Nitriles formation, hydrolysis

The basic hydrolysis (reaction with water) of a nitrile (R-CN) followed by acidification yields a carboxylic acid. In general, an reaction (nucleophilic substitution) of an alkyl halide is used to generate the nitrile before hydrolysis. Figure 12-12 illustrates the formation of a carboxylic acid beginning with an alkyl halide. 

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

The preparation of y-phenoxybutyric acid (61%) by acid hydrolysis of the phenoxycyanide is a typical example of the formation of an ether acid by this method. Nine alkoxypropionic acids, ROCH CHjCOjH, have been made in 4S> 86% yields by acid hydrolysis of the alkoxy nitriles. Basic hydrolysis gives readily polymerizable material propably because of partial decomposition of the alkoxy nitrile into the alcohol and acrylonitrile. ... 

Still another powerful method for the regeneration of carbonyl compounds from dialkylhydrazones is copper-catalyzed hydrolysis. The reagents that have been tested for this purpose are 2% aqueous cop-per(II) acetate solution at pH 4, copper(II) chloride in 0.05M phosphate buffer and 75% tetrahydrofu-ran/water, and copper(II) sulfate pentahydrate . Under the conditions of the hydrolysis, no reaction is observed in the absence of the copper(II) ion. Typical yields are 85-100%. Other functional groups like a-dicarbonyl, a-tricarbonyl, acetal and aldehydic formyl groups were not affected by this hydrolysis procedure. Nitrile formation in the case of aldehyde dimethylhydrazones was not a significant side reaction. However, reaction times ranged from 1 to 15 h. The reaction is believed to be nonoxidative in nature rather, the copper is believed to activate the C=N bond and catalyze hydrolysis. The dimethylhydrazine produced during hydrolysis also complexes irreversibly with the copper(II) ion to drive the reaction to completion. 

Hexamethylphosphoramide has found important uses as a solvent in various organic reactions, such as carboxylic ester formation, hydrolysis of sulphonamides, alkylation of ketones, decyanation of nitriles, the Beckmann rearrangement and so on. HMPA may be used to make cyclodiphospha-zanes (7.250). 

Another FGI that gives carboxylic acid products is the hydrolysis of carboxylic acid derivatives, such as esters and nitriles. Such hydrolysis reactions can either be acid catalyzed (H3O+) or base promoted (1. NaOH, H2O 2. H3O ) and involve an acyl substitution mechanism (addition-elimination) that replaces any acyl leaving group with a hydroxyl group. The synthesis of carboxylic acids via nitriles is especially noteworthy since the introduction of the cyano group via Sn2 with CN involves the formation of a new C-C bond (adds one new carbon to the alkyl halide carbon chain). 

Nitriles are also obtained from some indole derivatives and from A-phenyl-2-pyrazolines . In the reaction with hydrocarbons the initially formed N-chlorosulfonylcarboxamides 217 are treated with DMF or triethylamine to produce the aromatic nitriles 218 . Hydrolysis of the intermediates gives rise to the formation of... 

With the above methodology in hand, a similar strategy was attenq)ted for the synthesis of the aryl acetic acid 7 (Scheme 7). The aniline 5 was treated with 2,5-dimethoxytetrahy ofuran in toluene and acetic acid to get the W-aryl pyrrole 28. The Vilsmeier/Triedel-Crafts acylation of 28 followed by decarbonylation afforded the keto ester 30. However, the reduction of the keto ester proved to be difficult. Most of the general methods employed for the reduction of ketones gave a mixture of products. However, a two step process involving the formation of the thioketal 31 followed by desulfurization with Ni proved to be successful. Although, the standard Wolff-Kishner conditions could not be employed in the system due to the susceptibility of the nitrile to hydrolysis, a modified Wolff-Kishner reduction (8) proved to be fruitful. 

Nitrile groups m cyanohydrins are hydrolyzed under conditions similar to those of alkyl cyanides Cyanohydrin formation followed by hydrolysis provides a route to the preparation of a hydroxy carboxylic acids... 

Cycloahphatics capable of tertiary carbocation formation are candidates for nucleophilic addition of nitriles. HCN in strong sulfuric acid transforms 1-methyl-1-cyclohexanol to 1-methyl-1-cyclohexylamine through the formamide (47). The terpenes pinene (14) [2437-95-8] and limonene [5989-27-5] (15) each undergo a double addition of HCN to provide, after hydrolysis, the cycloahphatic diamine 1,8-menthanediamine (16) (48). 

Hydrolysis of Nitriles. The chemical hydrolysis of nitriles to acids takes place only under strong acidic or basic conditions and may be accompanied by formation of unwanted and sometimes toxic by-products. Enzymatic hydrolysis of nitriles by nitrile hydratases, nittilases, and amidases is often advantageous since amides or acids can be produced under very mild conditions and in a stereo- or regioselective manner (114,115). 

The hydrolysis of nitriles can be carried out with either isolated enzymes or immobilized cells. Eor example, resting cells of P. chlororaphis can accumulate up to 400 g/L of acrylamide in 8 h, provided acrylonitrile is added gradually to avoid nitrile hydratase inhibition (116). The degree of acrylonitrile conversion to acrylamide is 99% without any formation of acryUc acid. Because of its high efficiency the process has been commercialized and currentiy is used by Nitto Chemical Industry Co. on a multithousand ton scale. 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

Solvents influence the hydrogenation of oximes in much the same way as they do hydrogenation of nitriles. Acidic solvents prevent the formation of secondary amines through salt formation with the initially formed primary amine. A variety of acids have been used for this purpose (66 ), but acids cannot always be used interchangeably (43). Primary amines can be trapped also as amides by use of an anhydride solvent (2,/5,57). Ammonia prevents secondary amine formation through competition of ammonia with the primary amine in reaction with the intermediate imine. Unless the ammonia is anhydrous hydrolysis reactions may also occur. 

A very efficient and universal method has been developed for the production of optically pue L- and D-amino adds. The prindple is based on the enantioselective hydrolysis of D,L-amino add amides. The stable D,L-amino add amides are effidently prepared under mild reaction conditions starting from simple raw materials (Figure A8.2). Thus reaction of an aldehyde with hydrogen cyanide in ammonia (Strecker reaction) gives rise to the formation of the amino nitrile. The aminonitrile is converted in a high yield to the D,L-amino add amide under alkaline conditions in the presence of a catalytic amount of acetone. The resolution step is accomplished with permeabilised whole cells of Pseudomonas putida ATCC 12633. A nearly 100% stereoselectivity in hydrolysing only the L-amino add amide is combined with a very broad substrate spedfidty. 

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