Simultaneous C- and N-nitrosation of synephrine. A kinetic study

Abstract

A kinetic study of the initial step of the nitrosation of synephrine, N-acetylsynephrine and ephedrine by sodium nitrite has been carried out in acid medium at 310 K and ionic strength 0.36 mol dm^–1. In order to simplify the reaction, [nitrite] > [amine] has been used. The absorbance changes at 300 nm (synephrine and N-acetylsynephrine) and at 332/323 nm (ephedrine) were measured and then analysed according to the initial rate procedure. The results are interpreted on the basis of a simultaneous nitrosation of the amine and phenolic groups in synephrine. Unlike the early reports the global constants for N-nitrosation (0.142 dm⁶ mol^–2 s^–1) and C-nitrosation (3.6 × 10^–4 dm³ mol^–1 s^–1) obtained at pH 3 in unbuffered medium indicate that the rate of nitrosation of the amino group is one order of magnitude larger than that for the phenolic group.