1387. Bromcresol Purple

Nomenclature

CAS number: 115-40-2
4,4′-(1,1-Dioxido-3H-2,1-benzoxathiol-3-ylidene)bis[2-bromo-6-methylphenol]; 4,4′-(3H-2,1-benzoxathiol-3-ylidene)bis[2-bromo-6-methylphenol] S,S-dioxide; α-(5-bromo-4-hydroxy-m-tolyl)-α-(3-bromo-5-methyl-4-oxo-2,5-cyclohexadien-1-ylidene)-o-toluenesulfonic acid; 5,5′-dibromo-o-cresolsulfonphthalein; bromocresol purple.
C21H16Br2O5S; mol wt 540.22.
C 46.69%, H 2.99%, Br 29.58%, O 14.81%, S 5.94%.

Description and references

Prepd by treating o-cresol red with bromine in glacial acetic acid: See refs under Bromcresol Green.

Chemical structure

Properties

Minute, slightly yellow crystals, mp 241-242°. Practically insol in water. Sol in alcohol, dil alkalies. pKa 6.3. pH 5.2 yellow; pH 6.8 purple. 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.

Derivative

Sodium salt.

Nomenclature

CAS number: 62625-30-3
C21H15Br2NaO5S; mol wt 562.20.
C 44.86%, H 2.69%, Br 28.43%, Na 4.09%, O 14.23%, S 5.70%.

Use

As pH indicator, especially in microbiological culture media. In instrumentation systems for ammonia detection. Vital stain in differentiation between live and dead yeast. Analytical stain for carbonic anhydrase isoenzymes.