Determination of the stoichiometry of cupric levopimarate

A primary component of marine antifouling paint is rosin, an extract of pine tree resin. Rosin controls the solubility and thus the release of cuprous oxide, the toxicant. During paint manufacture, rosin reacts with the cuprous oxide pigment to form a bluish-green complex. The effect of the complex on the paint is not known. A model of the complex was synthesized from 1-methyl-1-cyclohexane carboxylic acid and cupric sulfate. Degree of protonation of the acid and the reactant metal to ligand molar ratios were varied. The isolated products were analyzed by iodometric titration for copper, by potentiometric titration with tetrabutylammonium hydroxide for the acid, and by an elemental analysis for carbon, hydrogen, and copper. Levopimaric acid, one of the resin acids comprising rosin, was reacted with cupric sulfate. Both infrared and ultraviolet spectra were obtained for the isolated complexes and compared with those for a paint sample. All complexes were found to have a metal to ligand ratio of 1:2 under all conditions.