The hypophosphorous acid, also known as phosphinic acid hypophosphite or HPA is an inorganic compound of formula H 3 PO 2. It is a phosphorous oxacid or hydroxyphosphine oxide, with monobasic character (PH 3 oxide containing an OH-).
It is used for the descriptive presentation of derivatives or salts, whose hydrogen atoms bound to phosphorus are replaced by organic groups, called phosphinates. The term hypophosphite is also used for any salt, ester, or anion derived from the name hypophosphorous acid (HYPOPHOSPHOROUS ACID, SF).
Figure 1: Structure of hypophosphorous acid.
This compound is formed, together with phosphoric acid and hydrogen phosphide, when phosphorus is boiled in an alkaline or alkaline earthly caustic solution. Hypophosphorous acid is isolated by decomposing its barium salt with sulfuric acid (Wills, 1858).
The barium salt, Ba H 2 PO 2) 2, is easily recrystallized and the free acid can be prepared from it by double decomposition of a fifth molar solution, with the calculated amount of 20 to 25% sulfuric acid.
The filtered solution can be evaporated first to a tenth of its volume and then until the temperature rises to 105 ° C.
It is filtered hot and then evaporated at a temperature of 110 ° C. This stepwise evaporation is continued until the temperature rises to 130 ° C or even 138 ° C without decomposition.
The liquid is then poured into a closed flask and cooled to 0 ° C, practically solidifying to a mass of crystals. Crystallization can be induced if necessary by seeding with a crystal of the acid.
Commercial acid normally contains calcium salts. These can be removed by adding alcohol and a lot of ether to the evaporated solution, when the salts are precipitated. Alcohol and ether are removed by distillation (atomistry.com, 2008-2012).
Physical and chemical properties
Hypophosphorous acid is a colorless oily liquid or deliquescent crystals (it slowly liquefies), with a molecular weight of 66 g / mol.
It has a melting point that varies between 17.4 and 26.5 degrees Celsius. This depends on the amount of water in the acid crystals (National Center for Biotechnology Information, SF). The appearance of the compound in liquid state is presented in Figure 2.
Figure 2: appearance of hypophosphorous acid.
HPA has a density of 1.49 g / ml in solid state and 1.22 g / ml in aqueous solution at 50% w / w. It is soluble in water, alcohol and ether and its heat of formation is 137.7 Cal in the liquid state and 140.0 Cal in the solid state (Royal Society of Chemistry, 2015).
The compound decomposes into phosphoric acid and hydrogen phosphide (phosphine) when heated to temperatures between 130 and 140 degrees centigrade depending on the reaction:
2H 3 PO 2 → H 3 PO 4 + PH 3
Hypophosphorous acid is a strong reducing agent even stronger than phosphorous acid. In addition, it may be reduced to phosphine when it encounters a strong reducing agent. Reacts with silver nitrate to give a white precipitate that darkens quickly, even at low temperatures.
It oxidizes with sulfuric acid, releasing sulfur dioxide and sulfur. It can react explosively with mercury (II) oxide and violently with mercury (II) nitrate (Chemical Datasheet HYPOPHOSPHOROUS ACID, 2016).
Reactivity and hazards
Hypophosphorous acid is a compound that is corrosive to the eyes and skin. The amount of tissue damage will depend on the length of the contact, and may attack the cornea or cause blindness.
Contact with the skin can cause inflammation and blisters. Inhalation of dust will produce irritation of the gastrointestinal or respiratory tract, characterized by burning, sneezing and coughing. Severe overexposure can cause lung damage, suffocation, loss of consciousness, or death.
Repeated exposure of the eyes to small amounts of dust can irritate the eyes and lead to local destruction of the skin, or dermatitis.
Repeated inhalation of dust can produce a variable degree of respiratory irritation or lung damage (Material Safety Data Sheet Phosphorous acid, 2013).
The victim should be taken to fresh air immediately and if breathing is irregular or stops, artificial respiration should be given. Call a doctor or poison control center immediately.
In case of contact with the skin, it should be washed with plenty of water and a doctor should be consulted if necessary. In case of contact with clothing, it should be removed immediately and washed with water. It is important not to wear the garments until you are sure they are decontaminated.
In case of contact with the eyes, it should be rinsed carefully with water for several minutes. In case of wearing contact lenses, they must be removed immediately (Special material company, 2015).
Applications
Hypophosphorous acid is used as a reducing agent for electroplating without electrolysis. This product is widely used as a reducing agent, Ag, Cu, Ni, Hg and other metals are reduced to the corresponding metal for the verification of As, Nb, Ta and other reagents (ChemicalBook, 2016).
It is used as an esterification catalyst. It is also used as a polymerization and polycondensation catalyst.
Hypophosphorous acid is used in medicine in the determination of arsenic, tellurium, and the separation of tantalum, niobium, and other reagents. HPA can be used as a stimulant in pharmaceuticals and as an antioxidant.
It is a strong reducing agent, and can be used for the preparation of sodium hypophosphite, calcium phosphate and other hypophosphites, which in turn are used in synthetic fibers as dispersing agents, emulsifiers and wetting antistatic agents.
Hypophosphorous acid is used as a bleaching or decolorizing agent for plastics, synthetic fibers, and chemicals.
HPA is used as a bleaching agent and for color stabilization during the manufacture of chemicals and various plastics, including: nylon fibers, polyamides, polyester fiber, polyacrylonitrile, alkyd resins, epoxies, fatty acid esters and glycerols (Special Materials Company, 2017).
References
- Hypophosphorous Acid, H3PO2. Retrieved from atomistry.com.
- Chemical Datasheet HYPOPHOSPHOROUS ACID. (2016). Retrieved from cameo chemicals.
- (2016). Hypophosphorous acid. Retrieved from chemicalbook.com.
- HYPOPHOSPHOROUS ACID. (SF). Retrieved from chemicalland21.
- Material Safety Data Sheet Phosphorous acid. (2013, May 21). Retrieved from sciencelab.com.
- National Center for Biotechnology Information. (SF). PubChem Compound Database; CID = 3085127. Retrieved from PubChem.
- Royal Society of Chemistry. (2015). Hypophosphorous acid. Retrieved from ChemSpider.
- Special material company. (2015, February 25). SAFETY DATA SHEET Hypophosphorous Acid. Retrieved from hypophosphorousacid.net.
- Special Materials Company. (2017). Hypophosphorous Acid. Retrieved from hypophosphorousacid.ne.
- Wills, H. (1858). A Handbook of Chemical Analysis:. london: spottiswoode and co.