4-Dimethylaminopyridine (DMAP)

4-Dimethylaminopyridine (DMAP) is a derivative of pyridine with the chemical formula (CH3)2NC5H4N. This colourless solid is a useful nucleophilic catalyst for a variety of reactions such as esterifications with anhydrides, the Baylis-Hillman reaction, hydrosilylations, tritylation, the Steglich rearrangement, Staudinger synthesis of β-lactams and many more.In the case of esterification with acetic anhydrides the currently accepted mechanism involves three steps. First, DMAP and acetic anhydride react in a pre-equilibrium reaction to form an ion pair of acetate and the acetylpyridinium ion. In the second step the alcohol attacks the acetyl group of the acetylpyridinium ion to form an ester. In this step the acetate counterion acts as a base to remove the proton from the alcohol while the alcohol acts as a nucleophile and forms a covalent bond with the acetyl group.