Preparation:

Boric acid is prepared from the hydrolysis of boron halides, and then produces B₂O₃ on heating.

Structure:

B(OH)3 is H-bonded with planar B(O)3 units. The oxides contain linked triangular BO3 and tetrahedral BO4 units, eg. B2O54-.

Reactions:

B(OH)₃ is (mainly Lewis-) acidic (cf. Al(OH)₃, which is amphoteric, ie. it reacts with both acids and bases.)

Reaction of Boric acid with alcohols yields borate esters, [B(OR)₃]. These are much weaker Lewis acids than BX₃, as the O atom serves as an intra-molecular π donor, as does the halide atom.

Comparison with Silicon:

Borates contain B-O-B linkages as Silicates contain Si-O-Si linkages. Both B₂O₃ and SiO₂ are acidic, form mixed oxides with MO_x, and are glass-formers. The ability to form mixed oxides with alkali metals is of use as the addition of, eg. Na₂O, can change the properties, such as the viscosity, of the oxide glass. This is important in the manufacture of glass products.

However, the boron hydrides, or boranes, have no silicon analogues.