Iodomethane , also known as methyl iodide , and commonly abbreviated “MEI”, is the chemical compound with the formula CH3I . It is a dense , colourless, volatile liquid. In terms of chemical structure, it is related to methane by the replacement of one hydrogen atom by one atom of iodine . It is naturally excreted in small amounts by rice plantations. [5]It is estimated to be carried by algae and kelp in the world’s temperate oceans to more than 214,000 tonnes annually, and is produced in small amounts on land by terrestrial fungi and bacteria. it is used in Organic synthesis as a source of methyl groups .
Preparation and handling
Iodomethane is formed through the exothermic reaction that occurs when iodine is added to a mixture of methanol with red phosphorus. [6] The iodizing reagent is phosphorus triiodide which forms in situ :
3 CH 3 OH + PI 3 → 3 CH 3 I + H 2 PO 3 H
Alternatively, it is prepared by the reaction of dimethyl sulfate with potassium iodide in the presence of calcium carbonate: [6](CH 3 O) 2 SO 2 + KI → CH 3 I + CH 3 OsO 2 OK
Iodomethane can also be prepared by the reaction of methanol with aqueous hydrogen iodide:CH 3 OH + HI → CH 3 I + H 2 O
The generated iodomethane can be distilled from the reaction mixture.
Iodomethane can also be prepared by treating iodoform with potassium hydroxide and dimethyl sulfate under 95% ethanol. [7]
Storage and purification
Like many organoid compounds, iodomethane is usually stored in dark bottles to prevent corrosion caused by light to give iodine, giving the degraded samples a purple color. Commercial specimens can be stabilized with copper or silver wire. [8] It can be purified by washing with Na 2 S 2 O 3 to remove iodine and distillation.
Biogenic iodomethane
Most iodomethane is produced by microbial methylation of iodide. Oceans are the major source, but rice paddies are also important.
Reactions
Methylation reagent
Iodomethane is an excellent substrate for Sn2 substitution reactions. It is sterically open to attack by nucleophiles, and iodide is a good leaving group. It is used to alkylate carbon, oxygen, sulfur, nitrogen and phosphorus nucleophiles. [8] Unfortunately, it has a high equivalent weight: a mole of iodomethane weighs almost three times as much as a mole of chloromethane and about 1.5 times as much as a mole of bromomethane. On the other hand, chloromethane and bromomethane are gaseous to handle, thus harder, and are also weak alkylating agents. Iodide can act as a catalyst when reacting chloromethane or bromomethane with a nucleophile while iodomethane is formed in situ .
Iodides are generally more expensive relative to the more common chlorides and bromides, although iodomethane is reasonably inexpensive; On a commercial scale, the more toxic dimethyl sulfate is preferred, as it is cheaper and has a higher boiling point. The iodide leaving group in iodomethane may cause unwanted side effects. Finally, being highly reactive, iodomethane is more dangerous to laboratory workers than the related chlorides and bromides. For example, it can be used for the methylation of carboxylic acids or phenols:
In these examples, the base (K 2 CO 3 or Li 2 CO 3 ) removes the acidic proton to form the carboxylate or phenoxide ion, which acts as a nucleophile in the SN 2 substitution .
Iodide is a “soft” anion which means that methylation with MeI occurs at the “soft” end of a bivalent nucleophile. For example, the reaction with the thiocyanate ion favors the attack on S instead of the “hard” N, leading to methyl thiocyanate (CH 3 SCN) instead of the predominantly methyl isothiocyanate CH 3 NCS. This behavior is relevant for the methylation of stable enolates such as those derived from 1,3-dicarbonyl compounds. Methylation of these and related enolates can occur at the rigid oxygen atom or (usually desired) the carbon atom. With iodomethane, C-alkylation almost always predominates.
Other reactions
In the Monsanto process and the Cativa process, MEI forms by in situ reaction of methanol and hydrogen iodide. CH 3 I then reacts with carbon monoxide in the presence of rhodium or iridium complexes to form acetyl iodide, which is a precursor to acetic acid after hydrolysis. The Cativa process is generally preferred because it requires less water to use and has fewer byproducts.
MeI is used to prepare Grignard reagent, methylmagnesium iodide (“MeMgI”), a common source of ” Me-“. The use of MeMgI has been somewhat superseded by commercially available methyllithium. MeI can also be used to prepare dimethylmercury, a 2/1-molar mixture by reacting 2 mol of MeI with sodium (2 mol of sodium, 1 mol of mercury). Iodomethane and other organic iodine compounds are formed in the event of a serious nuclear accident, [11] after both Fukushima and Chernobyl iodine-131 were found as organic iodine compounds in Europe [12] and Japan [13] respectively .
