STRUCTURE AND REACTIVITY OF ALIPHATIC DIAZO COMPOUNDS .9. KINETICS OF THERMAL WOLFF-REARRANGEMENT IN ARYL-AROYL-DIAZOMETHANES

The thermal Wolff rearrangement of phenylbenzoyldiazomethane and its isomeric substituted derivatives VIa-g and VIIa-e (p-OCH3, p-C2H5, p-CH3, p-F, p-Cl, p-Br and p-NO2) in di-n-butylether in the presence of amines yields the corresponding diphenylacetamides and desylamines. In the temperature range of 60° to 95° the reaction is kinetically of the first-order for the α-diazoketone. The thermolyses proceeded at approximately the same rates in the presence or absence of nucleophilic reactants. The rate constants k1 are independent of the concentration and basicity of the amines. By comparing N,N-dideuteroaniline with the protium compound the isotope effect k1D/k1H was found to be approximately 1. The substituent effect on the reaction rate of the thermolysis of para-substituted phenylbenzoyldiazomethanes can be correlated by the Hammett relationship for both reaction series VI and VII. However the reaction constants ρ{variant} are different in sign. The thermal decomposition in dioxan-water mixtures yields diphenylacetic acid and the benzoin ester of diphenylacetic acid. The rate of thermolysis increases rapidly with increasing dielectric constant of the solvent mixture. No apparent solvent deuterium isotope effect was observed within the range of experimental error. The possible mechanisms of thermolysis of α-diazoketones have been discussed and based on experimental results the two-step α-ketocarben-keten mechanism with rate-controlling cleavage of nitrogen has been proposed. The attack of the diazo compound by the amine was excluded. © 1969.