A kinetic and thermodynamic study of the alpha-cyclodextrin mediated reaction of a range of p-substituted phenyl methyl sulfides with binding and non-binding peroxyacids

作者：Deary Michael E^*; Mousa Salem M; Davies D Martin

来源：Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2012, 74(1-4): 77-86.

DOI：10.1007/s10847-011-0085-5

• alpha-cyclodextrin
• Peroxyacids
• Phenyl methyl sulfides
• Enthalpy-entropy compensation

This paper presents a thermodynamic study of the rate and equilibria processes involved in the alpha-cyclodextrin mediated reaction of a range of 4-substituted phenyl methyl sulfides with two peroxyacids of different binding affinities. The results for the inclusion processes show that the formation of 1:1 and 2:1 (host:guest) complexes between alpha-cyclodextrin and phenyl methyl sulfides are generally enthalpically controlled, particularly so for the 2:1 complexes, as might be expected for a ternary complex. The data from this series of sulfides is presented as enthalpy-entropy compensation plots, yielding slopes of unity for each inclusion process. The formation of a 1:1 complex between cyclodextrin and the strongly associating 3-chloroperbenzoic acid (MCPBA) is also enthapically controlled. The other peroxyacid used, peroxomonosulfate, does not bind to alpha-cyclodextrin to any measurable degree. As described in our original study of this reaction system (Davies and Deary in J Chem Soc Perkin Trans 2:2423-2430, 1996), catalysis by alpha-cyclodextrin is effected by activation of the peroxide as a result its inclusion within the cyclodextrin cavity; hence for reactions of phenyl methyl sulfides with MCPBA, catalysis is observed, but is absent for PMS. In this study the reaction rates are analysed using the transition state pseudo-equilibrium approach of Tee (Carbohydr Res 192:181-195, 1989), whereby the transition state pseudoequilibrium constant K (TS) reflects the stabilisation imparted to the transition state by the association with one molecule of cyclodextrin. Enthalpy- entropy compensation plots for K (TS) give slopes close to unity; this is the first reported example of such plots being applied to transition state pseudoequilibrium constants.

• 出版日期2012-12