Bromothymol blue

From Wikipedia, the free encyclopedia


Bromothymol blue
Systematic (IUPAC) name
4,4'-(3H-2,1 Benzoxathiol-3-ylidene) bis [2 bromo-3-methyl-6-(1-methylethyl)phenol] S,S-dioxide
Abbreviations
BTB
Identifiers
CAS number	76-59-5
PubChem	6450
Chemical data
Formula	C₂₇H₂₈Br₂O₅S
Molar mass	624.39
pK_a	7.10
SMILES	CC(C)c1cc(c(C)c(Br)c1O)C3(O[S+] (=O)(O)c2ccccc23)c4cc(C(C)C)c(O)c(Br)c4C
Physical data
Density	1.25 g/cm³
Melt. point	202 °C (396 °F)
Complete data

Bromothymol Blue (also known as dibromothymolsulfonephthalein, 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).

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 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.

Bromothymol is also used in Obstetrics for detecting premature rupture of membranes.

The pKa for bromothymol blue is 7.10.