Flash vapour‐phase pyrolysis of thiophene 1,1‐dioxides

Abstract

Abstract Flash vapour‐phase pyrolysis 1 of 2,5‐ or 2,4‐dialkyl‐, 2,5‐diphenyl‐ and dibenzothiophene 1,1‐dioxides at temperatures above 800°C/10 −2 mm Hg results in the formation of the corresponding furans. Thiophenes are obtained as co‐products if stabilized cyclobutadiene‐type intermediates can occur, especially at lower temperatures (<700°C) and/or higher pressure (10 −1 mm Hg). Both tetraphenylthiophene 1,1‐dioxide and tetraphenylcyclopentadienone yield diphenylacetylene as the main product. Benzothiete is obtained from the pyrolysis of benzothiophene 1,1‐dioxide. A general reaction scheme, starting from one common intermediate, is proposed which interrelates the formation of the aforementioned products. On the basis of this scheme the seemingly unrelated results reported in the literature can be easily explained.