Thetrichloromethyl group is afunctional group that has theformula−CCl3. The naming of this group is derived from themethyl group (which has the formula−CH3), by replacing eachhydrogen atom by achlorine atom. Compounds with this group are a subclass of theorganochlorines.
Trichloromethyl is anelectron withdrawing group owing to the electronegativity of the three chlorides.[1]
| 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 |
Some simple trichloromethyl compounds includetrichloromethane, also known as chloroform (HCCl3),1,1,1-trichloroethane (H3CCCl3), andhexachloroethane (Cl3CCCl3). Trichloromethanol is however unstable, reflecting the lability associated with the RO-C-Cl center.[2] Indeed,triphosgene (bis(trichloromethyl) carbonate, OC(OCCl3)2) fragments upon heating by scission of a C-Cl bond. It is used as a substitute forphosgene.[3]
Because the trichloromethyl group is relatively electronegative, the behavior of trichloromethyl-substituted compounds can differ sharply vs the behavior of the methyl parents. Theacidity constant (pKa) oftrichloroacetic acidCCl3CO2H is 0.77, whereas that ofacetic acid is 4.76. In other words, trichloroacetic acid is 1000x the stronger acid. In a related manner, the trichloromethyl aldehydeCCl3CHO (chloral) tends to hydrate to givechloral hydrateCCl3CH(OH)2.
Many trichloromethylarenes can be prepared bychlorination of the corresponding methyl arenes. For exampletoluene and thexylene isomers as well as their substituted derivatives can often be converted to the corresponding trichloromethyl derivatives simply by treatment with chlorine. The conversion involves afree radical reaction:[4]
These trichloromethyl compounds are produced on an industrial scale as precursors to other useful compounds. Partial hydrolysis ofbenzotrichloride provides a route tobenzoyl chloride:[4]
By reaction withhydrogen fluoride, trichloromethylated arenes convert totrifluoromethyl derivatives and hydrogen chloride, which can be recycled. In this way,benzotrifluoride (C6H5CF3)andbis(trifluoromethyl)benzene are produced commercially:[5]
A trichloromethyl-containing agricultural chemical isnitrapyrin, which inhibitsnitrification, i.e. it enhances the efficiency of fertilizers.
Trichloromethyl-containing insecticides includemetrifonate andFolpet.
The list of trichloromethyl-containing pharmaceuticals includes the anorectic drugAmfecloral and the sedativetriclofos.
Thetrichloromethyl radical (Cl3C·) is a well known but transient intermediate in reactions.[6] It is the agent responsible for the toxicity ofcarbon tetrachloride.[7]
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