Cyclodimerisation and cyclotrimerisation during the ring-opening reactionsof ethylene sulfide (thiirane) over acidic molecular sieves and alumina

The transformations of ethylene sulfide were studied at three reaction temp eratures (423, 473 and 523 K) on different acidic molecular sieves (HZSM-5, HY and AlMCM-41) and alumina in a pulse system. The main reaction pathways were found to be desulfurisation, cyclo-oligomerisation, the latter being more important. In this reaction channel mainly direct dimer (six-membered ring: 1,4-dithiane) and trimer (1,4,7-trithiacyclononane) formation occurre d. The former product was always predominant, however, 1,4,7-trithiacyclono nane was also significant, especially on molecular sieves with larger pore openings and alumina. At elevated temperatures 2-methyl-1,3-dithiolane (a f ive-membered cyclic molecule) was also detected. This molecule was formed i n the highest amount on HZSM-5 among the catalysts applied revealing that a more constrained environment is advantageous for this dimerisation type to occur.