Bromocresol green

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Bromocresol green
Bromocresol green.png
Abbreviations BCG
CAS number 76-60-8 YesY
PubChem 6451
ChemSpider 6209 YesY
Jmol-3D images Image 1
Molecular formula C21H14Br4O5S
Molar mass 698.01 g mol−1
Appearance beige to brown powder
Odor odorless
Melting point 225 °C (437 °F; 498 K)
Acidity (pKa) 4.90[1]
λmax 423 nm[2]
R-phrases R36/38
S-phrases S24/25, S28, S37, S45
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity (yellow): no hazard code Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 YesY (verify) (what is: YesY/N?)
Infobox references

Bromocresol green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes).

Bromocresol green (pH indicator)
below pH 3.8 above pH 5.4
3.8 5.4

In aqueous solution, both solids ionize to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic form (blue),[3] which is stabilized by resonance:

Bromocresol green ionic equilibrium.png

The Dissociation constant (pKa) of this reaction is 4.8.[4]


Demonstration of the isosbestic point of bromocresol green at which the different forms have the same absorbance

The acid and basic forms of this dye have an isosbestic point in their spectra, around 515 nm.

An ethanol solution (0.04 wt.%) of bromocresol green has been proposed for TLC staining and is suitable for visualisation of the compounds with functional groups whose pKa is below 5.0 (carboxylic acids, sulfonic acids, etc.). These appear as yellow spots on a light or dark blue background; no heating is necessary. Bromophenol blue solution can be used for the same purpose.

The compound is synthesized by bromination of cresol purple (m-cresolsulfonphthalein).


It is used as a pH indicator and as a tracking dye for DNA agarose gel electrophoresis. It can be used in its free acid form (light brown solid), or as a sodium salt (dark green solid). It is also an inhibitor of the prostaglandin E2 transport protein.


It may cause irritation. Avoid skin and eye contact.


  1. ^ Kolthoff, I.M. Treatise on Analytical Chemistry, New York, Interscience Encyclopedia, Inc., 1959.
  2. ^ a b Bromocresol Green
  3. ^
  4. ^ D. Diamond, K.T. Lau, S. Brady, J. Cleary, Talanta, 2008, 75, 606-612