Change of Rate Limiting Step in General Acid-Catalyzed Benzo[a]pyrene Diol Epoxide Hydrolysis

The rates of reaction of (±)-7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (1) in 1:9 dioxane−water buffer solutions containing primary amines whose pKa values span the range of 5.4−10.7 have been determined. For those amines with pKa values ca. 8, both acid and base forms of the buffer react with 1. The magnitude of the kinetic term in the base form of the amine (RNH2) increases with amine pKa and is attributed to nucleophilic addition of the amine to the epoxide group. Curvatures in plots of the kinetic term due to buffer (kbuff)...