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 versatile reducing agent that finds wide application in chemistry, both in the laboratory and on a technical scale. Large amounts are used for bleaching wood pulp. The compound is soluble in alcohols and certain ethers but reacts with water in the absence of a base.

The compound was discovered in the 1940s by H. I. Schlesinger, who led a team that developed metal borohydrides for wartime applications (in particular, looking for a uranium compound more volatile than the hexafluoride to be used in isotope separation by gaseous diffusion; this line of research did not yield useful results). Their work was declassified and published only in 1953.

Properties

Sodium borohydride is an odorless white to gray-white microcrystalline powder which 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 will also react with these solvents to produce H₂; however, these reactions are fairly slow. Complete decomposition in excess methanol can take nearly 90 min at 20 °C. It will decompose in neutral or acidic aqueous solutions but is stable at pH 14. These conditions can be exploited to allow sodium borohydride to react in a homogeneous manner, with reduced lifespan being traded against increased reactivity.