Oxidation of phenol by aqueous hydrogen peroxide catalysed by ferric ion‐catechol complexes

Phenol has been oxidised with aqueous hydrogen peroxide under a wide variety of conditions and yields of the catechol and hydroquinone products recorded. Catalysts tested included a number of transition metal and related ions of which only Cu + , Cu 2+ , Cr 3+ , WO 4 2‐ , Hg 2+ , Fe 2+ , and Fe 3+ gave any degree of success. Extensive tests with ferric ion established 2.5:1000, Fe 3+ :phenol mole ratio as being the optimum catalytic range. Temperatures lower than 30°C gave relatively high catechol:hydroquinone product ratios, about 1.9:1, but lowered the yields of dihydroxybenzenes to about 70% of theory. From experiments conducted over the pH range of 1 to 8 the optimum pH for high yield reactions was found to be 2 to 3. Operating at a hydrogen peroxide:phenol mole ratio of 0.30:1.0 gave the highest catechol:hydroquinone product ratios, 1.6:1.0. The catechol:hydroquinone ratio produced decreased as the ratio of reacting peroxide to phenol was increased. Optimised conditions gave dihydroxybenzene yields of 84 and 53% on phenol and hydrogen peroxide respectively, and ratios of 1.5:1 and 2.0:1, catechol:hydroquinone. A research stage economic summary from averaged pairs of experimental results gave a value added of $3.19 (technical grade products) or $8.47 (pure grades) per kg of catechol on a raw material cost base of $2.87, as two among four calculated cost evaluation scenarios.