|1: 1 mixture (racemate) of the enantiomers : ( R ) form (left) and ( S ) form (right)|
|Molecular formula||C 4 H 10 FO 2 P|
colorless to yellow-brown, odorless liquid
|External identifiers / databases|
|Molar mass||140.09 g mol −1|
1.09 g cm −3
−57 ° C
147.3 ° C with partial decomposition
197 Pa (20 ° C)
|As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .|
Sarin is a chemical warfare agent from the group of phosphonic acid esters . The systematic name is isopropyl methyl fluorophosphonate . The common name sarin was introduced in 1943. Sarin was the second in a series of four organophosphorus compounds with potential as chemical warfare agents that were synthesized by IG Farben in the 1930s and 1940s . The others were Tabun (1936), Soman (1944), and Cyclosarin (1949).
From insecticide research to chemical weapons
In 1934 Gerhard Schrader was commissioned to develop pesticides that were not dependent on imports. Due to the already known, highly toxic aliphatic fluorocarbon compounds (fluorocarboxylic acids and derivatives, fluoroalcohols), the element fluorine, which had been neglected until then, attracted attention. From 1934 the systematic investigation of organic acid fluorides for their suitability as pesticides began (first sulfonic acid fluorides, later fluorides of organic phosphoric acids). One of the first substances examined was methanesulfonic acid fluoride, which was synthesized by Davies and Dick in England in 1932. This highly toxic compound was soon discarded as it is strongly absorbed by grain and food and poisoned them for a long time. In addition to methanesulfonic acid fluoride, aminosulfonic acid fluorides such as dimethylaminosulfonic acid fluoride, which has a weaker insecticidal effect, were also investigated.
At the same time, Schrader was also working on plasticizers based on organic phosphorus compounds. The synthesized substances (esters and amides of phosphoric acid) were also tested by Kükenthal for a possible insecticidal effect for the sake of completeness. Numerous substances unexpectedly turned out to be extremely effective. The systematic investigation of organic phosphorus compounds was then tackled. In analogy to methanesulfonic acid fluoride and the aminosulfonic acid fluorides, methanephosphonic acid (ester) fluorides and aminophosphoric acid (ester) fluorides were also investigated. Of the compounds initially prepared, dimethylaminophosphoric acid difluoride (as a P-analogue to dimethylaminosulfonic acid fluoride) proved to be only weakly insecticidal. In contrast, the dimethylaminophosphoric acid ethyl ester fluoride (fluorine tabun) showed a very strong effect. In 1936, replacement of the fluorine atom with a cyano radical led to the even more toxic dimethylaminophosphoric acid ethyl ester cyanide ( Tabun , Trilon 83, T 83). Tabun was the first compound of the so-called “Trilone”, which aroused considerable interest in specialist circles due to its unexpectedly high toxicity and was reported to the Army Weapons Office.
Methane phosphonic acid (ester) fluorides have also been produced as P analogs to methanesulfonic acid fluoride. In 1938 Schrader synthesized the methanephosphonic acid ethyl ester fluoride under the experiment number 113. Systematic structural modifications then led in 1939 to the synthesis of the far more toxic isopropyl methanephosphonate fluoride (T 144, Trilon 144, later T 46, Trilon 46, Sarin). Sarin proved to be an extraordinarily strong poison, the toxicity of which exceeded all compounds produced up to that point in its warm-blooded animals and was 3–4 times more toxic than tabun. This connection was also reported to the Army Weapons Office. The methane phosphonic acid isopropyl ester fluoride was given the code name Sarin, which was formed from letters of the names of the people involved in the discovery and large-scale technical development: S chrader, A mbros , R itter and von der L in de (the head of the "Heeresgasschutzlaboratoriums" in Spandau , where the Development was going on). In the older literature there is the false claim that instead of the chemist Gerhard Ritter ( Reichsamt für Wirtschaftsausbau ), Colonel Rüdiger from the gas protection department (Wa Prüf 9) in the Army Weapons Office was one of the namesake - without citing the source . This has been corrected in recent research.
