The separation of polar and steric effects. Part XIII. Kinetics of the reactions of cinnamic acid and meta-substituted cinnamic acids with diazodiphenylmethane in various alcohols and in aprotic solvents

Abstract

Rate coefficients have been determined for the reactions at 30 °C of diazodiphenylmethane with cinnamic acid and meta-substituted cinnamic acids (substituents: Me, Cl, or NO2) in 12 alcohols, in ethyl acetate, and in acetone.The reactions of cinnamic acid with diazodiphenylmethane in alcohols show a good linear free-energy relationship with the corresponding reactions of benzoic acid. The solvent effect can be interpreted in terms of the dielectric constant and the influence of hydrogen bonding. Multiple linear correlation with three suitable solvent parameters is quite successful. Comparisons are made with the benzoic and the phenylacetic acid system.The Hammett ρ-values (ρ3) for the reactions of cinnamic acids are correlated with solvent parameters and comparisons are made with ρ-values for the benzoic (ρ1) and the phenylacetic (ρ2) acid system. The expressions ρ3= 0.39ρ1, and ρ2= 0.60 (ρ1– 0.25) hold, and are interpreted in terms of Bowden, Chapman, and Shorter's treatment of the transmission of polar effects through side-chains.