Autoxidation of trimethylamine in aqueous solutions

The autoxidation of trimethylamine in aqueous solutions has been studied at 100°C and at O₂ pressures up to 153 atm. Trimethylamine N-oxide is a major product. Its yield accounts for as much as, but never in excess of 50%, the balance being Me₂NH and HCONMe₂. The reaction follows second-order kinetics, -d[Me₃N]/dt = k[Me₃N]P_o2, where k = 8.7 × 10^-7 atm^-1 s^-1. In solutions buffered with 0.1 N NaOH, the yield of Me₃NO is reduced. These results are interpreted in terms of a rate-limiting electron-transfer reaction between Me₃N and dioxygen, followed by reactions dictated by the radical ions, Me₃N^.+ and O₂ ^.-, thus generated. It is noted that only one oxygen atom in the O₂ molecule is incorporated into Me₃NO, the other being used in the sacrificial oxidations to give other products.