chloroformate

Chloroformate refers to esters of chloroformic acid with alkyl or aryl groups, and their general structure is ClCOOR. They are reactive acylating agents used in organic synthesis. The most common examples are alkyl chloroformates such as methyl chloroformate and ethyl chloroformate, as well as aryl chloroformates.

Synthesis typically involves reaction of phosgene with the corresponding alcohol (ROH) to give ClCOOR and HCl. Alternative routes include chlorination of formate esters or related chloroformic acid derivatives.

Reactions and applications: The carbonyl carbon in chloroformates is highly activated toward nucleophilic attack, and the chloride leaving group enables acyl transfer. They readily transfer the chloroformate group to nucleophiles. Reaction with amines yields carbamates (urethanes) after loss of HCl and alcohol, while reaction with alcohols forms carbonate esters. They are commonly used to protect amines as carbamates, to activate alcohols, and to prepare urethanes and related derivatives. In organic synthesis, ethyl and methyl chloroformates are employed for carbamate formation, ester activation, and in peptide coupling contexts. They also find use in polymer chemistry for synthesis and modification of materials.

Safety: Chloroformates are moisture-sensitive and can be lachrymatory and corrosive. They hydrolyze to release HCl and related byproducts upon contact with water. Handle them in a fume hood with appropriate protective equipment and store under inert or dry conditions.