Deuterium Kinetic Isotope Effect in the Oxidation of Deuteriated Butyric Acid-D7 with Chromium Trioxide in 85% Orthophosphoric Acid

A comparative study of the deuterium kinetic isotope effect in the oxidation of the deuteriated butyric acid-D₇ with Cr(VI) in 85% orthophosphoric acid has been carried out.The (k_HH/k_DD) KIE values between 5.7 and 7.0 indicate that the tunnelling is not involved in oxidation of deuteriated aliphatic carboxylic acids with chromium trioxide in acidic media and the oxidation KIE is determined by the zero point energy difference corresponding to the C-H/C-D stretching vibrations lost in the transition state.The results were compared with the large D-KIE observed in the oxidation of butyrate-D₇ with alkaline manganate caused by the simultaneous operation of zeropoint energy effect and tunnelling.