Methyl 4,4'-dihydroxy-[1,1'-biphenyl]-2-carboxylate (50 g, 0.20 mol) was used as a raw material and mixed with ZnCl2 (50 g, 0.37 mol) and polyphosphoric acid (PPA, 33 mL). The reaction mixture was stirred at 110-120 °C for 2 hours. Upon completion of the reaction, it was cooled to room temperature and water (500 mL) was slowly added to precipitate the product. The precipitate was collected by filtration and dried to give 40 g of reddish brown crystalline powder (2,7-dihydroxy-9-fluorenone). The yield was 95%; melting point 336-337°C (literature value 338°C [24]); IR (KBr) ν (cm^-1): 3388.9, 3360.6 (OH), 1700.7 (C=O); ESI-MS (m/z): 211.0 [M+H]^+, molecular formula C13H8O3 (molecular weight 212.0); 1H- NMR (300MHz, DMSO-d6) δ (ppm): 9.89 (s, 2H), 7.37 (d, J=4.8Hz, 2H), 6.90 (dd, J=4.9,2.4Hz, 2H), 6.86 (d, J=2.4Hz, 2H).
![[1,1'-Biphenyl]-2-carboxylic acid, 4,4'-dihydroxy-, methyl ester](/CAS/20200611/GIF/765944-63-6.gif)
