Bromothymol blue

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Bromothymol blue
Bromothymol blue bottle sample solution.jpg
Bromothymol blue in solid form and as solution at pH < 6.5 (yellow), pH 6.5-7.2 (green) and pH > 7.2 (blue)
Other names
Molar mass 624.38 g/mol
Appearance Colorless solid (fresh)
Lilac/mauve solid (old)
Odor Odorless
Density 1.25 g/cm3
Melting point 202 °C (396 °F; 475 K) (decomposes)
Boiling point Decomposes
Slightly soluble in water
Solubility Soluble in acetone, diethyl ether, ethanol, methanol
Poorly soluble in aq. ammonia
Slightly soluble in chloroform, isopropanol
Insoluble in glycerol, hexane, petroleum ether
Vapor pressure ~0 mmHg (20 °C)
Safety data sheet AcrosOrganics
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Bromothymol blue (IUPAC: 4,4′-(1,1-Dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2-bromo-6-isopropyl-3-methylphenol)) is a pH indicator, commonly used for determining the neutral pH of a solution, as the indicator turns the solution green in a very narrow range (6.5-7.2). It has the chemical formula C27H28Br2O5S.



Bromothymol blue turns yellow in solutions with pH < 6.5, green between 6.5 - 7.2 and blue at pH > 7.2.

Bromothymol blue slowly oxidizes in air, turning lilac/purple, though this does not affect its pH sensitivity.


Bromothymol blue is an odorless colorless solid, that turns lilac/purple over long periods of time in contact with air. It is almost insoluble in water, but soluble in aq. alkali, acetone, methanol, diethyl ether and ethanol, slightly soluble in aq. ammonia, chloroform, isopropanol and insoluble in glycerol as well as non-polar solvents such as hexane, petroleum ether.


Bromothymol blue can be purchased online or from chemical suppliers. It can be found on eBay.


Bromothymol blue is best purchased than synthesized, as it's a lot cheaper.


  • pH indicator



Bromothymol blue is irritant and should be handled with care.


Bromothymol blue should be kept in closed bottles, away from corrosive vapors.


Bromothymol blue can be neutralized with a strong oxidizing solution, such as chromic acid, Fenton's reagent or piranha solution, followed by neutralization and then poured down the drain after all the bromothymol blue has been neutralized. Since most of bromothymol blue neutralized this way is either as solution or traces, there is little risk of splashing.


Relevant Sciencemadness threads