Solvent Red 43

2321-07-5

15086-94-9

The general procedure for the synthesis of 2',4',5',7'-tetrabromo-3',6'-dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthene]-3-one from 3',6'-dihydroxy-3H-spiro[isobenzofuran-1,9'-xanthene] is as follows: fluorescein in the form of the lactone (1 eq.), NaBr (16 eq.), and Oxone ( 6 equiv, 2KHSO5-KHSO4-K2SO4) were mixed and ground in an agate mortar until uniformly fine. The resulting solid mixture was reacted in an oven at 200 °C for 12 h. Upon completion of the reaction, the target product tetrabromofluorescein (4Br-F) was obtained in near 100% yield in the commercial disodium salt form known as eosin Y. The reaction mixture was diluted with water and the product was extracted with ethyl acetate. The product was characterized by mass spectrometry (ESI-MS) and spectroscopic techniques (1H-NMR and 13C-NMR). The specific data were as follows: ESI-MS (+) of 4Br-F: m/z 670.4 [M + H]+; 1H NMR (CH3OD): δ 7.04 ppm (s, 1H and 8H), 7.23 (d, J = 8.0 Hz, 3H), 7.72 (ddd, J = 8.0, 8.0, 1.2 Hz, 5H), 7.79 (ddd, J = 8.0, 8.0, 1.2 Hz, 4H), 8.09 ppm (d, J = 8.0 Hz, 6H).