The stability of pentadecylcatechol (PDC) in various solvents, under aerobic conditions, is markedly dependent on various factors such as the nature of the solvent, the purity of the PDC and the presence of light, moisture and basic compounds. The marked changes in the uv absorption spectra of PDC solutions in alcohols, during their aerobic aging, are the result of the formation of pentadecylo-benzoquinone (PDQ) and the products (especially biphenyhc) derived from its interaction with water, alcohols, and phenolic bodies. In the PDQ anhydrous ethanol solutions, under aerobic conditions, PDC is always regenerated, and PDQ reacts with the solvent to restore aromatic systems.
It has been proposed that the hapten role of the alkyl and alkenylcatechols, which comprise the allergenic principles (Urushiols) of poison ivy, poison oak, and related plants, is dependent on the oxidative conversion of the catechol to the corresponding ortho-benzoquinone (8). This conversion and accompanying transformations appear to be the cause of the spectral changes that have been observed when such catechols, in different solvents, are exposed to aerobic conditions for varying periods. Because of their allergenic properties, much interest has developed concerning the solution stability of such catechols.
H. S. Mason (9) was the first to report that when PDC solutions in ethanol are allowed to stand for several weeks at room temperature, the intensity of the absorption at the original 277 nm maximum increases, "the spectral curve shifting to slightly shorter wave lengths." These hyper-and hypsochromic changes were found to be more pronounced in acetone and less marked in hexane. In a later section of his article, 1 The hydrogenated form of the allergenic principle of the poison ivy plant (Rhus toxicodendron radicans)
has been shown to have the structure of 3-pentadecylcatechol (PDC) (1). This saturated colorless crystalline substance, also known as Hydrourushiol, is allergenically active (2), readily synthesized (3), and has been extensively used in clinical investigations of delayed hypersensitivity (4-7).