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Bromothymol Blue Chemical Structure

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What is Bromothymol Blue

Bromothymol blue belongs to the family of 2,1-benzoxothioles. It is an organobromine compound which acts as a weak acid in a solution, however, it can exhibit both acid or base form, depending on the pH of the solution.

In addition to acting as a dye and a two-color indicator, it can also serve as an acid-base indicator owing to its property of being yellow in acidic solutions, blue in basic solutions and green in neutral solution.

Macsen Laboratories is the leading manufacturer & supplier of Bromothymol Blue Dye with ISO certification.
Name of Product Bromothymol Blue
IUPAC Name 2-bromo-4-[3-(3-bromo-4-hydroxy-2-methyl-5-propan-2-ylphenyl)-1,1-dioxo-2,1λ6-benzoxathiol-3-yl]-3-methyl-6-propan-2-ylphenol
Synonyms Dibromothymolsulfophthalein; 3,3'-Dibromothymolsulfonphthalein; Bromthymolblau; Azul de bromotimol; Blu di bromotimolo; Bleu de bromothymol
CAS No 76-59-5
Molecular Formula C27H28Br2O5S
Molecular Weight 624.4 g/mol
Pubchem CID 6450
Pubchem SID 469688485

Chemical Properties

SR. No Criteria Limit/Specification
1 Appearance (Form) Solid powder
2 Appearance (Color) White to cream-coloured
3 Melting point 201.0 °C
4 Density 1.25 g/cm3
5 Solubility Sparingly soluble in water
6 Acidity (pKa) 7.0
7 λmax 420 nm
8 Storage temp. Room temp.


  • Bromothymol blue can be used to investigate photosynthetic processes or as a biomarker of respiratory activities.
  • It serves as a pH indicator in the range from 6.0 to 7.6 because of the precise color transition at neutrality.
  • In conjunction with phenol red, it has been used to monitor the asparaginase enzyme activity in fungi.
  • It is used as a vital stain to trace the movement of fluids from the lymph and to define cell walls or nuclei under the microscope
  • It is also used in obstetrics for detecting premature rupture of membranes.


Q. What is the color of Bromothymol  Blue in acid, base and neutral mediums?

Bromothymol Blue shows yellow color in acidic solutions, blue color in basic solutions and green color in neutral solutions respectively.

Q. Is bromothymol blue toxic?

Bromothymol blue is harmful if inhaled and may cause moderate respiratory tract irritation. Also, It is very dangerous if swallowed/ingested and cause gastrointestinal irritation with nausea, vomiting and diarrhea.

Q. Where to buy bromothymol blue?

Macsen Labs is a leading manufacturer and supplier of bromothymol blue with ISO certification.

Q. What is the pKa of bromothymol blue?

The pKa of Bromothymol Blue is approximately 7.0 to 7.2 at 25°C.
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