Iodomethane – preparation and application

Iodomethane [74-88-4] or methyl iodide a dense, colorless, volatile liquid with the melting point of 41-43 °C. ^[1] It is typically stored in dark bottles to inhibit degradation caused by light. Iodomethane exhibits moderate to high acute toxicity and cancerogenity for inhalation and ingestion.^[2] It has an LD50 for oral administration to rats 76 mg/kg, and in the liver it undergoes rapid conversion to S-methylglutathione.^[3]

Preparation of Iodomethane:

Iodomethane is formed in the exothermic reaction that occurs when iodine is added to a mixture of methanol with red phosphorus via the in situ formed iodinating reagent phosphorus triiodide. Alternatively, it can be prepared from the reaction of dimethyl sulfate with potassium iodide in the presence of calcium carbonate.^[4] Iodomethane can also be prepared by the reaction of methanol with aqueous hydrogen iodide. Biogenic iodomethane is produced by microbial methylation of iodide in the oceans (300 000 tons per year), in the rice paddies and biomass burning (214 000 tons per year).^[5]

Application:

It is used in organic synthesis as a source of methyl groups for alkylating carbon, oxygen, sulfur, nitrogen, and phosphorus nucleophiles. Methyl iodide forms in situ from the reaction of methanol and hydrogen iodide in the Monsanto and the Cativa processes to produce acetic acid. Iodomethane then reacts with carbon monoxide in the presence of a rhodium or iridium complex to form acetyl iodide, the precursor to acetic acid after hydrolysis.^[6] Iodomethane had also been proposed for use as a fungicide, herbicide, insecticide, nematicide, and as a soil disinfectant, replacing methyl bromide. It is manufactured by Arysta LifeScience and sold under the brand name MIDAS (mixture of iodomethane and chloropicrin) in the U.S., Mexico, Morocco, Japan, Turkey, and New Zealand.^[7]

Product categorization (Chemical groups):

Main category:

• Halides / Halide containing compounds

Second level:

• Aliphatic compounds

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