Kinetics of base-catalysed hydrolysis and cyclisation of substituted acetamide and benzamide O-(phenoxycarbonyl)oximes

The reaction kinetics of acetamide O-(4-nitrophenoxycarbonyl)oxime have bee n studied in aqueous buffers at pH 2-11. At pH > 9, the pH dependence of k( obs) is linear with slope 1, the cyclisation to 3-methyl-1,2,4-oxadiazol-5 (4H)-one and 4-nitrophenol being the only reaction. At pH < 7.5, the only r eaction is the hydrolysis giving 4-nitrophenol and acetamidoxime. The depen dence of k(obs) on pH has been used to determine the rate equation and to p ropose the reaction mechanism. The cyclisation kinetics of substituted benz amide O-(phenoxycarbonyl)oximes have been studied in the pH range from 9.25 to 11. The reaction mechanism has been proposed based on the rho constants found. In the first reaction step, the proton is split off from the NH2 gr oup; the subsequent, rate-limiting step involves simultaneous N-C bond form ation and C-G bond splitting.