Chloromethane, also called Methyl chloride, or simply R-40 or HCC 40, is a chemical compound of the group of organic compounds called haloalkanes. It was once widely used as a refrigerant. It is a colorless extremely flammable gas with a slightly sweet odor, which is, however, detected at possibly toxic levels. Due to concerns about its toxicity, it is no longer present in consumer products.
Methyl chloride was first synthesized by the French chemists Jean-Baptiste Dumas and Eugene Peligot in 1835 by boiling a mixture of methanol, sulfuric acid, and sodium chloride. This method is similar to that used today.
Large amounts of chloromethane are produced naturally in the oceans by the action of sunlight on biomass and chlorine in sea foam. However, all chloromethane that is used in industry is produced synthetically
Most chloromethane is prepared by reacting methanol with hydrogen chloride, according to the chemical equation
CH3OH + HClCH3Cl + H2O
This can be carried out either by bubbling hydrogen chloride gas through boiling methanol with or without a zinc chloride catalyst, or by passing combined methanol and hydrogen chloride vapors over an alumina catalyst at 350 °C.
Chloromethane was a widely used refrigerant, but due to its toxicity this use has been discontinued. Chloromethane was also once used for producing lead-based additives for gasoline, but leaded gasoline has been phased out in most of the industrialized world (an important exception being the former Soviet Union).
The most important use of chloromethane today is as a chemical intermediate in the production of silicone polymers. Smaller quantities are used as a solvent in the manufacture of butyl rubber and in petroleum refining.
Chloromethane is also employed as a methylating and chlorinating agent in organic chemistry. 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.