Trichloromethyl group
The trichloromethyl group is a functional group that has the formula. The naming of this group is derived from the methyl group, by replacing each hydrogen atom by a chlorine atom. Compounds with this group are a subclass of the organochlorines.
Trichloromethyl is an electron withdrawing group owing to the electronegativity of the three chlorides.
| Methyl group | Formula | Electronegativity |
| Methyl | CH3 | 2.472 |
| Phenyl | C6H5 | 2.717 |
| Chloromethyl | CH2Cl | 2.538 |
| Dichloromethyl | CHCl2 | 2.602 |
| Trichloromethyl | CCl3 | 2.666 |
| Trifluoromethyl | CF3 | 2.985 |
Trichloromethyl alkanes and derivatives
Some simple trichloromethyl compounds include trichloromethane, also known as chloroform, 1,1,1-trichloroethane, and hexachloroethane. Trichloromethanol is however unstable, reflecting the lability associated with the RO-C-Cl center. Indeed, triphosgene carbonate, OC fragments upon heating by scission of a C-Cl bond. It is used as a substitute for phosgene.Because the trichloromethyl group is relatively electronegative, the behavior of trichloromethyl-substituted compounds can differ sharply vs the behavior of the methyl parents. The acidity constant of trichloroacetic acid is 0.77, whereas that of acetic acid is 4.76. In other words, trichloroacetic acid is 1000x the stronger acid. In a related manner, the trichloromethyl aldehyde tends to hydrate to give chloral hydrate.
Trichloromethyl arenes
Many trichloromethylarenes can be prepared by chlorination of the corresponding methyl arenes. For example toluene and the xylene isomers as well as their substituted derivatives can often be converted to the corresponding trichloromethyl derivatives simply by treatment with chlorine. The conversion involves a free radical reaction:These trichloromethyl compounds are produced on an industrial scale as precursors to other useful compounds. Partial hydrolysis of benzotrichloride provides a route to benzoyl chloride:
By reaction with hydrogen fluoride, trichloromethylated arenes convert to trifluoromethyl derivatives and hydrogen chloride, which can be recycled. In this way, benzotrifluoride and bis(trifluoromethyl)benzene are produced commercially:
Bioactive derivatives
[image:Folpet.png|thumb|right|120px|Folpet, a trichloromethyl-containing insecticide.]A trichloromethyl-containing agricultural chemical is nitrapyrin, which inhibits nitrification, i.e. it enhances the efficiency of fertilizers.
Trichloromethyl-containing insecticides include metrifonate and Folpet.
The list of trichloromethyl-containing pharmaceuticals includes the anorectic drug Amfecloral and the sedative triclofos.