KINETIC STUDY OF HYDROLYSIS OF BENZOATES.PART XXVI.VARIATION OF THE SUBSTITUENT EFFECT WITH SOLVENT IN ALKALINE HYDROLYSIS OF SUBSTITUTED ALKYL BENZOATES

摘要

The second-order rate constants k_2 (dm~3 mol~(-1) s~(-1)) for the alkaline hydrolysis of substituted alkyl benzoates C_6H_5CO_2R have been measured spectrophotometrically in aqueous 0.5 M Bu_4NBr at 50 and 25 deg C (R=CH_3,CH_2Cl,CH_2CN,CH_2C ident to CH,CH_2C_6H_5,CH_2CH_2Cl,CH_2CH_2OCH_3,CH_2CH_3) and in aqueous 5.3 M NaClO_4 at 25 deg C (R=CH_3,CH_2Cl,CH_2CN,CH_2C ident to CH).The dependence of the alkyl substituent effects on different solvent parameters was studied using the following equations:DELTA log k=c_0+C_1 sigma_I+c_2 E_s~B+c_3 DELTA E+c_4 DELTA Y+c_5 DELTA P+c_6 DELTA E sigma_I:+c_7 DELTA Y sigma_I+c_8 DELTA P sigma_I DELTA log k=c_0+C_1 sigma sigma*+c_2 E_s~B+c_3 DELTA E+c_4 DELTA Y+c_5 DELTA P+c_6 DELTA E sigma*+c_7 DELTA Y sigma*+c_8 DELTA P sigma* .DELTA log k=log k~R-log k~(CH_3).sigma_I and sigma* are the Taft inductive and polar substituent constants.E,Y and P are the solvent electrophilicity,polarity and polarizability parameters,respectively.In the data treatment DELTA E=E_s-E_(H_2O),DELTA Y=Y_S-Y_(H_2O),DELTA P=P_s-P_(H_2O) were used.The solvent electrophilicity,E,was found to be the main factor responsible for changes in alkyl substituent effects with medium.When sigma_I constants were used,variation of the polar term of alkyl substituents with the solvent electrophilicity E was found to be similar to that observed earlier for meta and para substituents,but twice less when sigma* constants were used.The steric term for alkyl substituents was approximately independent of the solvent parameters.