Correlation of the Rates of Solvolysis of Chlorodiphenylphosphine Using the Extended Grunwald–Winstein Equation

Abstract

Specific rates of solvolysis involving displacement of chloride from the trivalent phosphorus of chlorodiphenylphosphine (Ph₂PCl, 1) are reported for ethanol, methanol, and aqueous binary mixtures incorporating ethanol, methanol, acetone, 2,2,2-trifluoroethanol (TFE), and 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP). The 25 solvents give an extended Grunwald–Winstein correlation with an l value of 1.25 ± 0.09, m value of 0.46 ± 0.06, and correlation coefficient (R) of 0.954. The reactions in aqueous acetone were unusually fast, and these data points lie above the plot. Specific rate values are also reported for TFE–ethanol mixtures. For five representative solvents, values were obtained at three additional temperatures and activation parameters are presented. Rather low enthalpies of activation (8.4 to 11.8 kcal mol⁻¹) are accompanied by very negative entropies of activation (−33 to −46 cal mol⁻¹K⁻¹). The kinetic features observed are consistent with an S_N2 reaction incorporating appreciable bond formation and bond breaking at the transition state, and they are very similar to those previously observed for diphenylphosphinyl chloride (Ph₂POCl).

Keywords:

• Chlorodiphenylphosphine
• solvent ionizing power
• solvent nucleophilicity
• solvolysis

Acknowledgments

Presented, in part, at the 17th International Conference on Phosphorus Chemistry (ICPC-17), April 15–21, 2007, Xiamen, China, and briefly summarized in the proceedings of the conference: H. J. Koh, S. J. Kang, and D. N. Kevill, Phosphorus, Sulfur, and Silicon, 183, 364 (2008). H.J.K. thanks Chonju National University of Education for the granting of a sabbatical leave during the time that this research was carried out. Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research.

Notes

^a Substrate concentration of 0.0065 mol dm⁻³.

^b Unless otherwise indicated, on a vol/vol basis, at 25.0°C, with the other component water.

^c With associated standard deviations.

^d From refs. 12 and 14.

^e From refs. 15 and 16.

^f From ref. 9.

^g Solvent prepared on weight/weight basis.

^h T-E represent 2,2,2-trifluoroethanol-ethanol mixtures.

^a Concentration of stock solution in MeCN, in solution: 3·5 × 10⁻³M, 6·6 × 10⁻³ M, and 14.2 × 10⁻³M.

^b The k values are the averages of three or more runs, and with associated standard deviation.

^a Averages of three or more runs, with standard deviation.

^b Values at 25.0°C, from Table I, are also used in the calculation; the activation parameter values are accompanied by the standard error.

^c On a volume–volume basis at 25.0°C, other component is water.

^d On a weight–weight basis, the other component is water.

^a Number of solvents.

^b From Equation (1) and with associated standard error.

^c Multiple correlation coefficient.

^d With the TFE–EtOH data points excluded from the correlation.

^e From ref. 9.

^f From ref. 6.

^g From ref. 21.

^h From ref. 22.