SOME NEW REACTIONS AND DERIVATIVES OF KOJIC ACID

Abstract

The stability of the ring structure in kojic acid toward various reagents was investigated. Cleavage to an open-chain, dienol derivative in N sodium hydroxide at 25°, or fragmentation of the structure, was very slow. The benzoyl group in the fifth (phenolic) position of dibenzoylkojic acid was removed by hydroxylamine hydrochloride in pyridine so selectively that the method was of value in synthesizing certain new derivatives. Although catalytic hydrogenation readily reduced the pyrone ring in kojic acid to undefined substances, zinc dust in glacial acetic acid reduced the hydroxymethyl group in the dibenzoate to a methyl group and yielded benzoylallomaltol. The ring in dibenzoylkojic acid was apparently opened, with retention of both benzoyl groups, by semicarbazide hydrochloride and pyridine to yield two isomeric "disemicarbazones", C22H22N6O7, decomp., 215° and 172–173°, respectively. The higher-melting isomer when boiled with dilute acid gave a compound C21H15N3O5, m.p. 244°, which was apparently cyclic; the same isomer with nitrous acid yielded two isomeric, apparently open-chain "monosemicarbazones", C21H19N3O7, decomp., 215° and 178–179°, respectively. The structures of these five compounds were not determined. The following substances were thought to be new: sodium kojate, a white powder, and its crystalline tetrahydrate; 5-hydroxy-2-(methoxymethyl)-γ-pyrone, m.p. 75–76°, and its crystalline aluminum salt, decomp. 270–271°; molecular addition compound of dibenzoylkojic acid and benzoic acid, m.p. 120–121°; 2-(acetoxymethyl)-5-benzoxy-γ-pyrone, m.p. 144°; 2-(benzoxymethyl)-5-hydroxy-γ-pyrone, m.p. 180–181°; and 2-(benzoxymethyl)-5-methoxy-γ-pyrone, m.p. 110–111°. A more convenient synthesis was discovered for 5-benzoxy-2-(hydroxymethyl)-γ-pyrone, and the published melting point was revised from 136° to 143–144°; the melting point of 5-benzoxy-2-(triphenylmethoxymethyl)-γ-pyrone was revised from 206–08° to 213–214°.