Phthalein dye

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Chemical structure of phenolphthalein, a common phthalein dye

Phthalein dyes are a class of dyes mainly used as pH indicators, due to their ability to change colors depending on pH.[1] The are formed by the reaction of phthalic anhydride with various phenols. They are a subclass of triarylmethane dyes.

Common phthalein dyes include:


  1. ^ Sabnis, Ram W. (2010). "Phthalein Dyes". Kirk-Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.phthsabn.a01. ISBN 978-0471238966.