Kinetics and mechanism of acid-catalyzed hydration of 5-hydroxymethyl- and5-phenoxymethylnorborn-2-enes

The disappearance rate constants for exo- and endo-5-hydroxymethylnorborn-2 -enes (3 and 4) and exo- and endo-5-phenoxymethylnorborn-2-enes (5 and 6) w ere measured in aqueous perchloric acid by a capillary GC method at differe nt temperatures and acid concentrations. The rate constants, activation par ameters, excess acidity plots and products (for 3 and 4 only) are in agreem ent with the rate-determining protonation of the double bond (Ad(E)2 mechan ism). No proof of endo protonation of the double bond via the protonated en do-5-CH2OH group was obtained. The excess acidity plots were corrected acco rding to the partial protonation of the hydroxylic or ether oxygen atom. In the case of 3 and 4, the slope parameter m double dagger, indicative of th e transition state, decreases slightly with increasing temperature, the int ercept parameter log (k(o)/M-1 s(-1)) depends reasonably on the temperature , and the protonation site parameters of the hydroxymethyl group, m' and pK (S'H+,) are temperature-independent. The corresponding parameters for 5 and 6 at 303 K are normal except the peculiar pK(S'H+) values, ca. -2.5.