organophosphate organophosphate in organic chemistry, organophosphates (also known as phosphate esters, or opes) are a class of organophosphorus compounds with the general structure o=p(or)3, a central phosphate molecule with alkyl or aromatic substituents. they can be considered as esters of phosphoric acid. general chemical structure of the organophosphate functional group like most functional groups, organophosphates occur in a diverse range of forms, with important examples including key biomolecules such as dna, rna and atp, as well as many insecticides, herbicides, nerve agents and flame retardants. opes have been widely used in various products as flame retardants, plasticizers, and performance additives to engine oil. the popularity of opes as flame retardants came as a substitution for the highly regulated brominated flame retardants. the low cost of production and compatibility to diverse polymers made opes to be widely used in industry including textile, furniture, electronics as plasticizers and flame retardants. these compounds are added to the final product physically rather than by chemical bond. due to this, opes leak into the environment more readily through volatilization, leaching, and abrasion. opes have been detected in diverse environmental compartments such as air, dust, water, sediment, soil and biota samples at higher frequency and concentration. synthesis alcoholysis of pocl3 phosphorus oxychloride reacts readily with alcohols to give organophosphates. this is the dominate industrial route and is responsible for almost all organophosphate production. o=pcl3 + 3 roh → o=p(or)3 + 3 hcl esterification of phosphoric acid in stark contrast to carboxylic acids, phosphoric acid does not readily esterify with alcohols. the use of activating species such as trichloroacetonitrile or acetic anhydride permit mono-esters to be formed, but tri-substituted organophosphates cannot be made in this way. op(oh)3 + roh → op(oh)2(or) + h2o oxidation of phosphite esters organophosphites can be easily oxidised to give organophosphates. this might normally be considered a specialised method for academic labs, however large quantities of organophosphites are produced as antioxidant stabilisers for plastics, with their gradual oxidation forming organophosphates in the human environment. p(or)3 + → op(or)3 phosphorylation the formation of organophosphates is an important part of biochemistry and living systems achieve this using a variety of enzymes. phosphorylation is essential to the processes of both anaerobic and aerobic respiration, which involve the production of adenosine triphosphate (atp), the "high-energy" exchange medium in the cell. properties the phosphate esters bearing oh groups are acidic and partially deprotonated in aqueous solution. for example, dna and rna are polymers of the type n. polyphosphates also form esters; an important example of an ester of a polyphosphate is atp, which is the monoester of triphosphoric acid (h5p3o10). opes contain a phosphate molecular group. in the case of organophosphate (op) triesters, these are three ester bonds with alkyl or aromatic substituents. however, op diesters are distinct from the triesters as one of the alkyl ester groups is replaced by a hydroxyl group, making op diesters phosphoric acids. the wide variety of substitutes used in organophosphate esters results in great variations in physicochemical properties, varying from highly polar to very hydrolysis resistant characteristics. opes exhibit a wide range of octanol–water partition coefficients, where log kow values range from −0.98 up to 10.6. the predominant opes used as flame retardants and plasticizers have a positive log kow values, signifying hydrophobicity, with values ranging from 1.44 and 9.49. because of this hydrophobicity, opes are presumably bioaccumulated and biomagnified in aquatic ecosystems. laboratory experiments had shown that the non-halogenated opes are prone to photolysis, but the chlorinated opes such as tcep and tcpp seemed to be resistant to degradation by sunlight. in nature guanitoxin guanitoxin is a naturally occurring organophosphate produced by cyanobacteria. the detection of opes in the air as far away as antarctica at concentrations around 1 ng/m3 suggests their persistence in air, and their potential for long-range transport. opes were measured in high frequency in air and water and widely distributed in northern hemisphere. the chlorinated opes (tcep, tcipp, tdcipp) in urban sampling sites and non-halogenated like tboep in rural areas respectively were frequently measured in the environment across multiple sites. in the laurentian great lakes total opes concentrations were found to be 2–3 orders of magnitude higher than concentrations of brominated flame retardants measured in similar air. waters from rivers in germany, austria, and spain have been consistently recorded for tboep and tcipp at highest concentrations. from these studies, it is clear that ope concentrations in both air and water samples are often orders of magnitude higher than other flame retardants, and that concentrations are largely dependent on sampling location, with higher concentrations in more urban, polluted locations. pesticides today, organophosphates make up about 50% of the killing agents in chemical pesticides. organophosphate pesticides (opps), like some nerve agents, inhibit acetylcholinesterase (irac mode of action 1b), which is broadly essential for normal function in insects, but also in humans and many other animals. opps affect this enzyme in varied ways, a principal one being through irreversible covalent inhibition, and so create potentials for poisoning that vary in degree. the brain sends out neurotransmitters to the nerve endings in the body; organophosphates disrupt this process from occurring. this chemical, organophosphate works by disrupting the enzyme acetylcholinesterase. acetylcholinesterase breaks down the acetylcholine neurotransmitter, which sends out signals to other nerve endings in the body. for instance, parathion, one