The Continuous Catalytic Debenzylation of 1,4-Dibenzyloxybenzene with H₂ in THF Expanded with High Pressure CO₂

The continuous debenzylation of 1,4-dibenzyloxybenzene (1a) with H₂ and supported Pd catalysts has been studied in high-pressure CO₂ + tetrahydrofuran. A range of parameters and catalysts have been tested, with one of the most successful results giving 86% conversion and 86% selectivity to the monodebenzylated product, 1,4-(benzyloxy)phenol (2a). In the absence of CO₂, the reaction was unselective with no formation of 2a. When complete debenzylation was required, the best catalyst was 5% Pd supported on Deloxan APII, giving quantitative yields of hydroquinone (3), the completely debenzylated product, at temperatures as low as 50 °C. This Deloxan-supported catalyst was also substantially active at only 30 °C.