Disproportionation of dihydroarenes by Sol-Gel entrapped RhCl{sub 3}-quaternary ammonium ion pair catalysts
- Hebrew Univ., Jerusalem (Israel)
The ion pairs generated from RhCl{sub 3}{center_dot}3H{sub 2}O and the quaternary ammonium salts [(C{sub 8}H{sub 17}){sub 3}NMe]Cl (Aliquat 336) and [Me{sub 3}N(CH{sub 2}){sub 3}Si(OMe){sub 3}]Cl were physically and chemically entrapped, respectively, in SiO{sub 2} sol-gel matrices under mild conditions. The resulting immobilized ion pairs proved to be stable, leach-proof, and recyclable catalysts for disproportionation of 1,3,-cyclohexadiene and several other vic-dihydroarenes. In these reactions, equimolar quantities of the respective tetrahydro- and fully aromatic compounds were obtained. The entrapped catalysts, in most cases, proved to be more efficient and more selective than their homogeneous analogues. The reaction rates and conversions were shown to depend strongly on steric effects of substituents and on the bulkiness of the substrate skeleton. The recorded first order kinetics in the substrates (organic reactants) suggests that the mechanism involves stepwise addition of two molecules of the dihydroarenes to the rhodium nucleus, and that the addition of the first substrate molecule is rate limiting. 28 refs., 5 figs., 2 tabs.
- OSTI ID:
- 468687
- Journal Information:
- Journal of Catalysis, Vol. 164, Issue 2; Other Information: PBD: Dec 1996
- Country of Publication:
- United States
- Language:
- English
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