Kinetics of hydrogen peroxide oxidation of alkyl dimethyl amines

We measured the absolute rate constants for the hydrogen peroxide oxidation of two different octyl dimethyl amines in isopropanol/water mixtures at 23 degrees C. The amines were 1-octyl dimethyl amine (1) and 2-ethylhexyl dimethyl amine (2); their structures were analogous to those most often encountered in commercial alkyl dimethyl amine oxide production. The observed first-order rate constants for the disappearance of amine across a range of H2O2 concentrations (0.5-8 M) indicated that the overall rate was first-order in amine and 3/2-order in H2O2. Calculations showed k(1)=0.16 M(-1) h(-1), k(2)=0.046 M(-1) h(-1), and k(1)/k(2)=3.5. The rates appeared to decrease with increasing steric hindrance around the nitrogen atom. We also investigated the effect of water on the reaction rates. When [H2O] <similar to 4.5 M in isopropanol, the rates increased with increasing [H2O]; for [H2O]>similar to 4.5 M, the rates were insensitive to [H2O].