Tetra-n-butylammonium Tribromide


[38932-80-8]  · C12H36Br3N  · Tetra-n-butylammonium Tribromide  · (MW 482.23)

(mild and efficient brominating agent; useful for synthesis of vicinal dibromides from alkenes and alkynes; synthesis of a-bromo acetals; determination of multiple bonds; oxidation in nonaqueous medium)

Alternate Name: TBABr3.

Physical Data: mp 84 °C (76 °C when crude); lmax (MeCN): 268 nm (67 000), l 380 nm (810).

Solubility: insol H2O; sol anhydrous acetic acid (50 g/100 mL), MeCN (300 g/100 mL), CHCl3, trichloroethylene (10 g/100 mL), THF, dioxane; very sol DMF, DMSO; slightly sol alcohols; sol acetone with slow reaction, giving lachrymatory solution.

Form Supplied in: anhydrous, orange nonhygroscopic stable solid; purity more than 98%; stable bromine degree (1 g = 2.07 mequiv Br2). Red crystals when recrystallized from DMF solution.

Handling, Storage, and Precautions: avoid washing reaction vessels with acetone prior to using with this reagent. Should be handled in a fume hood.

Bromination of Alkenes.

The application of pyridinium, quinolinium, or trimethylphenylammonium tribromide as brominating reagents is known but little used.1 Tetra-n-butylammonium tribromide allows easy double bond bromination under mild conditions and with very good yields (Table 1).2 For example, an equimolar amount of TBABr3 is slowly added to a solution of alkene in CHCl3 to give, after solvent evaporation, a residue which is washed with 5% aqueous Na2S2O3 solution and ethanol, and then filtered and recrystallized. Yields are generally in the range 85-95%.

Bromination of Alkynes.

The bromination of alkynes is usually difficult and gives mixtures of products.3 The use of TBABr3 in CCl4, at rt leads to the (E) isomer of 1,2-dibromo alkenes in high yields (85-95%) (Table 2).4

Synthesis of a-Bromo Acetals.

a-Bromo acetals are useful reagents for the synthesis of a,b-unsaturated ketones.5 These derivatives are usually prepared in two steps including bromination.5,6 and yields are often poor. TBABr3 is a convenient reagent which gives a-bromo acetals from ketones when used with ethylene glycol.2 Thus, to a solution of 120 mL of dry ethylene glycol and 0.1 mol of ketone is added an equimolar amount of TBABr3 until the red solution turns yellow (generally 6-10 h). The mixture is then poured into 70 mL of pentane, 70 mL of 10% Na2CO3 and 20 mL of 5% aqueous Na2S2O3. The organic phase is separated, water washed, dried (Na2SO4), and concentrated. The desired a-bromo acetals are obtained in yields of 75-80% (Table 3).

Oxidizing Bromination.

4-Bromo-1,1-diphenylbuten-3-one can be prepared in a one-pot synthesis from 1,1-diphenyl-3-ethylenedioxy-1-butanol by the action of TBABr3 in dry CHCl3.7

Regioselective Bromination of Aromatic Amines.

The reaction of TBABr3 with aminopyridine and aromatic amines PhNR1R2 (R1 = H, Me, Ph, Cy; R2 = H; R1 = R2 = Et) in an aprotic and nonbasic solvent at 20 °C gives exclusively the para-brominated compounds in high yields (95%).8

Selective Bromination of Phenols.

Phenols were brominated in the para position (95%) using TBABr3 in chloroform (or in the ortho position if the para position was substituted).8a,9

Determination of Unsaturation Number.

A method for the determination of the unsaturation number in organic compounds is based on bromination with TBABr3 in nonpolar media followed by electrochemical monitoring of Br3-.10

1. (a) Marquet, A.; Jacques, J.; Tchoubar, B. BSF 1965, 511. (b) Rosenmund, K. W.; Kuhnhernn, W. CB 1923, 56, 1262. (c) Rosenmund, K. W.; Kuhnhernn, W.; Lesch, W. CB 1923, 56, 2042.
2. Fournier, M.; Fournier, F.; Berthelot, J. BSB 1984, 93, 157.
3. (a) De La Mare, P. B.; Bolton, R. Electrophilic Addition to Unsaturated Systems; Elsevier: New York, 1966. (b) Uemura, S.; Okazaki, H.; Okano, J. JCS(P1) 1978, 1278.
4. Berthelot, J.; Fournier, M. CJC 1986, 64, 603.
5. Johnson, W. S.; Bass, J. D.; Williamson, K. L. T 1963, 19, 861.
6. Wanzlick, H.-W.; Gollmar, G.; Milz, H. CB 1955, 88, 69.
7. Berthelot, J.; Fournier, F.; Fournier, M. SC 1985, 15, 213.
8. (a) Berthelot, J.; Guette, C.; Desbène, P.-L.; Basselier, J.-J.; Chaquin, P.; Masure, D. CJC 1989, 67, 2061. (b) Berthelot, J.; Guette, C.; Essayegh, M.; Desbene, P. L.; Basselier, J. J. SC 1986, 16, 1641.
9. Berthelot, J.; Guette, C.; Ouchefoune, M.; Desbene, P. L.; Basselier, J. J. JCR(S) 1986, 381.
10. Berthelot, J.; Basselier, J. J.; Desbene, P. L.; Desbene-Monvernay, A. Analusis 1987, 15, 22 (CA 1987, 107, 69 995y).

Michel J. L. Fournier

Université Pierre & Marie Curie, Paris, France

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