Chemical and ESCA investigations of some halogenated heterocyclic systems

Abstract

2,3,4,5,6,7-Hexachlorobenzo-[b]-thiophen reacted with n-butyllithium to give either the 2-lithio derivative or the 2,6-dilithio derivative depending on the reaction conditions; a mixture of mono (2-) and di(2,6-) Grignard reagents were formed from hexachlorobenzo-[b]-thiophen and magnesium. Nucleophilic replacement of the 2-chlorine atom has been established for the reaction of hexachlorobenzo-[b]-thiophen with lithium aluminium hydride; sodium benzenethiolate replaced a chlorine in the five membered ring; sodium isopropoxidc gave a mono substituted product, while sodium thiomethoxide caused multiple substitution to give a dichlorotetrathiomethoxybenzo-[b]-thiophen. Catalytic hydrogenation of nexachlorobenzo-[b]-thiophen [Pd/C] gave 4,5,6,7-tetrachlorobenzo-[b]-thiophen which was also synthesised unambiguously by a reaction sequence which involved the initial treatment of sodium pentachlorobe.izenethiolate with diethyl acetylenedicarboxy'ate to give diethyl 4,5,6,7-tetrachlorobenzo-[b]- thiophen (A), followed by de-esterification and decarboxylation. 4,5,6,7-Tetrachlorobenzo-[b]-thiophen served as a model for (^1)H n.m.r. spectroscopy studies. Under certain conditions both the cyclised material (A) and the uncyclised product, trans-diethy:-1-pentachloro- thiophenoxybutenedioic acid were formed. With ethyl propiolate, sodium pentachlorobenzenethiolate gave only the uncyclised product, cis-ethyl β-pentachlorophenylthioacrylate. Hexechlorobenzo-[b]- thiophen readily formed the 1,1-dioxide on treatment with peroxytri- fluoroacetic acid, the vacuum pyrolysis of which gave hexachloro- phenylacetylene. 4,5,6,7-Ietrachlorobenzo-[b]-thiophen undergoes multiple substitution with thiolates. With sodium benzenethiolate the major product was a dichloro-dithiophenoxybenzo-[b]-thiophen, the minor, mono substituted product was only identified by Mass Spectroscopy. With sodium thiomethoxide mixtures of mon- and di-thiomethoxy or di- and tri-thiomethoxy substituted products were formed, depending on the reaction conditions. ESCA spectra have been recorded and molecular core binding energies determined for indene, indole, benzo-[b]-thiophen, benzo-[b]-thiophen-1,1-dioxide, benzo-[b]-furan and some of their chloro and fluoro derivatives. Binding energies were assigned and data interpreted with the aid of CNDO/2 SCF MO calculations and the charge potential model.