Mechanism of nitriles

The mechanism of nitrile hy drolysis will be described in Section 20 19... 

Scheme 19.5 Mechanism of nitrile butadiene rubber (NBR) hydrogenation catalyzed by Ru(CH=CH(Ph))CI(CO)(PCy3)2.

Jensen, C.M. and Trogler, W.C. (1986) Kinetics and mechanism of nitrile hydration catalyzed by unhindered hydridobis(phosphine)platinum(ll) complexes. Regioselective hydration of acrylonitrile. J. Am. Chem. Soc., 108, 723-729. 

The first question in considering the mechanism of nitrile hydrogenation is the mode of adsorption on the catalyst surface. Two adsorption modes are envisaged, corresponding to the end-on (ct, or and side-on (71- or Figure 10) modes of coordination of a nitrile to a metal that have been demonstrated in coordination and organometallic compounds. Each adsorption model leads to... 

The mechanism of nitrile hydrolysis in both acid and base consists of three parts [1] nucleophilic addition of H2O or OH to form the imidic acid tautomer [2] tautomerization to form the amide, and [3] hydrolysis of the amide to form RCOOH or RCOO. The mechanism is shown for the basic hydrolysis of RCN to RCOO (Mechanism 22.11). 

One mechanism of nitrile toxicity requires that the cyano moiety be released from the molecule (Figure 4). This particular example illustrates the in vivo transformation by cytochrome P450, a very common oxidation enzyme found primarily in the liver but also in other tissues. 

By hydrolysis of cyanohydrins and other nitriles. We saw, in Section 16.9, that aldehydes and ketones can be converted to cyanohydrins and that these can be hydrolyzed to ct-hydroxy acids. In the hydrolysis the —CN group is converted to a — CO2H group. The mechanism of nitrile hydrolysis is discussed in Section 17.8H ... 

The mechanism of nitrile hydrolysis involves acid or base promoted addition of water across the triple bond. This gives an intermediate imidate that tautomerizes to an amide. The amide is then hydrolyzed to the carboxylic acid. The addition of water to the nitrile resembles the hydration of an alkyne (eq. 3.52). The oxygen of water behaves as a nucleophile and bonds to the electrophilic carbon of the nitrile. Amide hydrolysis will be discussed in Section 10.20. 

Taniguchi K, Noguchi T, Yohda M, Odaka M. Catalytic mechanism of nitrile hydratase proposed by time-resolved X-ray crystallography using a novel substrate, tert-butylisonitrile. J Biol Chem 2008 283 36617-23. 

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