User:Pep-k/Lithium tetrahydridogallate

Lithium tetrahydridogallate is the inorganic compound with formula LiGaH4. It was first prepared by Finholt, Bond and Schlesinger in1947.

Synthesis
Lithium tetrahydrogallate is prepared by reacting an excess of highly divided lithium hydride powder and an ethereal solution of gallium trichloride:


 * GaCl3 + 4 LiH → LiGaH4 + 3 LiCl

The reactants are mixed together at -80 °C and then allowed to get to room temperature. Higher yields (80-95%) and reaction rates are possible by using gallium tribromide.

Properties
Lithium tetrahydrogallate is easaily dissolved in diethyl ether with which it forms a so stable complex that the complete removal of the solvent is very difficult. Ethereal solutions of LiGaH4 are indefinitely stable if sealed in glass vessels at 0 °C. Lithium tetrahydrogallate can also be dissolved in tetrahydrofuran and diglyme.

Lithium tetrahydrogallate slowly decomposes at room temperature. The decomposition is fast at 70 °C and the reaction produces lithium hydride, gaseous hydrogen and metallic gallium. The reaction is autocatalyzed by the small particles of metallic gallium being formed.

Reactivity
It can be generally stated that lithium tetrahydrogallate's reactivity is similar to lithium tetrahydroalluminate's reactivity, but the first is less stable. Lithium tetrahydrogallate violently reacts with water by releasing 4 moles of gaseous hydrogen.

Ethereal solutions of LiGaH4 are strongly reductant but less than LiBH4 and LiAlH4. It reacts with primary and secondary ammines to release gaseous hydrogen. LiGaH4 reduces acetamide and acetonitrile to ethylamine. Alifatic acids, aldehydes and ketones are reduced to the corresponding alcohols. Aromatic nitriles, aldehydes, ketones and esters are not reduced.