Phosphine and Phosphorus Chloride

Imagine you are in a place where Chemistry plays a vital role in almost all facets of life, right from the food you eat to the gadgets you use and to the industrial processes that are carried out. One such interesting case is with phosphine which is used in many industries and most chemical processes. It provides doping agents in the industry of semiconductors with such gas and gives out the poison and flammable nature of such gas. These doping agents create advanced electronic devices which make up the impetus of modernization in today's world. Other phosphorus chlorides include phosphorus trichloride and phosphorus pentachloride.

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This Story also Contains

1. Phosphine and Phosphorus Chloride
2. Different Aspects of Phosphine and Phosphorus Chloride
3. Phosphine
4. Phosphorus Trichloride
5. Phosphorus Pentachloride
6. Relevance and Applications to Real Life and Academia
7. Some Solved Examples
8. Summary

Phosphine and Phosphorus Chloride

Phosphine or hydrogen phosphide is a colourless, highly flammable, highly toxic gas with an odour like garlic. The compound is made by the reaction of phosphorus and hydrogen. Among the aforementioned, phosphorus chlorides primarily consist of Phosphorus trichloride and phosphorus pentachloride in the molecular formula of PCl₅. Firstly, phosphorus trichloride occurs in the form of a yellowish substance that is fuming, while white phosphorus is presented in crystalline forms. These chemicals can be utilized as major kinds of intermediate products in the synthesising of chemicals in multiple industrial fields.

Phosphine can be produced through the reaction of white phosphorus and sodium or potassium hydroxide, while phosphorus trichloride is available from the chlorination of elemental phosphorus. The critical aspects and means by which such compounds get prepared press in on their significance to industries.

Different Aspects of Phosphine and Phosphorus Chloride

The two forms of low-molecular-weight phosphine are pure phosphine and substituted phosphines, where one or more hydrogen atoms are replaced by organic groups. Pure phosphine also finds uses as a fumigant in agriculture and as a doping agent in the semiconductor industry. Applications of substituted phosphines are found in catalysis and for a variety of organic syntheses.

The applications of phosphorous trichloride and pentachloride form the basis for the receipt of many other phosphorus-containing compounds. Phosphorus trichloride is a very good reagent for the preparation of pesticides, flame retarders, and plastifiers. Phosphorus pentachloride, on the other, hand is a very strong chlorinating agent in an enormous number of processes and allows one to receive organic compounds. Such a broad line of application as noted above allows talking about the growing importance of phosphorus chlorides in a score of big industries.

Phosphine

• Preparation
  Phosphine is prepared by the reaction of calcium phosphide with water or dilute HCl.
  $\begin{array}{r}{\mathrm{Ca}}_3{\mathrm{P}}_2+6{\mathrm{H}}_2\mathrm{O}\to 3\mathrm{Ca}(\mathrm{OH}{)}_2+2{\mathrm{PH}}_3\\ {\mathrm{Ca}}_3{\mathrm{P}}_2+6\mathrm{HCl}\to 3{\mathrm{CaC}}_{}\end{array}$$\begin{aligned} & \mathrm{Ca}_3 \mathrm{P}_2+6 \mathrm{H}_2 \mathrm{O} \rightarrow 3 \mathrm{Ca}(\mathrm{OH})_2+2 \mathrm{PH}_3 \\ & \mathrm{Ca}_3 \mathrm{P}_2+6 \mathrm{HCl} \rightarrow 3 \mathrm{CaCl}_2+2 \mathrm{PH}_3\end{aligned}$
  
  
• In the laboratory, it is prepared by heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO₂.
  $\mathrm{P}_4+3 \mathrm{NaOH}+3 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{PH}_3+3 \mathrm{NaH}_2 \mathrm{PO}_2$
  ${\mathrm{P}}_4+3\mathrm{NaOH}+3{\mathrm{H}}_2\mathrm{O}\to {\mathrm{PH}}_3+3{\mathrm{NaH}}_2{\mathrm{PO}}_2$
• When pure, it is non-inflammable but becomes inflammable owing to the presence of P₂H₄ or P₄ vapours. To purify it from the impurities, it is absorbed in HI to form phosphonium iodide (PH₄I) which on treatment with KOH gives off phosphine.
  $\mathrm{PH}_4 \mathrm{I}+\mathrm{KOH} \rightarrow \mathrm{KI}+\mathrm{H}_2 \mathrm{O}+\mathrm{PH}_3$ ${\mathrm{PH}}_4\mathrm{I}+\mathrm{KOH}\to \mathrm{KI}+{\mathrm{H}}_2\mathrm{O}+{\mathrm{PH}}_{}$
  
