alpha-(acyloxy)dialkylnitrosamines: Effects of structure on the formation of N-nitrosiminium ions and a predicted change in mechanism

The decay of alpha-(acyloxy)dialkylnitrosamines in aqueous solutions has be en studied with a view toward elucidating mechanistic details and effects o f structure on mechanism and reactivity. Rate constants (k(1)) for the pH-i ndependent decay of 43 alpha-(acyloxy)dialkylnitrosamines have been determi ned. Observations from these and other experiments rule out decomposition v ia an anchimeric assistance mechanism involving the Z isomer that had previ ously been suggested. All of the reported data for most of the compounds is consistent with a mechanism involving the formation of N-nitrosiminium ion s in or before the rate-limiting step. Structure reactivity correlations in dicate that the stability of alpha-(acyloxy)dialkylnitrosamines is determin ed by electronic properties of substituents at R-N and R-C as well as by th e ability of substituents R-C to engage in hyperconjugative interactions of C-H bonds with the developing cationic center in the transition state for nitrosiminium ion formation. Attachment of substituents of sufficient elect ron-withdrawing power at R-N and R-C results in a predicted change in mecha nism to what appears to be an acyl group attack mechanism.