Phosphine is a poisonous gas which in its pure form does not have color or smell. From a chemical point of view, it is a volatile hydrogen phosphorus compounds. In chemistry, the phosphine formula has the form - PH 3 . Its properties have some similarities with ammonia. The substance is very dangerous because it has high toxicity and a tendency to self-ignition.
Getting
The best-studied method for producing phosphine is the reaction of the interaction of white phosphorus with a solution of strong alkali when heated. In this case, phosphorus disproportionates to metaphosphate and phosphine. By-products of this reaction are diphosphine (P 2 H 4 ) and hydrogen, so the yield of this reaction is small and does not exceed 40%.
The diphosphine formed in the reaction medium interacts with alkali, resulting in the formation of phosphine and hydrogen.
And the hypophosphite obtained in these reactions, when interacting with an alkali, passes into phosphate with the release of hydrogen.
NaH 2 PO 2 + 2NaOH = 2H 2 + Na 3 PO 4
After completion of all reactions, phosphine, hydrogen and phosphate are formed as a result of the interaction of alkali on phosphorus. This production method can also be carried out with alkaline oxides instead of alkalis. This experience is very beautiful, since the diphosphine formed immediately ignites and burns in the form of sparks, forming something similar to a firework.
When exposed to water or acid on metal phosphides, phosphine is also obtained.
During the thermal decomposition of phosphorous acid or its reduction with hydrogen at the moment of isolation, phosphine is also formed.
Phosphonium salts, when decomposed or in reaction with certain substances, give phosphine.
Physical properties
Phosphine is an odorless, colorless gas. But technical phosphine (with some impurities) can have a characteristic unpleasant odor, which is described in different ways. It is slightly heavier than air, at a temperature of -87.42 ° C it liquefies, and at -133.8 ° C it becomes a solid. Such low boiling and melting temperatures are due to rather weak hydrogen bonds. The substance is practically insoluble in water, but under certain conditions forms unstable hydrates with water . It is soluble in ethanol and diethyl ether. The density of phosphine under normal conditions is 0.00153 g / cm 3 .
Chemical properties
As already mentioned, the chemical formula of phosphine is PH 3 . Although phosphine is similar to ammonia, it has a number of differences in interactions with other substances. These features are due to the fact that the chemical bonds in phosphine (according to the formula it becomes clear) are covalent weakly polar. They are less polar than in ammonia, and therefore more durable.
With strong heating (approximately 450 ° C) without oxygen, phosphine decomposes into simple substances.
2PH 3 → 2P + 3H 2
At temperatures above 100 ° C, PH 3 self-ignites, reacting with atmospheric oxygen. The temperature threshold can be reduced by ultraviolet light. For this reason, phosphine released in the swamps often ignites spontaneously, causing the appearance of so-called “wandering lights”.
PH 3 + 2O 2 → H 3 PO 4
But simple burning can occur. Then phosphoric anhydride and water are formed.
2PH 3 + 4O 2 → P 2 O 5 + 3H 2 O
Like ammonia, phosphine can form salts by reacting with hydrogen halides.
PH 3 + HI → PH 4 I
PH 3 + HCl → PH 4 Cl
Based on the formula of phosphine, we can say that the phosphorus in it has a lower oxidation state. For this reason, it is a good reducing agent.
PH 3 + 2I 2 + 2H 2 O → H 3 PO 2 + 4HI
PH 3 + 8HNO 3 → H 3 PO 4 + 8NO 2 + 4H 2 O
Application
Due to its high toxicity, phosphine has found application in fumigation, i.e., the destruction of various pests (insects, rodents) using gas. For these procedures, there are special devices - machine-fumigators, using which they spray gas in the rooms. Usually, phosphine or preparations based on it are used to process warehouses of grain crops, prepared food products, furniture, as well as libraries, factory premises, train cars and other vehicles. The advantage of this treatment is that phosphine, even in small concentrations, easily penetrates into inaccessible places and does not interact with metals, wood and fabric.
The room is treated with phosphine, in a sealed state it is kept for 5-7 days. After this, at least two days need to be aired, otherwise it is dangerous for a person in it. After this, phosphine leaves no trace even on products, grain and other products.
Phosphine is also used in the synthesis of certain substances, especially organic ones. Also, chemically pure phosphorus can be obtained from it; semiconductors are doped using phosphine.
Toxicology
Phosphine is an extremely toxic compound. It quickly passes through the respiratory tract and interacts with the mucous membranes of the body. This can cause disturbances in the functioning of the nervous system, as well as metabolism in general. Signs of poisoning include dizziness, nausea, vomiting, headache, fatigue, and sometimes even convulsions. In severe cases of administration, a person may lose consciousness or stop breathing and palpitations. The maximum permissible concentration of phosphine in the air is 0.1 mg / m 3 . A concentration of 10 mg / m 3 immediately leads to death.
The first thing to do with a victim of phosphine poisoning is to take it to fresh air and to free it from contaminated clothing. It is also recommended that the victim be doused with water in order to quickly remove the remaining toxic gas. Inpatient treatment involves the use of an oxygen mask, monitoring of heart rate and liver condition, and treatment of pulmonary edema. It is necessary to monitor the patient for at least 2-3 days, even if there are no visible signs of poisoning. Some symptoms may occur only a few days after contact with phosphine.