Chloromethane

Template:Short description Template:Chembox

Chloromethane, also called methyl chloride, Refrigerant-40, R-40 or HCC 40, is an organic compound with the chemical formula Template:Chem2. One of the haloalkanes, it is a colorless, sweet-smelling, flammable gas. Methyl chloride is a crucial reagent in industrial chemistry, although it is rarely present in consumer products,<ref name=Ross/> and was formerly utilized as a refrigerant. Most chloromethane is biogenic.

OccurrenceEdit

Chloromethane is an abundant organohalogen, anthropogenic or natural, in the atmosphere. Natural sources produce an estimated 4,100,000,000 kg/yr.<ref>Template:Cite book</ref>

MarineEdit

Laboratory cultures of marine phytoplankton (Phaeodactylum tricornutum, Phaeocystis sp., Thalassiosira weissflogii, Chaetoceros calcitrans, Isochrysis sp., Porphyridium sp., Synechococcus sp., Tetraselmis sp., Prorocentrum sp., and Emiliana huxleyi) produce CH₃Cl, but in relatively insignificant amounts.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> An extensive study of 30 species of polar macroalgae revealed the release of significant amounts of CH₃Cl in only Gigartina skottsbergii and Gymnogongrus antarcticus.<ref>Template:Cite journal</ref>

BiogenesisEdit

The salt marsh plant Batis maritima contains the enzyme methyl chloride transferase that catalyzes the synthesis of CH₃Cl from S-adenosine-L-methionine and chloride.<ref name=Ni >Template:Cite journal</ref> This protein has been purified and expressed in E. coli, and seems to be present in other organisms such as white rot fungi (Phellinus pomaceus), red algae (Endocladia muricata), and the ice plant (Mesembryanthemum crystallinum), each of which is a known CH₃Cl producer.<ref name=Ni/><ref>Template:Cite journal</ref>

Sugarcane and the emission of methyl chlorideEdit

In the sugarcane industry, the organic waste is usually burned in the power cogeneration process. When contaminated by chloride, this waste burns, releasing methyl chloride in the atmosphere.<ref name="RefF">Template:Cite journal</ref>

Interstellar detectionsEdit

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The detections reveal that chloromethane can be formed in star-forming regions before planets or life is formed.Template:Cn

File:ALMA and Rosetta Detect Freon-40 in Space.jpg

CitationClass=web }}</ref>

ProductionEdit

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.<ref>Template:Cite book</ref> This method is the forerunner for that used today, which uses hydrogen chloride instead of sulfuric acid and sodium chloride.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Chloromethane is produced commercially by treating methanol with hydrochloric acid or hydrogen chloride, according to the chemical equation:<ref name=Ross>Template:Ullmann</ref>

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.<ref name=Ross/>

Template:Chem2

Dispersion in the environmentEdit

File:CH3Cl mm.png

CH₃Cl measured by the Advanced Global Atmospheric Gases Experiment (AGAGE) in the lower atmosphere (troposphere) at stations around the world. Abundances are given as pollution free monthly mean mole fractions in parts per trillion.

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.<ref name ="RefA">Template:Cite journal</ref><ref>Template:Cite journal</ref><ref>Template:Cite journal</ref>

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.<ref>Template:Cite book</ref><ref name="RefB">Template:Cite book</ref>

The amount of methyl chloride in the stratosphere is estimated to be 2Template:E tonnes per year, representing 20–25% of the total amount of chlorine that is emitted to the stratosphere annually.<ref name ="RefC">Template:Cite journal</ref><ref name ="RefD">Template:Cite journal</ref>

UsesEdit

Template:More citations needed section Large scale use of chloromethane is for the production of dimethyldichlorosilane and related organosilicon compounds.<ref name=Ross/> 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.

Obsolete applicationsEdit

Chloromethane was widely used as a refrigerant during the 1920s and 1930s, before being replaced by safer alternatives such as hydrofluorocarbons. In the late 1920s, some manufacturers promoted methyl chloride as a safer and less odorous option compared to sulfur dioxide and ammonia.<ref name="Hand 2023">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="NBK600826">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="Consumer Reports 1936">https://archive.org/details/sim_consumer-reports_1936-07_1_3/page/5/mode/1up Consumers Union Reports, Vol. 1, No. 3, July 1936, p. 5.</ref> However, a series of fatal leaks in 1928 and 1929 raised serious concerns related to its toxicity and flammability. Although chloromethane has a faint sweet odor, its subtle scent made leaks difficult to detect. To address this issue, acrolein was later added as a nasal-irritating tracer, enhancing leak detection and serving as a warning mechanism.<ref name="Hand 2023"/><ref name="NBK600826"/>

Chloromethane was also once used for producing the lead-based gasoline additive tetramethyllead.Template:Citation needed

SafetyEdit

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.<ref name=Ross/>

ReferencesEdit

Template:Reflist

External linksEdit

Template:Halomethanes

Template:Authority control