Anilines alkylanilines

V-Alkylaniline and /V,/V-di alkyl aniline hydrochlorides can be rearranged to C-alkyl anilines by heating the salts to 200—300°C. In this reaction, known as the Hofmann-Martius rearrangement, the alkyl group preferentially migrates to the para position. If this position is occupied, the ortho position is alkylated. 

Thermal or Lewis acid catalyzed rearrangement of N alkylanilines to o (p-) akylated anilines... 

Notes on the preparation of secondary alkylarylamines. The preparation of -propyl-, ijopropyl- and -butyl-anilines can be conveniently carried out by heating the alkyl bromide with an excess (2-5-4mols) of aniline for 6-12 hours. The tendency for the alkyl halide to yield the corresponding tertiary amine is thus repressed and the product consists almost entirely of the secondary amine and the excess of primary amine combined with the hydrogen bromide liberated in the reaction. The separation of the primary and secondary amines is easily accomplished by the addition of an excess of per cent, zinc chloride solution aniline and its homologues form sparingly soluble additive compounds of the type B ZnCl whereas the alkylanilines do not react with sine chloride in the presence of water. The excess of primary amine can be readily recovered by decomposing the zincichloride with sodium hydroxide solution followed by steam distillation or solvent extraction. The yield of secondary amine is about 70 per cent, of the theoretical. 

Harmata and co-workers introduced a procedure for the reductive desulfurization of selected 2,1-benzothiazines with sodium amalgam, leading to the formation of the 2-alkylanilines in high yields <94S142>. This method is regioselective and general. As an example, alkylation of 187 followed by treatment with Na/Hg resulted in the formation of the aniline 188 in 68% overall yield (Scheme 50). 

Thoma A process for alkylating aniline with methanol or ethanol, to produce mixtures of mono- and di-alkylanilines. Operated in hot, concentrated phosphoric acid in a vertical tubular reactor. The proportions of secondary and tertiary amines can be partly controlled by controlling the ratios of the reactants the products are separated by fractional distillation. Invented in 1954 by M. Thoma in Germany. 

We have developed a multimetallic catalyst for the large scale synthesis of sterically hindered mono-N-alkylanilines with very good selectivity and high catalytic activity. In contrast to copper chromite catalysts which allow the N-alkylation only with primary alcohols, the doubly promoted Pt/Si02 catalysts described here are useful for the reaction of ortho-substituted anilines with both primary and secondary alcohols. 

The catalyst must activate three reaction steps Dehydrogenadon of the alcohol, condensation of the aniline with the carbonyl compound produced and hydrogenation of the resulting imine to the desired N-alkylaniline. In the vapor phase the hydrogenation step is the most difficult to achieve under our reaction conditions. 

Af,Af-Dialkylanilines may be purified by refluxing with an excess of acetic anhydride any unchanged aniline and Af-alkylaniline is converted into the relatively non-volatile acetyl derivative. 

This reaction has found greatest use in the preparation of N-aryl-/3-ketoamides from diketene and arylamines. Acetoacetanilide is formed in 74% yield from diketene and aniline in benzene solution. N-Alkyl-acetoacetanilides are similarly prepared when an alkylaniline is substituted for aniline in the reaction. ... 

In contrast to pyridine adducts, those of pyridine-iV-oxide produce isotropic shifts which support a dominant -delocalization mechanism. Spin density distributions over the aromatic carbons have been determined from H and spectra of several Ni(acac)2(py-NO)2 complexes. (79) relaxation measurements indicate that Tj values arise mainly from hyperfine dipolar interaction induced by spin density localized on Ni(ii) and on the C-centred 2p orbital. Adducts of Ni(acac)2 with aniline, (80) fluoroanilines, (80,81) alkylanilines, (81-83) aniline derivatives, (541, 542) and nitrogen heterocycles (543) have been extensively studied. The results are consistent with a dominant n-spin delocalization mechanism. 

The influence of reaction conditions on the electrochemical oxidation of anilines and 7V-alkylanilines is shown in Table 1 [74], It has been proposed that electrochemical formation of the conducting polyaniline polymers occurs via the formation of p-aminodiphenylamine [31, 75-77],... 

Table 1. Influence of electrolysis conditions on product distribution in the anodic oxidation of aniline and A -alkylanilines. ...

The vapor-phase pyrolysis of phenyl azide yields azobenzene in 72 % yield . The pyrolysis in aniline solution leads to the production of dibenzamil , identified as an azepine by modern techniques in benzene and p-xylene, the major products are azobenzene and aniline, presumably originating from reactions of PhN in hydrocarbon solvents the thermolysis produces aniline, alkyl-anilines, azobenzene and polymer . It has been shown that aniline and iV-alkylanilines arise from triplet state nitrene reactions with the solvent. In the gas-phase thermolysis of phenyl azide at low pressures aniline and azobenzene are the major products whereas at higher pressures the formation of l-cyano-1,3-cyclopentadiene (or 2-anilino-7H-azepine in the presence of aniline) predominates . It was deduced that aniline and azobenzene arise from triplet nitrene reactions and that at high pressures, a hot singlet nitrene is formed, which undergoes intramolecular insertion to form an azocyclopropene intermediate, viz. 

Aniline and its derivatives may form three types of products (Scheme 3) If no para-substituent is present, tail-to-tail coupling results in the formation of benzidine derivatives (XIX) anilines and A-alkylanilines also can undergo head-to-tail coupling to give 4-ami-nodiphenylamines (XX) even in the presence of certain / flra-substituents, one of which is eliminated head-to-head coupling forming azo compounds (XXI) is possible with N-unsubstituted anilines. 

A generalized reaction scheme for anilines and A-alkylanilines based on results by Nelson [37] is shown in Scheme 4. 

Table 1 Influence of Electrolysis Conditions on Product Distribution for Anodic Oxidation of Aniline and A-Alkylanilines...

With anilines and AT-alkylanilines the way of dimerization is influenced by the reaction conditions and the substitution of the aryl ring [70]. The benzidines predominate in strongly acidic aqueous media. The formation of benzidine is further favored by a low substrate concentration and a high current density. The benzidine derivatives may be reversibly oxidized to their dications. Diphenylamines are the major products under neutral conditions and higher pH values, a low current density, a high substrate concentration, a small alkyl group in monoalkylanilines, and a non-aqueous solvent [Eq. (7)]. Under weakly acidic conditions in aqueous medium, an additional electron discharge followed by hydrolysis produces benzoquinones in almost quantitative yield. 

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