Thymolphthalein

 ( Ph Indicators ) 

Thymolphthalein is a phthalein dye used as an acid–base (pH) PH indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. The molar extinction coefficient for the blue thymolphthalein dianion is 38,000 M⁻¹ cm⁻¹ at 595 nm.

Thymolphthalein is also known to have use as a laxative and for disappearing ink.

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Preparation Thymolphthalein can be synthesized from thymol and phthalic anhydride.

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See also

• Phenolphthalein
• Thymolphthalexone

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