Hydrodesulfurization of aromatic sulfur compounds catalyzed by ruthenium hydride complexes

Abstract

Ruthenium hydride complex ([C5Me5RuH2]2) is prepared by the reaction of [C5Me5RuCl2]2 with LiA1H4. From the experimental data, it can be concluded that the optimum conditions in hydrodesulfurization reaction of benzothiophene was 24 hours reaction time, benzothiophene/Ru mole ratio = 10, temperature at 110ํC. The reaction product was characterized by NMR and FT-IR spectroscopies. These data show that this reaction may be promoted by the cooperation of metal atom in the catalytic intermediates. Moreover, the result indicated in-situ procedure gives higher % conversion of benzothiophene. In the case of the reaction with the addition of hydrogen gas, % conversion of benzothiophene increases. The complete hydrodesulfurization product is ethyl benzene, confirmed by GC-MS. Kinetic and mechanistic studies of benzothiophene hydrodesulfurization was carried out by using (PPh3)3RuCL2 as catalyst in toluene as solvent at 150ํC. The kinetic runs were carried out at different concentrations of catalyst, benzothiophene, and hydrogen and at different temperatures. The reaction proceeds according to the rate law is r=kcat[cat][H2]. Large negative value of S# indicates high degree of bond formation at the transition state. The experimental data are consistent with a mechanism in which the transfer of hydride to coordinated benzothiophene in (M(H)(C1)n2-(C=C)-BT]-(PPh3)2] is the rate determining step of the catalytic cycle. Dihydrobenzothiophene and ethylbenzene were obtained as end products of the (PPh3)2RuCl2 catalytic reaction at 200-250ํC and hydrogen pressure of 30 bar