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Zinc(II)/Ketoxime System as a Simple and Efficient Catalyst for Hydrolysis of Organonitriles

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posted on 2002-08-02, 00:00 authored by Maximilian N. Kopylovich, Vadim Yu. Kukushkin, Matti Haukka, João J. R. Fraústo da Silva, Armando J. L. Pombeiro
The hydrolysis of sterically hindered and unhindered alkyl nitriles, and also of benzyl and phenyl nitriles RCN (R = Me, CH2Cl, Et, n-Pr, i-Pr, n-Bu, t-Bu, p-MeOC6H4CH2, Ph), to carboxamides is catalyzed by a novel system of superior simplicity consisting of cheap, widely commercially available, and rather environmentally friendly compounds, that is, a ZnX2/ketoxime combination, but it does not proceed at all with either the zinc salt or the ketoxime taken alone. The nature of the anion X- in the zinc salt (X = NO3, Cl, CF3SO3) or of the ketoxime (Me2CNOH, C4H8CNOH, C5H10CNOH) does not affect strongly the catalytic properties of the system, but the best results were obtained so far with a Zn(NO3)2·6H2O/2-propanone oxime molar ratio of 1:4; turnover numbers are typically above ca. 100 but reach as high as 1000 for p-MeOC6H4CH2C(O)NH2. The previously unknown structures of the two carboxamide products n-BuC(O)NH2 and p-MeOC6H4CH2C(O)NH2 were determined by X-ray diffraction studies. The complexes [ZnX2(R2CNOH)2] (X = Cl, R2 = 2Me, C4H8, C5H10; X = NO3, R = C4H8), prepared by heating the appropriate zinc salts with 2 equiv of the ketoxime in acetone and characterized by C, H, N analyses, FAB-MS, 1H and 13C{1H} NMR spectroscopies, and also X-ray crystallography (for X = Cl, R2 = 2Me; X = NO3, R = C4H8), proved to be catalyst precursors in the conversions because the activity of these species is high only in the presence of 2 equiv of the ketoxime.

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