Study of photochemical reactions of coniferyl alcohol. I. Mechanism and intermediate products of UV radiation-induced polymerization of coniferyl alcohol

Ultraviolet light-induced photochemical transformations of coniferyl alcohol have been studied, using spectrophotometric and 1H NMR approaches. It was shown earlier that coniferyl alcohol can be polymerized not only enzymically but also by photoirradiation. This study furthers our knowledge on the UV radiation-induced polymerization of coniferyl alcohol. In the photochemical reaction of coniferyl alcohol, quinone-methide is the first transient formed. In subsequent reactions quinone-methide produces dimers, oligomers and a polymer as the end product. The reaction rate constants are pH dependent. The results are interpreted in terms of an ionic mechanism of the photochemical reaction, contrary to enzymic polymerization that involves formation of phenoxy radicals. The study may have ecological importance because of the increase of UV radiation reaching the earth's surface due to ozone layer depletion.