A cycloaddition is a chemical reaction, in which "two or more unsaturated molecules combine with the formation of a cyclic adduct in which there is a net reduction of the bond multiplicity." The resulting reaction is a cyclization reaction. Many but not all cycloadditions are concerted and thus pericyclic. Nonconcerted cycloadditions are not pericyclic; as a class of addition reaction, cycloadditions permit carbon–carbon bond formation without the use of a nucleophile or electrophile. Cycloadditions can be described using two systems of notation. An older but still common notation is based on the size of linear arrangements of atoms in the reactants, it uses parentheses:. The product is a cycle of size. In this system, the standard Diels-Alder reaction is a -cycloaddition, the 1,3-dipolar cycloaddition is a -cycloaddition and cyclopropanation of a carbene with an alkene a -cycloaddition. A more recent, IUPAC-preferred notation, first introduced by Woodward and Hoffmann, uses square brackets to indicate the number of electrons, rather than carbon atoms, involved in the formation of the product.
In the notation, the standard Diels-Alder reaction is a -cycloaddition, while the 1,3-dipolar cycloaddition is a -cycloaddition. Thermal cycloadditions are those cycloadditions where the reactants are in the ground electronic state, they have π electrons participating in the starting material, for some integer n. These reactions occur for reasons of orbital symmetry in a suprafacial-suprafacial or antarafacial-antarafacial manner. There are a few examples of thermal cycloadditions; these proceed in a suprafacial-antarafacial sense, such as the dimerisation of ketene, in which the orthogonal set of p orbitals allows the reaction to proceed via a crossed transition state. Cycloadditions in which 4n π electrons participate can occur via photochemical activation. Here, one component has an electron promoted from the HOMO to the LUMO. Orbital symmetry is such that the reaction can proceed in a suprafacial-suprafacial manner. An example is the DeMayo reaction. Another example is shown below, the photochemical dimerization of cinnamic acid.
The two trans alkenes react head-to-tail, the isolated isomers are called truxillic acids. Supramolecular effects can influence these cycloadditions; the cycloaddition of trans-1,2-bisethene is directed by resorcinol in the solid-state in 100% yield. Some cycloadditions instead of π bonds operate through strained cyclopropane rings, as these have significant π character. For example, an analog for the Diels-Alder reaction is the quadricyclane-DMAD reaction: In the cycloaddition notation i and j refer to the number of atoms involved in the cycloaddition. In this notation, a Diels-Alder reaction is a cycloaddition and a 1,3-dipolar addition such as the first step in ozonolysis is a cycloaddition; the IUPAC preferred notation however, with takes electrons into not atoms. In this notation, the DA reaction and the dipolar reaction both become a cycloaddition; the reaction between norbornadiene and an activated alkyne is a cycloaddition. The Diels-Alder reaction is the most important and taught cycloaddition reaction.
Formally it is a cycloaddition reaction and exists in a huge range of forms, including the inverse electron-demand Diels–Alder reaction, Hexadehydro Diels-Alder reaction and the related alkyne trimerisation. The reaction can be run in reverse in the retro-Diels–Alder reaction. Reactions involving heteroatoms are known; the Huisgen cycloaddition reaction is a cycloaddition. The Nitrone-olefin cycloaddition is a cycloaddition. Iron catalysts contain a redox active ligand in which the central iron atom can coordinate with two simple, unfunctionalized olefin double bonds; the catalyst can be written as a resonance between a structure containing unpaired electrons with the central iron atom in the II oxidation state, one in which the iron is in the 0 oxidation state. This gives it the flexibility to engage in binding the double bonds as they undergo a cyclization reaction, generating a cyclobutane structure via C-C reductive elimination. Efficiency of the reaction varies depending on the alkenes used, but rational ligand design may permit expansion of the range of reactions that can be catalyzed.
