High temperature catalytic hydrogenolysis and alkylation of anisole and phenol

Abstract

Hydrogenation of phenol at 2.8 MPa pressure with MoO 3 –NiO–Al 2 O 3 catalyst at 450 °C gave 60% benzene, 16% cyclohexane, and 7% methylcyclopentane, while anisole under the same conditions gave 60–70% less of each of these products and 52% methylated benzenes. In the presence of added methanol either phenol or anisole give 47–63% of methylbenzenes and 22% of methylated phenols. At 350–400 °C significant yields of cyclohexylbenzene and cyclohexylphenol were formed. The reactions are interpreted as involving electrophilic methylation or cyclotiexylation of phenol concurrent with ring hydrogenation and hydrogenolysis of C—O bonds. Cyclohexyl cations are proposed as reactive intermediates that act as cyclohexylating agents or rearrange to methylcyclopentyl cations, and the methylating species is derived from methanol or the methyl group of anisole. When phenol was reacted with H 2 and CD 3 OH the methylated aromatic products were only partially deuterated, indicating exchange with the H 2 atmosphere was occurring. Control experiments involving possible intermediates in the reaction are consistent with these conclusions. Nickel catalysts favour ring saturation over C—O bond cleavage.