of the first opps commercialized, is many times more potent than malathion, an insecticide used in combating the mediterranean fruit fly (med-fly) and west nile virus-transmitting mosquitoes. human and animal exposure to them can be through ingestion of foods containing them, or via absorption through the skin or lungs. the human and animal toxicity of opps make them a societal health and environmental concern; the epa banned most residential uses of organophosphates in 2001, but their agricultural use, as pesticides on fruits and vegetables, is still permitted, as is their use in mosquito abatement in public spaces such as parks. for instance, the most commonly used opp in the u.s., malathion, sees wide application in agriculture, residential landscaping, and pest control programs (including mosquito control in public recreation areas). as of 2010, forty such opps were registered for use in the u.s., with at least 73 million pounds used in one time period in agricultural and residential settings. commonly used organophosphates have included: parathion malathion methyl parathion chlorpyrifos diazinon dichlorvos phosmet fenitrothion tetrachlorvinphos azamethiphos azinphos-methyl terbufos studies have shown that prolonged exposure to opps—e.g., in the case of farm workers—can lead to health problems, including increased risks for cardiovascular and respiratory disease, and cancer. in the case of pregnant women, exposure can result in premature births. in addition, permanent damage to the brain's chemical make-up, and changes in human behavior and emotion can occur to the fetus in pregnant women. organophosphate pesticides degrade rapidly by hydrolysis on exposure to sunlight, air, and soil, although small amounts can be detected in food and drinking water. organophosphates contaminate drinking water by moving through the soil to the ground water. when the pesticide degrades, it is broken down into several chemicals. organophosphates degrade faster than the organochlorides. the greater acute toxicity of opps results in the elevated risk associated with this class of compounds (see the toxicity section below). nerve agents main article: nerve agents history early pioneers in the field include jean louis lassaigne (early 19th century) and philippe de clermont (1854). in 1932, german chemist willy lange and his graduate student, gerde von krueger, first described the cholinergic nervous system effects of organophosphates, noting a choking sensation and a dimming of vision after exposure on themselves, which they attributed to the esters themselves. this discovery later inspired german chemist gerhard schrader at company ig farben in the 1930s to experiment with these compounds as insecticides. their potential use as chemical warfare agents soon became apparent, and the nazi government put schrader in charge of developing organophosphate (in the broader sense of the word) nerve gases. schrader's laboratory discovered the g series of weapons, which included sarin, tabun, and soman. the nazis produced large quantities of these compounds, though did not use them during world war ii. british scientists experimented with a cholinergic organophosphate of their own, called diisopropylfluorophosphate, during the war. the british later produced vx nerve agent, which was many times more potent than the g series, in the early 1950s, almost 20 years after the germans had discovered the g series. after world war ii, american companies gained access to some information from schrader's laboratory, and began synthesizing organophosphate pesticides in large quantities. parathion was among the first marketed, followed by malathion and azinphosmethyl. the popularity of these insecticides increased after many of the organochlorine insecticides such as ddt, dieldrin, and heptachlor were banned in the 1970s. structural features effective organophosphates have the following structural features: a terminal oxygen connected to phosphorus by a double bond, i.e. a phosphoryl group two lipophilic groups bonded to the phosphorus a leaving group bonded to the phosphorus, often a halide fine tuning within these requirements, a large number of lipophilic and leaving groups have been used. the variation of these groups is one means of fine tuning the toxicity of the compound. a good example of this chemistry are the p-thiocyanate compounds which use an aryl (or alkyl) group and an alkylamino group as the lipophilic groups. the thiocyanate is the leaving group. flame retardants flame retardants (frs) are chemicals that have been used on diverse consumer materials to prevent combustion and to delay the spread of fire after ignition. the increased demand to satisfy fire safety standards for flammability of plastic materials used in devices and appliances along with the strict regulation of brominated flame retardants has driven the high volume of production and consumption of opes. most flame retardants used are halogenated opes, and the effectiveness of the flame retardant increases with the increased number of halogenated substituents. opes are utilized as additive flame retardants which means the concentration of these flame retardants decreases with time as they readily leak into the environment. there are several mechanisms flame retardants use to prevent fire, however the most effective ones are the gas phase and the solid phase reactions. in the solid phase, halogenated flame retardants produce a char layer on burning materials suffocating the combustion, as well as in the gas phase they remove h+ and oh− radicals from the flammable gasses, by reaction with the br and cl atoms to further slow down the burning process. non-halogenated opes are effective mainly in the solid phase of burning materials. upon exposure to heat the phosphorus compounds react to form a polymeric form of phosphorous acid. the acid causes a char layer that covers the burning material, blocking it from contact with oxygen, which in turn slows down the combustion reaction. health effects poisoning main article: organophosphate poisoning