Cheletropic reactions are a subclass of cycloadditions. The key distinguishing feature of cheletropic reactions is that on one of the reagents, both new bonds are being made to the same atom; the classic example is the reaction of sulfur dioxide with a diene. Other cycloaddition reactions exist: cycloadditions, photocycloadditions, photocycloadditions Cycloadditions have metal-catalyzed and stepwise radical analogs, however these are not speaking pericyclic reactions; when in a cycloaddition charged or radical intermediates are involved or when the cycloaddition result is obtained in a series of reaction steps they are sometimes called formal cycloadditions to make the distinction with true pericyclic cycloadditions. One example of a formal cycloaddition between a cyclic enone and an enamine catalyzed by n-butyllithium is a Stork enamine / 1,2-addition cascade reaction
Lewis acids and bases
A Lewis acid is a chemical species that contains an empty orbital, capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base is any species that has a filled orbital containing an electron pair, not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH3 is a Lewis base. Trimethylborane is a Lewis acid. In a Lewis adduct, the Lewis acid and base share an electron pair furnished by the Lewis base, forming a dative bond. In the context of a specific chemical reaction between NH3 and Me3B, the lone pair from NH3 will form a dative bond with the empty orbital of Me3B to form an adduct NH3•BMe3; the terminology refers to the contributions of Gilbert N. Lewis; the terms nucleophile and electrophile are more or less interchangeable with Lewis base and Lewis acid, respectively. However, these terms their abstract noun forms nucleophilicity and electrophilicity, emphasize the kinetic aspect of reactivity, while the Lewis basicity and Lewis acidity emphasize the thermodynamic aspect of Lewis adduct formation.
In many cases, the interaction between the Lewis base and Lewis acid in a complex is indicated by an arrow indicating the Lewis base donating electrons toward the Lewis acid using the notation of a dative bond—for example, Me3B←NH3. Some sources indicate the Lewis base with a pair of dots, which allows consistent representation of the transition from the base itself to the complex with the acid: Me3B +:NH3 → Me3B:NH3A center dot may be used to represent a Lewis adduct, such as Me3B•NH3. Another example is boron trifluoride diethyl etherate, BF3•Et2O. Although there have been attempts to use computational and experimental energetic criteria to distinguish dative bonding from non-dative covalent bonds, for the most part, the distinction makes note of the source of the electron pair, dative bonds, once formed, behave as other covalent bonds do, though they have considerable polar character. Moreover, in some cases, the use of the dative bond arrow is just a notational convenience for avoiding the drawing of formal charges.
In general, the donor–acceptor bond is viewed as somewhere along a continuum between idealized covalent bonding and ionic bonding. Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR3 where R can be an organic substituent or a halide. For the purposes of discussion complex compounds such as Et3Al2Cl3 and AlCl3 are treated as trigonal planar Lewis acids. Metal ions such as Na+, Mg2+, Ce3+, which are invariably complexed with additional ligands, are sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base. Other reactions might be referred to as "acid-catalyzed" reactions; some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can either accept a pair of electrons or donate a pair of electrons, depending upon the reaction. Lewis acids are diverse. Simplest are those, but more common are those. Examples of Lewis acids based on the general definition of electron pair acceptor include: the proton and acidic compounds onium ions, such as NH4+ and H3O+ high oxidation state transition metal cations, e.g. Fe3+.
Again, the description of a Lewis acid is used loosely. For example, in solution, bare protons do not exist; some of the most studied examples of such Lewis acids are the boron trihalides and organoboranes, but other compounds exhibit this behavior: BF3 + F− → BF4−In this adduct, all four fluoride centres are equivalent. BF3 + OMe2 → BF3OMe2Both BF4− and BF3OMe2 are Lewis base adducts of boron trifluoride. In many cases, the adducts violate the octet rule, such as the triiodide anion: I2 + I− → I3−The variability of the colors of iodine solutions reflects the variable abilities of the solvent to form adducts with the Lewis acid I2. In some cases, the Lewis acid is capable of binding two Lewis base, a famous example being the formation of hexafluorosilicate: SiF4 + 2 F− → SiF62− Most compounds considered to be Lewis acids require an activation step prior to formation of the adduct with the Lewis base. Well known cases are the aluminium trihalides, which are viewed as Lewis acids. Aluminium trihalides, unlike the boron trihalides, do not exist in the form AlX3, but as aggregates and polymers that must be degraded by the Lewis base.
A simpler case is the formation of adducts of borane. Monomeric BH3 does not exist appreciably, so the adducts of borane are generated by degradation of diborane: B2H6 + 2 H− → 2 BH4−In this case, an intermediate B2H7− can be isolated. Many metal complexes serve as Lewis acids, but only after dissociating a more weakly bound Lewis base water. 2+ + 6 NH3 → 2+ + 6 H2O The proton is one of the strongest but is one of the most complicated Lewis acids. It is convention to ignore the fact that a proton is solvated (bound to solvent
A Schiff base is a compound with the general structure R2C=NR'. They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimines depending on their structure; the term is synonymous with azomethine which refers to secondary aldimines. A number of special naming systems exist for these compounds. For instance a Schiff base derived from an aniline, where R3 is a phenyl or a substituted phenyl, can be called an anil, while bis-compounds are referred to as salen-type compounds; the term Schiff base is applied to these compounds when they are being used as ligands to form coordination complexes with metal ions. Such complexes occur for instance in Corrin, but the majority of Schiff bases are artificial and are used to form many important catalysts, such as Jacobsen's catalyst. Schiff bases can be synthesized from an aliphatic or aromatic amine and a carbonyl compound by nucleophilic addition forming a hemiaminal, followed by a dehydration to generate an imine. In a typical reaction, 4,4'-diaminodiphenyl ether reacts with o-vanillin: Schiff bases have been investigated in relation to a wide range of contexts, including antimicrobial and anticancer activity.
