Kinetics and mechanism of hydrolysis of aryloxyphosphonium salts

Lonzetta, Charles M.; Kubisen, Steven J.; Westheimer, F. H.

doi:10.1021/ja00422a085

Cited by 7 publications

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“…The rates of hydrolysis in that solvent increase a millionfold between 0.2% and 34% water, but the rate a t any given concentration of water is sharply diminished by added acid; 1.8 M triflic acid in 34% aqueous acetonitrile decreases the rate about 100-fold. The rates are also strongly inhibited by salts,2 and, in particular, the rate of hydrolysis of I in 34% aqueous acetonitrile is decreased 30-fold by 1 IV another factor of 2.6 by replacing the lithium triflate by 1.8 M triflic acid. The question naturally arises as to whether this further decrease in rate, caused by the substitution of hydrogen ions for lithium ions, is the result of an inhibitory effect of acid, per se, or whether it represents a difference between the salt effects of lithium and hydrogen ions on the activity coefficient of water or other reaction species.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics and mechanism of the hydrolysis of aryloxyphosphonium salts. Salt effects

Kubisen¹,

Westheimer²

1979

J. Am. Chem. Soc.

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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.

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Section: Introductionmentioning

confidence: 99%

“…(RO)3PO + H+ ^(RO)3POH (RO) 3POH + H20products (1) The reactions summarized by eq 2 model the second step in this mechanism; ArOH is a phenol, and Ri, R2, and R3 can represent alkyl, aryl, or aryloxy groups.…”

Section: Introductionmentioning

confidence: 99%