Consideration of the extent of nucleophilic participation in the solvolyses of benzyl and substituted benzyl tosylates

Includes bibliographical references (pages 67-72)The solvolyses in eleven solvents of benzyl and p- methyl, p-chloro, p-bromo, p-trifluoromethyl, p-nitro and m-fluorobenzyl tosylate have been studied. Using the extended Grunwald-Winstein equation, we found that the susceptibility to nucleophilic attack of benzyl tosylate is comparable to that of the secondary isopropyl tosylate. The l and m values for solvolyses of benzyl tosylate at 50.0°C, using N[sub OTs] and Y[sub 0Ts] values, are perfectly consistent with the values obtained by calculation using the Schadt-Bentley equation. The l and m values for other compounds show that the p-nitro, p-trifluoromethyl and p-fluoro-benzyl tosylate are much more sensitive to nucleophilic attack. The l and m values of p-chloro and p-bromobenzyl tosylate solvolysis are close to those for the unsubstituted benzyl tosylate solvolysis. The solvolyses of p-methylbenzyl tosylate are very sensitive to the ionization power of the solvents, and the p-methylbenzyl tosylate solvolysis can be considered as an S[sub N]1 reaction but with a fairly strong nucleophilic solvation of the developing carbocation. From the Hammett plot of the solvolyses of benzyl and substituted benzyl tosylates in 95% acetone at 50.0°C, we see that the p-methylbenzyltosylate is far above the line of the other compounds. It implies that the p- methylbenzyltosylate solvolyzes via a different mechanism (S[sub N]1) from the other compounds (S[sub N]2).M.S. (Master of Science