![Phthalein dye Phthalein dye](/modules/owlapps_apps/img/errorimg.png)
Phthalein dyes are a class of dyes mainly used as pH indicators, due to their ability to change colors depending on pH. They are formed by the reaction of phthalic anhydride with various phenols. They are a subclass of triarylmethane dyes.
Common phthalein dyes include:
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