Bromocresol green

Bromocresol green
Skeletal formula of bromocresol green in cyclic form
Ball-and-stick model of the bromocresol green molecule in cyclic form
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
Bromcresol green
Identifiers
3D model (JSmol)
Abbreviations BCG
ChemSpider
ECHA InfoCard 100.000.885
Properties
C21H14Br4O5S
Molar mass 698.01 g·mol−1
Appearance Beige to brown powder
Odor Odorless
Melting point 225 °C (437 °F; 498 K) decomposes[1]
Sparingly soluble
Solubility in other solvents Soluble in benzene; very soluble in ethanol and diethyl ether[2]
Acidity (pKa) 4.90[3]
UV-vis (λmax) 423 nm[1]
Hazards
R-phrases (outdated) R36/38
S-phrases (outdated) S24/25-S28-S37-S45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
1
2
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Bromocresol green (pH indicator)
below pH 3.8 above pH 5.4
3.8 ⇌ 5.4

Bromocresol green (BCG) is a dye of the triphenylmethane family (triarylmethane dyes). It is used as a pH indicator in applications such as growth mediums for microorganisms and titrations.

Properties

From left to right solutions of 0.1 M HCl, 3 buffer solutions of pH 3.78, 3 of pH 4.00, 3 of pH 4.62 and NaOH 0.1 M after adding different amounts of bromocresol green (more in darker solutions)

In aqueous solution, bromocresol green will ionize to give the monoanionic form (yellow), that further deprotonates at higher pH to give the dianionic form (blue),[4] which is stabilized by resonance:

The acid dissociation constant (pKa) of this reaction is 4.8.[5]

Absorbance spectrum of bromocresol green at different pH values. The isosbestic point occurs where the acid and basic forms and mixtures thereof have the same absorbance

The acid and basic forms of this dye have an isosbestic point in their UV-Visible spectrum, around 515 nm, indicate that the two forms interconvert directly without forming any other substance.

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).

Uses

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.

Safety

Bromocresol green may cause irritation. Skin and eye contact should be avoided.

References

  1. 1 2 "Bromocresol Green". Sigma Aldrich.
  2. ↑ http://chemicalland21.com/specialtychem/finechem/BROMOCRESOL%20GREEN.htm
  3. ↑ Kolthoff, I.M. Treatise on Analytical Chemistry, New York, Interscience Encyclopedia, Inc., 1959.
  4. ↑ Fred Senese. "Acid-Base Indicators". Frostburg State University Dept. of Chemistry.
  5. ↑ Diamond, D.; Lau, K. T.; Brady, S.; Cleary, J. (2008). "Integration of analytical measurements and wireless communications—Current issues and future strategies". Talanta. 75 (3): 606. doi:10.1016/j.talanta.2007.11.022.
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