Bromothymol Blue

CAS Number:  76-59-5
Molecular Weight: 624.38
MDL number: MFCD00005872
EC Index Number: 200-971-2

General description

Bromothymol Blue, also known as, dibromothymolsulfonphthalein is a sulfonated hydroxyquinone in acidic aqueous solutions. In alkaline solutions, this dye is present as a moderately sized dianion. It is also known as bromthymol blue and dibromothymolsulfonphthalein. It is a pH-sensitive dye that changes color from yellow to blue.


Bromothymol blue dye serves as a pH indicator because of the precise color transition at neutrality. Other applications include:

  • as a vital stain to trace the movement of fluids from the lymph and to define cell walls or nuclei under the microscope
  • for the demonstration of fungal hyphae within plant roots
  • in the assessment of the soluble acidity within single rice grains
  • use in an agar gel medium for enumeration of Bacillus cereus
  • as a component of several bacterial growth and detection substrates such as cystine lactose electrolyte deficient (CLED/BROLACIN); polymyxin pyruvate egg yolk mannitol bromothymol blue (PEMBA) and MacConkey agar.


grade ACS reagent
Quality Level 200
form powder
composition Dye content, 95%
visual transition interval 6.0-7.6, yellow to blue(passes test)
mp 200-202 °C (lit.)
λmax 420 nm
ε (extinction coefficient) ≥17000 at 419-425 nm in methanol

≥8000 at 326-332 nm in methanol

≥9000 at 279-285 nm in methanol

storage temp. room temp
SMILES string CC(C)c1cc(c(C)c(Br)c1O)C2(OS(=O)(=O)c3ccccc23)c4cc(C(C)C)c(O)c(Br)c4C
InChI 1S/C27H28Br2O5S/c1-13(2)17-11-20(15(5)23(28)25(17)30)27(19-9-7-8-10-22(19)35(32,33)34-27)21-12-18(14(3)4)26(31)24(29)16(21)6/h7-14,30-31H,1-6H3