Ester Hydrolysis and Nitrosative Deamination of Novocaine in Aqueous Solutions

摘要

In aqueous solutions,the kinetic features of both the hydrolysis reaction of the ester function of novocaine in alkaline medium and the nitrosation reaction of the primary amine group of novocaine in mild acid medium were investigated by UV/vis spectroscopy.The ester hydrolysis shows first-order kinetics with respect to both the drug and the nucleophile,OH~-,concentrations,thus following a typical S_N2(Ac)mechanism.The rate of the reaction decreases strongly with the polarity of the reaction media,analyzed for both dioxane-water and Me_2SO-water mixtures.The effect of the presence of cationic micelles of tetradecyltrimethylammonium bromide,TTABr,was abnormal in that it inhibits the rate of the reaction throughout the analyzed concentration range of the surfactant.The same pattern of behavior is observed in the presence of anionic micelles of sodium dodecyl sulfate(SDS);however,the effect is more pronounced.The rate equation obtained in the kinetic study of the nitrosation reaction of novocaine in mild acid medium contains first-and second-order terms with respect to [nitrite],which correspond with the two parallel reaction paths due to nitrosation via both NO~+ and N_2O_3,respectively;the rate of the reaction also increases with both the [H~+] and the total acetic acid-acetate buffer concentration.In contrast to the ester hydrolysis,the nitrosation reaction is accelerated in aqueous micellar solutions of both cationic and anionic surfactants of TTABr and SDS,respectively.