Chloroform (CHCl3) is one of four organic chloromethanes. This compound is a dense and colourless liquid with a sweet smell. It can be used as a precursor for Teflon, as well as in refrigeration, although the latter is being phase out.
Initial preparations of this chemical involved variations of the haloform reaction, between calcium or sodium hypochlorite and acetone or ethanol. Although these reactions are no longer in use and have been replaced by safer alternatives, these are still important landmarks in the history of this compound. Essentially, when chlorine is mixed with alcohol at high temperatures, the methyl group is chlorinated and the alcohol group is oxidised to aldehyde, generating trichloro-acetaldehyde or chloral. Subsequently, in the presence of an alkali, the C-C bond is ruptured, originating chloroform and formate. Replacing alcohol, acetone and many other ketones (as long as they contain a CH3CO group) undergo a similar reaction in the presence of sodium or calcium hypochlorite.
Currently, the most common methods to produce chloroform involve the chlorination of methyl chloride or the chlorination of methane through the reaction of methanol and hydrogen chloride. This reaction is conducted at extremely high temperatures (400 to 500 degree Celsius), and original products become progressively more chlorinated compounds (Reactions 1 to 3).
(Reaction 1) Cl2 + CH4–> HCl + CH3Cl
(Reaction 2) Cl2 + CH3Cl –> HCl +CH2Cl2
(Reaction 3) Cl2 + CH2Cl2 –> HCl +CHCl3
If the reaction is allowed to proceed, chloroform itself is further chlorinated and forms carbon tetrachloride (CCl4, Reaction 4).
(Reaction 4) Cl2 + CHCl3 –> HCl + CCl4
This reaction generates a mixture of four chloromethanes, including carbon tetrachloride (CCl4), chloroform (CHCL3), dichloromethane (CH2Cl2) and chloromethane (CH3Cl). All these chemicals can be separated by distillation.
Widely used in spectroscopy, this compound is an isotopologue of chloroform with only one deuterium substitution. Deuterochloroform can be produced through various methods, including the haloform process, involving a reaction between acetone or ethanol and sodium or calcium hypochlorite; a reaction with deuteroxide and chloral hydrate or even from chloroform.
Formation of Chloroform by Accident
Although no longer used in industrial settings, the haloform reaction can easily occur accidently in a domestic setting. All reagents are common ingredients in cleaning products present in most households, from bleach (hypochlorite solution) to alcohol or acetone, and therefore care must be taken not to mix these products and produce this hazardous chemical at home.