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| Names | |||
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| Preferred IUPAC name Iodomethane[1] | |||
Other names
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| Identifiers | |||
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3D model (JSmol) | |||
| Abbreviations |
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| 969135 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.000.745 | ||
| EC Number |
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| 1233 | |||
| KEGG |
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| MeSH | methyl+iodide | ||
| RTECS number |
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| UNII | |||
| UN number | 2644 | ||
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| Properties | |||
| CH3I | |||
| Molar mass | 141.939 g·mol−1 | ||
| Appearance | Colorless liquid | ||
| Odor | Pungent, ether-like[2] | ||
| Density | 2.28 g/mL | ||
| Melting point | −66.5 °C; −87.6 °F; 206.7 K | ||
| Boiling point | 42.4 to 42.8 °C; 108.2 to 108.9 °F; 315.5 to 315.9 K | ||
| 14 g/L (at 20 °C, 68 °F)[3] | |||
| logP | 1.609 | ||
| Vapor pressure | 54.4 kPa (at 20 °C, 68 °F) | ||
Henry's law constant (kH) | 1.4 μmol/(Pa·kg) | ||
| −57.2×10−6 cm3/mol | |||
Refractive index (nD) | 1.530–1.531 | ||
| Structure | |||
| Tetrahedron | |||
| Thermochemistry | |||
| 82.75 J/(K·mol) | |||
Std enthalpy of formation(ΔfH⦵298) | −14.1 to −13.1 kJ/mol | ||
Std enthalpy of combustion(ΔcH⦵298) | −808.9 to −808.3 kJ/mol | ||
| Hazards | |||
| GHS labelling: | |||
  | |||
| Danger | |||
| H301,H312,H315,H331,H335,H351 | |||
| P261,P280,P301+P310,P311 | |||
| NFPA 704 (fire diamond) | |||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) |
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LC50 (median concentration) |
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LCLo (lowest published) | 3800 ppm (rat,15 min)[4] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA5 ppm (28 mg/m3) [skin][2] | ||
REL (Recommended) | Ca TWA2 ppm (10 mg/m3) [skin][2] | ||
IDLH (Immediate danger) | Ca [100 ppm][2] | ||
| Related compounds | |||
Related iodomethanes | |||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
Iodomethane, also calledmethyl iodide, and commonly abbreviated "MeI", is thechemical compound with the formulaCH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related tomethane by replacement of onehydrogen atom by an atom ofiodine. It is naturally emitted in small amounts by rice plantations.[5] It is also produced in vast quantities estimated to be greater than 214,000 tons annually by algae and kelp in the world's temperate oceans, and in lesser amounts on land by terrestrial fungi and bacteria. It is used inorganic synthesis as a source ofmethyl groups.
Iodomethane is formed via theexothermic reaction that occurs when iodine is added to a mixture ofmethanol withred phosphorus.[6] The iodinating reagent isphosphorus triiodide that is formedin situ:
Alternatively, it is prepared from the reaction ofdimethyl sulfate with potassium iodide in the presence ofcalcium carbonate:[6]
Iodomethane can also be prepared by the reaction of methanol with aqueoushydrogen iodide:
The generated iodomethane can be distilled from the reaction mixture.
Iodomethane may also be prepared by treatingiodoform withpotassium hydroxide and dimethyl sulfate under 95%ethanol.[7]
In theTennessee Eastman acetic anhydride process iodomethane is formed as an intermediate product by a catalytic reaction betweenmethyl acetate andlithium iodide.
Like many organoiodide compounds, iodomethane is typically stored in dark bottles to inhibit degradation caused by light to give iodine, giving degraded samples a purplish tinge. Commercial samples may be stabilized by copper or silver wire.[8] It can be purified by washing withNa2S2O3 to remove iodine followed by distillation.[9]
Most iodomethane is produced by microbial methylation of iodide. Oceans are the major source, but rice paddies are also significant.[10]
Iodomethane is useful as a reagent formethylation because it is excellent substrate forSN2 substitution reactions. It issterically open for attack bynucleophiles, and iodide is a goodleaving group. It is used for alkylating carbon, oxygen, sulfur, nitrogen, and phosphorus nucleophiles.[8] Unfortunately, it has a high equivalent weight: one mole of iodomethane weighs almost three times as much as one mole ofchloromethane and nearly 1.5 times as much as one mole ofbromomethane. On the other hand, chloromethane and bromomethane are gaseous, thus harder to handle, and are also weaker alkylating agents. Iodide can act as a catalyst when reacting chloromethane or bromomethane with a nucleophile while iodomethane is formed insitu.
