M. Bonnet

Hydrodesulfurization of oxidized sulfur compounds in benzothiophene, methylbenzothiophene, and dibenzothiophene series over CoOMoO3Al2O3 catalyst

Hydrodesulfurization experiments were carried out with a sulfided CoOMoO3Al2O3 catalyst at various elevated pressures (30 to 70 atm) and temperatures (200 to 300 °C) under stirred batch reactor conditions. The reactants were hydrogen and pure sulfur compounds including dibenzothiophene, benzothiophene and its methyl derivatives, and their oxidized products, sulfoxides and sulfones. In the case of dibenzothiophene the reaction is the CS bond scission without any observed hydrogenation of the aromatic ring. For the S-oxidized compounds a deoxygenation takes place first and the sulfide reacts as before. For benzothiophene (BT) and its methyl derivatives there is first a hydrogenation of the C2–3 thiophenic double bond and then desulfurization leading to ethylbenzene derivatives. For the sulfoxides a deoxygenation takes place first but for the sulfones (BTO2) as for the sulfide the hydrogenation is operative. Methyl substitution leads to a decrease in the rate of the hydrogenation step in the BT and BTO2 series. A correlation, related to the overall aromaticity of the system, between the rate constants and the vertical ionization potential of the molecules, suggests that electronic effects may be preponderant.

Catalytic hydrogenation of cycloalkanones on PtSiO2 and RuSiO2: The effects of ring size

The hydrogenations of cycloalkanones (C4C9) in the liquid phase on PtSiO2 and RuSiO2 have been studied from 0.1 to 150 bar in cyclohexane as solvent. Using competitive kinetic methods through the RAB parameter, a scale of reactivity is proposed. Adopting the value of 1 for cyclohexanone, we found 7.1 for cyclobutanone, 6.9 for cyclopentanone, 13.8 for cycloheptanone, 19.2 for cyclooctanone, and 17.9 for cyclononanone on PtSiO2. These results when compared with the relative rates for BH4 nucleophilic addition reactions on carbonyl compounds and with the corresponding rates for chromic acid oxidation of cycloalkanols give a good indication for a slow step in the catalytic hydrogenation in liquid phase corresponding to the fixation of the first hydrogen atom to a Π-adsorbed species, the hybridization of the C atom passing from sp2to sp3.

Hydrotreating of halogeno-benzo[b]thiophenes and their S-oxide and S-dioxide derivatives over CoO-MoO3Al2O3 catalyst

Hydrotreating experiments were carried out with a sulfided CoO-MoO3Al2O3 catalyst at various pressures and temperatures under stirred batch reactor conditions. The reactants were hydrogen and pure halogeno-sulfur compounds in the benzothiophene series. In the case of the benzo[b]-thiophene itself, the dehalogenation reaction takes place without any observed hydrogenation or hydrodesulfurization. For the S-oxidized derivatives a deoxygenation takes place first. For the halogeno-sulfone the dehalogenation is also the first step of the overall process. In the halogenobenzo[b]thiophene series a correlation between the rate constants and the ionisation potential of the molecules suggests that electronic effects may be preponderant.

Influence of a second reducible function on the mechanism of the hydrogenation of an ethylenic double bond

Abstract The hydrogenation of 2-cyclohexenone and 2-methyl-2-cyclohexenone was carried out with a Pt/SiO 2 catalyst under stirred batch reactor conditions. The selectivity in the hydrogenation of the double bond is very high (> 90%). A negative order in ketone is observed, in contrast with the positive experimental order for olefins like cyclohexene, but in accordance with the negative order already found for 1,4-cyclohexanedione and acetophenone. Comparison with the hydrogenation of 3,4-dihydro-2 H -pyran whose behavior is identical to that of cyclohexene (kinetic order: + 1.0) shows that the juxtaposition of electrons in α position to the double bond does not change the kinetic parameters which are modified when there is a second reducible function (CO). This result is probably due to an interaction of the π system of the second function with the active sites of the catalyst leading to an inhibition by the reactant itself.