On the influence of solvent and temperature on the speed of oxidation of some organic substances by chromic acid. III

The velocity of the reaction between succinic acid and chromic acid has been measured in mixtures of sulphuric acid and water containing from 62.50 to 95.36% sulph. ac. at temperatures between 313° and 413° K. In these solvents the velocity is nearly proportional to the concentration of both reagents. The temperature coëfficient of this velocity decreases with increasing temperature, the rate of this decrease being characteristic for each solvent. In this respect the solvents may be divided into two groups, the limit between the two lying at 70% sulph. ac. The “constants” A and E in Arrhenius' formula {article}{empty}{document}\[{ k} = { A}.{ e}^{-{{ E}}{{ RT}}}\]{document} are in this case dependent on the temperature. The variation of these values with the composition of the solvent leads to the conclusion that the velocity of the oxidation in solvents containing more than 70% sulph. ac. is determined by the presence of the hydrate SO3 3 aq., while in more dilute solutions the hydrate SO3 5 aq. may play a corresponding rôle.