Sodium borohydride

Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a reducing agent that finds application in chemistry, both in the laboratory and on a technical scale. It has been tested as pretreatment for pulping of wood, but is too costly to be commercialized. The compound is soluble in alcohols, certain ethers, and even water, although it slowly hydrolyzes. Sodium borohydride, also known as sodium tetrahydridoborate and sodium tetrahydroborate, is an inorganic compound with the formula NaBH4. This white solid, usually encountered as a powder, is a reducing agent that finds application in chemistry, both in the laboratory and on a technical scale. It has been tested as pretreatment for pulping of wood, but is too costly to be commercialized. The compound is soluble in alcohols, certain ethers, and even water, although it slowly hydrolyzes. The compound was discovered in the 1940s by H. I. Schlesinger, who led a team seeking volatile uranium compounds. Results of this wartime research were declassified and published in 1953. Sodium borohydride is an odorless white to gray-white microcrystalline powder that often forms lumps. It can be purified by recrystallization from warm (50 °C) diglyme. Sodium borohydride is soluble in protic solvents such as water and lower alcohols. It also reacts with these protic solvents to produce H2, however, these reactions are fairly slow. Complete decomposition of a methanol solution requires nearly 90 min at 20 °C. It will decompose in neutral or acidic aqueous solutions, but is stable at pH 14. NaBH4 is a salt, consisting of the tetrahedral BH4− anion. The solid is known to exist as three polymorphs: α, β and γ. The stable phase at room temperature and pressure is α-NaBH4, which is cubic and adopts an NaCl-type structure, in the Fm3m space group. At a pressure of 6.3 GPa, the structure changes to the tetragonal β-NaBH4 (space group P421c) and at 8.9 GPa, the orthorhombic γ-NaBH4 (space group Pnma) becomes the most stable. For commercial NaBH4 production, the Brown-Schlesinger process and the Bayer process are the most popular methods. In the Brown-Schlesinger process Sodium borohydride is industrially prepared following the original method of Schlesinger: sodium hydride (produced by reacting Na and H2) is treated with trimethyl borate at 250–270 °C: Millions of kilograms are produced annually, far exceeding the production levels of any other hydride reducing agent. Sodium borohydride can also be produced by the action of NaH on powdered borosilicate glass. Different from it, the Bayer process is based on the reaction among borax (Na2B4O7), Na, H2, and silicon oxide (SiO2) at 700 °C producing sodium borohydride and sodium silicate