They have been considered for the inhibition of amyloid-β aggregation. Schiff bases are common enzymatic intermediates where an amine, such as the terminal group of a lysine residue, reversibly reacts with an aldehyde or ketone of a cofactor or substrate; the common enzyme cofactor PLP forms a Schiff base with a lysine residue and is transaldiminated to the substrate. The cofactor retinal forms a Schiff base in rhodopsins, including human rhodopsin, key in the photoreception mechanism. Schiff bases are common ligands in coordination chemistry; the imine nitrogen exhibits pi-acceptor properties. The ligands are derived from alkyl diamines and aromatic aldehydes. Chiral Schiff bases were one of the first ligands used for asymmetric catalysis. In 1968 Ryōji Noyori developed a copper-Schiff base complex for the metal-carbenoid cyclopropanation of styrene. For this work he was awarded a share of the 2001 Nobel Prize in Chemistry. Schiff bases have been incorporated into MOFs. Conjugated Schiff bases absorb in the UV-visible region of the electromagnetic spectrum.
This absorption is the basis of the anisidine value, a measure of oxidative spoilage for fats and oils. Schiff bases can be used to mass-produce nanoclusters of transition metals inside halloysite; this abundant mineral has a structure of rolled nanosheets, which can support both the synthesis and the metal nanocluster products. These nanoclusters can be made of Ag, Ru, Rh, Pt or Co metals and can catalyze various chemical reactions. J. C. Hindson. Ulgut. H. Friend. C. Greenham. Norder. J. Dingemans. "All-aromatic liquid crystal triphenylamine-based polys as hole transport materials for opto-electronic applications". J. Mater. Chem. 20: 937–944. Doi:10.1039/B919159C. M. L. Petrus. Bein. J. Dingemans. "A Low Cost Azomethine-Based Hole Transporting Material for Perovskite Photovoltaics". J. Mater. Chem. A. 3: 12159–12162. Doi:10.1039/C5TA03046C.</ref> Organic field-effect transistor <ref>D. Isık. Santato. G. Skene. "Charge-Carrier Transport in Thin Films of π-Conjugated Thiopheno-Azomethines". Org. Electron. 13: 3022–3031.
Doi:10.1016/j.orgel.2012.08.018. L. Sicard. "On-Substrate Preparation of an Electroactive Conjugated Polyazomethine from Solution-Processable Monomers and its Application in Electrochromic Devices". Adv. Funct. Mater. 23: 3549–3559. Doi:10.1002/adfm.201203657
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
In chemistry, an ethyl group is an alkyl substituent derived from ethane. It has the formula –CH2CH3 and is often abbreviated Et. Ethyl is used in the IUPAC nomenclature of organic chemistry for a saturated two-carbon moiety in a molecule, whilst the prefix "eth-" is used to indicate the presence of two carbon atoms in the molecule. Ethylation is the formation of a compound by introduction of the ethyl group; the most practiced example of this reaction is the ethylation of benzene with ethylene to yield ethylbenzene, a precursor to styrene, a precursor to polystyrene. 24.7 million tons of ethylbenzene were produced in 1999. Many ethyl-containing compounds are generated by electrophilic ethylation, i.e. treatment of nucleophiles with sources of Et+. Triethyloxonium tetrafluoroborate BF4 is such a reagent. For good nucleophiles, less electrophilic reagents are employed, such as ethyl halides. In unsymmetrical ethylated compounds, the methylene protons in the ethyl substituent are diastereotopic. Chiral reagents are known to stereoselectively modify such substituents.
