Phosphonium and Ammonium Polyborates

Abstract

Polyborates were prepared by slow hydrolysis of boric acid esters B(OR)₃ (R=CH₃, i-C₃H₇, n-C₄H₉, c-C₆H₁₁, n-C₈H₁₇) in organic solvents such as acetone in the presence of solutions of quaternary tetraphenylphosphonium or triphenylmethylphosphonium hydroxides. Some amines, some ammonium hydroxides or, for comparison, tetraphenylarsonium hydroxide with a small quantity of water. The basic component must be basic enough and should be bulky; the less bulky bases build pentaborates, the more bulky ones heptaborates, independent of molar ratios, if only the boron concentration is sufficient. The acetone containing pentaborates (C₆H₅)₄P] B₅O₆(OH)₄] 0,5 acetone and (C₆H₅)₃PCH₃] B₅O₆(OH)₄] 0,5 acetone were isolated, in contrary to the solvent free (C₆H₅)₄As] B₅O₆(OH)₄]. Heptaborates with the anion B₇O₆(OH)₁₀] are formed with tetra-n-butyl-ammonium and tri-n-butylbenzylammonium cations.