Retentive solvolysis. 16. Reinvestigation of the retentive phenolysis of 1-phenylethyl chloride. The mechanism and the structure of ion pair intermediate.

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The effect of added aniline on the polarimetric (kp) and titrimetric rate constants (kt) has been reexamined for the phenolysis of 1-phenylethyl chloride (RCl) in phenol–benzene (1:1 w/w). The kp–kt plot against the aniline concentrations exhibited the pattern C, instead of A which was the previous results in our laboratory. It has been revealed that the previous rate constants at the lower aniline concentrations, including the case of absence of aniline, were underestimated due to overlooking the reverse reaction caused by the liberated hydrogen chloride. The pattern C indicates that the first ion pair intermediate, not the second one, is nucleophilically attacked by solvent phenol molecule. The major products were the partially retained o-RC6H4OH, the partially inverted p-RC6H4OH, together with the partially retained ROPh. The same kp–kt pattern C has been observed for the competitive solvolysis of RCl in phenol–methanol (85:15 w/w), which produced the partially retained ROMe and ROPh, the partially inverted o- and p-RC6H4OH, and styrene. Such stereochemical outcomes for both solvolyses demonstrate that the major first ion pair intermediate should be a rear-side-shielded ion pair intermediate.
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