Iodides are generally expensive relative to the more common chlorides and bromides, though iodomethane is reasonably affordable; on a commercial scale, the more toxic dimethyl sulfate is preferred, since it is cheap and has a higher boiling point. The iodide leaving group in iodomethane may cause unwanted side reactions. Finally, being highly reactive, iodomethane is more dangerous for laboratory workers than related chlorides and bromides.[citation needed]
For example, it can be used for the methylation ofcarboxylic acids orphenols:[11]
In these examples, the base (K2CO3 orLi2CO3) removes the acidic proton to form thecarboxylate orphenoxide anion, which serves as the nucleophile in the SN2 substitution.[citation needed]
Iodide is asoft anion, which means that methylation with MeI tends to occur at the softer end of anambidentate nucleophile. For example, reaction withthiocyanate ion favours attack by the softer sulfur rather than harder nitrogen, leading mainly tomethyl thiocyanate (CH3SCN) rather thanmethyl isothiocyanate (CH3NCS). This behavior is relevant to the methylation of stabilizedenolates such as those derived from 1,3-dicarbonyl compounds. Methylation of these and related enolates can occur on the harder oxygen atom or the softer carbon atom. With iodomethane, C-alkylation nearly always predominates. The result is a pracical method for carbon–carbon bond formation rather than givingenol ethers.[citation needed]
In theMonsanto process and theCativa process, MeI formsin situ from the reaction of methanol and hydrogen iodide. TheCH3I then reacts withcarbon monoxide in the presence of arhodium oriridium complex to formacetyl iodide, the precursor toacetic acid afterhydrolysis. The Cativa process is usually preferred because less water is required to use and there are less byproducts.[citation needed]
MeI is used to preparemethylmagnesium iodide (MeMgI), aGrignard reagent that is a common source ofMe− for nucleophilic reactions. The use of MeMgI has been somewhat superseded by the commercially availablemethyllithium. MeI can also be used to preparedimethylmercury, by reacting 2 moles of MeI with a 2/1-molar sodiumamalgam (2 moles of sodium, 1 mol of mercury).[citation needed]
Iodomethane and otherorganoiodine compounds form under the conditions of serious nuclear accidents.[12] After theChernobyl disaster andFukushima Daiichi nuclear disaster,iodine-131 was detected in organoiodine compounds in Europe[13] and Japan[14] respectively.[improper synthesis?]
Trideuteroiodomethane (CD3I) is anisotopologue of iodomethane in which the three hydrogen atoms aredeuterium atoms (2H rather than1H). Due to the value of the trideuteromethyl group inmedicinal chemistry,CD3I is a useful reagent for synthesizing potentially biologically active chemicals. Several specialized reactions have been developed for its use under especially mild reaction conditions on a variety of substrates.[15]
Iodomethane had also been proposed for use as afungicide,herbicide,insecticide,nematicide, and as a soil disinfectant, replacing methyl bromide (also known asbromomethane) (banned under theMontreal Protocol). Manufactured by Arysta LifeScience and sold under the brand name MIDAS, iodomethane is registered as a pesticide in the U.S., Mexico, Morocco, Japan, Turkey, and New Zealand and registration is pending in Australia, Guatemala, Costa Rica, Chile, Egypt, Israel, South Africa and other countries.[16]
Iodomethane was approved for use as apesticide by theUnited States Environmental Protection Agency in 2007 as a pre-plantbiocide used to control insects, plant parasitic nematodes, soil borne pathogens, and weed seeds. The compound was registered for use as a preplant soil treatment for field grown strawberries, peppers, tomatoes, grape vines, ornamentals and turf and nursery grown strawberries, stone fruits, tree nuts, and conifer trees.[9]
The use of iodomethane as a fumigant has drawn concern. For example, 54 chemists and physicians contacted the U.S. EPA in a letter, saying "We are skeptical of U.S. EPA's conclusion that the high levels of exposure to iodomethane that are likely to result from broadcast applications are 'acceptable' risks. U.S. EPA has made many assumptions about toxicology and exposure in the risk assessment that have not been examined by independent scientific peer reviewers for adequacy or accuracy. Additionally, none of U.S. EPA's calculations account for the extra vulnerability of the unborn fetus and children to toxic insults."[17][better source needed] EPA Assistant Administrator Jim Gulliford replied with a letter detailing the risk analysis performed and the procedures for approval, concluding, "We are confident that by conducting such a rigorous analysis and developing highly restrictive provisions governing its use, there will be no risks of concern,"[18] and in October 2007 the EPA approved the use of iodomethane as a soil fumigant in the United States.[19]
