Kinetics and mechanism of reserpine oxidation by nitrous acid. A reinterpretation of recent results

Abstract

Recently reported kinetic results from the reaction of reserpine and nitrous acid (to give 3,4-dehydroreserpine) are reinterpreted. Two possible mechanisms are consistent with the experimental observations involving either (a) the rapid and reversible formation of N¹-nitrosoreserpine (3), which then undergoes a rate-limiting acid-catalysed rearrangement to yield the product, or (b) the rapid and reversible attack at the tertiary N-atom yielding a quaternary nitrosamine ion, which breaks down in an acid-catalysed rate-limiting process, which takes place in parallel with the reversible and rapid formation of 3, Mechanism (b) has a close analogy to that involved in the nitrosation of simpler tertiary amines.