1) (a) Paquette, L. A.; Cottrell. D. M.; Snow, R. A,; Gifkins, K. B.; Clardy, J. J. Am. Chem. SOC. 1975, 97,3275. (b) Paquette, L. A,; Cottrell. D. M.; Snow, R. A. /bid. 1977, 99, 3723. (2) (a) Santiago, C.; Houk, K. N.; Snow, R. A,; Paquette, L. A. J. Am. Chern. SOC. 1976, 98, 7443. (b) Snow, R. A.; Cottrell, D. M.; Paquette. L. A. /bid. 1977, 99, 3734. (3) Paquette, L. A.; Ku, A. Y.: Santiago, C.; Rozeboom, M. D.; Houk, K. N.
Abstract:The rates of hydrolysis of methyltris(2,6-dimethylphenoxy)phosphonium triflate, I, of methylphenyldiphenoxyphosphonium triflate, 11, and of methyldiphenylphenoxyphosphonium triflate, 111, are decreased 30-,63-, and 83-f0ld, respectively, by the addition of 1.8 M lithium triflate in 34% aqueous acetonirile.These enormous salt effects are ascribed to a decrease in the activity of water in the mixed solvent. Substitution of triflic acid for lithium triflate at a constant ionic strength of 1.8 M further decreases the rate of hydrolysis of I and I1 by factors of 2.6 and 3.2, respectively, but has no influence on that of 111.These data can most simply be interpreted to mean that the rates of hydrolysis of I and I I are inhibited by acids per se, and that the observed decreases in rate with increasing concentration of acid at constant ionic strength are not simply caused by a difference between the effects of hydrogen and lithium ions on the activity coefficient of water. The inhibition by acid provides evidence that the hydrolysis proceeds by way of a phosphorane as intermediate.