STUDIES ON LIGNIN AND RELATED COMPOUNDS.: PART VII. A KINETIC STUDY OF THE ACTION OF HYPOCHLOROUS ACID ON SPRUCE LIGNIN AND ITS BEARING ON THE CONSTITUTION OF THE SPRUCE LIGNIN MOLECULE

Abstract

The action of hypochlorous acid on glycol-lignin in finely divided aqueous suspension, and in alkaline solution, is autocatalytic, the autocatalysis being due to formation of hydrochloric acid, which catalyzes the reaction strongly. Nitric acid apparently acts only by increasing the concentration of undissociated hydrochloric acid. The effect of the hydrochloric acid may be a direct catalytic effect of undissociated hydrochloric acid, or may be due to formation of chlorine.A comparison of the amounts of hypochlorous acid absorbed, and hydrochloric acid formed, by methylated and unmethylated lignin indicates that if ketomethylene groups are present in lignin they do not enolize sufficiently to play any appreciable part in the rapid reaction between hypochlorous acid and lignin.The rapid absorption of hypochlorous acid by lignin, dissolved in alkali, indicates that there is probably about 15% of a phenol nucleus in lignin. This value is supported by the rapid absorption of bromine from bromine water at very low concentrations, by lignin dissolved in alkali, and is based on the assumption of only one atom of halogen entering the phenol nucleus, which is true in the case of vanillin. If two or three halogen atoms enter the nucleus, this value of 15% has to be divided by two or three. It represents, in any case, a maximum value.The phenol nucleus accounts for only one third, or less, of the total rapid hypochlorous acid absorption. The remainder is probably due to addition of hypochlorous acid to an ethylene linkage, chlorination of a phenol ether, or a combination of both reactions.