Thymol blue

Thymol blue is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions.
It transitions from red to yellow at pH 1.2–2.8 and from yellow to blue at pH 8.0–9.6. It is usually a component of Universal indicator.
At wavelength nm, extinction coefficient > 8000 and at wavelength nm, the extinction coefficient > 12000.

Structures

Thymol blue has different structures at different pH.

Safety

It may cause irritation. Its toxicological properties have not been fully investigated. Harmful if swallowed, Acute Toxicity. Only Hazardous when percent values are above 10%.