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).6H(2)O/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, R-2 = 2Me, CA, 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, H-1 and C-13{H-1} NMR spectroscopies, and also X-ray crystallography (for X = Cl, R-2 = 2Me; X = NO3, R = C(4)A(8)), 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.