W.J.M. van Tilborg

Improved Method for the Synthesis of Dialkyl-substituted Thiophene 1, 1-Dioxides

Abstract The peracid oxidation of substituted thiophenes to thiophene 1, 1-dioxides has been extensively investigated by Melles and Backer1,2. Most oxidations, especially those of 3,4-disubstituted thiophenes, afford the sulfones in fair to good yields. Oxidation of 2,5-dimehtylthiophene, however, only yields 14% of the corresponding dioxide. As we needed considerable amounts of this dioxide and related compounds for oxidation studies3 and the preparation of cyclo-heptatrienes4, we had to improve the method of its synthesis. We found that using the commercially available m-chloroperbenzoic acid as the oxidant, freezing out (−55 °C) most of the m-chlorobenzoic acid formed and subsequently removing the residual acid with the aid of tert-amino-substituted macroreticular resins, the yield could be increased considerably (Table I). An additional advantage of using the above-mentioned ion-exchange resins is that they decompose any excess of the peracid. This procedure was also successfully applied to the synthe...

Mechanism of the metal-phthalocyanine-catalysed oxidation of cumene in the liquid phase

Abstract It is shown that the catalysis of the autoxidation of cumene by metal-phthalocyanines is not due to some type of oxygen activation, but is caused by a catalysed homolytic cleavage of hydroperoxides.

Pro-oxidant action of sulfur compounds : Catalysis of autoxidation by onium salts

Abstract It is shown that the initiation of the autoxidation of cumene by triphenylsulfonium salts is due not to oxygen activation, as stated in the literature, but to a sulfonium-catalysed homolytic cleavage of cumene hydroperoxide. The activity of triphenylsulfonium chloride is considerably enhanced by addition of solid calcium carbonate, which effect is attributed to the removal of chloride ions. In keeping with this, triphenylsulfonium hydroxide was found to display an even higher activity.