SOLUTION CHEMISTRY OF THE SYN-TETRAHYDRODIOL AND ANTI-TETRAHYDRODIOL EPOXIDES, THE SYN-TETRAHYDRODIMETHOXY AND ANTI-TETRAHYDRODIMETHOXY EPOXIDES, AND THE 1,2-TETRAHYDRO EPOXIDES AND 1,4-TETRAHYDRO EPOXIDES OF NAPHTHALENE

The hydrolyses of the syn- and anti-tetrahydrodiol epoxides (1 and 2), the syn- and anti-tetrahydrodimethoxy epoxides (3 and 4), and the 1,2-and 1,4-tetrahydro epoxides (5 and 6) of naphthalene occur by both hydronium ion (kH) and water (ko) catalysis. Consideration of the various values of kH and ko for 1-4 in H2O and in 75% dioxane-water suggests that there is no kinetic assistance from an internal hydrogen bond in the solvolysis of 1. Rather, the values of the various rate constants reflect solely the conformation of the hydroxy! and methoxyl substituents. The large difference in the value of kh in water for 5 relative to 1-4 is suggested to arise mainly from the pKa of protonated 5. From the dependence of the second-order rate constants for nucleophilic attack of β-mercaptoethanol anion upon the concentration of water in dioxane-water mixed solvents, it is concluded that assistance by internal hydrogen bonding to nucleophilic attack on 1 is absent in water but becomes apparent on decrease in the protic nature of the solvent. With the exception of H3PO4 and H2PO4- no buffer catalysis of solvolysis of 1, 2, or 5 was observed. The catalysis of the hydrolysis of 1, 2, and 5 by both H3PO4 and H2PO4- is suggested to be general acid in nature based on a study of the products obtained from 5. Of the epoxides in this study only 5 is subject to nucleophilic attack by chloride and bromide ion. Neither an A-l nor an A-2 mechanism entirely accounts for the kinetic and product studies with 5 and several suggestions are proposed. © 1979, American Chemical Society. All rights reserved.