Chloromethane

Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Natural sources produce an estimated 4,100,000,000 kg/yr.^[6]

Interstellar detections

Chloromethane has been detected in the low-mass Class 0 protostellar binary, IRAS 16293–2422, using the Atacama Large Millimeter Array (ALMA). It was also detected in the comet 67P/Churyumov–Gerasimenko (67P/C-G) using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA) instrument on the Rosetta spacecraft.^[13] The detections reveal that chloromethane can be formed in star-forming regions before planets or life is formed.^{[citation needed]}

Chloromethane (originally called "chlorohydrate of methylene") was among the earliest organochlorine compounds to be discovered when it was synthesized by French chemists Jean-Baptiste Dumas and Eugène-Melchior Péligot in 1835 by boiling a mixture of methanol, sulfuric acid, and sodium chloride.^[15] This method is the forerunner for that used today, which uses hydrogen chloride instead of sulfuric acid and sodium chloride.^[16]

Chloromethane is produced commercially by treating methanol with hydrochloric acid or hydrogen chloride, according to the chemical equation:^[5]

CH₃OH + HCl → CH₃Cl + H₂O

A smaller amount of chloromethane is produced by treating a mixture of methane with chlorine at elevated temperatures. This method, however, also produces more highly chlorinated compounds such as dichloromethane, chloroform, and carbon tetrachloride. For this reason, methane chlorination is usually only practiced when these other products are also desired. This chlorination method also cogenerates hydrogen chloride, which poses a disposal problem.^[5]

CH₄ + Cl₂ → CH₃Cl + HCl

CH₃Cl + Cl₂ → CH₂Cl₂ + HCl

CH₂Cl₂ + Cl₂ → CHCl₃ + HCl

CHCl₃ + Cl₂ → CCl₄ + HCl

Most of the methyl chloride present in the environment ends up being released to the atmosphere. After being released into the air, the atmospheric lifetime of this substance is about 10 months with multiple natural sinks, such as ocean, transport to the stratosphere, soil, etc.^[17][18][19]

On the other hand, when the methyl chloride emitted is released to water, it will be rapidly lost by volatilization. The half-life of this substance in terms of volatilization in the river, lagoon and lake is 2.1 h, 25 h and 18 days, respectively.^[20][21]

The amount of methyl chloride in the stratosphere is estimated to be 2×10⁶ tonnes per year, representing 20–25% of the total amount of chlorine that is emitted to the stratosphere annually.^[22][23]

This section needs additional citations for verification. (February 2023)

Large scale use of chloromethane is for the production of dimethyldichlorosilane and related organosilicon compounds.^[5] These compounds arise via the direct process. The relevant reactions are (Me = CH₃):

x MeCl + Si → Me₃SiCl, Me₂SiCl₂, MeSiCl₃, Me₄Si₂Cl₂, ...

Dimethyldichlorosilane (Me₂SiCl₂) is of particular value as a precursor to silicones, but trimethylsilyl chloride (Me₃SiCl) and methyltrichlorosilane (MeSiCl₃) are also valuable. Smaller quantities are used as a solvent in the manufacture of butyl rubber and in petroleum refining.

Chloromethane is employed as a methylating and chlorinating agent, e.g. the production of methylcellulose. It is also used in a variety of other fields: as an extractant for greases, oils, and resins, as a propellant and blowing agent in polystyrene foam production, as a local anesthetic, as an intermediate in drug manufacturing, as a catalyst carrier in low-temperature polymerization, as a fluid for thermometric and thermostatic equipment, and as a herbicide.

Inhalation of chloromethane gas produces central nervous system effects similar to alcohol intoxication. The TLV is 50 ppm and the MAC is the same. Prolonged exposure may have mutagenic effects.^[5]

• bromomethane
• dichloromethane
• trichloromethane
• tetrachloromethane