The name of the group is derived from the Aether, the first-born Greek elemental god of air and "hyle", referring to "stuff". The name "ethyl" was coined in 1835 by the Swedish chemist Jöns Jacob Berzelius. Functional group
A carbocation is an ion with a positively charged carbon atom. Among the simplest examples are the methenium CH+3, methanium CH+5 and vinyl C2H+3 cations. Carbocations that bear more than one positively charged carbon atom are encountered; until the early 1970s, all carbocations were called carbonium ions. In present-day chemistry, a carbocation is any ion with a positively charged carbon atom, classified in two main categories according to the coordination number of the charged carbon: three in the carbenium ions and five in the carbonium ions; this nomenclature was proposed by G. A. Olah. Carbonium ions, as defined by Olah, are characterized by a three-center two-electron delocalized bonding scheme and are synonymous with so-called'nonclassical carbocations', which are carbocations that contain bridging C–C or C–H σ-bonds. However, others have more narrowly defined the term'carbonium ion' as formally protonated or alkylated alkanes, to the exclusion of nonclassical carbocations like the 2-norbornyl cation.
According to the IUPAC, a carbocation is any cation containing an number of electrons in which a significant portion of the positive charge resides on a carbon atom. Prior to the observation of five-coordinate carbocations by Olah and coworkers and carbonium ion were used interchangeably. Olah proposed a redefinition of carbonium ion as a carbocation featuring any type of three-center two-electron bonding, while a carbenium ion was newly coined to refer to a carbocation containing only two-center two-electron bonds with a three-coordinate positive carbon. Subsequently, others have used the term carbonium ion more narrowly to refer to species that are derived from electrophilic attack of H+ or R+ on an alkane, in analogy to other main group onium species, while a carbocation that contains any type of three-centered bonding is referred to as a nonclassical carbocation. In this usage, 2-norbornyl cation is not a carbonium ion, because it is formally derived from protonation of an alkene rather than an alkane, although it is a nonclassical carbocation due to its bridged structure.
The IUPAC acknowledges the three divergent definitions of carbonium ion and urges care in the usage of this term. For the remainder of this article, the term carbonium ion will be used in this latter restricted sense, while nonclassical carbocation will be used to refer to any carbocation with C–C and/or C–H σ-bonds delocalized by bridging. Since the late 1990s, most textbooks have stopped using the term carbonium ion for the classical three-coordinate carbocation. However, some university-level textbooks continue to use the term carbocation as if it were synonymous with carbenium ion, or discuss carbocations with only a fleeting reference to the older terminology of carbonium ions or carbenium and carbonium ions. One textbook retains the older name of carbonium ion for carbenium ion to this day, uses the phrase hypervalent carbonium ion for CH+5. A carbocation with an two-coordinate sp-hybridized positive carbon is known as a vinyl cation, while a two-coordinate sp2-hybridized cation resulting from the formal removal of a hydride ion from an arene is termed an aryl cation.
These carbocations are unstable and are infrequently encountered. Hence, they are omitted from introductory and intermediate level textbooks; the IUPAC definition stipulates. The history of carbocations dates back to 1891 when G. Merling reported that he added bromine to tropylidene and heated the product to obtain a crystalline, water-soluble material, C7H7Br, he did not suggest a structure for it. This ion is predicted to be aromatic by Hückel's rule. In 1902, Norris and Kehrman independently discovered that colorless triphenylmethanol gives deep-yellow solutions in concentrated sulfuric acid. Triphenylmethyl chloride formed orange complexes with aluminium and tin chlorides. In 1902, Adolf von Baeyer recognized the salt-like character of the compounds formed, he dubbed the relationship between color and salt formation halochromy, of which malachite green is a prime example. Carbocations are reactive intermediates in many organic reactions; this idea, first proposed by Julius Stieglitz in 1899, was further developed by Hans Meerwein in his 1922 study of the Wagner–Meerwein rearrangement.
Carbocations were found to be involved in the SN1 reaction, the E1 reaction, in rearrangement reactions such as the Whitmore 1,2 shift. The chemical establishment was reluctant to accept the notion of a carbocation and for a long time the Journal of the American Chemical Society refused articles that mentioned them; the first NMR spectrum of a stable carbocation in solution was published by Doering et al. in 1958. It was the heptamethylbenzenium ion, made by treating hexamethylbenzene with methyl chloride and aluminium chloride; the stable 7-norbornadienyl cation was prepared by Story et al. in 1960 by reacting norbornadienyl chloride with silver tetrafluoroborate in sulfur dioxide at −80 °C. The NMR spectrum established. In 1962, Olah directly observed the tert-butyl carbocation by nuclear magnetic resonance as a stable species on dissolving tert-butyl fluoride in magic acid; the NMR of the norbornyl cation was first reported by Schleyer et al. and it was shown to undergo proton-scrambling over a barrier by Saunders et al.
