A Kinetic Study on Oxidation of a Pair of Associating Thiols Having Substituted Phenyl Groups with Oxygen

Abstract

Abstract The rates of oxidation of 1:1 mixtures of associating thiols, each having the binding site (Remark: Graphics omitted.) and the recognition site [p-(CH3)2NC6H4 or R], with O2 were measured in 80% (v/v) acetonitrile-20% water in the range of 20 to 50 °C. Oxidation of the thiol having the p-(CH3)2NC6H4 group proceeds about 100 times faster than that of the thiols with R. It has been found that oxidation of 1:1 mixtures of the thiols is first-order with respect to thiols and 0.7 th-order with respect to triethylamine by means of the method of initial rates. The k1.7 values for R=C6H5, p-CH3C6H4, and p-C2H5C6H4 were similar to one another; this makes a sharp contrast with our previous work that the selectivity (the logarithmeric ratio of the yield of the unsymmetrical disulfide to twice that of the symmetrical disulfide) changes greatly with the structures of R and temperature. It is concluded that the product ratio does not depend upon the k1.7. The large negative activation entropies (−51 to −45 cal K−1 mol−1) suggest that the oxidation would proceed through a highly ordered transition state.