hydrogen and carbon-halogen bonds break to form a double bond. The specifics of the reaction are as follows: E2 is a single step elimination, with a single transition state, it is undergone by primary substituted alkyl halides, but is possible with some secondary alkyl halides and other compounds. The reaction rate is second order, because it's influenced by both the base; because the E2 mechanism results in the formation of a pi bond, the two leaving groups need to be antiperiplanar. An antiperiplanar transition state has staggered conformation with lower energy than a synperiplanar transition state, in eclipsed conformation with higher energy.
The reaction mechanism involving staggered conformation is more favorable for E2 reactions. E2 uses a strong base, it must be strong enough to remove a weakly acidic hydrogen. In order for the pi bond to be created, the hybridization of carbons needs to be lowered from sp3 to sp2; the C-H bond is weakened in the rate determining step and therefore a primary deuterium isotope effect much larger than 1 is observed. E2 competes with the SN2 reaction mechanism if the base can act as a nucleophile. An example of this type of reaction in scheme 1 is the reaction of isobutylbromide with potassium ethoxide in ethanol; the reaction products are isobutylene and potassium bromide. E1 is a model to explain a particular type of chemical elimination reaction. E1 stands for unimolecular elimination and has the following specifications It is a two-step process of elimination: ionization and deprotonation. Ionization: the carbon-halogen bond breaks to give a carbocation intermediate. Deprotonation of the carbocation.
E1 takes place with tertiary alkyl halides, but is possible with some secondary alkyl halides. The reaction rate is influenced only by the concentration of the alkyl halide because carbocation formation is the slowest step, as known as the rate-determining step. Therefore, first-order kinetics apply; the reaction occurs in the complete absence of a base or the presence of only a weak base. E1 reactions are in competition with SN1 reactions because they share a common carbocationic intermediate. A secondary deuterium isotope effect of larger than 1 is observed. There is no antiperiplanar requirement. An example is the pyrolysis of a certain sulfonate ester of menthol: Only reaction product A results from antiperiplanar elimination; the presence of product B is an indication. It is accompanied by carbocationic rearrangement reactions An example in scheme 2 is the reaction of tert-butylbromide with potassium ethoxide in ethanol. E1 eliminations happen with substituted alkyl halides for two main reasons.
Substituted alkyl halides are bulky, limiting the room for the E2 one-step mechanism. Substituted carbocations are more stable than methyl or primary substituted cations; such stability gives time for the two-step E1 mechanism to occur. If SN1 and E1 pathways are competing, the E1 pathway can be favored by increasing the heat. Specific features: 1. Rearrangement possible 2. Independent of concentration and basicity of base The reaction rate is influenced by the reactivity of halogens and bromide being favored. Fluoride is not a good leaving group, so eliminations with fluoride as the leaving group have slower rates than other halogens. There is a certain level of competition between the elimination reaction and nucleophilic substitution. More there are competitions between E2 and SN2 and between E1 and SN1. Substitution predominates and elimination occurs only during precise circumstances. Elimination is favored over substitution when steric hindrance around the α-carbon increases. A stronger base is used.
Temperature increases. Bases with steric bulk, are poor nucleophiles. In one study the kinetic isotope effect was determin