Synthesis
The general procedure for the synthesis of 7-bromo-2-naphthol from 2,7-dihydroxynaphthalene was as follows:
1. Preparation of 2-bromo-7-methoxynaphthalene: Triphenylphosphine (89.7 g, 0.342 mol) and acetonitrile (350 mL) were added to a 1 L flask under nitrogen protection and the mixture was cooled to 10 °C. Bromine (17.6 mL, 0.342 mol) was added slowly and dropwise over 10 min. After removing the cooling bath, 2,7-dihydroxynaphthalene (50.0 g, 0.312 mol) was added and rinsed with 350 mL of acetonitrile. The resulting yellow-brown mixture was heated to reflux for 3 hours. Subsequently, the acetonitrile was removed by distillation under reduced pressure, taking about 2 hours to give an off-white solid.
2. Preparation of 7-bromo-2-naphthol: The above solid was heated to 280°C within 30 minutes to form a black liquid. The liquid was continued to be heated to 310°C within 20 minutes and maintained at this temperature for 15 minutes until gas release ceased. After the black mixture was cooled to room temperature, 34.5 g of the intermediate title compound was obtained by chromatographic separation as an off-white solid with HPLC purity of 87% (43% yield).
References
[1] Journal of the American Chemical Society, 2008, vol. 130, # 13, p. 4541 - 4552
[2] Dyes and Pigments, 2014, vol. 107, p. 174 - 181
[3] Patent: WO2015/121785, 2015, A1. Location in patent: Page/Page column 32; 33
[4] Helvetica Chimica Acta, 1999, vol. 82, # 7, p. 981 - 1004
[5] Chemical Communications, 2012, vol. 48, # 5, p. 750 - 752
