Phosphine is a poisonous gas that is colorless and odorless in its pure form. From a chemical point of view, it is a volatile hydrogen compound of phosphorus. In chemistry, the formula for phosphine is - PH3. By its properties, it has some similarities with ammonia. The substance is very dangerous, as it has a high toxicity and a tendency to self-ignite.
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The most well-studied way to obtain phosphine is the reaction of the interaction of white phosphorus with a strong alkali solution when heated. In this case, phosphorus disproportionates into metaphosphate and phosphine. By-products of this reaction are diphosphine (P2H4) and hydrogen, so the yield of this reaction is small and does not exceed 40%.
The resulting diphosphine in the reaction medium reacts with alkali, resulting in the formation of phosphine and hydrogen.
And the hypophosphite obtained in these reactions, withinteraction with alkali, goes into phosphate with the release of hydrogen.
NaH2PO2 + 2NaOH=2H2 + Na 3PO4
After completion of all reactions, as a result of the interaction of alkali on phosphorus, phosphine, hydrogen and phosphate are formed. This production method can also be carried out with alkali oxides instead of alkalis. This experience is very beautiful, as the resulting diphosphine immediately ignites and burns in the form of sparks, forming what looks like fireworks.
When exposed to water or acid, metal phosphides also produce phosphine.
During the thermal decomposition of phosphorous acid or its reduction with hydrogen, phosphine is also formed at the time of isolation.
Phosphonium s alts decompose or react with certain substances to give phosphine.
Physical properties
Phosphine is a colorless, odorless gas. But technical phosphine (with some impurities) can have a characteristic unpleasant odor, which is described in different ways. Slightly heavier than air, at -87.42 °C it liquefies, and at -133.8 °C it becomes a solid. Such low boiling and melting points are due to rather weak hydrogen bonds. The substance is practically insoluble in water, but under certain conditions forms unstable hydrates with water. Let's well dissolve in ethanol and diethyl ether. The density of phosphine under normal conditions is 0.00153 g/cm3.
Chemical properties
As already mentioned, the chemical formula of phosphine is PH3. 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 (it becomes clear from the formula) are covalent weakly polar. They are less polar than in ammonia and therefore more durable.
When strongly heated (about 450 °C) without oxygen, phosphine decomposes into simple substances.
2PH3 → 2P + 3H2
At temperatures above 100 °C PH3 self-ignites by reacting with atmospheric oxygen. The temperature threshold can be lowered with ultraviolet light. For this reason, phosphine released from swamps often ignites spontaneously, causing the appearance of so-called "will-o'-the-wisps".
PH3 + 2O2 → H3PO4
But simple combustion can also occur. Phosphoric anhydride and water are then formed.
2PH3 + 4O2 → P2O5 + 3H2O
Like ammonia, phosphine can form s alts by reacting with hydrogen halides.
PH3 + HI→ PH4I
PH3 + HCl→ PH4Cl
Based on the formula of phosphine, we can say that phosphorus in it has the lowest oxidation state. For this reason, it is a good reducing agent.
PH3 + 2I2+ 2H2O → H 3PO2 + 4HI
PH3 + 8HNO3→H3PO4 + 8NO2 + 4H2 O
Application
Due to its high toxicity, phosphine has found application in fumigation, i.e., the destruction of various kinds of pests (insects, rodents) using gas. For these procedures, there are special devices - fumigator machines, with the use of which gas is sprayed indoors. Usually, phosphine or preparations based on it are treated with warehouses of grain crops, ready-made 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 hard-to-reach places and does not interact with metals, wood and fabric in any way.
The room is treated with phosphine, it is kept in a sealed state for 5-7 days. After that, it is necessary to carry out ventilation for at least two days, otherwise it is dangerous for a person to be in it. After that, phosphine does not leave any traces even on food, grain and other goods.
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 disruption of the nervous system, as well as metabolism in general. Signs of poisoning can include dizziness, nausea, vomiting, headache, fatigue, sometimes evenconvulsions. In severe cases of departure, a person may lose consciousness or stop breathing and heartbeat. The maximum allowable concentration of phosphine in the air is 0.1 mg/m3. A concentration of 10 mg/m3 immediately fatal.
The first thing to do with victims of phosphine poisoning is to take them out to fresh air and free them from contaminated clothing. It is also recommended to douse the victim with water to quickly remove the remaining toxic gas. Inpatient treatment includes the use of an oxygen mask, monitoring of heart rate and liver condition, and treatment of pulmonary edema. The patient must be monitored for at least 2-3 days, even if there are no visible signs of poisoning. Some symptoms may not appear until several days after exposure to phosphine.
