LEAD CATALYSIS OF A THIOCARBONYL REDUCTION USING ZINC DUST

A catalytic amount of lead is necessary to promote the reduction of a 2-thioxo-4-thiazolidinone to the corresponding 4-thiazolidinone with z inc dust, If sufficient lead (>1000 ppm) is not contained in the comme rcially supplied zinc dust, a catalytic amount of lead dust or a lead salt may be added to consistently obtain the desired reactivity, Addit ion of larger amounts (>2 mol %) of lead salts or other metal salts re sults in a decrease in reactivity. Thallium(I) chloride is also a usef ul additive for increasing the reactivity of commercial zinc dust whic h does not contain lead. Identification of the catalytic role of lead allowed development of a robust process for the synthesis of 4-thiazol idinones.