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| 4-Dimethylaminopyridine | |
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| IUPAC name | 4-Dimethylaminopyridine |
| Other names | DMAP, 4-(Dimethylamino)-pyridine, N,N-Dimethyl-4-aminopyridin |
| Identifiers | |
| CAS number | 1122-58-3 |
| SMILES |
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| Properties | |
| Molecular formula | C7H10N2 |
| Molar mass | 122.17 g/mol |
| Melting point |
110-113 °C |
| Boiling point |
162 °C at 50 mmHg |
| Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox references |
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- DMAP redirects here. For the cyanide antidote see 4-Dimethylaminophenol
4-Dimethylaminopyridine (DMAP) is a nucleophilic 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.12
Contents |
Preparation
DMAP can be prepared in a two-step procedure from pyridine, which is first oxidized to 4-pyridylpyridinium cation. This cation then reacts with dimethylamine:3
- 3 C5H5N + Cl2 → [C5H5N+C5H4N]Cl- + [C5H5NH]+Cl-
- [C5H5N+C5H4N]Cl- + (CH3)2NH → (CH3)2NC5H4N + [C5H5NH]+Cl-
Esterification catalyst
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 acetylpyridinium 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 irrespective of the anhydride used，but the mechanism changes with the pKa value of the used alcohol. For example，the reaction runs prevourablely through a base catalyzed reaction pathway in the case of benzylic alcohol. In this case dmap acts as a base which deprotonates the alcohol, while the formed alcolate the anhydride attacks. 4
References
- ^ Catalysis by 4-dialkylaminopyridines Donald J Berry, Charles V Digiovanna, Stephanie S Metrick and Ramiah Murugan Arkivoc O-401R 2001 Online review
- ^ 4-Dialkylaminopyridines as Highly Active Acylation Catalysts Höfle, G., Steglich, W., Vorbrüggen, H. Angew. Chem. Int. Ed. Engl. 1978 , 17 , 569-583.
- ^ Shinkichi Shimizu, Nanao Watanabe, Toshiaki Kataoka, Takayuki Shoji, Nobuyuki Abe, Sinji Morishita, Hisao Ichimura "Pyridine and Pyridine Derivatives" in "Ullmann's Encyclopedia of Industrial Chemistry" 2007; John Wiley & Sons: New York.
- ^ The DMAP-Catalyzed Acetylation of Alcohols - A Mechanistic Study (DMAP = 4-(dimethylamino) -pyridine) S. Xu, I. Held, B. Kempf, H. Mayr, Wolfgang Steglich, H. Zipse, Chem. Eur. J. 2005, 11, 4751 - 4757
Further reading
- B. Neises, W. Steiglich (1990). "Esterification of Carboxylic Acids with Dicyclohexylcarbodiimide/4-Dimethylaminopyridine: tert-Butyl Ethyl Fumarate". Org. Synth.; Coll. Vol. 7: 93.
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- This page was last modified on 1 January 2009, at 12:00.
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