Eschenmoser's salt
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| Names | |
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| Preferred IUPAC name
N,N-Dimethylmethaniminium iodide | |
| Identifiers | |
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3D model (JSmol)
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| ChemSpider | |
| ECHA InfoCard | 100.046.968 |
PubChem CID
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| UNII | |
CompTox Dashboard (EPA)
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| Properties | |
| C3H8NI | |
| Molar mass | 185.01 g/mol |
| Appearance | colorless hygroscopic crystals |
| Melting point | 116 °C (241 °F; 389 K) |
| decomposes | |
| Hazards | |
| GHS labelling: | |
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| Warning | |
| H315, H319, H335 | |
| P261, P264, P271, P280, P302+P352, P304+P340, P305+P351+P338, P312, P321, P332+P313, P337+P313, P362, P403+P233, P405, P501 | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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In organic chemistry, Eschenmoser's salt (named for Albert Eschenmoser) is the ionic, organic compound [(CH3)2NCH2]I. It is the iodide salt of the dimethylaminomethylene cation [(CH3)2NCH2]+.
The dimethylaminomethylene cation is a strong dimethylaminomethylating agent, used to prepare derivatives of the type RCH2N(CH3)2.[1][2] Enolates, silyl enol ethers, and even more acidic ketones undergo efficient dimethylaminomethylation. Once prepared, such tertiary amines can be further methylated and then subjected to base-induced elimination to afford methylidenated ketones. The salt was first prepared by the group of Albert Eschenmoser[3] after whom the reagent is named.
Structure and bonding[edit]
Dimethylaminomethylene cation is described as a resonance hybrid of the carbocation and an iminium cation:
The C3N atoms are coplanar. The cation is isoelectronic with isobutene.
Preparation[edit]
Pyrolysis of iodomethyltrimethylammonium iodide affords the desired salt:[3]
![{\displaystyle {\ce {[(CH3)3N-CH2I]I -> [(CH3)2NCH2]I + CH3I}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1ef55f57992c279d24cd25843b851778be0d4078)
An alternative route starts with bis(dimethylamino)methane:
![{\displaystyle {\ce {[(CH3)2N]2CH2 + (CH3)3SiI -> [(CH3)2NCH2]I + (CH3)3SiN(CH3)2}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/a79dec87a81d283c410a7c32e737efdfa9dc2341)
Related salts[edit]
Other salts of the dimethylaminomethylene cation:
- Dimethyl(methylidene)ammonium trifluoroacetate.[4][1]
- Dimethyl(methylidene)ammonium chloride (Böhme's salt[1], after Horst Böhme)
See also[edit]
- Vilsmeier reagent, [(CH3)2NCHCl]Cl.
References[edit]
- ^ a b c E. F. Kleinman in "Dimethylmethyleneammonium Iodide and Chloride" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. doi:10.1002/047084289X.rd346
- ^ Horst Böhme; Eberhard Mundlos; Otto-Erich Herboth (1957). "Über Darstellung und Eigenschaften α-Halogenierter Amine". Chemische Berichte. 90 (9): 2003–2008. doi:10.1002/cber.19570900942.
- ^ a b Jakob Schreiber; Hans Maag; Naoto Hashimoto; Albert Eschenmoser (1971). "Dimethyl(methylene)ammonium Iodide". Angewandte Chemie International Edition in English. 10 (5): 330–331. doi:10.1002/anie.197103301.
- ^ Gaudry, Michel; Jasor, Yves; Khac, Trung Bui (1979). "Regioselective Mannich Condensation with Dimethyl(Methylene)Ammonium Trifluoroacetate: 1-(Dimethylamino)-4-Methyl-3-Pentanone". Organic Syntheses. 59: 153. doi:10.15227/orgsyn.059.0153.