Title: Bromcresol Purple
CAS Registry Number: 115-40-2
CAS Name: 4,4¢-(3H-2,1-Benzoxathiol-3-ylidene)bis[2-bromo-6-methylphenol] S,S-dioxide
Additional Names: a-(5-bromo-4-hydroxy-m-tolyl)-a-(3-bromo-5-methyl-4-oxo-2,5-cyclohexadien-1-ylidene)-o-toluenesulfonic acid; 5,5¢-dibromo-o-cresolsulfonphthalein
Molecular Formula: C21H16Br2O5S
Molecular Weight: 540.22
Percent Composition: C 46.69%, H 2.99%, Br 29.58%, O 14.81%, S 5.94%
Literature References: Prepd by treating o-cresol red with bromine in glacial acetic acid: See refs under Bromcresol Green.
Properties: Minute, slightly yellow crystals, mp 241-242°. Practically insol in water. Sol in alcohol, dil alkalies. pK 6.3. To prepare a soln for use as pH indicator, dissolve 0.10 g in 9.25 ml N/50 NaOH and dil with water to 250 ml. To prepare a soln for use as indicator in volumetric work, dissolve 0.05 g in 250 ml alc.
Melting point: mp 241-242°
pKa: pK 6.3
Use: As indicator, pH 5.2 yellow; pH 6.8 purple.