Solvent Effects on Anchimerically Assisted Solvolyses. II. Solvent Effects in Solvolyses of threo-2-Aryl-1-methylpropyl p-Toluenesulfonates

Article abstract of DOI:10.1246/bcsj.68.2603

The solvent effects on the solvolysis of threo-2-aryl-1-metkhylpropyl p-toluenesulfonates were analyzed with the aid of the extended Winstein-Grunwald Equation.The aryl-assisted k_Δ solvolysis of 2-(p-methoxyphenyl)-1-methylpropyl and 2-methyl-2-phenylpropyl p-toluenesulfonates failed to give a single linear correlation with the Y_OTs parameter.The dispersion against Y_OTs cannot be due to nucleophilic solvent assistance.The m values from the plots of 2-(p-methoxyphenyl)-1-methylpropyl and 2-methyl-2-phenyl-propyl p-toluenesulfonates against Y_OTs were significantly lower than m=1.0 for the limiting k_c solvolysis.Singificantly improved correlations (R > 0.99; SD < 0.14) were obtained for the p-methoxy, 3-chloro-4-methoxy, and p-methyl derivatives with the Y_Δ scale based on the solvolysis of 2-(p-methoxyphenyl)-2-methylpropyl p-toluenesulfonate, instead of with Y_OTs.No improvement by the Y_Δ treatment was obtained for the unsubstituted compound (R=0.97; SD=0.22).A new similarity comparison analysis in terms of Y_OTs and Y_Δ, i.e., log (k/k_80E)=m_cY_OTs+m_ΔY_Δ, was applied successfully to the present k_Δ solvolyses.The degree of Y_Δ character relative to the Y_OTs one, scaled by m_Δ/(m_c+m_Δ), varies for 1-methyl-2-phenylpropyl tosylates in the range from 1.0 to 0.00 in the consistent manner expected if the dispersion in the Y_OTs plot becomes less pronounced for solvolyses of less significant anchimeric assistance.There is a continuous spectrum of behavior between the extreme pure k_c mechanism and the extreme pure k_Δ one.