• Properties
  It is a colourless gas with a rotten fish smell and is highly poisonous. It explodes on contact with traces of oxidising agents like HNO₃, Cl₂ and Br₂ vapours. It is slightly soluble in water. The solution of PH₃ in water decomposes in the presence of light giving red phosphorus and H₂. When absorbed in copper sulphate or mercuric chloride solution, the corresponding phosphides are obtained.
  $\begin{aligned} & 3 \mathrm{CuSO}_4+2 \mathrm{PH}_3 \rightarrow \mathrm{Cu}_3 \mathrm{P}_2+3 \mathrm{H}_2 \mathrm{SO}_4 \\ & 3 \mathrm{HgCl}_2+2 \mathrm{PH}_3 \rightarrow \mathrm{Hg}_3 \mathrm{P}_2+6 \mathrm{HCl}\end{aligned}$ $\begin{array}{r}3{\mathrm{CuSO}}_4+2{\mathrm{PH}}_3\to {\mathrm{Cu}}_3{\mathrm{P}}_2+3{\mathrm{H}}_2{\mathrm{SO}}_4\\ 3{\mathrm{HgCl}}_2+2{\mathrm{PH}}_3\to {\mathrm{Hg}}_3{\mathrm{P}}_2+6\mathrm{HCl}\end{array}$
• Uses
  The spontaneous combustion of phosphine is technically used in Holme’s signals. Containers containing calcium carbide and calcium phosphide are pierced and thrown in the sea when the gases evolved to burn and serve as a signal. It is also used in smoke screens.

Phosphorus Trichloride

• Preparation

It is obtained by passing dry chlorine overheated white phosphorus.
$\mathrm{P}_4+6 \mathrm{Cl}_2 \longrightarrow 4 \mathrm{PCl}_3$
It can also obtained by the action of thionyl chloride with white phosphorus.$\mathrm{P}_4+8 \mathrm{SOCl}_2 \longrightarrow 4 \mathrm{PCl}_3+4 \mathrm{SO}_2+2 \mathrm{~S}_2 \mathrm{Cl}_2$

• Properties

It is a colourless oily liquid and hydrolyses in the presence of moisture.
$\mathrm{PCl}_3+3 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{H}_3 \mathrm{PO}_3+3 \mathrm{HCl}$
It reacts with organic compounds containing –OH group and replaces it with a -Cl group $\mathrm{RCOOH}+\mathrm{PCl}_3 \longrightarrow \mathrm{RCOCl}+\mathrm{H}_3 \mathrm{PO}_3$

$\mathrm{RCH}_2 \mathrm{OH}+\mathrm{PCl}_3 \longrightarrow \mathrm{RCH}_2 \mathrm{Cl}+\mathrm{H}_3 \mathrm{PO}_3$

Phosphorus Pentachloride

• Preparation

It is obtained by the reaction of excess dry chlorine with white phosphorus.
$\mathrm{P}_4+10 \mathrm{Cl}_2 \longrightarrow 4 \mathrm{PCl}_5$
It can also obtained by the reaction of sulphuryl chloride with white phosphorus.$\mathrm{P}_4+10 \mathrm{SO}_2 \mathrm{Cl}_2 \longrightarrow 4 \mathrm{PCl}_5+10 \mathrm{SO}_2$

• Properties

It is a colourless oily liquid and hydrolyses in the presence of moisture.
$\mathrm{PCl}_5+\mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{POCl}_3+2 \mathrm{HCl}$ (partial hydrolysis)

$\mathrm{POCl}_3+3 \mathrm{H}_2 \mathrm{O} \longrightarrow \mathrm{H}_3 \mathrm{PO}_4+3 \mathrm{HCl}$ (complete hydrolysis)

It reacts with organic compounds containing –OH group and replaces it with a -Cl group

