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I want to make Mercury dibromofluorescein disodium salt accroding to US Patent 1535003, but I have trouble in making 2,7-dibromofluorescein. I can only buy 4,5-dibromofluorescein, so making it  is necessary for me. help me, help me...

[Custos]

The method of Kolthoff (1929) will work - just use bromoresorcinol instead of chlororesorcinol.

Dichlorofluorescein.-Ten grams of phthalic anhydride mixed intimately with
19.7 g. of monochlororesorcinol was heated to 160 degC in an iron crucible by means of an
oil-bath. Five grams of anhydrous zinc chloride, finely ground, was then added with
stirring during a period of about ten minutes. The temperature was then raised to
175-180 degC and maintained for about two and one-half hours. After cooling, the reaction
product was ground and then boiled for fifteen to twenty minutes in dilute hydrochloric
acid (10 cc. of concd. acid to 200 cc. of water) and filtered.
The precipitate was dissolved at room temperature in a saturated aqueous solution
of sodium bicarbonate, filtered, heated to boiling and then acidified with hydrochloric
acid (approx. 4 N). After cooling and filtering, the precipitate was refluxed with acetic
anhydride for several hours (2 g. of crude dichlorofluorescein to 10-12 cc. of acetic anhydride).
The diacetate crystallized out upon cooling. It was filtered off and the above
process repeated four or five times. The diacetate (almost colorless) was then digested
with a small amount of alcohol, cooled and filtered. After drying for several hours
at 100 degC it was analyzed for chlorine.
Anal. (Carius). Calcd.: C1, 14.64. Found: C1, 14.49, 14.98.
The diacetate was then saponified by refluxing 2-3 g. with alcoholic potassium
hydroxide (6-7 g. of base in 40 cc. of alcohol) for two hours. Water was then added,
the solution transferred to a distilling flask and the alcohol removed by distillation.
The solution was then filtered (if necessary), heated to boiling and acidified with hydrochloric
acid.

I take it you are trying to make mecurochrome?