Aniline is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine, its main use is in the manufacture of precursors to polyurethane and other industrial chemicals. Like most volatile amines, it has the odor of rotten fish, it ignites burning with a smoky flame characteristic of aromatic compounds. Aniline is a pyramidalized molecule, with hybridization of the nitrogen somewhere between sp3 and sp2; the amine is flatter than an aliphatic amine, owing to conjugation of the lone pair with the aryl substituent. Thus, the experimental geometry reflects a balance between the stabilization of lone pairs in orbitals with higher s character and better stabilization via conjugation with the aryl ring for an orbital of pure p character; the pyramidalization angle between the C–N bond and the bisector of the H–N–H angle is 142.5°. The C−N distance is correspondingly shorter. In aniline, the C−N and C−C distances are close to 1.39 Å, indicating the π-bonding between N and C.
Industrial aniline production involves two steps. First, benzene is nitrated with a concentrated mixture of nitric acid and sulfuric acid at 50 to 60 °C to yield nitrobenzene; the nitrobenzene is hydrogenated in the presence of metal catalysts: The reduction of nitrobenzene to aniline was first performed by Nikolay Zinin in 1842, using inorganic sulfide as a reductant. Aniline can alternatively be prepared from phenol derived from the cumene process. In commerce, three brands of aniline are distinguished: aniline oil for blue, pure aniline. Many analogues of aniline are known; these include toluidines, chloroanilines, aminobenzoic acids and many others. They are prepared by nitration of the substituted aromatic compounds followed by reduction. For example, this approach is used to convert toluene into toluidines and chlorobenzene into 4-chloroaniline. Alternatively, using Buchwald-Hartwig coupling or Ullmann reaction approaches, aryl halides can be aminated with aqueous or gaseous ammonia The chemistry of aniline is rich because the compound has been cheaply available for many years.
Below are some classes of its reactions. The oxidation of aniline has been investigated, can result in reactions localized at nitrogen or more results in the formation of new C-N bonds. In alkaline solution, azobenzene results, whereas arsenic acid produces the violet-coloring matter violaniline. Chromic acid converts it into quinone, whereas chlorates, in the presence of certain metallic salts, give aniline black. Hydrochloric acid and potassium chlorate give chloranil. Potassium permanganate in neutral solution oxidizes it to nitrobenzene, in alkaline solution to azobenzene and oxalic acid, in acid solution to aniline black. Hypochlorous acid gives para-amino diphenylamine. Oxidation with persulfate affords a variety of polyanilines compounds; these polymers exhibit rich acid-base properties. Like phenols, aniline derivatives are susceptible to electrophilic substitution reactions, its high reactivity reflects that it is an enamine, which enhances the electron-donating ability of the ring. For example, reaction of aniline with sulfuric acid at 180 °C produces sulfanilic acid, H2NC6H4SO3H.
If bromine water is added to aniline, the bromine water is decolourised and a white precipitate of 2,4,6-tribromoaniline is formed. To generate the mono-substituted product, a protection with acetyl chloride is required: The reaction to form 4-bromoaniline is to protect the amine with acetyl chloride hydrolyse back to reform aniline; the largest scale industrial reaction of aniline involves its alkylation with formaldehyde. An idealized equation is shown: 2 C6H5NH2 + CH2O → CH22 + H2OThe resulting diamine is the precursor to 4,4'-MDI and related diisocyanates. Aniline is a weak base. Aromatic amines such as aniline are, in general, much weaker bases than aliphatic amines. Aniline reacts with strong acids to form anilinium ion. Traditionally, the weak basicity of aniline is attributed to a combination of inductive effect from the more electronegative sp2 carbon and resonance effects, as the lone pair on the nitrogen is delocalized into the pi system of the benzene ring.: Missing in such analysis is consideration of solvation.
Aniline is, for example, more basic than ammonia in the gas phase, but ten thousand times less so in aqueous solution. Aniline reacts with acyl chlorides such as acetyl chloride to give amides; the amides formed from aniline are sometimes called anilides, for example CH3-CO-NH-C6H5 is acetanilide. At high temperatures aniline and carboxylic acids react to give the anilides. N-Methylation of aniline with methanol at elevated temperatures over acid catalysts gives N-methylaniline and dimethylaniline: C6H5NH2 + 2 CH3OH → C6H5N2 + 2H2ON-Methylaniline and dimethylaniline are colorless liquids with boiling points of 193–195 °C and 192 °C, respectively; these derivatives are of importance in the color industry. Aniline combines directly with alkyl iodides to form tertiary amines. Boiled with carbon disulfide, it gives sulfocarbanilide, which may be decomposed into phen