Condensation of 2,2′-thiodiethanethiol with benzaldehyde and other carbonyl compounds (or equivalents thereof)

Abstract

The acid-catalysed condensation of 2,2′-thiodiethanethiol 1 with carbonyl compounds (or equivalents thereof) can, under properly chosen conditions, lead in good yield to thiocrown ethers containing thioacetal units. The reaction with benzaldehyde 2 has been examined in detail and the monomer (3), dimer (4), and polymer (5) products have all been characterized. The effects of solvent, concentration, and reaction time on the product distribution have been determined. In benzene all three products are in equilibrium in the presence of acid. At a concentration of 0.2 mol dm^–3 in reactants in benzene at reflux, a mixture of products 3, 4 and 5 is obtained after several hours. By proper choice of conditions the reaction can be driven in good yield to any of these products. The structures of compounds 3 and 4 have been established by X-ray crystallography. The structure of compound 4 has a centre of symmetry and trans stereochemistry. The molecular-mass distribution of polymer 5 is M_w 21 394, M_n 11 246 and D= 1.90 as determined by gel permeation chromatography. The thermogravimetric analysis and differential scanning calorimetry analysis data for compounds 3, 4 and 5 show all these compounds to be thermally quite stable in the absence of acids. X-Ray structures have also been obtained for 2-(4-chlorophenyl)-1,3,6-trithiacyclooctane 7, 7,10,13,20,23,26-hexathiadispiro[5.7.5.7]hexacosane 14 and 2-(4-nitrophenyl)-1,3,6-trithiacyclooctane 19.