Nitriles, catalytic hydrogenation compounds

In catalytic hydrogenation, a compound is reduced with molecular hydrogen in the presence of a catalyst. This reaction has found appHcations in many areas of chemistry including the preparation of amines. Nitro, nitroso, hydroxylamino, azoxy, azo, and hydrazo compounds can all be reduced to amines by catalytic hydrogenation under the right conditions. Nitriles, amides, thioamides, and oximes can also be hydrogenated to give amines (1). Some examples of these reactions foUow ... 

Hydrogenation Catalysts. The key to catalytic hydrogenation is the catalyst, which promotes a reaction which otherwise would occur too slowly to be useful. Catalysts for the hydrogenation of nitro compounds and nitriles are generally based on one or more of the group VIII metals. The metals most commonly used are cobalt, nickel, palladium, platinum, rhodium, and mthenium, but others, including copper (16), iron (17), and tellurium... 

Nitrile Intermediates. Most quaternary ammonium compounds are produced from fatty nitriles (qv), which are ia turn made from a natural fat or oil-derived fatty acid and ammonia (qv) (Fig. 2) (see Fats AND FATTY oils) (225). The nitriles are then reduced to the amines. A variety of reduciag agents maybe used (226). Catalytic hydrogenation over a metal catalyst is the method most often used on a commercial scale (227). Formation of secondary and tertiary amine side-products can be hindered by the addition of acetic anhydride (228) or excess ammonia (229). In some cases secondary amines are the desired products. 

Amination. A continuous process in which aliphatic and aromatic amines are produced by (1) high pressure, catalytic hydrogenation of nitro compounds (-NO2 or nitriles (-CN)) and (2) action of ammonia on a chloro- or hydroxy-compound. 

CARBON SKELETON. The technique of precolumn catalytic hydrogenation can be applied to reduce certain unsaturated compounds to their parent hydrocarbons. Compounds analyzed by this technique include esters, ketones, aldehydes, amines, epoxides, nitriles, halides, sulfides, and fatty acids. Fatty acids usually give a hydrocarbon that, is the next lower homolag than the parent acid. For most systems utilizing hydrogenation, hydrogen is also used as the carrier gas. Usually 1% palladium or platinum on a non-adsorptive porous support such as AW-Chromosorb P is used as the catalytic packing material. 

In the course of the catalytic hydrogenation of a,us dinitriles over Raney nickel, by-products are obtained from C-N and C-C bond formation. The mechanism of the formation of these compounds was investigated. Cyclic and linear secondary amines can result from the same secondary imine through a transimination process involving a ring-chain tautomerism. Stereochemical results for 2-aminomethyl-cyclopentylamine (AMCPA) are in accordance with a specific cyclisation pathway favored by an intramolecular hydrogen bond giving rise to the cis isomer from aminocapro-nitrile, unfavored in the case of adiponitrile which leads to the trans AMCPA as the major isomer. 

The well-known Thorpe-Ziegler condensation reaction (Ref. 2) involves the nucleophilic addition of a carbanion to an electrophilic center. Starting from adiponitrile, enamino nitrile 9 is recovered. Catalytic hydrogenation of this compound gives trans AMCPA as the major isomer (scheme 4) ... 

Lithium aluminum hydride is a convenient reagent for reduction of nitro compounds, nitriles, amides, azides, and oximes to primary amines. Catalytic hydrogenation works also. Aromatic nitro compounds are reduced best by reaction of a metal and aqueous acid or with ammonium or sodium polysulfides (see Section 23-12B). Reduction of /V-substituted amides leads to secondary amines. 

A convenient route to 1-amino-1 //-2,3-benzopyrrolizines (28) was achieved by a Mannich reaction of aldehyde 27. Catalytic hydrogenation of either the base (28a) or trimethylammonium iodide (29) was accompanied by elimination to give compound 30. Treatment of 29 with potassium cyanide gave nitrile 31.28... 

Hilditch and Pathak (58) studying the catalytic reduction of methyl eleostearate, found that the reaction at 110° and at 170° was extremely selective in the presence of Raney nickel. No methyl stearate was formed until 90% of the linoleate had been transformed into octadeceno-ates. Ehrhart (59) used Raney nickel to hydrogenate compounds of the type RCH(CN)NHCOR The nitrile was reduced to the amine, but the amide was untouched. 

Compounds (82)-(84) were synthesized as outlined in Scheme 3.12. Reaction of naltrexone with 4-hydrazinobenzonitrile [143] under Fischer indole conditions afforded the 5 -nitrile (86) which was catalytically hydrogenated to the primary amine (87) using Raney nickel. The amidines (82)-(84) were prepared by reacting amine (87) with the appropriate iminoester [144, 145],... 

A few 6- and 8-cyanopurines have been prepared and undergo characteristic nitrile addition reactions rather readily. Thus, alkaline hydrolysis produces carboxamides, then carboxylic acids, alcoholysis leads to imidates, ammonolysis to amidines, hydrazinolysis to amidhydrazines, hydroxylamine to amidoximes, and hydrogen sulfide to thioamides. Acid hydrolysis tends to give the decarboxylated acid derivative. Reduction either by sodium-ethanol or, preferably, by catalytic hydrogenation affords aminoalkylpurines and addition of Grignard reagents produces, in the first place, acylpurines. As with aldehydes, most of the compounds examined have been relatively non-polar derivatives. Table 28 lists some reactions and relevant literature. 

The selective and rapid reduction of nitro compounds is an active area of research, particularly when other potentially reducible moieties are present in the molecules. Anhydrous ammonium formate has been developed as a catalytic hydrogen transfer agent for selectively reducing nitro groups in the presence of acid, ester, amide, halogen and nitrile groups (equation 13). ... 

The reduction of nitriles is of wide scope and has been applied to many nitriles. When catalytic hydrogenation is used, secondary amines, (RCH2)2NH, are often side products.These can be avoided by adding a compound, such as acetic anhydride, which removes the primary amine as soon as it is formed, or by the use of excess ammonia to drive the equilibria backward. Sponge nickel or nickel on silica gel have been used for the catalytic hydrogenation of aryl nitriles to amines. 

Catalytic hydrogenation of electrophilic cyclopropanes normally yields ring-opened products (equation 229) . Catalytic hydrogenation of 1,1-cyclopropanedicarbo-nitriles (659) gives rise to )5-cyanoenamines (661) via hydrogenation of the dinitriles (660) (equation 230) Hydrogenation of the tetramethyl compound 662 provides 663 via... 

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