Formation of 7-ketodehydroabietic acid at the radiata pine wood surface, and its effect on wood yellowing

Dehydroabietic acid (1), an extractive of radiata pine has been shown to undergo light-catalysed oxidation at the wood surface to 7-ketodehydroabietic acid (3), identified by spectrometry as the methyl ester (4), and compared with authentic compound. 7-Ketodehydroabietic acid (3) was not generally further oxidised, except in two samples examined which contained a trace amount of 7-ketoabieta-6,8,11,13-tetraen-18-oic acid (7). Consequently, 7- ketodehydroabietic acid (3) accumulated as a major oxidised resin acid product at the radiata pine wood surface when the surface was exposed to air and light After one year, the compound (3) comprised approximately half of the extractable aromatic ring-C resin acids. Application of synthetic 7- ketodehydroabietic acid (3) to exhaustively methylene chloride extracted radiata pine wood blocks, and exposure of treated and untreated blocks to sunlight did not result in alteration of the yellowing rate of the wood surface.