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4-Dimethylaminopyridine (DMAP) is a nucleophilic catalyst which catalyzes a variety of reactions. For example esterifications with anhydrides, Baylis-Hillman reaction, hydrosilylation, tritylation, the Steglich rearrangement, Staudinger synthesis of β-lactams and many more.
Additional recommended knowledge
In the case of esterification with acetic anhydrides the currently accepted mechanism involves three steps. First, DMAP and acetic anhydride form in a pre-equilibrium reaction a labile ion pair between the acetate and the acetylpyridium ion. In the second step the alcohol attacks the acetyl group to form the ester. In this step the acetate counterion pulls away the proton from the alcohol while the alcohol forms a covalent bond with the acetyl group. The bond from the acetyl group to the catalyst gets cleaved to generate the catalyst and the ester. The described bond formation and breaking process runs synchronous concerted without the appearance of a tetrahedral intermediate. The acetic acid formed will then protonate the DMAP. In the last step of the catalytic cycle the auxiliary base (usually triethylamine) deprotonates the protonated DMAP, reforming the catalyst. The reaction runs through the described nucleophilic reaction pathway irrespectively from the used anhydride.
B. Neises, W. Steiglich, Organic Syntheses, Coll. Vol. 7, p.93 (1990); or Vol. 63, p.183 (1985).
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "4-Dimethylaminopyridine". A list of authors is available in Wikipedia.|