Preparation method of bromofluorescein type cosmetic dyestuff

The invention discloses a preparation method of a bromofluorescein type cosmetic dyestuff. Specifically, the dyestuff disclosed by the invention is prepared from 4',5'-dibromofluorescein (C.I.45370: 1) , 2',4',5',7'-tetrabromofluorescein (C.I.45380: 2), 2',4',5',7'-tetrabromo-4,7-dichlorofluorescein (C.I.45405: 1) and 2',4',5',7'-tetrabromo-4,5,6,7-tetrabromofluorescein (C.I.45410: 1). The preparation method comprises the following steps: (I) putting bromine into liquid alkali and a water solution of sodium hypochlorite at low temperature to prepare a sodium hypobromite solution; (II) dissolving fluorescein or corresponding chlorofluorescein or partially dissolving the fluorescein or the corresponding chlorofluorescein into an acid-containing solvent; dropwise adding the sodium hypobromitesolution at room temperature and carrying out bromination; (III) after reaching a bromination finishing point, adding a proper amount of a reducing agent to eliminate hypobromous acid if residual hypobromous acid exists; aft