Synthesis of eosin (3,4,5,6-tetrabromofluorescein)

Preparation of eosin (3,4,5,6-tetrabromofluorescein)

Preparation of eosin

To a 200 ml three-necked round bottom flask equipped with a mechanical stirrer, thermometer and addition funnel, 100 ml of ethanol and 16.6 g (0.05 mole) of pure fluorescein were placed. With constant stirring 36 g (0.45 mol) of bromine were added. During the addition  the heat was evolved and reaction must be controlled so that the temperature did not exceed 40° C. After the introduction of half of the bromine precipitate of fluorescein disappears as dibromfluorescein forms readily soluble in alcohol. During the further addition of bromine gradually crystals of 3,4,5,6-tetrabromofluorescein (eosin) were obtained. To complete the reaction after addition of bromine the mixture was stirred for another 15 minutes and then allowed to crystallize for a day. The separated crystals are filtered on a Buchner funnel and washed with 20 ml of alcohol. Crystal eosin contains 1 part alcohol. For removal of the alcohol eosin is dried at a temperature of 110 ° C. Yield 30 g (92% of theory).

Препаративная органическая химия, Вульфсон Н.С., 199-200, 1959 (Preparative organic chemistry, Wolfson N. S., 199-200, 1959)

Related Syntheses:

Synthesis of eosin disodium salt Synthesis of 2-bromobenzoic acid Synthesis of 2-bromo-3-methylbutanoyl bromide Synthesis of bromosuccinic acid Synthesis of 4-bromoanisole