|Systematic IUPAC name
|Molar mass||122.17 g/mol|
|Melting point||110 to 113 °C (230 to 235 °F; 383 to 386 K)|
|Boiling point||162 °C (324 °F; 435 K) at 50 mmHg|
|Acidity (pKa)||17.95 (pKa of conjugate acid in acetonitrile)|
|EU classification||T C|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
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. Chiral DMAP analogues are used in kinetic resolution experiments of mainly secondary alcohols and Evans auxiliary type amides.
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. 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 or pyridine) deprotonates the protonated DMAP, reforming the catalyst. The reaction runs through the described nucleophilic reaction pathway irrespective of the anhydride used, but the mechanism changes with the pKa value of the alcohol used. For example, the reaction runs through a base-catalyzed reaction pathway in the case of a phenol. In this case, DMAP acts as a base and deprotonates the phenol, and the resulting phenolate ion adds to the anhydride.
DMAP has a relatively high toxicity and is particularly dangerous because of its ability to be absorbed through the skin. It is also corrosive.
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- DMAP MSDS - Fischer Science
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