General procedure for the synthesis of 1,4-dibromo-2,5-bis(trifluoromethyl)benzene from 2,3-difluorotoluene:
1. 1,4-bis(trifluoromethyl)benzene (19 g, 88.7 mmol, ABCR), trifluoroacetic acid (250 ml, SDS), and 99% sulfuric acid (60 ml, Acros) were sequentially added to a 1-liter round-bottomed flask fitted with a condenser and magnetic stirrer.
2. The reaction mixture was heated to 60 °C at which temperature N-bromosuccinimide (47.4 g, 267 mmol, Aldrich) was added in batches and the dosing process lasted for 5 hours.
3. After completion of the addition, the reaction was kept at 60 °C with continued stirring for 48 hours.
4. The reaction mixture was poured into ice (500 ml) and precipitate was precipitated and collected by filtration.
5. The precipitate was dried under vacuum (1 mmHg) for 24 hours.
6. The dried product was purified by sublimation to give 30 g (91% yield) of white solid product 2,5-dibromo-1,4-bis(trifluoromethyl)benzene.
Product characterization:
- Melting point: 65±0.2°C;
- 1H NMR (200MHz, CDCl3): δ 8.01 (2H, s);
- 19F NMR (188MHz, CDCl3): δ -64.1 (2×CF3, s).
