Methyl iodide

Methyl iodide

Freshly prepared methyl iodide, stored over copper
Names
IUPAC name Iodomethane
Other names Methyl iodine Monoiodomethane
Identifiers
Jmol-3D images	Image
SMILES CI
Properties
Chemical formula	CH3I
Molar mass	141.94 g/mol
Appearance	Colorless liquid Brownish liquid (old sample)
Odor	Pungent, ether-like
Density	2.28 g/cm3 (at 20 °C)
Melting point	−66.5 °C (−87.7 °F; 206.7 K)
Boiling point	42.5 °C (108.5 °F; 315.6 K)
Solubility in water	1.4 g/100 ml (at 20 °C)
Solubility	Miscible with acetone, alcohols, carbon tetrachloride, chloroform, diethyl ether
Vapor pressure	54.4 kPa (at 20 °C)
Thermochemistry
Std enthalpy of formation (ΔfHo298)	−14.1–−13.1 kJ/mol
Hazards
Safety data sheet	ScienceLab
Lethal dose or concentration (LD, LC):
LD50 (Median dose)	76 mg/kg (oral, rat) 800 mg/kg (dermal, guinea pig)
LC50 (Median concentration)	1550 ppm (rat, 30 min) 860 ppm (mouse, 57 min) 220 ppm (rat, 4 hr)
Related compounds
Related compounds	Iodine Iodoform Ethyl iodide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Methyl iodide or iodomethane is an organic chemical compound, which appears as a dense liquid, insoluble in water, mainly used as a methylating agent. It has the chemical formula CH₃I, sometimes written as MeI.

Properties

Chemical

Methyl iodide will hydrolyze in the presence of an alkali to methanol and iodide:

CH₃I + MOH → CH₃OH + MI

Methyl iodide will react with a nitrite salt, yielding nitromethane if sodium or potassium nitrite are used, with methyl nitrite as minor product. If silver nitrite is used, methyl nitrite will be the majority product, due to the fact that the silver ion in solution has a stabilizing effect on the formation of carbocation intermediates, increasing the percent yield of methyl nitrite. If nitrogen dioxide is bubbled in methyl iodide, methyl nitrite will be the sole product obtained.

CH₃I + NO₂ → CH₃NO₂ + ½ I₂

Physical

Methyl iodide is a dense, colorless (though old samples have a brownish color) liquid, immiscible in water, but miscible with many solvents such as diethyl ether, ethanol, methanol and soluble in acetone and carbon tetrachloride. Methyl iodide has a strong and pungent ether-like odor.

Availability

Methyl iodide is sold by various chemical suppliers, though it's difficult to acquire. It can sometimes be found on eBay.

Methyl iodide used to be available as a pesticide up until 2012, when it was removed due to its carcinogenic effects.

Preparation

Methyl iodide can be prepared by reacting methanol with hydroiodic acid or hydrogen iodide. While the methanol does not need to be anhydrous, excess water may lower the yield.

Phosphorus triiodide can also be used. This can be made in situ by adding iodine and then adding red phosphorus in dry methanol and refluxing the mixture.

Projects

• Make esters
• Make toluene

Handling

Safety

Iodomethane is toxic and carcinogenic.

Methyl iodide MUST be kept away from heavy metals, such as mercury, lead, cadmium, arsenic or thallium, as this will generate extremely toxic heavy methyl iodides, which are more toxic than their corresponding metals. It's ABSOLUTELY CRUCIAL to avoid contact with mercury amalgam, as this will yield the volatile compound dimethylmercury, one of the most deadly contact poisons known, second only to nerve agents, which readily penetrates butyl, latex, neoprene and PVC protective equipment.

Storage

Methyl iodide must be stored in amber bottles, in dark well ventilated places, away from light. Copper or silver wire can be added as a stabilizer.

Disposal

Methyl iodide can be hydrolyzed to methanol with sodium hydroxide, which can be safely burned, while sodium iodide can be recycled.

References

Relevant Sciencemadness threads

• Preparation of Iodomethane
• Methyl Iodide Synthesis ?