Bromphenol Blue

Title: Bromphenol Blue
CAS Registry Number: 115-39-9
CAS Name: 4,4¢-(3H-2,1-Benzoxathiol-3-ylidene)bis[2,6-dibromophenol] S,S-dioxide
Additional Names: a,a-bis(3,5-dibromo-4-hydroxyphenyl)-a-hydroxy-o-toluenesulfonic acid g-sultone; 3,3¢,5,5¢-tetrabromophenolsulfonphthalein
Trademarks: Albutest (Miles)
Molecular Formula: C19H10Br4O5S
Molecular Weight: 669.96
Percent Composition: C 34.06%, H 1.50%, Br 47.71%, O 11.94%, S 4.79%
Literature References: Prepd by slow addition of excess bromine to a hot soln of phenolsulfonphthalein in glacial acetic acid: White, Acree, J. Am. Chem. Soc. 41, 1205 (1919); Orndorff, Sherwood, ibid. 45, 495 (1923). See also ref given under Bromcresol Green.
Properties: Elongated hexagonal prisms from acetic acid + acetone. Dec 279°. (An orange discoloration with formation of a green sublimate sets in at 210°). Soluble in water (about 0.4 g/100 ml); more sol in methyl and ethyl alcohol, and in benzene. Freely sol in NaOH solns with the formation of a water-sol sodium salt. pK = 4.0. To prepare a soln for use as pH indicator, dissolve 0.10 g in 7.45 ml N/50 NaOH and dil with water to 250 ml.
pKa: pK = 4.0
Use: As indicator, pH 3.0 yellow; pH 4.6 purple.
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