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| Names | |
|---|---|
| Preferred IUPAC name Methyl fluoroacetate | |
Other names
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| Identifiers | |
3D model (JSmol) | |
| ChemSpider | |
| ECHA InfoCard | 100.006.563 |
| EC Number |
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| UNII | |
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| Properties | |
| FCH2CO2CH3 | |
| Molar mass | 92.069 g·mol−1 |
| Appearance | Colorless liquid |
| Odor | Odorless or faint fruity |
| Melting point | −40 °C (−40 °F; 233 K) |
| Boiling point | 104 °C (219 °F; 377 K) |
| 117 g/L at 25 °C | |
| Hazards | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Extremely toxic |
| GHS labelling: | |
    | |
| Danger | |
| H226,H300,H315,H319,H335,H400 | |
| P210,P233,P240,P241,P242,P243,P261,P264,P270,P271,P273,P280,P301+P310,P302+P352,P303+P361+P353,P304+P340,P305+P351+P338,P312,P321,P330,P332+P313,P337+P313,P362,P370+P378,P391,P403+P233,P403+P235,P405,P501 | |
| Flash point | −32 °C (−26 °F; 241 K) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) | 6 mg/kg (mice) |
| Related compounds | |
Related compounds | |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Methyl fluoroacetate (MFA) is anorganic compound with thechemical formulaFCH2CO2CH3. It is the extremely toxicmethylester offluoroacetic acid. It is a colorless, odorless liquid at room temperature. It is used as a laboratory chemical and as arodenticide. Because of its extreme toxicity, MFA was studied for potential use as achemical weapon.[1]
The general population is not likely to be exposed to methyl fluoroacetate. People who use MFA for work, however, can breathe in or have direct skin contact with the substance.[2]
MFA was first synthesized in 1896 by the Belgian chemistFrédéric Swarts by reactingmethyl iodoacetate withsilver fluoride. It can also be synthesized by reactingmethyl chloroacetate withpotassium fluoride[1]
Because of its toxicity, MFA was studied for potential use as achemical weapon duringWorld War II. It was considered a good waterpoison since it is colorless and odorless and therefore it can toxify the water supply and kill a big part of the population. By the end of the war, several countries began to make methyl fluoroacetate to debilitate or kill the enemy.[2]
The synthesis of methyl fluoroacetate consists of a two-step process:[3]
Methyl fluoroacetate is a methylester offluoroacetic acid.
MFA is a liquid, which is odorless or can have a faint, fruity smell. The boiling point of MFA is 104.5 °C and the melting point is −35.0 °C. It is soluble in water (117 g/L at 25 °C) and slightly soluble in petroleum ether.[2]
MFA is resistant to the displacement offluorine bynucleophiles, so there is higher stability of theC−F bond compared to the otherhalogens (C−Cl,C−Br,C−I). The other haloacetates are more powerfulalkylating agents that react with−SH group ofproteins. This, however, does not happen for MFA and gives it a unique toxic action.[2] Moreover, MFA is a derivative offluoroacetate (FA) compound which is as toxic and has similarbiotransformation to MFA.
Generally, fluoroacetates are toxic because they are converted tofluorocitrate byfluoroacetyl coenzyme A. Fluorocitrate can inhibitaconitate hydratase, which is needed for the conversion ofcitrate, bycompetitive inhibition.[4] This interrupts thecitric acid cycle (TCA cycle) and also causes citrate to accumulate in the tissues and eventually in the plasma.[clarification needed] MFA is mainly biotransformed byglutathione transferaseenzyme in aphase 2 biotransformation process. The GSH-dependent enzyme couples glutathione to MFA and therebydefluorinating MFA.[clarification needed] As a result, afluorideanion andS-carboxymethylglutathione are produced. The decoupling of fluoride is mediated by afluoroacetate-specific defluorinase.[clarification needed] The defluorinating activity is mainly present in theliver, but alsokidneys,lungs, theheart, and thetesticles show activity. In thebrain, there are no signs of defluorination. Eventually,fluorocitrate (FC) is formed which is the main toxic compound. It binds theaconitase enzyme with a very high affinity and therefore intervenes in the TCA cycle. Citrate in normal circumstances is converted tosuccinate, but the process is inhibited. The cycle stops andoxidative phosphorylation is prevented sinceNADH,FADH2 and succinate are required from the TCA cycle. Respiration stops shortly. The poison acts very quickly and has noantidote.
