Hydrogenation of anisole

Scheme 4 Hydrogenation of anisole by polyoxoanion-stabilized Rh(0) nanocluster catalyst...

A similar result is obtained with 30 equivalents of H2O added but a long reaction time is required namely 215 h. Nevertheless, in all cases a black precipitate of bulk Rh(0) is visible at the end of the reaction justifying the destabilization of nanoclusters due to the interaction of H or H2O with the basic P2Wi5Nb3062 polyoxoanion. Finally, the partial hydrogenation of anisole to yield 1-methoxycyclohexane (up to 8%) with a soluble nanocluster catalyst has been reported by Finke and coworkers (see Sect. 3). 

Scheme 5 Hydrogenation of anisole by surfactant-stabilized Rh(0) and lr(0) catalysts...

Finally, Jessop and coworkers describe an organometalhc approach to prepare in situ rhodium nanoparticles [78]. The stabilizing agent is the surfactant tetrabutylammonium hydrogen sulfate. The hydrogenation of anisole, phenol, p-xylene and ethylbenzoate is performed under biphasic aqueous/supercritical ethane medium at 36 °C and 10 bar H2. The catalytic system is poorly characterized. The authors report the influence of the solubility of the substrates on the catalytic activity, p-xylene was selectively converted to czs-l,4-dimethylcyclohexane (53% versus 26% trans) and 100 TTO are obtained in 62 h for the complete hydrogenation of phenol, which is very soluble in water. 

In fact, partial hydrogenations are rarely described with soluble nanoparticle catalysts. Two examples are explained in the Uterature, one reported by Finke and coworkers in the hydrogenation of anisole with polyoxoanion-stabihzed Rh(0) nanoclusters [26] and one reported by Dupont and coworkers in the hydrogenation of benzene with nanoscale ruthenium catalysts in room temperature imidazoUiun ionic Uquids [69]. hi these two cases, the yields are very modest. 

In summary, partial hydrogenation of anisole to 1-methylcyclohexene by polyoxoanion-stabilized Rh(0) nanoclusters is very modest but could in the future be an interesting additive study in the monocyclic arene hydrogenation research area. 

Scheme 9.10 Hydrogenation of anisole by reusable surfactant-stabilized lr(0) colloids in water. TEM micrograph and size distribution of Ir(0). (Adapted from [102].)...

The rates of hydrogenation of anisole, veratrole, resorcinol dimethyl ether, hydroquinone dimethyl ether, and 1,2,3-trimethoxybenzene have been determined employing both Adams platinum and 5% rhodium on alumina catalysts. The activation energies were of the order of 4-8 kcal./mole. For a given compound the activation energy was found to be greater for the rhodium catalyst. 

Fig. 11.3 Catalytic activities in the hydrogenation of anisole under hydrogen pressure. Comparison of aqueous suspensions of rhodium and iridium stabilized with HEAisCl.

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