The systematic structural modifications led to the synthesis of methanephosphonic acid pinacolyl ester fluoride ( soman ) in 1944 , the toxicity of which was about three times as high as that of sarin. In contrast to Tabun and Sarin, Soman was not developed by Gerhard Schrader, but by Nobel Prize winner Richard Kuhn and his colleague Konrad Henkel . Soman was a product of chemical weapons research; Tabun and sarin were not purely military-chemical developments.
The chosen collective name “Trilone” is said to have been used to mislead, as textile and dyeing aids were also on the market under this name. These were Trilon A (based on the sodium salts of nitrilotriacetic acid) and Trilon B (based on the sodium salts of ethylenediaminetetraacetic acid). Research in this area continued after the war. In 1949, methane phosphonic acid cyclohexyl ester fluoride ( cyclosarin ) was produced.
Sarin is structurally similar to the pesticides parathion (E605) and malathion and also to the warfare agents tabun, soman and VX . In July 1944, 30 tons of sarin were produced in German test factories; but these were never used in combat. Two large plants for mass production were under construction in Germany at the end of the Second World War . In addition to the plant in Dyhernfurth , which was mainly used for tabun production, it was decided in 1943 to build a new plant in Falkenhagen ( Falkenhagen bunker ). The reason was that while sarin was more difficult to make than tabun, it was better as a chemical weapon (it was more toxic and volatile). The supplies in the Dyhernfurth production facility in Silesia fell into the hands of the Red Army at the end of the war in 1945 . The latter had already learned about sarin through espionage in 1943 and synthesized it during the war in Kazan under the direction of Alexander Arbusow .
After the Second World War
Large quantities of sarin were stored in the United States and the Soviet Union during the Cold War . The UK admitted in 2003 that a Royal Air Force soldier had died while experimenting with sarin on humans in their poison gas laboratory in Porton Down , Wiltshire, in 1953 .
Sarin was also used in the Ghouta poison gas attacks on August 21, 2013 . In an attack on Chan Schaichun also Sarin was used on April 4, 2017 at 6:30 am, the Organization for the Prohibition of Chemical Weapons (OPCW) in its report of 29 June 2017. The use of sarin and chlorine gas in Ltamenah on On March 24th and 25th, 2017, the OPCW confirmed in June 2018.
Pure sarin is a colorless, almost odorless, relatively volatile liquid. It can be mixed with water in any ratio. In water, sarin decomposes depending on the pH value : at pH 7, the half-life of the hydrolysis of the ester is about 100 to 150 hours; In acidic solution the same amount decomposes in two hours, in alkaline solution in one hour. Technical sarin can sometimes be yellowish to brownish in color due to impurities and have a slightly fruity odor. In its highly pure form, however, it is almost odorless. Depending on the purity, the odor is described as a typical weak “ester odor”, which is supposed to be reminiscent of highly diluted ethyl acetate. In a series of tests, the odor could be perceived from a concentration in the range of around 1.5 mg / m 3 , although the odor could not be defined by the test persons at this concentration. The test persons also stated that odor recognition is unlikely. For comparison: Soman is said to have a stronger odor at the same concentration, which was individually described as camphor-like, musty and dull, spicy or even fruity.
In numerous human studies with sublethal doses of sarin, its effects on humans under a wide variety of conditions have been examined in detail. Accidents while handling sarin showed that inhaling high concentrations of sarin is extremely dangerous and can lead to unconsciousness and cramps within a few seconds, followed by respiratory arrest 1–2 minutes later. At lower concentrations, on the other hand, symptoms of poisoning develop much more slowly.
Mode of action
Nerve agents like sarin are lethal in very small amounts. The target area is the entire body, with absorption taking place in particular through the eyes , skin and respiratory organs ; The latter make up the main part, since sarin is highly volatile . Protection against the penetration of sarin into the body is therefore only offered by a full-body protective suit with a respirator .
