boric acid(redirected from Boron hydroxide)
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(also orthoboric acid), H3BO3, a weak inorganic tribasic acid; colorless crystals in the form of flakes. Density, 1.48 g/cm3. Moderately soluble in cold water and more soluble in hot water, which is used to purify it (solubility per 100 g H2O: 2.66 g at 0° C; 39.7 g at 100° C). Boric acid is soluble in alcohol and other organic substances. When heated it loses water, turning first into metaboric acid, HBO2, and then into boric anhydride, B2O3. The salts of boric acid—borates—are derived mainly from various polyboric acids with the general formula nB2O3 · mH2O. When boric acid reacts with alcohols in the presence of concentrated H2SO4 (for bonding water), esters—for example, boric methyl ester—are formed:
3CH3OH + H3BO3 = B(OCH3)3 + 3H2O
When ignited, the esters of boric acid burn with a green flame, which is a qualitative reaction for boron. Boric acid is found in nature in hot springs as a dissolved form and as vapor. It evolves in the form of the mineral sassolite from hot springs and excrustations in volcanic craters. The industrial significance of natural boric acid is relatively small; it is usually obtained during the processing of borates.
Large quantities of boric acid are used to produce enamel wares. In laboratory practice boric acid is used in the preparation of buffer systems. In medicine it is used as an antiseptic. Aqueous solutions of boric acid serve as mouth and throat rinses and eyewashes. Ointments, pastes, and powders with boric acid and boric alcohol (boric acid dissolved in alcohol) are administered for some skin diseases (boric alcohol is also prescribed as ear drops). Boric acid is an ingredient in contraceptives.
V. L. VASILEVSKII