Calcium hydride

Preparation

Calcium hydride is prepared from its elements by direct combination of calcium and hydrogen at 300 to 400 °C.

Uses

Reduction of metal oxides

is a reducing agent for the production of metal from the metal oxides of Ti, V, Nb, Ta, and U. It is proposed to operate via its decomposition to Ca metal: :

Hydrogen source

has been used for hydrogen production. In the 1940s, it was available under the trade name "Hydrolith" as a source of hydrogen: The trade name for this compound is "hydrolith"; in cases of emergency, it can be used as a portable source of hydrogen, for filling airships. It is rather expensive for this use. The reference to "emergency" probably refers to wartime use. The compound has, however, been widely used for decades as a safe and convenient means to inflate weather balloons. Likewise, it is regularly used in laboratories to produce small quantities of highly pure hydrogen for experiments. The moisture content of diesel fuel is estimated by the hydrogen evolved upon treatment with CaH.

Desiccant

The reaction of with water can be represented as follows: :

The two hydrolysis products, gaseous and , are readily separated from the dried solvent.

Calcium hydride is a relatively mild desiccant and, compared to molecular sieves, probably inefficient. Its use is safer than more reactive agents such as sodium metal or sodium-potassium alloy. Calcium hydride is widely used as a desiccant for basic solvents such as amines and pyridine. It is also used to dry alcohols.

Despite its convenience, has a few drawbacks:

• It is insoluble in all solvents with which it does not react vigorously, in contrast to , thus the speed of its drying action can be slow.
• Because and are almost indistinguishable in appearance, the quality of a sample of is not obvious visually.

History

During the Battle of the Atlantic, German submarines used calcium hydride as a sonar decoy called bold.

Other calcium hydrides

Although the term calcium hydride almost always refers to CaH, a number of molecular hydrides of calcium are known. One example is (Ca(μ-H)(thf)(nacnac)). Dimeric calcium hydrides arise through the reaction of a calcium amide with phenylsilane. Subsequent studies have expanded the library of stabilizing ligands, but all are multidentate ligands that coordinate through nitrogen sites.

References

References

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