Reduction of Carbocyclic Aromatics

Hydrogenation over rhodium (5% on alumina) in acetic acid at room temperature and 3-4 atm of hydrogen was successfully used for reduction of benzene rings in compounds containing functions which would be hydrogen-olyzed over platinum or palladium catalyst [390], Palladium at low temperature usually does not reduce benzene rings and is therefore suited for hydro-genolysis of benzyl derivatives (pp. 150, 151). 

Specially prepared highly active Raney nickel (W-6) can also be used for hydrogenation of some benzene homologs under the same mild conditions that are used with noble metals [45]. In diphenyl selective hydrogenation of one benzene ring is possible. 

Hydrogenation of benzene and its homologs over other nickel catalysts requires higher temperatures (170-180°) and/or higher pressures [43,48,391], 

Copper chromite (Adkins catalyst) does not catalyze hydrogenation of benzene rings. 

Benzene and its homologs can be converted to the corresponding cyclo-hexadienes and cyclohexenes, and even cyclohexanes, by treatment with dissolving metals lithium, sodium, potassium or calcium in liquid ammonia or amines. Conversions are not complete, and the ratio of cyclohexadienes to cyclohexenes depends on the metal used, on the solvent, and on the presence of hydrogen donors (alcohols) added to the ammonia or amine [392, 393, 394]. 

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