Potassium arsenite (KAsO₂) is an inorganic compound that exists in two forms, potassium meta-arsenite (KAsO₂) and potassium ortho-arsenite (K₃AsO₃). It is composed of

arsenite In chemistry, an arsenite is a chemical compound containing an arsenic oxyanion where arsenic has oxidation state +3. Note that in fields that commonly deal with groundwater chemistry, arsenite is used generically to identify soluble AsIII anions. ...

ions (AsO₃³⁻ or AsO₂⁻) with arsenic always existing in the +3 oxidation state. Like many other arsenic containing compounds, potassium arsenite is highly toxic and

carcinogen A carcinogen is any substance, radionuclide, or radiation that promotes carcinogenesis (the formation of cancer). This may be due to the ability to damage the genome or to the disruption of cellular metabolic processes. Several radioactive subs ...

ic to humans. Potassium arsenite forms the basis of Fowler’s solution, which was historically used as a medicinal tonic, but due to its toxic nature its use was discontinued. Potassium arsenite is still, however, used as a rodenticide.Potassium Arsenite. http://nj.gov/health/eoh/rtkweb/documents/fs/1557.pdf

Structure

The two unique forms of potassium arsenite can be attributed to the different number of oxygen atoms. Potassium meta-arsenite (KAsO₂) contains two oxygen atoms one of which is bonded to the arsenic atom via a double bond. Conversely, Potassium ortho-arsenite (K₃AsO₃) consists of three oxygen atoms all bound to the arsenic atom via single bonds. In each of these cases, arsenic exists in the +3 oxidation state and is known as arsenite, hence the single name referring to two different structures. Additionally, both the meta and ortho forms of potassium arsenite have identical properties.

Properties

Potassium arsenite is an inorganic salt that exists as an odorless white solid. It is largely soluble in water and only slightly soluble in alcohol. Solutions of potassium arsenite contain moderate concentrations of

hydroxide Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. I ...

, and are thus slightly basic. While potassium arsenite is noncombustible, heating it results in its decomposition and the formation of toxic fumes that include

arsine Arsine (IUPAC name: arsane) is an inorganic compound with the formula As H3. This flammable, pyrophoric, and highly toxic pnictogen hydride gas is one of the simplest compounds of arsenic. Despite its lethality, it finds some applications in ...

arsenic oxide Arsenic oxide may refer to any of the following: * Arsenic dioxide, As2O4 *Arsenic trioxide Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses ...

s, and

potassium oxide Potassium oxide ( K O) is an ionic compound of potassium and oxygen. It is a base. This pale yellow solid is the simplest oxide of potassium. It is a highly reactive compound that is rarely encountered. Some industrial materials, such as fertili ...

s. Potassium arsenite also reacts with acids to yield toxic arsine gas.

Preparation

Aqueous potassium arsenite, more commonly known as Fowler’s solution, can be prepared by heating

arsenic trioxide Arsenic trioxide, sold under the brand name Trisenox among others, is an inorganic compound and medication. As an industrial chemical, whose major uses include in the manufacture of wood preservatives, pesticides, and glass. As a medication, it ...

(As₂O₃) with potassium hydroxide (KOH) in the presence of water. The reaction is shown below :As₂O₃ (aq) + 2 KOH (aq) → 2 KAsO₂ (aq) + H₂O

Uses

In the eighteenth century English physician Thomas Fowler (1736–1801) utilized a potassium arsenite solution called Fowler’s solution to remedy a number of conditions including

anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...

, rheumatism,

psoriasis Psoriasis is a long-lasting, noncontagious autoimmune disease characterized by raised areas of abnormal skin. These areas are red, pink, or purple, dry, itchy, and scaly. Psoriasis varies in severity from small, localized patches to complete ...

eczema Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...

dermatitis Dermatitis is inflammation of the skin, typically characterized by itchiness, redness and a rash. In cases of short duration, there may be small blisters, while in long-term cases the skin may become thickened. The area of skin involved can ...

asthma Asthma is a long-term inflammatory disease of the airways of the lungs. It is characterized by variable and recurring symptoms, reversible airflow obstruction, and easily triggered bronchospasms. Symptoms include episodes of wheezing, co ...

, cholera, and syphilis. Furthermore, in 1865 the potential uses of potassium arsenite expanded as Fowler’s solution was used as the first chemotherapeutic agent to treat

leukemia Leukemia ( also spelled leukaemia and pronounced ) is a group of blood cancers that usually begin in the bone marrow and result in high numbers of abnormal blood cells. These blood cells are not fully developed and are called ''blasts'' or ...

, however the chemotherapeutic effects were only temporary. Surprisingly enough, this specific use was inspired by potassium arsenite’s role in improving digestion and producing a smoother coat in horses. Potassium arsenite is also a key inorganic component of certain rodenticides, insecticides, and herbicides. Furthermore, its role as an insecticide also made it a great wood preservative; however, the solubility and toxicity made it a potential risk factor for the environment.

Health effects

The toxicity of potassium arsenite arises from arsenic’s high affinity for sulfhydryl groups. The formation of these arsenite-sulfur bonds impairs the functionality of certain enzymes such as

glutathione reductase Glutathione reductase (GR) also known as glutathione-disulfide reductase (GSR) is an enzyme that in humans is encoded by the GSR gene. Glutathione reductase (EC 1.8.1.7) catalyzes the reduction of glutathione disulfide ( GSSG) to the sulfhydryl f ...

glutathione peroxidase Glutathione peroxidase (GPx) () is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage. The biochemical function of glutathione peroxidase is to reduce lipid h ...

thioredoxin reductase Thioredoxin reductases (TR, TrxR) () are enzymes that reduce thioredoxin (Trx). Two classes of thioredoxin reductase have been identified: one class in bacteria and some eukaryotes and one in animals. In bacteria TrxR also catalyzes the reduction ...

, and thioredoxin peroxidase. These enzymes are all closely affiliated with the defense of free radicals and the metabolism of pyruvate. Thus, exposure to potassium arsenite and other arsenite containing compounds results in the production of damaging oxygen free radicals and the arrest of cellular metabolism. Additionally, arsenite containing compounds have also been labeled carcinogens. The carcinogenicity of potassium arsenite arises from its ability to inhibit DNA repair and methylation. This impairment of the cellular machinery can lead to cancer because the cells can no longer repair or arrest mutations and a tumor results. All of these conditions exhibit the hazardous nature of potassium arsenite and other arsenite containing compounds. This is evidenced by a LD₅₀ of 14 mg/kg for rats and a TDL of 74 mg/kg for humans.

Notes

{{Potassium compounds Arsenites Potassium compounds