Preliminary study of the fungicidal and structural variability in copper naphthenates and naphthenic acids
T Schultz, D D Nicholas, L L Ingram Jr, T H Fisher
Copper naphthenates, an oil-borne wood preservative listed by the American Wood-Preservers' Association (AWPA), is manufactured by complexing copper(II) with naphthenic acids. Prior to AWPA listing as a wood preservative, field experiments showed that copper naphthenates generally had good stability and were active against wood-destroying organisms. Recently, however, there have been reports of some copper naphthenate-treated poles rapidly failing. One possible explanation for the varying effectiveness could be that the structure, and resulting biological activity, of the naphthenic acids used to make copper naphthenate may vary. To test this hypothesis several naphthenic acids and copper naphenates were obtained and their fungicidal activity against three wood-destroying fungi measured. In addition, the chemical structure of the naphthenic acids were examined by proton- and carbon- NMR. Different activities were observed, especially against a copper-tolerant fungus. Some apparent correlations were seen between the fungicidal activity and chemical structures for the few samples studied.