Experimental and computational determination of Brønsted coefficients for equilibrium transfer of the O,O‐dimethyl phosphorothioyl group between oxyanion nucleophiles |
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Authors: | David R Edwards Christopher I Maxwell Robert W Harkness Alexei A Neverov Nicholas J Mosey R Stan Brown |
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Institution: | 1. Department of Chemistry, Queen's University, , Kingston, Ontario, K7L 3N6, Canada;2. 613 533 2650613 533 6669;3. 613 533 2400613 533 6669 |
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Abstract: | An experimental determination of the βEq value for equilibrium transfer of the O,O‐dimethyl phosphorothioyl group between oxyanion nucleophiles in water and methanol at 25 °C is presented. The respective βEq values in the two solvents are experimentally the same at ?1.45 ± 0.08 and ?1.39 ± 0.12. Based on the observation that the Brønsted correlation for the nucleophilic reaction of phenoxides in water with substrate 1d (dimethyl 4‐nitrophenyl phosphorothioate, pKaHOAr of 7.14) is linear over the entire range of phenoxides employed (5.53 ≤ pKaNu ≤ 12.38), the reaction for phenoxide nucleophiles displacing phenoxide leaving groups is probably concerted. The obtained data allow one to calculate, for a symmetrical transition state involving 2,4,5‐trichlorophenoxide as a nucleophile and leaving group, an approximately 60% P–OAr cleavage and about 40% P–Nuc bond formation. A computational method is presented for the rapid prediction of the βEq values for such processes in water and methanol, and the results are compared with known values from the literature. Copyright © 2011 John Wiley & Sons, Ltd. |
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Keywords: | Brø nsted hydrolysis methanolysis phosphorthioate esters solvolysis |
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