Bromothymol blue

Bromothymol blue
IUPAC name 4,4'-(1,1-dioxido-3H-2,1-benzoxathiole-3,3-diyl)bis(2-bromo-6-isopropyl-3-methylphenol)
Identifiers
CAS number	76-59-5 Y
PubChem	6450
ChemSpider	6208 Y
UNII	VGU4LM0H96 Y
Jmol-3D images	Image 1
SMILES Brc1c(O)c(cc(c1C)C3(OS(=O)(=O)c2ccccc23)c4cc(c(O)c(Br)c4C)C(C)C)C(C)C
InChI 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 Y Key: NUHCTOLBWMJMLX-UHFFFAOYSA-N Y InChI=1/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 Key: NUHCTOLBWMJMLX-UHFFFAOYAD
Properties
Molecular formula	C27H28Br2O5S
Molar mass	624.38 g mol−1
Density	1.25 g/cm3
Melting point	202 °C, 475 K, 396 °F
Acidity (pKa)	7.10
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Y (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Bromothymol blue (also known as bromothymol sulfone phthalein, Bromthymol Blue, and BTB) is a chemical indicator for weak acids and bases. The chemical is also used for observing photosynthetic activities or respiratory indicators (turns yellow as CO₂ is added).^[1][2]

Bromothymol blue acts as a weak acid in solution. It can thus be in protonated or deprotonated form, appearing yellow and blue respectively. It is bluish green in neutral solution. It is typically sold in solid form as the sodium salt of the acid indicator. It also finds occasional use in the laboratory as a biological slide stain. At this point it is already blue, and a drop or two is used on a water slide. The cover slip is placed on top of the water droplet and the specimen in it, with the blue coloring mixed in. It is sometimes used to define cell walls or nuclei under the microscope.

Bromothymol blue is mostly used in measuring substances that would have relatively low acidic or basic levels (near a neutral pH). It is often used in managing the pH of pools and fish tanks, and for measuring the presence of carbonic acid in a liquid.

A common demonstration of BTB's pH indicator properties involves exhaling through a tube into a neutral solution of BTB. As carbon dioxide is absorbed from the breath into the solution, forming carbonic acid, the solution changes color from green to yellow. Thus, BTB is commonly used in middle school science classes to demonstrate that the more that muscles are used, the greater the CO₂ output.

Bromothymol is also used in obstetrics for detecting premature rupture of membranes. Amniotic fluid typically has a pH > 7.2, bromothymol will therefore turn blue when brought in contact with fluid leaking from the amnion. As vaginal pH normally is acidic, the blue color indicates the presence of amniotic fluid. The test may be false-positive in the presence of other alkaline substances such as blood, semen, or in the presence of bacterial vaginosis.

The pKa for bromothymol blue is 7.10.

Bromthymol Blue is sparingly soluble in water; soluble in alcohol and in aqueous solutions of alkalies. Also soluble in ether. Less soluble in benzene, toluene, xylene. Practically insoluble in petroleum ether. To prepare a solution for use as pH indicator, dissolve 0.10 g in 8.0 mL N/50 NaOH and dilute with water to 250 mL. To prepare a solution for use as indicator in volumetric work, dissolve 0.1 g in 100 mL of 50% (v/v) ethanol.^[3]

Indicator colors

BTB indicator in acidic, neutral, and alkaline solutions (left to right).

Structure at different pH ranges

References

See also

• pH indicator
• Litmus
• Phenolphthalein
• Methyl orange
• Universal indicator

External links

• J.T.Baker MSDS
• Bromothymol Blue (Sodium Salt) -Sigma Aldrich