Synthesis of arsine

Preparation of arsine

Preparation of arsine from arsenic trioxide and lithium aluminium hydride

Most convenient method for the small-scale synthesis of arsine is the reaction between lithium aluminium hydride and arsenic trioxide since no volatile reagents or solvents are employed, arsine obtained by such method is easily separated. However, the disadvantage of such method is the low yield (~10%) of the final product.

Preparation of arsine from arsenic trioxide and lithium aluminium hydride

Preparation of arsine from arsenic trioxide and lithium aluminium hydride

If lithium aluminium hydride has diethyl ether as an impurity ethylene is also obtained. To remove diethyl ether, lithium aluminium hydride is heated 110-150° C and then cooled to room temperature before the synthesis. The arsenic trioxide and fresh, finely ground lithium aluminium hydride were well mixed and placed in a long-necked 250-ml round-bottom reaction flask. The reaction flask was attached to the vacuum system. The long neck of the reaction flask was plugged with a loose plug of glass wool in order to prevent solid particles from being carried into the vacuum system. The flask is connected to a 500 ml surge bulb in order to protect the apparatus from the large volume of hydrogen suddenly evolved. Further,  five traps in series immersed in liquid nitrogen were attached and the vacuum was applied to the reaction vessel. During the reaction, any volatile material formed in the reaction vessel would be pumped continuously through five traps in series immersed in liquid nitrogen. A mixture of arsenic trioxide 9.77 g and lithium aluminium hydride (free from diethyl ether) 0.17g (or in the molar ratio 10: 1) was heated to 148° C in a silicon oil bath. A very vigorous reaction takes place which is complete from few seconds to few minutes. The only volatile material is pure arsine, which is collected in the trap and the yield of the reaction is 10.9%.

Inorg. Chem., 1968, 7 (10), pp 2070–2072

Arsine also could be prepared according to older methods

The action of zinc on an arsenious acid solution produces a gas containing 70%, by volume of arsine. Sodium amalgam containing not more than 8% of sodium (4 g of sodium in 50 ml of mercury), by its action on a concentrated solution of arsenious acid, produces a gas containing 86%, by volume of arsine. A gas containing a large quantity of arsine may be prepared by the action of aluminium on a dilute alkaline solution of potassium arsenite, furthermore very pure arsine  free from arsenic could be obtained by reacting a solution of arsenic sulphide in potassium caronate, when subjected to the action of aluminium.

Laboratory manual of inorganic preparations, by H. T. Vulte, 136, 1895

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