Mechanism of the N-Nitrosodimethylamine Formation from Trimethylamine and Trimethylaminoxide

Abstract

The kinetics of nitrosation of trimethylamine (TMA) and trimethylaminoxide (TMAO) to give N-nitrosodimethylamine (NDMA) have been studied. The nitrosation rates of TMA and TMAO when determined at 100°C in sealed tubes gave maximum values at about pH 3, while at temperatures lower than 75°C the pH profiles of the nitrosation of these compounds were similar to those occurring in alkylamides. The initial reaction rate of NDMA formation from TMAO determined at pH 3.0 and 25°C was found to be in proportion to the TMAO and nitrite concentrations, not to the square of nitrite concentration. In contrast, the rates of NDMA formation from TMA and TMAO when reacted at pH 3.0 and 100°C in sealed tubes were found to be proportional to the square and cube of the nitrite concentrations respectively. These results may strongly suggest that NDMA formation at higher temperatures involves the oxidative cleavage of tertiary amine to produce secondary amine (dimethylamine, DMA) which may react with nitrite to form NDMA. On the other hand, at lower temperatures, NDMA may be formed from TMA or TMAO through a pathway not forming DMA.