The effect of pressure on the rate of the benzidine rearrangement VI : 2-methoxy-2'-methylhydrazobenzene

Abstract

The effect of pressure on the rate of the acid-catalyzed rearrangement of 2-methoxy-2'methylhydrazobenzene in an aqueous ethanolic solution of 85 vol % was studied under the condition of 15～30℃ and 1～1, 500kg/cm^2. It was observed that the rearrangement was of first order with respect to the concentration of hydrogen ion and was accelerated by pressure. Comparing the activation parameters obtained, i.e. E≠=15.1kcal/mole, ΔS≠=-9.4 e.u., ΔV≠=-8.5 cm^3/mole for one-proton mechanism, with those previously obtained, it was concluded that the transition state of one-proton mechanism was strongly solvated, polar and compact. For this one-proton mechanism, by correcting the pK_a values for the steric effect of ortho-substituents, a good linear free energy relationship between the rate constants and pK_a of ortho-substituted anilinium ions was obtained.