Preparation and Properties Of Phosphine

Phosphine is a chemical that is classified as an organophosphorus compound. The structure of phosphine is trigonal pyramidal. Metal phosphides react with water or HCl to create phosphine. It’s a colourless gas that’s particularly toxic. The concentration of this chemical in the atmosphere fluctuates. It plays an essential role in the phosphorus biochemical cycle. In nature, phosphine may be found in human blood, urine, and saliva.

When aluminium, calcium, magnesium, or zinc phosphide pellets are exposed to water vapour, phosphine gas is formed. Aluminium phosphide is largely employed in the treatment of grain and tobacco warehouses. Its pellet composition lends itself to application in the treatment of shipping containers.

Phosphine is an insecticide that is used to fumigate grains, animal feed, and leaf-stored tobacco.
In humans, acute (short-term) phosphine inhalation exposure can produce headaches, dizziness, exhaustion, sleepiness, searing substernal discomfort, nausea, vomiting, cough, difficulty breathing, chest tightness, pulmonary irritation, pulmonary oedema, and tremors. Convulsions may occur after a brief period of apparent recovery. Chronic (long-term) occupational phosphine exposure may result in the nasal cavity and throat inflammation, weakness, dizziness, nausea, gastrointestinal, cardiorespiratory, and central nervous system symptomology, jaundice, liver consequences, and increased bone density.

Overview:

Phosphine, denoted by the formula PH₃, is a phosphorus hydride. Phosphine is a dangerous, flammable gas. Because of its vital industrial applications, it is extensively manufactured in businesses and laboratories.

Phosphine is a chemical that is classified as an organophosphorus compound. Philippe Gengembre discovered this chemical for the first time in 1783. He made phosphine by heating phosphorous in an aqueous potassium carbonate solution. The concentration of this chemical in the atmosphere fluctuates. It plays an essential role in the phosphorus biochemical cycle. In nature, phosphine may be found in human blood, urine, and saliva.

Phosphine is found in extremely low and very variable amounts in the Earth’s atmosphere. It has the potential to make a large contribution to the global phosphorus biogeochemical cycle.

Structure of Phosphine:

The structure of phosphine is trigonal pyramidal. The lone pair of electrons on phosphorus changes the symmetry of the molecule. Phosphorus undergoes sp3 hybridization. There are three bond pairs and one lone pair of electrons. The H–P–H bond has a 93.5°angle, while the P–H bond has a length of 1.42 pm.

Preparation of Phosphine:

1. Metal phosphides hydrolyze with calcium phosphide- Metal phosphides react with water or HCl to create phosphine.

Ca₃P₂+6H₂O→2PH₃+3Ca(OH)₂

Ca₃P₂+6HCl→2PH₃+3CaCl₂

2. Pure phosphine is synthesized from phosphorous acid by the breakdown of H₃PO₃.

4H₃PO₃→3H₃PO₄+PH₃

 

3. Heat white phosphorus in a concentrated NaOH solution in an inert CO₂ atmosphere to create PH₃.

P₄+3NaOH+3H₂O→PH₃+3NaH₂PO₂

 

Purification of Phosphine:

Pure phosphine is a non-flammable liquid. It becomes flammable due to the presence of P2H4 or P4 vapours. By absorbing phosphine in HI and turning it to PH₄l, phosphine is purified. When this is combined with potassium hydroxide, phosphine is formed.

PH₄I+KOH→PH₃+KI+H₂O

 

Physical Properties of Phosphine:

• It’s a colourless gas that’s particularly toxic.
• It smells strongly of rotting fish.
• It is only marginally soluble in water.
• Its boiling point is –87.7 degrees Celsius.
• As previously established, pure phosphorus is non-flammable. Despite this, it is flammable due to the presence of P₄ vapour. Phosphorus may catch fire when it comes into contact with oxidizing chemicals such as HNO₃, chlorine, or bromine vapours. It can catch fire even if just a tiny amount of these oxidizing substances is present.

Chemical Properties of Phosphine:

• Phosphine is a Lewis base, just like ammonia. It creates phosphonium compounds when it combines with HI, HBr, and HCl.

PH₃+HI→PH₄I

PH₃+HBr→PH₄Br

PH₃+HCl→PH₄Cl

• Phosphorus pentoxide and water are produced when phosphorus is burnt.

2PH₃+4O₂→P₂O₅+3H₂O

 

• Reaction with chlorine

PH₃+4Cl₂ →PCl₅+3HCl

• It will not ignite under normal conditions. When heated, it bursts with flame, producing phosphoric acid.
• It bursts dramatically when exposed to oxidizing chemicals such as HNO₃, Cl₂, and Br₂.
• In the presence of light, PH₃ in water decomposes to create red P and H₂O.

PH₃(H₂O)→P(red)+H₂O

• When phosphine is absorbed in copper sulfate or mercuric chloride, copper phosphide and mercuric phosphide are formed.

3CuSO₄+2PH₃→Cu₃P₂+3H₂SO₄

3HgCl₂+2PH₃→Hg₃P₂+6HCl

Uses of Phosphine:

• Phosphine is a chemical that is utilized in the production of metallic phosphides.
• Phosphorus is present in Holme’s signal and Smokescreens.

Holme’s indication: Because phosphine spontaneously burns, it is a potential candidate for use in Holme’s signal. When a ship needs help, calcium carbide and calcium phosphide-filled containers are perforated and hurled into the ocean. As a result of the contact with water, acetylene and phosphine gases are generated. When these gases burn in the air, they send a signal.

The screen of smoke: When calcium phosphide is soaked in water, a significant amount of phosphine is produced, resulting in a smokescreen. During the war, this was used to hide troops from the enemy.

• Phosphine fumigants are used in rodent and insect control formulations.

Chlorodiphenylphosphine:

Chlorodiphenylphosphine abbreviated Ph₂PCl is an organophosphorus chemical having the formula (C₆H₅)₂PCl. It is a colourless oily liquid with a strong odour that has been characterized as garlic-like and is perceptible even at low concentrations (ppb). It is an effective reagent for introducing the Ph₂P group into molecules, which includes a wide range of ligands. Ph₂PCl, like other halophosphines, is reactive with various nucleophiles, including water, and is quickly oxidized even by air.

Chlorodiphenylphosphine, like other chlorophosphines, is utilized in the manufacture of phosphines.

Ph₂PCl-derived phosphines are further developed and used as pesticides (such as EPN), plastic stabilizers (Sandostab P-EPQ), various halogen compound catalysts, flame retardants (cyclic phosphinocarboxylic anhydride), and UV-hardening paint systems (used in dental materials), making Ph₂PCl an important intermediate in the industrial world.

FAQs

Q. What are the characteristics of phosphine?

ANS:

• Phosphine is a colourless and very poisonous gas.
• It has a strong rotten-fish odour.
• It is insoluble in water.

Q. Is phosphine a non-polar element?

ANS: No. Although phosphine is a polar element, it has non-polar molecular bonding. This is clear from the chemical formula PH₃ (3 Hydrogen bonds with a lone pair of electrons).

Q. How is phosphine purified?

ANS: Phosphine is refined by absorbing impurities in HI, which produces PH₄I, which is then treated with potassium hydroxide to produce phosphine.

PH₄I+KOH→KI+H₂O+PH₃