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

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.