One-pot synthesis of cyclohexylphenol via isopropyl alcohol-assisted phenol conversion using the tandem system RANEY® Nickel plus hierarchical Beta zeolite

Abstract

Cyclohexylphenols are valuable intermediate chemicals applied in the manufacture of dyes, resins, and pharmaceutical drugs. However, they are synthesized using raw chemicals derived from fossil fuels rather than sustainable sources (e.g., lignin-derived phenol). In this article, we report a one-pot synthesis of cyclohexylphenols via phenol-assisted conversion with isopropyl alcohol over the tandem catalytic system formed by RANEY® Nickel plus hierarchical Beta zeolite. Over this tandem catalytic system, cyclohexylphenols were synthesized with remarkable selectivity (∼70%) at high conversion rates (64%) after 1 h of reaction at 150° C. In contrast, higher temperatures (175 °C) were required to obtain alkylphenols over the Al-SBA-15 catalyst, which is highly accessible thanks to its uniform mesoporous structure, albeit with weaker Lewis acid sites. Additionally, selectivity to cyclohexylphenols over Al-SBA-15 was far lower (19%) than over hierarchical Beta zeolite, and cresols were instead the most abundant alkylphenol (26%). Therefore, the combination of suitable accessibility and Brønsted acidity of hierarchical Beta with the hydrogenating ability of RANEY® Ni through catalytic hydrogen transfer from isopropyl alcohol drives the selectivity of this tandem system towards the production of cyclohexylphenols.