Use as insecticide
Iodomethane was also proposed for use as a fungicide, herbicide, insecticide, nematide and a soil disinfectant, replacing methyl bromide (also known as bromomethane) (banned under the Montreal Protocol). Manufactured by Arista Lifescience and sold under the brand name MIDAS, iodomethane is registered as an insecticide in the US, Mexico, Morocco, Japan, Turkey and New Zealand and is pending registration in Australia, Guatemala, Costa Rica, Chile, Egypt, Israel . , South Africa and other countries. [14] The first commercial application of MIDAS soil fumigant in California began in Fresno County in May 2011. [ citation needed ]
Iodomethane was approved for use by the United States Environmental Protection Agency in 2007 as an insecticide, a pre-treatment used to control insects, plant parasitic nematodes, soil-borne pathogens, and weed spores. -Plant was in the form of biocide. [15] The compound is registered for use as a preplant soil treatment for field-grown strawberries, peppers, tomatoes, vines, ornamental and turf and nursery-grown strawberries, stone fruits, tree nuts and coniferous trees had gone. After the discovery phase in a consumer lawsuit, the manufacturer withdrew Fumigant, citing a lack of viability in the market.
The use of iodomethane as a fumigant has caused concern. For example, 54 chemists and physicians contacted the US EPA in a letter saying, “We suspect the conclusion of the US EPA that exposure to high levels of iodomethane that would likely result in broadcast applications was ‘acceptable’.” There are risks. The US EPA has made several assumptions about risk in toxicology and risk assessment that have not been examined by independent scientific peer reviewers for adequacy or accuracy. Additionally, any calculation of the US EPA may not be applicable to the unborn fetus and the unborn fetus. does not account for children’s additional vulnerability to toxic insults.” [17]“We are confident that conducting such a rigorous analysis and developing highly restrictive provisions governing its use will pose no risk of concern,” EPA assistant administrator Jim Gulliford responded, and in October the EPA approved the use of iodomethane. As a soil fumigant in the United States.
The California Department of Pesticide Regulation (DPR) concluded that iodomethane is “highly toxic”, adding that “any anticipated scenario for agricultural or structural fumigation use of this agent would result in a risk to a large number of the public and thus a significant adverse effects on public health”, and adequate control of the chemical under these circumstances would be “impossible if not difficult”. [18] Iodomethane was approved as an insecticide in California that December. [19]A lawsuit was filed on 5 January 2011 challenging California’s acceptance of iodomethane. Subsequently, the manufacturer withdrew the fumigant and requested that the California Department of Pesticide Regulation cancel its California registration, citing a lack of viability in the market. [16]
Security
Toxicity and biological effects
Iodomethane exhibits moderate to high acute toxicity to inhalation and ingestion, according to the United States Department of Agriculture. [20] The Centers for Disease Control and Prevention (CDC) lists inhalation, skin absorption, ingestion, and eye contact as potential exposure routes with target organs of the eyes, skin, respiratory system, and central nervous system. Symptoms may include eye irritation, nausea, vomiting, dizziness, ataxia, slurred speech and dermatitis. [21] Acute poisoning in high doses, as may occur in industrial accidents, includes encephalopathy with seizures and coma with a characteristic pattern of metabolic disturbances, renal failure, venous and arterial thrombosis and brain injury.
Iodomethane has an LD50 of 76 mg/kg for oral administration to rats, and in the liver it undergoes rapid conversion to S-methyl glutathione.
In its risk assessment of iodomethane, the US EPA conducted an exhaustive scientific and medical literature search over the past 100 years for reported cases of human toxicity due to the compound. Citing the EPA as its source, the California Department of Pesticide Regulation concluded, “In the past century, only 11 incidents of iodomethane poisoning have been reported in the published literature.” (Hermoet, C. et al. 1996 and Appel, GB et al. 1975) “An updated literature search for iodomethane poisoning on May 30, 2007 produced only one additional case report.” (Schwartz MD, et al.2005). All accidents except one were industrial—not agricultural—accidents, and the remaining case of poisoning was an apparent suicide. Iodomethane is routinely and routinely used in industrial processes as well as in most university and college chemistry departments for study and learning related to various organic chemical reactions.
Carcinogenicity in mammals
It is considered a potential occupational carcinogen by the US National Institute for Occupational Safety and Health (NIOSH), the US Occupational Safety and Health Administration and the US Centers for Disease Control and Prevention. [24] The International Agency on Cancer Research concluded on the basis of studies performed after methyl iodide was listed in Proposition 65: “Methyl iodide is not classified as to its carcinogenicity to humans (Group 3).” As of 2007 the Environmental Protection Agency classified it as “unlikely to be carcinogenic to humans in the absence of thyroid hormone homeostasis,” i.e. it is a human carcinogen, but only at doses large enough for thyroid function (of excess iodide). through) to interrupt. [25]However this finding is disputed by the Pesticide Action Network which states that the EPA’s cancer rating “appears to be based on only one rat inhalation study involving 66% of the control group and 54–62% of the other rats before the end of the study.” groups died”. They continue: “The EPA appears to be rejecting initial peer-reviewed studies in favor of two non-peer-reviewed studies conducted by registrants that were flawed in design and execution.” [26] Despite the US EPA’s request to the Pesticide Action Network to provide scientific evidence for their claims, they have not done so.
