Preparation of Phosphine

Colorless, highly poisonous, and flammable, the chemical compound phosphine (IUPAC name: phosphane) has the chemical formula PH3 and is classified as a pnictogen hydride, which means it burns when exposed to flame. However, because of the presence of substituted phosphine and diphosphane in technical-grade samples, they have a strong rotting fish aroma that is extremely unpleasant to the nose and throat (P2H4). Because of the presence of P2H4, PH3 is spontaneously combustible in air (pyrophoric), resulting in the production of a very bright flame. Phosphine is an extremely poisonous respiratory toxin that is immediately lethal at concentrations of 50 parts per million (ppm). Phosphine has a trigonal pyramidal structure, similar to that of phosphorus.

Preparation of phosphine

Phosphine can be made in a number of different methods. It can be produced industrially through the reaction of white phosphorus with sodium or potassium hydroxide, with the by-product potassium or sodium hypophosphite being produced as a by-product.

3 KOH + P4 + 3 H2O → 3 KH2PO2 + PH3

Alternatively, the disproportionation of white phosphorus catalysed by acid results in the formation of phosphoric acid and phosphine. Both procedures are useful in industry; however, the acid route is the favoured approach if further reactivity of the phosphine to substituted phosphines is required after the initial reaction. Purification and pressurisation are required for the acid method. A metal phosphide, such as aluminium phosphide or calcium phosphide, can also be synthesised via hydrolysis (as stated above) in the presence of water. Using the action of potassium hydroxide on phosphonium iodide, it is possible to obtain pure samples of phosphine that are devoid of P2H4 contamination (PH4I).

Laboratory preparation

Calcium phosphide is diluted with water or used to dilute HCl solutions. The production of phosphine is the outcome of this reaction.

Ca3P2 + 6H2O → 3Ca(OH)2 + 2PH3

Ca3P2 + 6HCl → 3CaCl2 + 2PH3

A pure white phosphorous solution is heated in the laboratory with concentrated sodium hydroxide solution under an inert environment of CO2 to produce phosphine.

P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2

It is typically made by heating white phosphorus with a 30-40 percent solution of caustic soda in an inert atmosphere of CO2 until the white phosphorus is completely dissolved.

P4 + 3NaOH + 3H2O → PH3 + 3NaH2PO2 (Sodium hypophosphite)

The phosphophine prepared in this manner is impure. When it is passed through an aqueous solution of hydrogen iodide, the compound PH4I is produced. When PH4I is heated with either KOH or NaOH, pure phosphine is formed as a byproduct.

PH3 + HI → PH4I

PH4I + NaOH → PH3 + NaI + H2O

A concentrated solution of sodium hydroxide is used in this procedure to hydrolyze white phosphorus, which results in the formation of phosphine.

The phosphophine prepared in this manner is impure. When it is passed through an aqueous solution of hydrogen iodide, the compound PH4I is produced. When PH4I is heated with either KOH or NaOH, pure phosphine is formed as a byproduct.

Chemical properties

Dissociation: Phosphine dissociates at around 723 degrees Celsius, releasing red phosphorus.

4PH3 P4 →(23K)→ 6H2

The action of air is as follows: it burns with oxygen, resulting in the formation of phosphorus pentoxide.

4PH3 + 8 O2 → P4O10 + 6H2O

Physical properties

• Phosphine is a colourless gas that smells like rotten fish.
• It is a gas that is exceedingly poisonous.
• PH3 is just slightly soluble in water, however it is highly soluble in organic solvents.
• When PH3 interacts with hydrogen iodide, it behaves as a Lewis base by donating its lone pair of electrons to the reaction.
• Under normal conditions, it is a non-ignitable gas that cannot be ignited. However, when heated, it erupts in flames, releasing phosphoric acid into the air.
• When we expose it to oxidising chemicals, it explodes in a violent manner.
  

Uses

• It is employed as a dopant in the semiconductor industry, although only in trace levels.
• The element PH3 is employed in Holme’s signal because of its ability to spontaneously ignite.
• Screens made of smoke
• When PH3 is burned, it creates a dense plume of smoke that can be used to create smoke screens.
• Holme’s signal

Filling the containers with calcium phosphide and calcium carbide is done through perforations in the bottom and a hole in the top. In the end, they are dumped into the ocean. In this experiment, water is introduced into the container from the bottom and combines with calcium carbide and calcium phosphide to produce acetylene and phosphine. Phosphine ignites spontaneously when it comes into touch with air, and it also ignites acetylene when exposed to air.

As a result of the burning of phosphine, a bright red flame is produced, which is followed by a tremendous amount of smoke. As a warning to oncoming ships, this is done in this manner.

Ca3P2 + 6H2O → 2 PH3 ↑ + 3Ca(OH)2

CaC2 + 2H2O → C2H2 ↑ + Ca(OH)2

Conclusion

Phosphine is a colourless, poisonous, and flammable gas with the atomic number 3 (PH3) that has a weaker base than ammonia and is mostly used to fumigate grain that has been stored for a long period of time.

When it comes to the semiconductor business, phosphone is a chemical molecule that is used to incorporate the element phosphorus into silicon crystals. There are numerous applications for this chemical, which includes use as a fumigant, a polymerization initiator, and an intermediary in the synthesis of various flame retardants. Although it has an odour that is comparable to that of garlic or decomposing fish when it is pure, phosphone is completely odourless when it is diluted.