Chloroformates are a class of organic compounds with the formula ROC(O)Cl. They are formally esters of

chloroformic acid Chloroformic acid is an unstable chemical compound with the formula ClCO2H. It is the single acyl-halide derivative of carbonic acid (phosgene is the double acyl-halide derivative). Chloroformic acid is also structurally related to formic acid, w ...

. Most are colorless, volatile liquids that degrade in moist air. A simple example is

methyl chloroformate Methyl chloroformate is the methyl ester of chloroformic acid. It is an oily colorless liquid, although aged samples appear yellow. It is also known for its pungent odor. Preparation Methyl chloroformate can be synthesized using methanol and ...

, which is commercially available. Chloroformates are used as reagents in organic chemistry. For example,

benzyl chloroformate Benzyl chloroformate, also known as benzyl chlorocarbonate or Z-chloride, is the benzyl ester of chloroformic acid. It can be also described as the chloride of the benzyloxycarbonyl (Cbz or Z) group. In its pure form it is a water-sensitive oily ...

is used to introduce the Cbz (carboxybenzyl) protecting group and

fluorenylmethyloxycarbonyl chloride Fluorenylmethyloxycarbonyl chloride (Fmoc-Cl) is a chloroformate ester. It is used to introduce the fluorenylmethyloxycarbonyl protecting group as the Fmoc carbamate. Preparation This compound may be prepared by reacting 9-fluorenylmethanol wi ...

is used to introduce the FMOC protecting group. Chloroformates are popular in the field of chromatography as derivatization agents. They convert polar compounds into less polar more volatile derivatives. In this way, chloroformates enable relatively simple transformation of large array of metabolites (aminoacids, amines, carboxylic acids, phenols) for analysis by gas chromatography / mass spectrometry.

Reactions

The reactivity of chloroformates and

acyl chloride In organic chemistry, an acyl chloride (or acid chloride) is an organic compound with the functional group . Their formula is usually written , where R is a side chain. They are reactive derivatives of carboxylic acids (). A specific example o ...

s are similar. Representative reactions are: * Reaction with

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent suc ...

s to form

carbamate In organic chemistry, a carbamate is a category of organic compounds with the general formula and structure , which are formally derived from carbamic acid (). The term includes organic compounds (e.g., the ester ethyl carbamate), formally ob ...

s: :ROC(O)Cl + H₂NR' → ROC(O)-N(H)R' + HCl * Reaction with

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s to form

carbonate ester In organic chemistry, a carbonate ester (organic carbonate or organocarbonate) is an ester of carbonic acid. This functional group consists of a carbonyl group flanked by two alkoxy groups. The general structure of these carbonates is and they ...

s: :ROC(O)Cl + HOR' → ROC(O)-OR' + HCl * Reaction with

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

s to form mixed anhydrides: :ROC(O)Cl + HO₂CR' → ROC(O)-OC(O)R' + HCl Typically these reactions would be conducted in the presence of a base which serves to absorb the HCl.

References

{{organic-chemistry-stub Functional groups