Bromocresol green

Bromocresol green

Names
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
CAS Number	76-60-8 Y
3D model (JSmol)	Interactive image
Abbreviations	BCG
ChEMBL	ChEMBL145704 Y
ChemSpider	6209 Y
ECHA InfoCard	100.000.885
PubChem CID	6451
CompTox Dashboard (EPA)	DTXSID9044459
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
SMILES Brc1cc(c(c(Br)c1O)C)C3(OS(=O)(=O)c2ccccc23)c4cc(Br)c(O)c(Br)c4C
Properties
Chemical formula	C21H14Br4O5S
Molar mass	698.02 g/mol
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) 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), 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.

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

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

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).

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

References

CID 6451 from PubChem