The Thermal Behavior of Some Resin Acids at 400-500 °C

The hot tube pyrolysis of dehydroabietic acid ( 1 ) at 400-500 °C was found to produce as major products the three possible A-ring olefins (19-norabieta-4,8,11,13-tetraene ( 2 ); 19-norabieta-4(18),8,11,13-tetraene ( 3 ); and 19-norabieta-3,8,11,13-tetraene ( 4 )) resulting from the elimination of the carboxylate moiety. The i.r., n.m.r., u.v., and mass spectrum of each olefln was obtained and discussed. The pyrolysis of abietic acid ( 7 ) and levopimaric acid ( 8 ) under identical conditions was found to yield A-ring olefins; to isomerize to yield varying mixtures of palustric, 7 , and neoabietic acids; to dehydrogenate to yield 1 ; and to eliminate propylene to form deisopropyldehydroabietic acid ( 15 ). A mechanism to explain the formation of 15 from the dienoic resin acids is given.