Tetramethylammonium Bromide1

Me4NBr

[64-20-0]  · C4H12BrN  · Tetramethylammonium Bromide  · (MW 154.07)

(phase transfer catalyst; source of nucleophilic bromide; cleavage of cyclopropane; salt effects)

Physical Data: mp 230 °C (dec) bp 360 °C (sub. vac.); d 1.56 g cm-3.

Solubility: sol H2O, MeOH.

Form Supplied in: white solid; commercially available.

Analysis of Reagent Purity: tetraalkylammonium salts can be titrated with potassium 3,5-di-t-butyl-2-hydroxybenzenesulfonate and iron(III) chloride.1a

Purification: the commercially available compound can be recrystallized from EtOH, EtOH-diethyl ether, MeOH-acetone, H2O, or acetone-EtOH (4:1). It is then dried at 110 °C under reduced pressure for 24 h.

Phase Transfer Catalyst.

It has been generally observed that Me4NBr is one of the least effective ammonium salts for phase transfer catalysis. A number of studies have shown that increasing the size of the alkyl groups on the nitrogen is generally beneficial for the promotion of phase transfer reactions by ammonium salts. For example, this salt was shown to be inferior to BuNEt3Br in the O- and C-alkylation of aryl ketones (eq 1),2 to Tetra-n-butylammonium Iodide in the Horner-Emmons alkenation of aldehydes (eq 2),3 to (C8H17)3NMeCl in the S-alkylation of thiophenol,4 to Et4NBr in the oxybromination of aromatic compounds,5 and to Tetra-n-butylammonium Bromide and Bu4PBr in the alkylation of K2CO3.6 Me4NBr was a very effective phase transfer catalyst for the N-alkylation of aromatic heterocyclic compounds (eq 3).7

Nucleophilic Opening of Cyclopropyl Ketones.

In combination with acetyl methanesulfonate, Me4NBr was shown to promote the efficient cleavage of cyclopropyl ketones to produce g-bromovinyl esters (eqs 4 and 5).8


1. (a) Sjöberg, K. Aldrichim. Acta 1980, 13, 55. (b) Jones, R. A. Aldrichim. Acta 1976, 9, 35. (c) Weber, W. P.; Gokel, G. W. Phase Transfer Catalysis in Organic Synthesis; Springer: New York, 1977. (d) Starks, C. M.; Liotta, C. Phase Transfer Catalysis; Academic: New York, 1978. (e) Dehmlow, E. V.; Dehmlow, S. S. Phase Transfer Catalysis; Verlag Chemie: Deerfield Beach, FL, 1980. (f) Loupy, A.; Tchoubar, B. Salt Effects in Organic and Organometallic Chemistry; VCH: Weinheim, 1992.
2. Halpern, M.; Sasson, Y.; Rabinovitz, M. T 1982, 38, 3183.
3. Mikolajczyk, M.; Grzejszczak, S.; Midura, W.; Zatorski, A. S 1975, 278.
4. Herriott, A. W.; Picker, D. JACS 1975, 97, 2345.
5. Dakka, J.; Sasson, Y. CC 1987, 1421.
6. (a) Cella, J. A.; Bacon, S. W. JOC 1984, 49, 1122. (b) Ishido, Y.; Tsutsumi, H.; Inaba, S. JCS(P1) 1977, 5, 521.
7. Dou, H. J.-M.; Metzger, J. BSF(2) 1976, 1861.
8. Demuth, M.; Raghavan, P. R. HCA 1979, 62, 2338.

André B. Charette

Université de Montréal, Québec, Canada



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