Beryllium hydride

Description

BeH2 was first synthesized in 1951 by reacting dimethylberyllium, Be(CH3)2, with lithium aluminum hydride, LiAlH4. A purer grade of BeH2 can also be formed from the pyrolysis of di-tert-butylberyllium, {Be(C(CH3)3)2} at 210°C. The purest beryllium hydride is obtained by the reaction of triphenylphosphine, i.e. PPh3,with berylliumborohydride,Be(BH4)2 by the reaction:
Be(BH4)2+2PPh3→2Ph3PBH3 + BeH2
Note that unlike the other elements in Group IIA where the hydride can be prepared by reaction of the elements, the reaction of the metal with hydrogen to produce beryllium hydride has not proved possible. BeH2 is usually formed as an amorphous white solid, but a hexagonal crystalline form with a higher density (~0.78 g/cm3) has also been reported. This was prepared by heating amorphous BeH2 under pressure, with 0.5–2.5% LiH as a catalyst. A more recent investigation found that crystalline beryllium hydride has a bodycentered orthorhombic unit cell, containing a network of corner-sharing BeH4 tetrahedra (there are 12BeH2 molecules in the unit cell) in contrast to the flat, hydrogen-bridged, infinite chains previously thought to exist in crystalline BeH2. Studies of the amorphous form also find that it consists of a network of cornershared tetrahedra. The density is 0.755 g/cm3.

Chemical properties

white, amorphous solid; inert to laboratory air; can be prepared by continuous thermal decomposition of a di-t-butylberyllium ethyl ether complex in a boiling hydrocarbon; has found use as rocket fuel and as a moderator for nuclear reactors [KIR80] [MER06]

Chemical properties

Beryllium Hydride, BeH2 is an amorphous, colorless, highly toxic polymeric solid (H = 18.3%) that is stable to water but hydrolyzed by acid. It is insoluble in organic solvents but reacts with tertiary amines at 160 °C to form stable adducts, eg, (R3N· BeH2)2. Beryllium hydride was formerly of interest as a rocket fuel and as a moderator for nuclear reactors. Toxicity has been a serious barrier to its commercialization.

Physical properties

White amorphous solid; density 0.65 g/cm³; decomposes at 250°C; reacts with water.

The Uses of Beryllium hydride

Beryllium hydride (BeH2) liberates hydrogen gas when mixed with water. It is used as a source of hydrogen in experimental rockets and fuel cells.

Preparation

Beryllium hydride is made by treating an ethereal solution of beryllium borohydride with triphenylphosphine, or by pyrolysis of di-tert-butylberyllium.

Definition

ChEBI: Beryllium dihydride is a beryllium hydride.

Manufacturing Process

The only known method of producing high purity beryllium hydride (95 – 98 wt % BeH2) is the pyrolysis of di-tert-butylberyllium diethyl etherate in a high boiling hydrocarbon at 200 ℃:

Safety Profile

Confirmed carcinogen. Adangerous fire hazard. When heated to 220°C it liberatesexplosive hydrogen gas. Reacts violently with methanol,water, and dilute acids. When heated to decomposition itemits toxic fumes of BeO. See BERYLLIUMCOMPOUNDS and HYDRIDE