Complexation of boric acid with polyhydroxy compounds and its relevance to practical aspects

Complexes of boric acid/borate and polyols play an important role in many fields because of the biological significance in organism metabolism and the practical significance in the electronic industry and agriculture of removing boric acid/borate from water. To thoroughly understand the boron chemistry of the polyols concerned, many studies have been done. Here, an experimental approach to the interaction and its recent progress are first mentioned. ¹¹B NMR spectroscopy is one of the excellent tools for elucidating the nature of the interaction between boric acid/borate and polyols. Its combination with other methods enables basic understanding of the chemical reactions. The complexation is then discussed on a thermodynamic and kinetic basis. Reaction paths for 1:1 complexation are in general divided into two: neutral polyols react directly with tetrahedral borate, whereas acidic polyols can react with trigonal boric acid in a 1:1 complexation. Both of the reactions produce tetrahedral anionic complexes, followed by a condensation reaction between the 1:1 monochelate complex and the undissociated diols to yield the 1:2 bischelate complex. A basic understanding of the complexation makes it possible to clarify the principles on the practical aspects of the complexation, which is finally reviewed.