Thymolphthalein is a phthalein dye used as an acid– base ( pH)

indicator Indicator may refer to: Biology * Environmental indicator of environmental health (pressures, conditions and responses) * Ecological indicator of ecosystem health (ecological processes) * Health indicator, which is used to describe the health o ...

. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The

molar extinction coefficient In chemistry, the molar absorption coefficient or molar attenuation coefficient is a measurement of how strongly a chemical species absorbs, and thereby attenuates, light at a given wavelength. It is an intrinsic property of the species. The SI ...

for the blue thymolphthalein

dianion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

is 38,000 M⁻¹ cm⁻¹ at 595 nm. Thymolphthalein is also known to have use as a

laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, lub ...

and for disappearing ink.

Preparation

Thymolphthalein can be synthesized from

thymol Thymol (also known as 2-isopropyl-5-methylphenol, IPMP), , is a natural monoterpenoid phenol derivative of ''p''-Cymene, isomeric with carvacrol, found in oil of thyme, and extracted from '' Thymus vulgaris'' (common thyme), ajwain, and va ...

and

phthalic anhydride Phthalic anhydride is the organic compound with the formula C6H4(CO)2O. It is the anhydride of phthalic acid. Phthalic anhydride is a principal commercial form of phthalic acid. It was the first anhydride of a dicarboxylic acid to be used comm ...

. :

References

{{reflist PH indicators Triarylmethane dyes Phthalides Phenols Isopropyl compounds