REDUCTION OF ORGANIC SULFONIC-ACIDS, SODIUM SULFONATES, AND SULFONIC ESTERS TO THE CORRESPONDING DISULFIDES WITH POLYPHOSPHORIC ACID-DERIVATIVES, POTASSIUM-IODIDE AND TETRABUTYLAMMONIUM IODIDE SYSTEM

Organic sulfonic acids, sodium sulfonates, and alkyl sulfonates were readily reduced to the corresponding disulfides in moderate yields upon treatment with a mixture of a polyphosphoric acid derivative and iodide. In these reactions, formation of mixed anhydrides each having a P-O-S linkage is the key step, and subsequent attack of iodide on the sulfur atom gives the corresponding sulfonyl iodides which are reduced further exothermally to the disulfides with the hydrogen iodide. Actually, p-toluenesulfonyl chloride was isolated in the reaction of p-toluenesulfonic acid and polyphosphoric acid derivatives with chloride ion. The competitive reduction of various aromatic sulfonic acids reveals that an aromatic sulfonic acid bearing an electron-donating para-substituent is more readily reduced to the disulfide than that which has an electron-withdrawing para-substituent.