The California Department of Pesticide Regulation (DPR) concluded that iodomethane is "highly toxic," that "any anticipated scenario for the agricultural or structural fumigation use of this agent would result in exposures to a large number of the public and thus would have a significant adverse impact on the public health", and that adequate control of the chemical in these circumstances would be "difficult, if not impossible."[20] Iodomethane was approved as a pesticide in California in December of 2010.[21] A lawsuit was filed on January 5, 2011, challenging California's approval of iodomethane.[22] The first commercial applications of iodomethane soil fumigant in California began in Fresno County in May 2011.[23] Subsequently, the manufacturer withdrew the fumigant and requested that California Department of Pesticide Regulation cancel its California registration, citing its lack of market viability.[24]
According to theUnited States Department of Agriculture iodomethane exhibits moderate to high acute toxicity for inhalation and ingestion.[25] TheCenters for Disease Control and Prevention (CDC) lists inhalation, skin absorption, ingestion, and eye contact as possible exposure routes with target organs of the eyes, skin, respiratory system, and thecentral nervous system. Symptoms may include eye irritation, nausea, vomiting, dizziness,ataxia, slurred speech, anddermatitis.[26] In high dose acute toxicity, as may occur in industrial accidents, toxicity includes metabolic disturbance, renal failure, venous and arterial thrombosis and encephalopathy with seizures and coma, with a characteristic pattern of brain injury.[27]
Iodomethane has anLD50 for oral administration to rats76 mg/kg, and is rapidly converted in the liver toS-methylglutathione.[28]
In its risk assessment of iodomethane, the U.S. EPA conducted an exhaustive scientific and medical literature search over the past 100 years for reported cases of human poisonings attributable to the compound.[citation needed] Citing the EPA as its source, the California Department of Pesticide Regulation said: "Over the past century, only 11 incidents of iodomethane poisoning have been reported in the published literature."[29][30] "An updated literature search on May 30, 2007 for iodomethane poisoning produced only one additional case report."[31] All but one were industrial—not agricultural—accidents, and the remaining case of poisoning was an apparent suicide. Iodomethane is routinely and regularly used in industrial processes as well as in most university and college chemistry departments for study and learning related to a variety of organic chemical reactions.[citation needed]
In 2024, a case of a person being injected with iodomethane emerged. The subject, who was the victim of attempted murder by ageneral practitioner disguised as a community nurse, went on to developnecrotizing fasciitis but survived.[32]
The U.S.National Institute for Occupational Safety and Health (NIOSH), the U.S.Occupational Safety and Health Administration and the U.S.Centers for Disease Control and Prevention consider iodomethane a potential occupational carcinogen.[33]
TheInternational Agency for Research on Cancer concluded based on studies performed after methyl iodide was put on theProposition 65 list that: "Methyl iodide is not classifiable as to its carcinogenicity to humans (Group 3)."[citation needed] As of 2007[update] theEnvironmental Protection Agency classifies it as "not likely to be carcinogenic to humans in the absence of altered thyroid hormone homeostasis," i.e. it is a human carcinogen but only at doses large enough to disrupt thyroid function (via excess iodide).[34] However this finding is disputed by thePesticide Action Network, which states that the EPA's assessment "appears to be based solely on a single rat inhalation study in which 66% of the control group and 54–62% of the rats in the other groups died before the end of the study". They go on to state: "The EPA appears to be dismissing early peer-reviewed studies in favor of two nonpeer-reviewed studies conducted by the registrant that are flawed in design and execution."[35] Despite requests by the U.S. EPA to thePesticide Action Network to bring forth scientific evidence of their claims, they have not done so.[citation needed]
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