The poisonous effect of sarin is based on an intervention in the transmission of excitation in the nerve tracts: an excitation is transmitted between two nerve cells by a neurotransmitter , which is transmitted through the synaptic gap from the "sender cell" ( presynaptic ending ) to the receptors of the "recipient cell " (postsynaptic region) arrives and thus passes the excitement on to the latter. Often the neurotransmitter is acetylcholine . Immediately after it has been released into the synaptic gap , the acetylcholine is broken down by the enzyme acetylcholinesterase , whereby the excitation is terminated and the recipient cell is available for the next transmission of excitation.
Sarin blocks the acetylcholine esterase in all synapses of the parasympathetic autonomic nervous system , in the acetylcholine-mediated synapses of the sympathetic and on the neuromuscular or motor endplates . This increases the acetylcholine level in the synaptic gap and all affected nervous systems are permanently excited.
Depending on the severity of the poisoning , the following symptoms occur: runny nose, visual disturbances, pupil constriction , eye pain, shortness of breath , salivation , muscle twitching , cramps , sweating, vomiting , uncontrollable stool , unconsciousness , central and peripheral respiratory paralysis and death. The effect on the eye occurs even at lower concentrations than the effect in the respiratory tract , so that accommodation disorders and constriction of the pupils can already be observed at concentrations and exposure times at which the other signs of intoxication are not yet noticeable.
Since the sarin, like other cholinesterase inhibitors, cannot be released from the blocked enzyme, or only very slowly, the treatment of poisoning with such warfare agents is extremely difficult.
Effects similar to those of sarin can also be seen with the chemically related warfare agents tabun, soman and VX as well as with poisoning with various insecticides such as parathion (E605), with sarin being around 1000 times more effective and thus more toxic than E605. The British warfare agent researcher Saunders pointed out at the time that the splitting off of the fluorine atom leads to a decrease in the toxicity of sarin. According to Saunders, dehydrofluorinated isopropylmethylphosphonic acid (IMPA) is a "non-toxic acid". This is also underlined by analyzes of the well-known sarin degradation products IMPA, methylphosphonic acid (MPA), diisopropylmethylphosphonic acid (DIMP), fluoride and methylphosphonyl difluoride. IMPA, MPA and DIMP show low toxicity in short and long term studies.
Protective measures and decontamination
Extensive freely accessible information is available on general protective measures, signs of the use of chemical warfare agents such as exposure to sarin, and decontamination.
Before using warfare agents, oxime tablets or carbamates such as pyridostigmine or physostigmine can be taken. In the case of poisoning, one injects atropine (see hyoscyamine , poison of the deadly nightshade), a parasympatholytic that is supposed to neutralize the effect of the excess acetylcholine at the receptors. In the course of the weeks of follow-up treatment, one can try to regenerate the acetylcholinesterase with an oxime . Obidoxime is preferred in German-speaking countries, while pralidoxime is preferred in Anglo-American countries .
For decontamination, both oxidizing agents such as chlorinated lime or calcium hypochlorite and alkaline solutions, but also non-aqueous media such as ethanolamine, can be used for decontamination, as nerve agents are sensitive to oxidizing agents and are easily hydrolyzed in a basic environment . Sodium carbonate solution can also be used on sensitive surfaces, but this naturally works more slowly.
Another possibility for decontamination is the use of suitable enzymes , which bring about rapid hydrolysis of this and other G-series warfare agents. One of these enzymes is DFPase ( diisopropyl fluorophosphatase , EC 18.104.22.168 ), an enzyme from the common squid Loligo vulgaris . The natural benefits of the enzyme are so far unknown. 105 µg of sarin are completely hydrolyzed in situ within 20 minutes .
Structure and manufacture
Sarin has a stereocenter on the phosphorus atom, so there are two enantiomers , one has an ( R ) configuration, the other has an ( S ) configuration. The manufacturing processes described here produce a racemic sarin, that is to say a 1: 1 mixture of the ( R ) -methylfluorophosphonic acid isopropyl ester and the ( S ) -methyl fluorophosphonic acid isopropyl ester.
