STUDIES IN THE POLYOXYPHENOL SERIES: VI. THE OXIDATION OF PYROGALLOL AND VANILLIN BY ALKALINE HYPOIODITE AND HYPOCHLORITE

Abstract

Approximately 0.003 M solutions of pyrogallol and of vanillin in boric acid – sodium hydroxide buffers were used at 25 °C. to reduce hypoiodite and hypochlorite solutions made from sixfold molar amounts of the halogens. In all four cases the reduction reached a maximum in a narrow range near pH 9, and with hypoiodite the production of iodoform was restricted to this range. Slower secondary reductions were superimposed on very fast primary reactions. When oxidized with an equimolar amount of halogen near pH 8.5, vanillin gave a 90% yield of 5-iodovanillin and 65% of the 5-chloro derivative. These yields decreased with increasing alkalinity as the halogenations became slower. A new, simple preparation of trichloropyrogallol in 72% yield consisted of carrying out the chlorination with 3 moles of hypochlorite at pH 12. An equilibrium between pyrogallol–hypoiodite and 3-hydroxy-1,2-benzoquinone–iodide appeared to exist at the same pH.