Hydrogenation aromatic nitriles

The cyano group in aromatic nitriles can be converted directly to a methyl group in vapor phase over 30% Ni-on-AljOj prereduced by hydrogen i>i situ... 

The other way of reducing nitriles to aldehydes involves using a metal hydride reducing agent to add 1 mol of hydrogen and hydrolysis, in situ, of the resulting imine (which is undoubtedly coordinated to the metal). This has been carried out with LiAlH4, LiAlH(OEt)3, LiAlH(NR2)3, and DIBAL-H. The metal hydride method is useful for aliphatic and aromatic nitriles. 

Bagley and coworkers have described the preparation of primary thioamides by treatment of nitriles with ammonium sulfide in methanol solution (Scheme 6.139) [276], While the reactions with electron-deficient aromatic nitriles proceeded at room temperature, other aromatic and aliphatic nitriles required microwave heating at 80-130 °C for 15-30 min to furnish the thioamides in moderate to high yields. This protocol avoids the use of hydrogen sulfide gas under high pressure, proceeds in the absence of base, and usually provides thioamides without the need for chromatographic purification. 

The complex hydride reductions of nitriles to aldehydes compare favorably with the classical Stephen reduction which consists of treatment of a nitrile with anhydrous stannous chloride and gaseous hydrogen chloride in ether or diethylene glycol and applies to both aliphatic and aromatic nitriles [183,285, 1152]. An advantage of the Stephen method is its applicability to polyfunctional compounds containing reducible groups such as carbonyl that is reduced by hydrides but not by stannous chloride [1153]. 

As substitute for hydrogen cyanide, which does not add aromatic nitrile oxides, 1,3,5-triazine has been recommended for the preparation of 5-unsubstituted 1,2,4-oxadiazoles <78BCJ1484). 

Lithium aluminum hydride in tetrahydrofuran has been found to reduce aromatic nitriles to give an amine and to give an imine which is formed from the addition of the amine to the nonisolatable imine intermediate followed by an elimination of ammonia [24] (Eq. 14). This is simpler than catalytic hydrogenation of nitriles [25], which gives poor yields of imines. 

Reaction conditions which are particularly applicable to aromatic nitriles involve the use of an aqueous solution of sodium hydroxide containing hydrogen peroxide, but alkyl cyanides do not always give good results the method is illustrated by the preparation of toluamide (Expt 6.167). 

The preparation of toluamide (Expt 6.167) illustrates a useful procedure for the conversion of aromatic nitriles into acid amides with the aid of alkaline hydrogen peroxides (see discussion, Section 5.12.4, p. 708). 

Aromatic ketones arylations, 10, 140 asymmetric hydrogenation, 10, 50 G—H bond alkylation, 10, 214 dialkylzinc additions, 9, 114-115 Aromatic ligands mercuration, 2, 430 in mercury 7t-complexes, 2, 449 /13-77-Aromatic nitriles, preparation, 6, 265 Aromatic nucleophilic substitution reactions, arene chromium tricarbonyls, 5, 234... 

Homogeneous hydrogenation of nitriles, Saturated nitriles are hydrogenated to primary amines in 67-100% yield with 1 as catalyst in THF. The catalytic activity of 1 for aromatic nitriles is not so high as for hydrogenation of aliphatic nitriles. The C=C bond of unsaturated nitriles is reduced more readily than the C=N bond. This catalyst is also eflective for dehydrogenation of amines (benzylamine — benzonitrile, 27% yield). 

Aromatic nitriles are relatively stable under oxidation conditions even at higher temperatures compared to the equivalent oxy products. Therefore these compounds are often used as intermediates for subsequent hydrogenation or reduction steps (Scheme 20.2). 

Nitriles may be converted to their imino chloride salts by the action of dry hydrogen chloride in ether. These intermediates ate reduced by anhydrous stannous chloride to stannic aldimonium chlorides, which on hydrolysis yield aldehydes. Chloroform may be added to facilitate the solution of the nitrile. The quality of the stannous chloride catalyst is important the preparation of an active and dependable form has been described. The yields are usually high for many aromatic nitriles, as in the preparation of /3-naphthaldehyde (95%). The reaction has also been employed in the heterocyclic series, as in the synthesis of 4-methyl-thiazole-5-aldehyde (40%). The reduction of the cyano group in the... 

Hydrogen peroxide reacts with aliphatic and aromatic nitriles in alkaline solution at 50° to give amides in 50-95% yields. 

This method has been used chiefly for the preparation of acyl derivatives of aromatic primary and secondary amines. The anhydride and amine are heated together, sometimes with a small amount of sulfuric acid as in the preparation of o-nitro-N-methylacetanilide (73%). ° Catalytic hydrogenation of nitriles in acetic anhydride solvent leads to high yields of... 

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