Kinetics and mechanism of the oxidation of ethanol and propanol by chromium (VI) in acidic medium

Abstract

The stoichiometry of the reaction of ethanol or propanol respectively with chromium (VI) has been determined by spectrophotometric titration to be 1:3 at Y = 350nm, T = 26.0 +_0.5^oC and [H+] = 0.58 mol dm^-3. The reactions were found to follow a general rate law:
Where alcohol is either ethanol or propanol and k2, the second order rate constant were determined to be (4.00+_ 0.09) mol^-1dm³min^-1 and (3.00 +_0.10) mol^-1dm³min^-1 respectively. The rates of reactions were respectively dependent on [H+] to the order of one. The activation parameters, H, S, were determined as –49.11 kJmol^-1, -112 J mol^-1 and –47 kJ mol^-1, -100 J mol^-1 respectively for ethanol and
 propanol. The reactions were catalyzed by added anions and cations and polymerization test suggested the absence of any radical intermediate. It is proposed that the oxidation reactions proceed by a cyclic proton transfer without the formation of a radical intermediate.