Microwave induced synthesis of diphenylthiophenes from elemental sulfur and styrene

Abstract

Thiophene and its substituted derivatives (particularly diphenylthiophenes) find a wide practical use and they continue to attract the attention of investigators as building blocks for organic synthesis [1][2][3]. One of the routes to the synthesis of diphenylthiophenes is the reaction of elemental sulfur with styrene. Unfortunately this is unselective and heating elemental sulfur with styrene (140-230°C) forms a complex mixture of acyclic and cyclic (2,4-diphenylthiophene, 2,4-diphenylthiophane, 2,5-diphenyl-1,4-dithiane, 2,5-diphenyl-2,3-dehydrothiane) products among which rubber like polysulfide oligomers and polymers predominate [4][5][6]. Increasing the selectivity of the synthesis of diphenylthiophenes from styrene and elemental sulfur remains an unresolved problem.We have found that styrene reacts with elemental sulfur in the strongly basic medium KOH-DMSO [7] in the presence of hydroquinone under microwave irradiation (600 watts, 4 min) to form a 1: 12 mixture of 2,4-and 2,5-diphenylthiophenes 1a,b in overall 30% yield (not optimized). Ph S Ph Ph S Ph PhThe diphenylthiophenes are not formed when the elemental sulfur and styrene are heated (85-90°C, 6 h) in the system KOH-DMSO-hydroquinone in the absence of the microwave irradiation and the unreacted styrene is recovered.In the absence of the hydroquinone the reaction is less selective. Along with the thiophenes 1a,b GC-MS analysis of the reaction mixture shows the presence of bis(2-phenylethyl) sulfide, bis(2-phenylethyl) disulfide, 1,4-diphenylbuta-1,3-diene, and 1,3,5-triphenylbenzene. _______ * Dedicated to Academician M. G. Voronkov, Russian Academy of Sciences in his 85 th year. __________________________________________________________________________________________ A. E.

Multibubble sonolysis and sonoluminescence in molten elementary sulfur and sulfur—styrene mixture

“…13 The yield of 1 under ther molysis conditions can be increased up to 15% only in the presence of a palladium catalyst. 14 At the same time, ther molysis results in 2,5 diphenylthiophene (2) as major product whose yield strongly depends on the reaction conditions, being at most 30% (see .…”

Recent Advances in Organic Reactions Involving Elemental Sulfur

“…Styrene was found to react with elemental sulfur in the strongly basic medium KOH‐DMSO in the presence of hydroquinone under microwave irradiation (600 W, 4 min) to form a 1:12 mixture of 2,4‐ and 2,5‐diphenylthiophenes ( 29 and 30 ) in overall 30% yield (Scheme ) . In the absence of the microwave heating, these products were not formed and styrene remains unchanged.…”