Products / pH Indicators

p-XYLENOL BLUE Print Download

C.A.S. No. 125-31-5
M.F. C23H22O5S
M.W. 410.49gm/mole


Dye Content (by Spectrophotometry) >90%
Solubility 0.1 % (MeOH) Clear solution
Transition range pH 8.0-9.6
Absorption maximum (in MeOH) ?max 424+/-5nm
Absorptivity (A1%/1cm, in MeOH) >200
Loss on drying (110°C) <3%

Chemical Name

4,4'-(3H-2,1-Benzoxathiol-3-ylidene)bis(2,5-dimethylphenol) S,S-dioxide

InChI Key



Soluble in acetone, alcohol, and dilute aqueous alkali. Sparingly soluble in water.

Product Description:

Xylenol Blue is a dark brown powder and it belongs to the class of sulfonephthalein dyes. Xylenol Blue changes color from red (pH 1.2) to yellow (2.8) and yellow (8.0) to blue (9.6). It is widely used in food storage, drugs, determining bacterial growth, microbial assays and determining lipase.


Xylenol Blue is a useful alternative to thymol blue developed in the 1920s. Xylenol Blue can be used at half the concentration that thymol blue requires. It is functional at the same two pH ranges, acidic (pH 1-3), which transitions from red to yellow, and basic (pH 8-10), which transitions from yellow to blue. Used in electrochromic displays, chemical sensors, fiber-optic pH sensors, optical quality films, ink, corrosion testing, lubricants, TTI indicators, food storage, cosmetics, bacterial growth, microbiological assays, determining lipase, drugs.

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