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)
Names
Other names
BTB
3,3'-Dibromothymolsulfonphthalein
Dibromothymolsulfophthalein
Properties
C27H28Br2O5S
Molar mass 624.38 g/mol
Appearance Mauve solid
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)
Hazards
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.

Properties

Chemical

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

Physical

Bromothymol blue is an odorless mauve solid, 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.

Availability

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

Preparation

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

Projects

  • pH indicator

Handling

Safety

Bromothymol blue is irritant and should be handled with care.

Storage

In closed bottles, away from corrosive vapors.

Disposal

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.

References

Relevant Sciencemadness threads