Borohydrides

Borohydrides are a family of chemical compounds containing the borohydride anion BH4− or salts derived from it. The most common species are alkali metal borohydrides, including sodium borohydride (NaBH4), lithium borohydride (LiBH4), and potassium borohydride (KBH4). The BH4− anion has a tetrahedral boron center bonded to four hydride ligands, and it functions as a hydride donor in many chemical reactions.

These compounds are widely used as reducing agents in organic synthesis. Sodium borohydride is a mild and selective reducer of aldehydes and ketones to primary and secondary alcohols and is generally compatible with water and alcohol solvents. Lithium borohydride is more reactive and can reduce esters and certain carboxylic derivatives under appropriate conditions, though it is more sensitive to moisture and air than NaBH4. Most borohydride salts are solid at room temperature and exhibit varying degrees of solubility in water and common solvents; LiBH4, in particular, is notably moisture sensitive and reactive with water.

In addition to serving as reducing agents, borohydrides are of interest as potential hydrogen storage materials. They can release hydrogen gas upon hydrolysis or in more complex chemical processes, and studies explore their use as solid hydride sources for energy applications. However, handling requires care due to hydrolysis, generation of hydrogen gas, and sensitivity to air and moisture.

Synthesis generally involves reactions that transfer hydride to boron, such as the reduction of borates or boron halides with hydride donors. Borohydrides are typically stored in dry conditions and handled under inert atmospheres to prevent decomposition or unwanted reactions.