Magnesium hydride (MgH2)

DescriptionMgH2 contains 7.66% by weight of hydrogen and has been studied as a potential hydrogen-storage medium. It was discovered in 1912, during the pyrolysis of ethyl magnesium iodide (a Grignard reagent), which produced small amount of MgH2. In 1951, preparation from the elements was first reported involving direct hydrogenation of Mg metal at high pressure and temperature (200 atmospheres, 500°C)with magnesium iodide as a catalyst: Mg＋H2→MgH2 Lower temperature production from Mg and H2 using nano-crystalline Mg produced in ball mills has been investigated. Other preparations include: 1. The hydrogenation of magnesium anthracene under mild conditions: Mg(anthracene)＋H2→MgH2＋C14H10 2. The reaction of diethyl magnesium with LiAlH4 3. An adduct of complexed MgH2, e.g. MgH2·THF by the reaction of phenylsilane (C6H8Si) and dibutyl magnesium in ether or hydrocarbon solvents in the presence of THF (C4H8O) using TMEDA (Tetramethylethylenediamine＝(CH3)2NCH2CH2N (CH3)2) as a ligand.

UsesMagnesium hydride contains a high proportion of hydrogen (7.65 wt %), which can be liberated by heat. The catalytically produced compound displays rapid rates of hydrogenation and dehydrogenation and it is therefore of interest as a hydrogen reservoir. The high activity of catalytically produced magnesium hydride also enables it to take part in an addition reaction with 1-alkenes to form organomagnesium compounds:MgH2+2 CH2 = CHR→Mg（CH2CH2R）2These dialkylmagnesium compounds have become industrially important in the production of very active Ziegler catalysts. The Mg – H2 system can also be used for the simultaneous removal and purification of pure hydrogen from gas mixtures. Magnesium hydride is also used as a drying agent for organic solvents and gases and in chemical syntheses.

General DescriptionMagnesium hydride is a white crystalline solid. Magnesium hydride reacts violently with water and may ignite upon contact with air. Magnesium hydride is used to make other chemicals.