$\begin{aligned} & \mathrm{RCOOH}+\mathrm{PCl}_5 \longrightarrow \mathrm{RCOCl}+\mathrm{POCl}_3+\mathrm{HCl} \\ & \mathrm{RCH}_2 \mathrm{OH}+\mathrm{PCl}_5 \longrightarrow \mathrm{RCH}_2 \mathrm{Cl}+\mathrm{POCl}_3+\mathrm{HCl}\end{aligned}$

It can convert finely divided metals into their corresponding chlorides on heating

$\begin{aligned} & 2 \mathrm{Ag}+\mathrm{PCl}_5 \longrightarrow 2 \mathrm{AgCl}+\mathrm{PCl}_3 \\ & \mathrm{Sn}+2 \mathrm{PCl}_5 \longrightarrow \mathrm{SnCl}_4+2 \mathrm{PCl}_3\end{aligned}$

Relevance and Applications to Real Life and Academia

The roles that phosphine and its chlorides play start from the industry right to the academy for research and actualization, respectively. Si wafers, a building block for all electronic gadgets in this semiconductor industry, are doped with phosphine gas. In the agricultural sector, it is used as a fumigant, which ensures that stored grains are pest-free and hence food security is assured.

Modern applications of trichloride include the use of phosphorus in agriculture, for example, herbicides. Herbicides help control the attack in weed stresses, particularly manifested in fields, resulting in increased crop yield and efficiency. Besides that, phosphorus trichloride participates in the synthesis of flameproof products, which ensures increased fire safety for products ranging from textiles to applications in electronic devices.

Phosphorus pentachloride forms one of the important chlorinating agents in organic chemistry and can be able to make a wide array of compounds. It can never be done away with in any chemical laboratory due to its use in the pharmaceuticals and agrochemicals areas.

These facts show that the compounds are being applied in real life and are of academic importance because they can be used to enhance technology, agriculture, and safety.

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Some Solved Examples

Question 1: When white P₄ is heated with concentrated NaOH in an inert atmosphere, it produces:
1) Sodium hypophosphite
2) Sodium phosphate
3) Phosphine
4) Both 1 and 3

Solution: The laboratory preparation of phosphine involves heating white phosphorus with concentrated NaOH solution in an inert atmosphere of CO₂. The reaction is:
$\mathrm{P}_4+3 \mathrm{NaOH}+3 \mathrm{H}_2 \mathrm{O} \rightarrow \mathrm{PH}_3+3 \mathrm{NaH}_2 \mathrm{PO}_2$
(Phosphine) (Sodium hypophosphite)

Therefore, the answer is option (4): Both sodium hypophosphite and phosphine are produced.

Question 2: When PH₃ reacts with air, it gives:
1) P₄
2) H₃PO₃
3) H₃PO₂
4) P₂O₅

Solution: Phosphine burns in air to form phosphorus pentoxide and water:
$\mathrm{PH}_3+4 \mathrm{O}_2 \rightarrow \mathrm{P}_2 \mathrm{O}_5+3 \mathrm{H}_2 \mathrm{O}$

Therefore, the answer is option (4): P₂O₅.

Question 3: AgNO₃ + PH₃ → Black ppt + HNO₃. The black ppt. is:
1) Ag₂O
2) Ag
3) Ag₃P
4) Ag₃N

Solution: The reaction of phosphine with silver nitrate produces a black residue of silver phosphide:
$3 \mathrm{AgNO}_3+\mathrm{PH}_3 \rightarrow \mathrm{Ag}_3 \mathrm{P}+3 \mathrm{HNO}_3$
(Black ppt.)

Therefore, the answer is option (3): Ag₃P.

Summary

Only phosphine and its compound with phosphorus chloride deliver the profile of two key chemical compounds with astonishingly broad fields of application in industry and academia, respectively. Phosphine is an industry-critical compound; it is widely used in the semiconductor industry, as well, it is of paramount importance in agriculture. On the other side, the chemical synthesis and manufacturing age has opened new avenues for their extensive uses in the form of phosphorus trichloride and pentachloride. Hence, definitions, properties, forms, and practical applications of these compounds behaving across such wide-ranging fields mentioned in the paper are also tried to be elaborated.