Bromocresol Purple

Structural formula
General
Surname	Bromocresol Purple
other names	Bromocresol Red 5 ', 5' '- dibromo- o -cresolsulfonphthalein
Molecular formula	C 21 H 16 Br 2 O 5 S
Brief description	pale yellow solid
External identifiers / databases
CAS number 115-40-2 EC number 204-087-8 ECHA InfoCard 100.003.716 PubChem 8273 Wikidata Q425039
properties
Molar mass	540.22 g mol −1
Physical state	firmly
Melting point	240 ° C (dec.)
pK s value	pK s 2 : 6.3
solubility	almost insoluble in water soluble in alkalis and ethanol
safety instructions
GHS labeling of hazardous substances no GHS pictograms H and P phrases H: no H-phrases P: no P-phrases
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Bromocresol purple (also bromocresol red ) is a triphenylmethane dye and belongs to the group of sulfonphthaleins. It is used as a pH indicator .

Properties and use

Bromocresol Purple

The yellow colored sultone form of bromocresol purple is stable in acid . From pH = 5.2 the purple colored open quinoid form becomes noticeable. This dominates at pH = 6.8, so that a bromocresol purple solution is colored purple above this value. It should be noted that due to the stronger absorption capacity of the open form, the indicator is already clearly colored purple, even if the concentration of the acidic form is still predominant.

Equilibrium between the quinoid and lactiod form of bromocresol purple

Web links

Commons : Bromocresol Purple  - collection of images, videos, and audio files

• chemie-master.de: bromocresol purple, bromocresol red

Individual evidence

1. ↑ ^{a b c} Entry on bromocresol purple. In: Römpp Online . Georg Thieme Verlag, accessed on December 28, 2014.
2. ↑ ^{a b c} Datasheet Bromocresol Purple from Sigma-Aldrich , accessed on June 12, 2018 ( PDF ).
3. ^ Merck Index, 13th edition, 2001.