F-19 NMR-STUDY OF THE REACTION OF PARA-FLUOROBENZENETHIOL AND DISULFIDE WITH PERIODATE AND OTHER SELECTED OXIDIZING-AGENTS

The products of the reactions of both p-fluorobenzenethiol and p-fluorobenzene disulfide with a series of oxidants were examined using 19F NMR spectroscopy. Two commonly used mild oxidants (periodate and hydrogen peroxide), a “non-oxygen-transfer” oxidant (tetranitromethane(TNM)) and a strong metal oxidant (Au(III)) were examined in several solvent systems. Under the conditions of our experiments disulfides are not oxidized by periodate, peroxide, or TNM. Au(III) is the only reagent that both oxidizes thiols and cleaves disulfides to sulfonic acids at room temperature. In the periodate oxidation of thiols, the products depend on the solvent and can be best explained if the reaction of periodate with a nucleophilic sulfur atom results in the formation of a complex or mixed anhydride. In aqueous dioxane the products are disulfide and thiosulfonate. The thiosulfonate is formed by the reaction of sulfinic acid with sulfenic acid and not from the oxidation of disulfide. In anhydrous ethanol, the products are ethyl sulfinate and the disulfide. We propose that ethyl sulfinate is formed by the reaction of a sulfinic/iodic acid anhydride with ethanol. The products in aqueous ethanol appear to be a combination of the products observed in aqueous dioxane and anhydrous ethanol. A thiosulfinate/periodate complex may also account for ester formation and other products observed during the oxidation of unsymmetrical thiosulfinates. Even though hydrogen peroxide is the most common oxidant for converting a thiol to disulfide, it appears to be one of the poorer reagents to use, since the reaction yields sulfonic acid as well as disulfide. With TNM a sulfenyl nitrite is formed initially and then either reacts with thiol to give disulfide or isomerizes to a nitrosonium sulfenate to give thiosulfinate and thiosulfonate. © 1990, American Chemical Society. All rights reserved.