Fig. 3
Schemes of important modifications of rosin (using the major component abietic acid as model) which change their technical and skin-sensitizing properties. (a) Esterification of abietic acid with glycerol forming monoabietate (weak allergen). (b) Formation of maleopimaric acid (strong allergen) and fumaropimaric acid (weak allergen) by Diels-Alder reactions with maleic anhydride and fumaric acid, respectively. (c) Hydrogenation of abietic acid which reduces the sensitizing capacity of the acid