Paraquat (trivial name; ), or N,N′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is an organic compound with the chemical formula [(C6H7N)2]Cl2. It is classified as a viologen, a family of redox-active heterocycles of similar structure. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic (lethal) to human beings and animals due to its redox activity, which produces superoxide anions. It has been linked to the development of Parkinson's disease and is banned in several countries. Paraquat may be in the form of salt with chloride or other anions; quantities of the substance are sometimes expressed by cation mass alone (paraquat cation, paraquat ion). The name is derived from the para positions of the quaternary nitrogens. Production Pyridine is coupled by treatment with sodium in ammonia followed by oxidation to give 4,4′-bipyridine. This chemical is then dimethylated with chloromethane to give the final product as the dichloride salt. Use of other methylating agents gives the bispyridinium with alternate counterions. For example, Hugo Weidel's original synthesis used methyl iodide to produce the diiodide. Herbicide use Although first synthesized in 1882, paraquat's herbicidal properties were not recognized until 1955 in the Imperial Chemical Industries (ICI) laboratories at Jealott's Hill. Paraquat was first manufactured and sold by ICI in early 1962 under the trade name Gramoxone, and is today among the most commonly used herbicides. Paraquat is classified as a non-selective contact herbicide. The key characteristics that distinguish it from other agents used in plant protection products are: It kills a wide range of annual grasses and broad-leaved weeds and the tips of established perennial weeds. It is very fast-acting. It is rain-fast within minutes of application. It is partially inactivated upon contact with soil. These properties led to paraquat being used in the development of no-till farming. The European Union approved the use of paraquat in 2004 but Sweden, supported by Denmark, Austria, and Finland, appealed this decision. In 2007, the court annulled the directive authorizing paraquat as an active plant protection substance stating that the 2004 decision was wrong in finding that there were no indications of neurotoxicity associated with paraquat and that the studies about the link between paraquat and Parkinson's disease should have been considered. Thus, paraquat has been banned in the European Union since 2007. In the United States, paraquat is