Thymol blue

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Thymol blue

General
Systematic name	4-[9-(4-hydroxy-2-methyl-5-propan-2-yl-phenyl)-7,7-dioxo-8-oxa-7λ6-thiabicyclo[4.3.0]nona-1,3,5-trien-9-yl]-5-methyl-2-propan-2-yl-phenol
CAS name	4,4'-(3H-2,1-Benzoxathiol-3-ylidene)bis[5-methyl-2-(1-methylethyl)phenol]S,S-dioxide
Other names	α-hydroxy-α,α-bis(5-hydroxycarvacryl)-o-toluenesulfonic acid γ-sultone thymolsulfonephthalein
Molecular formula	C₂₇H₃₀O₅S
SMILES	CC1=CC(=C(C=C1C2(C3=CC=CC=C3S(=O)(=O)O2)C4=CC(=C(C=C4C)O)C(C)C)C(C)C)O
Molar mass	466.59^[1] g mol⁻¹
Appearance	Brownish-green crystal powder
CAS number	[76-61-9]
Properties
Solubility in water	Insoluble
In alcohol	Soluble
In dilute alkali solutions	Soluble

Thymol blue is a brownish-green crystal powder that is used as an 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 from at pH 8.0–9.6.