Kinetics of hemolytic dehydrogenation by chloranil

ABSTRACT

1-Phenylsemicarbazide is dehydrogenated to phenylazoformamide by chloranil in dioxane medium. The reaction obeys second order rate laws [first order with respect to each reactant]. Unlike the dehydrogenation in alcohol and alcohol water media, no semiquinone radical anion was observed during the progress of the reaction. Furthermore, the positive entropy of activation [delta S[number sign] = 7.0 + 0.5 J.K[-1]. Mol[-1]] suggests that the dehydrogenation proceeds by a homolytic mechanism in which abstraction of hydrogen atom by chloranil gave tetrachloroquinol radical in a slow step, followed by a fast abstraction of hydrogen atom