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Secondary Valence Force Catalysis . VI. Catalysis of Hydrolysis of Methyl Orthobenzoate by Sodium Dodecyl Sulfate’ R. Bruce Dunlap and E. H. Cordes2 Contribution No. 1593 from the Department of Chemist ry, Indiana University, Bloomington, Indiana 47401. Received February 5, 1968 Abstract: The acidic hydrolysis of methyl orthobenzoate is subject to marked catalysis by sodium dodecyl sulfate.
Below the critical micelle concentration (cmc) for this surfactant, second-order rate constants for this reaction are independent of surfactant concentration; above the cmc, these rate constants increase rapidly, level off, and finally decrease slowly with increasing surfactant concentration. The surfactant-dependent hydrolysis of methyl orthobenzoate is subject to marked inhibition by cations. For example, 0.09 M sodium ion decreases the second-order rate constant 4-fold, 0.01 M dimethylammonium ion decreases it 25-fold, and 0.001 M tetrapropylammonium ion decreases it 20-fold when the reaction is conducted in the presence of 0.01 M sodium dodecyl sulfate. Inhibition by alkali metal cations increases with increasing hydrated radius of the cation, that by alkaline earth cations is rather independent of the nature of the cation, and that by ammonium ions increases with increasing hydrophobic character of the cation. Chromatography of methyl orthobenzoate on Sephadex G-15 in the presence of various concentrations of sodium dodecyl sulfate yields an approximate equilibrium constant for association of ortho ester with micelles derived from this surfactant of 73 M - l in dilute aqueous solutions of carbonate buffer, pH 9.2. This value seems not to be substantially altered by addition of 0.24 M ammonium or sodium ions but is decreased by the addition of 0.24 M tetramethylammonium ion or 0.12 M tetraethylammonium ion. The maximum rate increase for the hydrolysis of methyl orthobenzoate elicited by a series of alkyl sulfates increases with increasing alkyl chain length and decreases with increasing temperature.
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nterest in the kinetics and mechanism for organic reactions occurring on the surface of micelles formed from ionic detergents has been sharpened by the realization of a relationship between these processes and those which are enzymatic in While it is (1) Supported by Grant AM-0232-04 from the National Institutes of Health. (2) Career Development Awardee of the National Institutes of Health. (3) For leading references to the kinetics of nonenzymatic reactions in micellar systems, see ref 4-28. For related properties of enzymatic reactions, we suggest consulting the following: H . R. Mahler and E. H. Cordes, “Biological Chemistry,” Harper and Row, New York, N. Y., 1966; M. Dixon and E. C. Webb, “Enzymes,” 2nd ed, Academic Press Inc., New York, N. Y., 1964; W. P. Jencks, Ann. Reu. Biochem., 32,639 (1963). (4) J. G. Fullington and E. H. Cordes, Proc. Chem. Soc., 224 (1964). ( 5 ) M. T. A. Behme, J. G. Fullington, R. Noel, and E. H. Cordes, J . Am. Chem. Soc., 87, 266 (1965). (6) M. T. A. Behme and E. H. Cordes, ibid., 87, 260 (1965). (7) A. Ochoa-Solano, G. Romero, and C. Gitler, Science, 156, 1243 (1967). (8) T. C. Bruice, J. Katzhendler, and L. R. Fedor, J . Phys. Chem., 71, 1961 (1967); J . Am. Chem. Soc., 90, 1333 (1968). (9) E. F. J. Duynstee and E. Grunwald, ibid., 81, 4540, 4542 (1959). (10) L. J. Winters and E. Grunwald, ibid., 87, 4608 (1965). (11) D. G. Herries, W. Bishop, and F. M. Richards, J . Phys. Chem., 68, 1842 (1964). (12) S. Riegelman, J . Am. Pharm. Assoc. Sci. Educ., 49, 339 (1960). (13) A. G. Mitchell, J. Pharm. Pharmacol., 14, 172 (1962). (14) J. L. Kurz, J . Phys. Chem., 66, 2239 (1962). (15) R. L. Reeves, J . A m . Chem. Soc., 84, 3332 (1962). (16) R. L. Reeves and L. I
