Bromothymol blue

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Structural formula
Structural formula of bromothymol blue
General
Surname Bromothymol blue
other names
  • 3 ', 3' '- dibromothymolsulfonphthalein
  • BTB
Molecular formula C 27 H 28 Br 2 O 5 S
Brief description

pink powder

External identifiers / databases
CAS number 76-59-5
EC number 200-971-2
ECHA InfoCard 100,000,884
PubChem 6450
Wikidata Q407506
properties
Molar mass 624.39 g mol −1
Physical state

firmly

Melting point

200-202  ° C

solubility
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 .

Bromthymol blue is a triphenylmethane dye and belongs to the group of sulfonphthaleins . It is accessible by bromination of thymol blue . The sodium salt is a pH indicator .

properties

Bromothymol blue changes from yellow to blue at a pH value of 5.8–7.6. Neutral solutions (pH = 7.0) are colored green. His pK s value is 7.1. The color change is based on a change in the chemical structure. In an acidic medium, the molecule is in the pale yellow sulton structure . A ring opening with formation of the intensely blue colored, quinoid triphenylmethane structure takes place in a basic medium.

Bromthymol blue ph.png
Bromthymol blue pH color scale

Bromthymol blue in different stages of protolysis

use

Bromthymol blue can be used as an indicator in acid-base titration and to determine the neutral point (pH = 7.0) in titration , as the color changes to green at 7.0. This is used, for example, as an indicator for the CO 2 content of an aquarium. The desired value of the CO 2 supply can be set via the typical color change .

Furthermore, bromothymol blue is used as a dye in bacteriological culture media and as a sensitizer in electrophotography .

In obstetrics Bromthymolblau is used for the diagnosis of membrane rupture.

  • Bromothymol blue solution: acidic (yellow) and basic / alkaline (blue).

Individual evidence

  1. ↑ a b c Entry on bromothymol blue. In: Römpp Online . Georg Thieme Verlag, accessed on November 10, 2014.
  2. ↑ a b c Datasheet Bromothymol Blue, ACS reagent, Dye content 95% from Sigma-Aldrich , accessed on December 1, 2019 ( PDF ).
  3. ^ Ricardo E. Felberbaum: Specialist examination in gynecology and obstetrics. Elsevier, 2005 ( limited preview in Google Book Search).

Web links

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