Difference between revisions of "Bromothymol blue"

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[[Category:Aromatic compounds]]
 
[[Category:Aromatic compounds]]
 
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[[Category:Triarylmethane dyes]]
 
[[Category:PH indicators]]
 
[[Category:PH indicators]]

Latest revision as of 19:17, 23 November 2023

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 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)
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.

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

Physical

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.

Availability

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

Preparation

Bromothymol blue can be synthesized by addition of elemental bromine to thymol blue in a solution in glacial acetic acid. Thymol blue itself can be prepared by reacting saccharin with thymol.

Bromothymol blue however, 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

Bromothymol blue should be kept 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