Bromocresol green

Bromocresol green
IUPAC name 2,6-Dibromo-4-[7-(3,5-dibromo-4-hydroxy-2-methyl-phenyl)-9,9-dioxo-8-oxa-9λ6-thiabicyclo[4.3.0]nona-1,3,5-trien-7-yl]-3-methyl-phenol
Other names 3,3',5,5'-Tetrabromo-m- cresolsulfonphthalein
Identifiers
Abbreviations	BCG
CAS number	76-60-8 Y
PubChem	6451
ChemSpider	6209 Y
ChEMBL	CHEMBL145704 Y
Jmol-3D images	Image 1
SMILES Brc1cc(c(c(Br)c1O)C)C3(OS(=O)(=O)c2ccccc23)c4cc(Br)c(O)c(Br)c4C
InChI InChI=1S/C21H14Br4O5S/c1-9-12(7-14(22)19(26)17(9)24)21(13-8-15(23)20(27)18(25)10(13)2)11-5-3-4-6-16(11)31(28,29)30-21/h3-8,26-27H,1-2H3 Y Key: FRPHFZCDPYBUAU-UHFFFAOYSA-N Y InChI=1/C21H14Br4O5S/c1-9-12(7-14(22)19(26)17(9)24)21(13-8-15(23)20(27)18(25)10(13)2)11-5-3-4-6-16(11)31(28,29)30-21/h3-8,26-27H,1-2H3 Key: FRPHFZCDPYBUAU-UHFFFAOYAS
Properties
Molecular formula	C21H14Br4O5S
Molar mass	698.01 g mol−1
Acidity (pKa)	4.90 [1]
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Infobox references

Bromocresol Green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes), which 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.

In aqueous solution, both solids ionize to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic form (blue), ^[2] which is stabilized by resonance:

Reaction showing both the acidic and basic forms of Bromocresol green.

The pK (pKa) of this reaction is 4.8.^[3]

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

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

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 pK_a is below 5.0 (carboxylic acids, sulfonic acids etc.). These appear as yellow spots on 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).

References

1. ↑ Kolthoff, I.M. Treatise on Analytical Chemistry, New York, Interscience Encyclopedia, Inc., 1959.
2. ↑ http://antoine.frostburg.edu/chem/senese/101/acidbase/indicators.shtml
3. ↑ D. Diamond, K.T. Lau, S. Brady, J. Cleary, Talanta, 2008, 75, 606-612