Borohidrid

Borohidrid, or borohydride, refers to the borohydride anion BH4− and the family of salts and reagents derived from it. In BH4− boron is in a tetrahedral coordination and bears a -3 oxidation state; the four hydride ligands act as hydridic donors. The anion forms stable salts with alkali and alkaline‑earth metals, the most common being sodium borohydride (NaBH4) and lithium borohydride (LiBH4).

Sodium borohydride and lithium borohydride are widely used reducing agents in organic synthesis. Sodium borohydride reduces aldehydes and ketones to primary and secondary alcohols under appropriate conditions, but generally does not efficiently reduce esters or carboxylic acids. Lithium borohydride is more reactive and can reduce a broader range of carbonyl compounds, including certain esters, but it is more moisture sensitive and typically employed in dry solvents or specialized conditions. Both reagents are typically prepared and sold as dry solids or solutions and must be kept away from moisture and strong acids, as hydrolysis or protonation releases hydrogen gas.

Derivatives such as sodium cyanoborohydride (NaBH3CN) are related borohydride reagents with milder reducing power, widely used for reductive amination under mildly acidic conditions. These related reagents offer complementary selectivity for specific synthetic transformations.

Safety and handling: borohydride reagents can be irritants and react with water or acids to evolve hydrogen gas. They are usually stored and handled under dry, inert conditions and appropriate protective equipment. They should be used with proper ventilation and in accordance with relevant safety guidelines.

In addition to laboratory synthesis, borohydrides have been studied for other applications, including hydrogen storage research, where complex metal borohydrides are of interest for potential energy technologies.