The effect of radiation on some salicylates. 1. Steady state studies

This work was undertaken to obtain more quantitative information on the extent and nature of the degradation of some salicylates by ionizing radiation, especially gamma rays, and to gather data that could assist in the evaluation of the use of radiation for sterilization of this group of compounds which are extensively used as antipyretics, analgesics and anti-rheumatics. Salicylamide is not only a common medicinal, but also a model for the study of the effect of radiation on biological systems. A 3200 Ci Co-60 facility was used. Three salicylates were subjected to solid phase irradiation, namely: salicylamide, phenylsalicylate, and acetyl salicylic acid (aspirin). These compounds were purified by repeated recrystallization from water, methanol and benzene, respectively, until a constant melting point was obtained. Irradiation in the solid phase was made in doses from 2.5 to 240 Krad. Irradiation in the liquid phase (solution) was carried out in doses, ranging from 2000 to as high as 270,000 rad depending on the reactivity of the solution. The degradation products were separated by thin layer chromatography using Kieselgel F254 and SIF with fluorescence scintillator (Riedel-de Haen). The products were visualized with a Camag UV Universal lamp. Irradiation of the three salicylates showed very little decomposition even at doses very much higher than those required for radiation sterilization. Salicylamide appears to be the most stable giving an initial G(-salicylamide)-0.50. For both phenylsalicylate and acetylsalicylic acid only the G values at 150 Mrad were obtained as the amounts degraded at lower doses were too low for the sensitivity of the diffused reflectance method used. A G(-phenylsalicylate)-2 and G(-acetylsalicylate)-1.2 were obtained by this method. Salicylic acid is formed when aspirin is irradiated. It is concluded that this acid is one of the degradation products. Barring any toxic property of the minute substances formed, solid phase sterilization is feasible for the three salicylates studied