Selective Hydrogenation of Phenol

Abstract

The selective hydrogenation of phenol to cyclohexanone has attracted a great deal of attention both in industry and academia. In this review, the significance, strategies and mechanisms for the production of cyclohexanone are briefly described. Then, the evolution of phenol hydrogenation in gas/liquid phase is summarized according to catalyst type. In situ hydrogenation techniques including catalytic transfer hydrogenation (CTH) and electrocatalytic hydrogenation (ECH) of phenol are also discussed. Although the technology for catalyst design has developed rapidly within the past decades, direct evidence to understand the reaction mechanisms and kinetics is still scarce. Therefore, it is still challengingto explore the function mechanisms and design advanced catalysts with high activity and high selectivity (>95%) for direct hydrogenation of phenol to cyclohexanone. This review may provide guidance for these attempts.

Ni-Catalyzed reductive amination of phenols with ammonia or amines into cyclohexylamines

“…In an ideal reaction, visualized by the scheme in Figure 2, phenol ( 1) is first partially reduced to 1-cyclohexenol which undergoes enol-keto tautomerization to cyclohexanone (2). 46,47 In our prior reports, we found that polar solvents can aid in the proton transfer needed for this tautomerization; but in the case of Ni catalysts, Ni might interact too strongly with protic solvents and hamper the hydrogenation activity. Next, acid-catalyzed condensation of cyclohexanone with ammonia gives rise to cyclohexanimine (3).…”

Selective Hydrogenation of Phenol to Cyclohexanone over a Highly Stable Core-Shell Catalyst with Pd-Lewis Acid Sites

“…Cyclohexanone is widely used in coatings, pesticides, dyes, lubricants, and other industries due to its high solubility and low volatility. − Specifically, cyclohexanone can also be used as a precursor for producing other high-value chemicals such as adipic acid and caprolactam, which are used to manufacture nylon 66 and nylon 6, respectively. In the past few decades, cyclohexane oxidation or phenol hydrogenation has been widely applied to the industrial production of cyclohexanone. − Compared with the oxidation route, selective direct hydrogenation of phenol to cyclohexanone has more application potential because of its simple reaction route, mild reaction conditions, and low equipment requirements.…”

Directing nitrogen-doped carbon support chemistry for improved aqueous phase hydrogenation catalysis

“…The hydrogenation of phenol follows a consecutive pathway (Scheme 1). 12 To synthesize cyclohexanone, the aromatic ring of phenol must be selectively hydrogenated to 1-hydroxy-cyclohexene, itself undergoing tautomerization to cyclohexanone. 13 Further hydrogenation leads to the undesired product, cyclohexanol.…”