Difference between revisions of "Bromothymol blue"
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Latest revision as of 19:17, 23 November 2023
 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.
Contents
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.
