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Synlett 2004(7): 1318-1320  
DOI: 10.1055/s-2004-825598
LETTER
© Georg Thieme Verlag Stuttgart · New York

Pentylpyridinium Tribromide: A Vapor Pressure Free Room Temperature Ionic Liquid Analogue of Bromine

José Salazar*, Romano Dorta*
Departamento de Química, Universidad Simón Bolívar, Caracas 1080A, Venezuela
Fax: +58(212)9063961; e-Mail: jsalazar@usb.ve; e-Mail: rdorta@usb.ve;
Further Information

Publication History

Received 26 February 2004
Publication Date:
10 May 2004 (online)

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Abstract

The synthesis and characterization of the room temperature ionic liquid pentylpyridinium tribromide (2) is described. Tribromide 2 was used as a vapor pressure free bromine analogue for the bromination of ketones, aromatics, alkenes, and alkynes. The brominations were carried out in the absence of organic solvents and in most cases the only extraction solvent needed was water. Selectivities and reactivities were shown to be superior to current protocols. The spent reagent pentylpyridinium bromide (1) was easily recycled.

Key words

pentylpyridinium tribromide - room temperature ionic liquid - solvent-free brominations

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9

Pentylpyridinium Tribromide (2). Bromine (64.48 g, 404.7 mmol) was added over 30 min to solid crushed pentylpyridinium bromide (1, 93.07 g, 404.4 mmol) under mechanical stirring and cooling in a water bath affording a deep red liquid. After stirring for 2 h the liquid was left in vacuo overnight. Yield: 156 g (99%); mp 0 °C; κ = 8.09 mS cm-1; d = 1.79 g cm-3; η35-500 0.038 Pa s (all at 25° C). 1H NMR (CD2Cl2): δ = 0.80-1.00 (m, 3 H), 1.30-1.55 (m, 4 H), 2.00-2.15 (m, 2 H), 4.60-4.75 (m, 2 H), 8.10-8.20 (m, 2 H), 8.50-8.65 (m, 1 H), 8.80-8.95 (m, 2 H). 13C NMR (400.14 MHz, CD2Cl2): δ = 13.62 (s), 22.12 (s), 28.20 (s), 31.33 (s), 63.14 (s), 129.08 (s), 144.42 (s), 145.86 (s). Anal. Calcd for C10H16NBr3: C, 30.80; H, 4.14; N, 3.59. Found: C, 30.95; H, 4.11; N, 3.71.