Karbodiimides

Karbodiimides are a class of organic compounds characterized by the functional group R-N=C=N-R', where R and R' are typically alkyl or aryl groups. This functional group contains a cumulative double bond system. The simplest carbodiimide is carbodiimide itself, HN=C=NH. Dicyclohexylcarbodiimide (DCC) and diisopropylcarbodiimide (DIC) are commonly used examples in organic synthesis.

Carbodiimides are highly reactive electrophilic species. They are widely employed as coupling agents in organic chemistry, particularly for the formation of amide and ester bonds. In this role, the carbodiimide activates a carboxylic acid by forming a reactive O-acylisourea intermediate. This intermediate is then susceptible to nucleophilic attack by an amine or alcohol, leading to the desired amide or ester product. This method is frequently used in peptide synthesis.

Beyond amide and ester formation, carbodiimides can also be used in the dehydration of alcohols to form ethers and in the synthesis of anhydrides. Their reactivity also makes them useful in modifying polymers and in cross-linking reactions. However, their electrophilic nature means they can react with nucleophilic functional groups present in other molecules, which can sometimes lead to unwanted side reactions. The handling of carbodiimides requires care due to their potential for skin sensitization and allergic reactions.