Ionic liquid promoted regioselective monobromination of aromatic substrates with N-bromosuccinimide

Tetrahedron Letters

Volumn 44, Issue 9, 2003, Pages 1815-1817

  Rajagopal, R ^a   Jarikote, D V ^a   Lahoti, R J ^a   Daniel, Thomas ^a   Srinivasan, K V ^a  

^a NATIONAL CHEMICAL LABORATORY   (India)

Author keywords

13C NMR; Bromination; Ionic liquid; NBS

Indexed keywords

1,3 DIBUTYLIMIDAZOLIUM TETRAFLUOROBORATE; AROMATIC COMPOUND; IMIDAZOLE DERIVATIVE; N BROMOSUCCINIMIDE; UNCLASSIFIED DRUG;

ARTICLE; BROMINATION; CARBON NUCLEAR MAGNETIC RESONANCE; CATALYST; COMBINATORIAL CHEMISTRY; ISOMER; POLARIZATION; PROTON NUCLEAR MAGNETIC RESONANCE; STEREOCHEMISTRY; TEMPERATURE DEPENDENCE;

EID: 0037463477     PISSN: 00404039     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0040-4039(03)00092-3     Document Type: Article

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23. 14] at 28°C, NBS (0.018 mol) was added in one portion when the temperature rose to ∼35°C. A clear solution resulted immediately. The reaction was monitored by TLC and complete conversions were achieved after 5 min for most of the substrates. At this stage, the reaction mixture turned turbid due to the precipitation of succinimide. The mixture was extracted with ether (3×10 ml) when all the products were extracted into it leaving behind a slurry of succinimide in IL. The ether layer was separated, washed with water, brine, dried over sodium sulphate and solvent evaporated to furnish the products which were further purified by chromatography through a column of silica gel (60-120 mesh) or by distillation under reduced pressure. The remaining mixture of IL with succinimide was diluted with ethyl acetate and filtered to recover succinimide. The filtrate consisting of the IL in ethyl acetate was subjected to distillation under reduced pressure to remove ethyl acetate. The recovered IL was pure enough for at least two recycles.
24. 4 (50 g) at 28°C, NBS (41.25 g, 0.23 mol) was introduced in small portions slowly over 30 min in such a way as to maintain the temperature of the reaction at 30±2°C. After the complete addition, the mixture was stirred further for 15 min at 30°C. The completion of the reaction was monitored by GC. The reaction mixture was subjected to distillation under reduced pressure when 4-bromoanisole distilled out at 90°C/8 mmHg in 98% yield. The distillation residue was diluted with ethyl acetate (100 ml) and the thin slurry was filtered to remove succinimide. The filtrate was subjected to distillation under reduced pressure to remove ethyl acetate and to recover the IL completely. The recovered IL could be recycled four times for the bromination of anisole successfully.
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