The rates of oxidation of several aromatic aldehydes with chromic acid have been measured using several mixtures of acetic acid and water as solvents. This study points to the fact that the oxidation proceeds by an iondipole mechanism. Evidence has also been obtained from these studies that the active oxidant is a cationic species, such as HCrO_3/+ or H₃CrO_4/+. Amis’ equation for an ion-dipole reaction gives remarkably good values of ‘r’ thus confirming an ion-dipole mechanism.

Both structural and solvent influences on the rate of oxidation of a series of aromatic aldehydes by chromic acid show the following features: the formation of a chromate ester is not a prerequisite to oxidation; in the rate-determining step of the reaction the C-H hydrogen is removed as a hydride anion. That the rate-dermining step involves a two-electron transfer has been proved by a study of the Induction Factor method. A tentative mechanism, based on an analogy to the well-known ‘S_N2’ process, has been proposed.

The effect of added salts and oxidizable cations on the chromic acid oxidation of aromatic aldehydes in acetic acid-water mixtures is discussed and a tentative scheme for the intermediate stages of reduction of the chromium species is presented.