Pathways of decomposition of propylbenzilylcholine mustard in neutral and alkaline solution

High-voltage electrophoresis has been used to follow the decomposition of propylbenzilylcholine mustard (PrBCM) in aqueous solution. Dilute solutions of PrBCM in 10 mM phosphate buffer, pH 7.5, or Krebs-Henseleit solution allowed to stand for 1 h at room temperature (22-24 degrees C) contain mainly the aziridinium ion derivative. At pH 7.5 the concentration of this ion declines slowly, giving rise first to the N-hydroxyethyl derivative and then ultimately, following hydrolysis of the ester bond, to NN-bis(2-hydroxyethyl)propylamine and benzilic acid. In contrast, in 5 mM NaOH the ester bond undergoes rapid hydrolysis, so that the major species present after 15 min at room temperature is the N-hydroxyethylaziridinium ion. This ion then undergoes slow reaction with hydroxy ion to yield the same final decomposition product, NN-bis(2-hydroxyethyl)propylamine, as is observed at pH 7.5.