Nitriles from nitrobenzenes

It is often possible to replace a primary amine in a reductive alkylation by a nitrogen compound such as a nitro or nitroso compound or nitrile that can be converted into the primary amine by the reduction. For example, A-alkyl-and A,iV-dialkyl-anilines can be prepared from nitrobenzene in a single operation.1010,1011 Directions for the preparation of A-alkylarylamines from aromatic nitro compounds are given on page 555. 

The solubility of the catalyst salt is improved by the use of 3,5-bis(trifluoromethyl)phenylborate or triflate anions. Unsaturated fatty acids can be reduced in the same way.173 Hydrogenations in sc carbon dioxide can be more selective than in the gas phase while using 35 times less catalyst.174 Cyclohexene was reduced with hydrogen and a polysilox-ane-supported palladium catalyst in in a continuous-flow reactor in 95-98% yields. Epoxides, oximes, nitriles, aldehydes, ketones, and nitro compounds can also be reduced. By varying the temperature, the products from the reduction of nitrobenzene can be selected from aniline, cyclo-hexylamine, dicyclohexylamine, and cyclohexane. In the... 

Method A (Without Solvent) The aromatic nitrile (30-50 mmol) and PC15 (3-5 mmol) (molar ratio 10 1) were placed in a 30-mL glass tube, and anhyd HCI (g) (15-25 mmol) was bubbled into the mixture under cooling. The tube was stoppered, cooled in dry ice/acetone, scaled carefully and heated to 100-105 C in an oil bath for the appropriate time. Then the tube was chilled in dry ice/acetone and opened. The mixture was poured into water and the insoluble 1,3,5-triazines were recrystallized from a suitable solvent (acetone, nitrobenzene or HOAc). 

In the first of a series of new reactions, Meerwein heated JV-phenylbenz-imidoyl chloride (56) with acetonitrile and aluminum chloride to obtain 4-methyl-2-phenylquinazoline (see 1). He postulated that the nitrilium salt (57) (not isolated) was the intermediate. Aromatic nitriles could also be used. The imidoyl chloride could be replaced by a mixture of benzanilide and thionyl chloride other Lewis acids could replace the aluminum chloride. The solvent could be tetrachloroethane, nitrobenzene, or an excess of the nitrile. Best reaction temperatures ranged from 90° to 160°C and yields were usually excellent. Imidate esters, e.g., PhNC(Ph)OEt, could replace the imidoyl chloride.41... 

Nitro compounds are reduced to the corresponding amine. Unlike hydride reductions, both alkyl nitro compounds (2-methyl-2-nitro-1,3-propanediol was reduced to l-amino-2-methyl-1,3-propanediol in 95% yield)566 and aromatic nitro derivatives [nitrobenzene was reduced to aniline with Ti(S04)3 in sulfuric acid and cetyltrimethylammonium bromide] are electrolytically reduced. 7 jf conditions are modified, reductive coupling can give azoxy compounds such as 568 (from 569) or diazo compounds. A variety of acid derivatives are reduced under electrochemical conditions, including nitriles (to amines), acids (to alcohols),5 E572 estejs (jq alcohols), and amides (to alcohols). It is possible to selectively reduce a cyclic imide to a lactam.575... 

Figure 9.9 Plots of log Po vs. log k for a series of 21 aromatic compounds. AC18 column was used with (a) methanol-water 50 50 (v/v), and (b) 0.05 M SDS with 2% 1-propanol. Compounds (1) benzyl alcohol, (2) benzaldehyde, (3) 2,4-dinitrophenol, (4) benzo-nitrile, (5) acetophenone, (6) nitrobenzene, (7) p-nitroanisole, (8) methylbenzoate, (9) anisole, (10) benzene, (11) toluene, (12) chlorobenzene, (13) bromobenzene, (14) ethylbenzene, (15) resorcinol, (16) catechol, (17) phenol, (18) p-nitrophenol, (19) o-chlorophenol, (20) o-bromophenol and (21) 2,4-dichlorophenol. Reprinted from Ref 15 with permission ofElsevier.

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