THE RELATION BETWEEN KOLBE’S REACTION AND HYDROGEN ION CONCENTRATION. VII. THE MECHANISM OF KOLBE’S REACTION

Abstract

Abstract (1) 0.1–0.7 Per cent. solution of potassium propionate gave neither ethylene nor signs that the solution had undergone any oxidation, when electrolysed by passing a current of DA = 10 A/dm2. at 9–12°C. (2) When 1.0% potassium propionate solution was electrolysed under the same conditions, ethylene was produced, and at the same time oxidizing action of the solution became observable. Hydrogen peroxide was also found present. (3) The presence of ammonium carbonate proved so effective as to produce ethylene even from the most dilute solution. Ethylene formation was always accompanied by oxidizing action of solutions in all cases alike. (4) Electrolyses of a solution containing 5.0 gr. potassium propionate and 2.0 gr. propionic acid and the one containing 5.0 gr. potassium propionate and as much ammonium carbonate, each in 100 c.c, were investigated. (5) The assumption of propionyl peroxide at the intermediate product provides a very satisfactory explanation of Kolbe’s Reaction and also of other reaction related to it in the electrolysis of a propionate; the production of ethylene, hydrogen peroxide and similar oxidizing substances may all be explained to take place according to the following scheme : (C2H5COO)2+H2O = C2H5COOH+C2H5COOOH, C2H5COOOH = CO2+H2O+C2H4 (Ethylene formation), C2H5COOOH+H2O = C2H5COOH+H2O2 (Hydrogen peroxide formation). (6) The difference observed between electrolyses of potassium propionate and potassium acetate will easily be understood, if we take notice of the higher stability of propionyl peroxide in comparison with acetyl peroxide.