CIS ADDITION-REACTION OF THIOPHENOL TO ETHYNYLBENZENE AND ISOMERIZATION OF ADDUCT AS A MODEL OF POLY(1,4-BENZENEDITHIOL-CO-1,4-DIETHYNYLBENZENE)

The mechanisms of cis polyaddition of 1,4-benzenedithiol to 1,4-diethynylbenzene were studied by means of a model reaction. As the model reaction, the addition reaction of thiophenol (TP) to ethynylbenzene (EB) was carried out in a NMR glass tube at 34-degrees-C under atmosphere of nitrogen and the reaction course was monitored by H-1 NMR method. Under an atmosphere of nitrogen an anti-Markownikoff type product, beta-phenylthiostyrene, with 80% of the cis structure was obtained at various molar ratios of TP to EB. On the other hand, under an atmosphere of air, the addition reaction proceeded almost quantitatively for 4h to form the anti-Markownikoff type adduct, which was initially rich in the cis structure, but cis content decreased gradually to below 50% even after the hundred conversion. In the case of the polyaddition of 1,4-benzenedithiol to 1,4-diethynylbenzene, high cis polymers were obtained initially both in solution and also in solid state polymerization. Consequently, the cis polymerization mechanism is the same as the cis adduct formation. MINDO/3 calculations with intermediates and products indicated that the trans adduct is more stable that the cis adduct, while the intermediate radical for the cis adduct (cis*) is 3.4 kcal mol-1 lower than that for the trans adduct (trans*). Accordingly, the cis adduct and cis vinylene of the polymer are preferentially formed by kinetic control. The effects of oxygen, thiophenol, AIBN and reaction temperature on the isomerization of the cis to trans adduct were also studied by H-1 NMR method. It was found that the isomerization of the cis to trans adduct hardly occurred in the absence of oxygen, AIBN or phenylthio radical at 34-degrees-C.