Mammals are intolerant to MFA. However, a fewAustralian species (e.g.brush-tailed possum) show a level of tolerance to fluoroacetate bymetabolizing it usingglutathione-S-transferase.[5] Fluoride can be removed from fluoroacetate or fluorocitrate. It is involved in detoxifying thearyl andalkyl groups by converting them intoglutathione conjugates. TheC−F bond iscleaved because of anucleophilic attack ofcarbon resulting in the formation ofS-carboxymethyl glutathione. This can be afterward excreted in the form ofS-carboxymethylcysteine.[5]
The eliminationhalf-life of biotransformed MFA is about 2 days. When administered, the MFA mainly resides inblood plasma, but can also be traced in the liver, kidney, andmuscle tissue.[6]
MFA is aconvulsant poison. It causes severeconvulsions in poisoned victims.[7] Death results fromrespiratory failure.[6]
For a variety of animals, the toxicity of methyl fluoroacetate has been determined orally and through subcutaneous injection. The dosage ranges from 0.1 mg/kg in dogs to 10–12 mg/kg in monkeys indicating considerable variation. An order of decreasing susceptibility has been determined within these animals which is: dog, guinea-pig, cat, rabbit, goat, and then likely horse, rat, mouse, and monkey. For the rat and mouse, the toxicity by inhalation has been investigated more fully than for other animals. TheLD50 for the rat and mouse are 450 mg/m3 and above 1,000 mg/m3 for 5 minutes, respectively. In dogs, guinea-pigs, cats, rabbits, goats, horses, rats, mice, and monkeys, the pharmacological effects of this substance have been investigated by mouth and by injection. Methyl fluoroacetate causes progressive depression of respiration and is a convulsant poison in most animals. When applied to the skin it is not toxic, yet through inhalation, injection and by mouth it is. For the rat, cat and the rhesus monkey, the effects of methyl fluoroacetate have been determined similar to those ofnicotine,strychnine,leptazol,picrotoxin, and electrically induced convulsions. The convulsive pattern is considered to be similar to that of leptazol. Little besides signs ofasphyxia is found post-mortem in these animals. Estimations have been made for blood sugar, hemoglobin, plasma proteins, non-protein nitrogen, and serum potassium, calcium, chloride, and inorganic phosphate in a small number of rabbits, dogs, and goats. Blood changes include a rise of 20 to 60% in hemoglobin, a rise of up to 90% in blood sugar, a rise of 70 to 130% in inorganic phosphate, and a less significant rise in serum potassium with a terminal rise in non-protein nitrogen and potassium. The whole central nervous system is affected by methyl fluoroacetate just like with leptazol, with the higher centers being more sensitive than the lower ones. Small doses of methyl fluoroacetate have little effect on blood pressure yet in large doses it has an action similar to nicotine. It further stimulates the rate and volume of respiration and then causes failure of the respiration, probably central in origin as seen through graphic records. The knee jerk reaction appears to be accentuated through methyl fluoroacetate until convulsions occur due to the irradiation of the stimuli being so facilitated. Nervous conduction is increased and the threshold stimulus lessened in the reflex arc of a spinal cat. Methyl fluoroacetate reduces the electric convulsive threshold about 10 times in rats. The difficulties of treatments are stressed as methyl fluoroacetate is both a powerful convulsant and a respiratory depressant, yet suggestions for treatment in man are made. Methyl fluoroacetate presents a serious hazard as a food and water contaminant in the case that it is used as a poison against rodents and other vermin, as it is not easily detected or destroyed and is equally toxic by mouth and by injection.[6]
Methyl fluoroacetate is produced and used as a chemical reagent and it can be released to the environment through several waste streams. When it was used as a rodenticide, it was released directly to the environment where it would be broken down in the air. If released to air, an estimated vapor pressure of 31mmHg at 25 °C indicates methyl fluoroacetate will exist solely as a vapor in the atmosphere.[2] Vapor-phase methyl fluoroacetate will be degraded in the atmosphere by reaction with photochemically produced hydroxyl radicals. The half-life for this reaction in air is estimated to be 98 days.
MFA does not containchromophores that absorb at wavelengths > 290 nm and therefore it's not expected to be susceptible to directphotolysis bysunlight.[2]
The effects on animals occur very rapidly and strongly, all resulting in death. Exposure to a high concentration of MFA vapor does not show any symptoms in animals until 30–60 minutes.[6] Then violent reactions and death took place in a few hours, according to studies. From intravenous injection mice, rats, and guinea pigs show symptoms after 15 min to 2 hours. The animals become quiet and limp. Rabbits show a similar latent time period and muscle weakness.[6] Dogs show symptoms of hyperactivity. They are more sensitive because of higher rates of metabolism and, eventually, they also fail to respirate. Fish are more resistant because of slow metabolism[4] and therefore it is not expected that the substance will build up in fish. Also, Australian herbivores (e.g. possum and seed-eating birds) that live in a habitat consisting of plants with traces of fluoroacetate, have some tolerance. This can happen by detoxifying fluoroacetate or more resistivity of aconitase to fluorocitrate in the presence of GSH. Some insects can store the toxin in vacuoles and use it later.[4] The highly hazardous MFA cannot be used for poisoning animals without risking human life.
There is no knownantidote against MFA, but there are some suggestions regarding the treatment of MFA poisoning. Advised is to use an intravenous injection of fast-acting anesthetics directly after poisoning. The anesthetic should be pentothal sodium or evipan sodium followed by an intramuscular injection of long-acting cortical depressants like sodium phenobarbitone or rectal avertin. Afterward, careful supervision of oxygen supply is necessary together with a BLB mask[clarification needed] and the use of artificial respiration. Possibly, the use of hypertonic glucose intravenously is required as in status epilepticus. At last, careful use oftubocurarine chloride should be applied to control any convulsions.[6] If any vomiting occurs, lean the patient forward to maintain an open airway.
Alternatively, there is a therapy aimed at the prevention of fluorocitrate synthesis, the blocking of aconitase within the mitochondria, and to provide a citrate outflow from the mitochondria to keep theTCA cycle going. For now, ethanol has proven to be the most effective against FC formation. When ethanol is oxidized, it increases blood acetate levels which inhibits FC production. In humans, an oral dose of 40-60 mL 96% ethanol is advised followed by 1.0-1.5 g/kg of 5-10% ethanol intravenously during the first hour and 0.1 g/kg during the following 6–8 hours. This therapy is meant for fluoroacetate (FA) poisoning which is highly related MFA, so this therapy aimed at MFA may result in other outcomes.[8]
Treatment withmonoacetin (glycerol monoacetate) helped against FA poisoning. It aids in increasing acetate levels of the blood and it decreases citrate levels in the heart, brain, and kidneys. However, this is only tested experimentally. In monkeys, monoacetin even reverses the effects of FA: all biological effects normalized.[8] As with ethanol, monoacetin is effective against FA poisoning.
There is up until now, no proven treatment against MFA. However, the beforementioned treatments can provide starting points for therapy aimed at MFA since FA and MFA are closely related compounds.[8]