By the action of methyl iodide ( 2 ) is removed from the phosphorous acid ester ( 1 () Diisopropylfluorphosphit ) in a Phosphonatsynthese the fluorine methyl phosphonic acid isopropyl ester Sarin ( 3 ) (+ 2-iodopropane ( 4 )) are prepared:
The American method of making sarin is based on the use of dimethyl methylphosphonate ( 1 ). This is converted with thionyl chloride to methylphosphonic acid dichloride ( 2 ) which, after fluorination with hydrofluoric acid , reacts to methylphosphonic acid difluoride ( 3 ):
The methylphosphonic acid difluoride can finally be converted to sarin by adding isopropanol :
When used in binary warfare projectiles, the last reaction above is used, in that methylphosphonic acid difluoride and isopropanol react to sarin after the grenades have been fired - with the aid of a reaction accelerator; the end product is formed after 10 seconds with a 70% yield.
The optical isomers of sarin were obtained from enantiomerically pure O -isopropyl-methylphosphonthiolic acid sodium salt [MeP (O) (SNa) (O i Pr)] and picryl fluoride (2,4,6-trinitrofluorobenzene) in methyl acetate ( acetone is less favorable as a solvent , since small amounts of diacetone alcohol that are difficult to separate by distillation are formed here). Optically active sarin is unstable in its pure form and racemizes completely within 20 hours at room temperature. Fluoride ions (e.g. in the form of ammonium fluoride ) catalyze the racemization very strongly. Rapid racemization also takes place in aqueous buffered solution (pH 4.5) . In contrast, dilute solutions of sarin (0.1–0.14 mol / l) in dry isopropanol, acetone or methyl acetate are stable for several weeks.
The optical isomers differ greatly in their toxicity. The main active enantiomer is (-) - sarin, which is around two times more toxic than (±) - sarin, while (+) - sarin is rapidly enzymatically degraded by the sarinase. The table shows the toxicological data of the two enantiomers [( S ) -sarine and ( R ) -sarine] and of the racemate [1: 1 mixture of ( S ) -sarine and ( R ) -sarine] and for comparison corresponding values of Tabun and VX under analogous conditions.
Toxicity of sarin, tabun and VX in mice after intravenous administration:
|Substance or isomer||LD 50 (mouse, µg / kg, iv)|
|(±) -Sarin [( RS ) -Sarin]||83|
|(-) - Sarin [( S ) -Sarin]||41|
|(+) - Sarin [( R ) -Sarin]||not available|
|(±) -Tabun [( RS ) -Tabun]||208|
|(-) - Tabun [( S ) -Tabun]||119|
|(+) - Tabun [( R ) -Tabun]||837|
|(±) -VX [( RS ) -VX]||20.1|
|(-) - VX [( S ) -VX]||12.6|
|(+) - VX [( R ) -VX]||165|
The substance can be reliably identified by suitable sample preparation and subsequent gas chromatography or high-performance liquid chromatography coupled with mass spectrometry . Both urine and blood samples can be used to reliably detect exposure to sarin. As a rule, the metabolites such as B. the alkyl methylphosphonic acids isolated with adequate sample preparation and optionally derivatized for GC-MS analysis .
The safe and reliable destruction of chemical warfare agents such as sarin and the like is tied to expensive and time-consuming procedures. The main methods apply hydrolytic and / or catalytic processes, mostly at high temperatures and with the use of strong oxidizing agents such as e.g. B. hydrogen peroxide .
As a chemical on list 1 in the international disarmament treaty CWC, sarin is controlled by the competent authority, the Organization for the Prohibition of Chemical Weapons (OPCW), based in The Hague . Manufacture or possession is prohibited; This does not apply to work that only serves to protect against these substances or for research. In Germany, any non-governmental handling of sarin must be approved by the Federal Office of Economics and Export Control (BAFA) and reported to the OPCW.
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