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°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 H 2 O 2 concentrations (0.5–8 M) indicated that the overall rate was first‐order in amine and 3/2‐order in H 2 O 2 . 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 [H 2 O]<∼4.5 M in isopropanol, the rates increased with increasing [H 2 O]; for [H 2 O]>∼4.5 M, the rates were insensitive to [H 2 O].