Comparisons of reactivities in photolysis and thermolysis reactions of 1,9-bis(alkylthio)dibenzothiophenes with stabilities of their dithia dications in concentrated sulfuric acid

Abstract

1,9-Dithia substituents in dibenzothiophenes are in close proximity, being within the van der Waals S-S contact contact distance (3.70 A) [1], and hence, these two sulfur atoms affect each other by strong through-space interaction. Cyclic and acyclic dibenzothiophene derivatives bearing two sulfur atoms at the 1,9-positions, such as dibenzothiophene[1,9-fgh][1,5]dithionin (5) and 1,9-bis(methylthio)dibenzothiophene (1a) and their monosulfoxides 2a and 6 were treated with concd sulfuric acid as an oxidizing or deoxygenating reagent to produce the corresponding dithia dications 7 and 3a. The dithia dications 3a and 7 in concd sulfuric acid gave the monosulfoxides upon treatment with water. On the other hand, a rapid monodealkylation reaction proceeded in the case of 1,9-bis(ethylthio)dibenzothiophene (1b) and 1,9-bis(isopropylthio)dibenzothiophene (1c) and their monosulfoxides, on dissolution in concd sulfuric acid, afforded high yields of the sequentially dimerized disulfides 4b and 4c after treatment with water. The structure of the dimerized disulfide 4c was determined by X-ray crystallographic analysis, and the following results were obtained: orthorhombic, P212121, a = 10.892(1) A, b = 11.284(2) A, c = 22.719(3) A, V = 2792.1(5) A3, Z = 4, ρ = 1.377 g/cm3, μ(MoKa) = 5.09 cm−1, R = 0.030 (Rw = 0.030). In this structure, the four sulfur atoms attached at the 1,9- and 1′,9′-positions of compound 4c are located in an approximately linear arrangement, and the two dibenzothiophene rings are separated by an average intraplanar ring distance of 3.58(8) A. Furthermore, thermolysis and photolysis of compounds 1a–c were performed, and their reactivities were compared. © 1996 John Wiley & Sons, Inc.