Studies on the photochemistry of 2-methyl-1,4-naphthoquinone.

It has been known since the isolation of the vitamins K that derivatives of 2-methyl-1,4-naphthoquinone (MN&) are unstable to light (l-5). However, the exact nature of the chemical change is still under discussion (6, 7). An interesting observation by MacCorquodale and coworkers (3) that the vitamin is quite stable as it exists in crude extracts, only becoming labile after a fair degree of purification, has apparently gone unnoticed. In subsequent investigations with the purified vitamin, elaborate precautions have been taken to avoid exposure to light. In connection with an investigation in this laboratory of the metabolism and of the effect of x-ray irradiation’ on the vitamins K, it was found that physiological sodium chloride solutions of MN& are stable even when exposed to direct sunlight for periods of up to 1 hour. Consequently, an investigation of several substances was undertaken to determine which protect the vitamin in solution and what limits of concentration afford protection. Ewing and coworkers (5) determined the rate of decomposition of vitamin K by ultraviolet light, and from the changes in the ultraviolet spectra thus produced, drew conclusions as to the nature of the chemical changes which took place. The results of similar experiments we have performed with MNQ in ultraviolet light and direct sunlight are illustrated in Figs. 1 and 2 respectively. Several points in these families of curves are of interest. First, it may be noticed that, aside from the greater rate of change produced by sunlight compared with the Hanovia lamp, there appears to be a qualitative difference2 in the curves which may point to some difference in the types of reactions involved and the products formed.