Enhanced Anti-Fungal Activity of the Organo-Soluble Borate Ester, Tetra-n-butylammonium Bis(ortho-hydroxymethylphenolato)borate

The borate ester, tetra-n-butylammonium bis(ortho-hydroxymethylphenolato)borate, NBu4[B(o-hmp)2], was synthesized and characterized by NMR spectroscopy (1H, 13C, 11B), ES-MS, and X-ray crystallography. The anti-fungal activity of this compound, as well as its sodium salt, the parent phenol, tetra-n-butylammonium bromide, and boric acid were evaluated against two wood decay fungi. The tetraalkylammonium borate NBu4[B(o-hmp)2] shows the highest activity out of the compounds examined. This finding suggests that the formation of lipophilic borate esters is a promising approach for the development of leach-resistant, borate-based wood preservatives.