Synthesis of phosphine (phosphane; hydrogen phosphide)

Preparation of phosphine

Phosphine is prepared by hydrolyzing metal phosphide with water or mineral acid.

Tin and zinc phosphides are prepared by adding the equivalent quantity of amorphous phosphorus to the respective metals in the molten state covered with ammonium carbonate. Iron phosphide, by heating finely divided iron and amorphous phosphorus together, copper phosphide, by heating copper filings with amorphous phosphorus; magnesium phosphide, by adding the equivalent quantity of amorphous phosphorus to melted magnesium; sodium phosphide by carefully adding yellow phosphorus to fused sodium under petroleum. The phosphides of tin, zinc, iron, and copper are not decomposed by water; meanwhile sodium magnesium and calcium are decomposed by water. From magnesium phosphide, whether decomposed by water or by dilute hydrochloric acid, non-spontaneously inflammable hydrogen phosphide is obtained. From sodium phosphide, spontaneously inflammable hydrogen phosphide is obtained, which, in a great measure, readily changes to solid phosphide. The phosphides of tin and zinc are decomposed by cold dilute hydrochloric or sulfuric acid, but those of iron and copper are but slightly attacked even on boiling.

For the preparation of hydrogen phosphide from the phosphides of tin, zinc or magnesium, an Erlenmeyer flask of 200 to 300 ml capacity is fitted with a stopper carrying three tubes, one of which conducts carbon dioxide gas to the bottom of the flask to displace the air, the second admits the dilute acid from a tap-funnel, the third is the delivery tube. To the latter is attached a tube, filled with glass wool, from which the gas passes out. In the case of tin phosphide the flask is warmed gently on the water-bath at the commencement, after which the reaction proceeds regularly for thirty minutes to one hour, when as the reaction becomes slower, the flask may again be warmed. In the case of zinc or magnesium phosphides, no external heating is required. The method is preferable to the preparation with potassium hydroxide and phosphorus or to that with calcium phosphide, and demonstrates the formation of the phosphide of hydrogen in analogous manner to the other compounds of hydrogen with the non-metals, ammonia excepted. The preparation of zinc phosphide is also especially recommended as being simple. The synthesis of hydrogen phosphide may be shown by putting sodium phosphite or hypophosphite into a Kipp’s apparatus when the phosphide is readily detected in the gas evolved.

Laboratory manual of inorganic preparations, by H. T. Vulte, 133-135, 1895

Preparation of phosphine from phosphorus pentoxide and lithium aluminium hydride

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

Preparation of phosphine from phosphorus pentoxide and lithium aluminium hydride

Preparation of phosphine from phosphorus pentoxide 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 phosphorus pentoxide 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 phosphorus pentoxide 7.13 g and lithium aluminium hydride (free from diethyl ether) 0.21g (or in the molar ratio 8.3: 1) was heated to 165° 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 phosphine, which is collected in the trap and the yield of the reaction is 8%. Since both white and red phosphorus are produced in this reaction, the reaction vessel should be filled with nitrogen before disconnecting it from the vacuum system at the completion of the experiment.

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

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