Kinetics of oxidative coupling of phenols. Oxidation of pyrogallol by alkaline hexacyanoferrate(III)

Abstract

The reaction of pyrogallol with alkaline hexacyanoferrate(III) at constant ionic strength gave 3,3′,5,5′-tetrahydroxy-4,4′-diphenoquinone in a yield of 80%. The rate is dependent on the first powers of the concentrations of substrate, oxidant and alkali. The reaction pathway could be visualized as proceeding via a radical intermediate formed in the rate determining step. This radical was detected by ESR spectroscopy as two triplets with the intensity ratios of (1,2,1), (1,2,1), and showed absorptions at 655 nm, and at 1560 cm−1 in the infrared region.