Question

Question. Propose a mechanism for the coupling of acetic acid and aniline using DCC as a coupling agent.

Short answer

Representation of DCC as c-Hx

Mechanism for the coupling of acetic acid aniline

Step-by-step solution

Step1: Introduction to DCC

DCC or N,N’-Dicyclohexylcarbodiimide is used in the coupling reactions of amino acids during peptide synthesis. It has a low melting point and can be handled easily. Often, in reactions, we use the abbreviation ‘c-Hx’ to stand for cyclohexyl in DCC.

Representation of DCC as c-Hx

Mechanism for the reaction

The nitrogen of aniline firstly abstracts hydrogen from acetic acid-forming acetate ion and anilinium ion. Then, the oxygen of the acetate ion acts as a nucleophile and attacks thecarbon center of DCC, which is an electrophile. DCC thereby activatesthe carboxyl group,converting it into an excellent leaving group. Further, a reaction with another molecule of aniline occurs inthis activated carboxyl group, and lastly, the leaving group leaves, which is resonance-stabilized, and the final product is formed.

Mechanism for the coupling of acetic acid aniline