Polar Effects in the Reactions of a Series of Substituted Diphenyldiazomethanes with Chloranil

Article abstract of DOI:10.1246/bcsj.53.3284

The kinetics and products of the reactions of fifteen meta- and para-substituted diphenyldiazomethanes with chloranil were investigated in tetrahydrofuran.The second-order rate constants, k, increased with the electron-donating ability of the substituents, and the values could be correlated with the Yukawa-Tsuno equation: log k/k_o=-1.67(?^o+0.66Δ?_R⁺)+0.009, (r=0.996).The ρ value, -1.67, indicates the large development of a positive charge at the diazo carbon in the transition state, while the R value, 0.66, confirms the considerable stabilization of the positive charge by the ?-electronic contribution of the para substituents.The products of these reactions were the corresponding 2,3,5,6-tetrachlorohydroquinone poly(benzhydryl)ethers, but these polyethers were easily hydrolyzed into the corresponding benzophenones and tetrachlorohydroquinone(HQ).On the other hand, the initial presence of water or methanol as an additive changed the reaction features to give benzophenone or α,α-dimethoxydiphenylmethane, together with HQ.Reaction mechanisms which account for the results are discussed.