1. Any of a class of synthetic organic compounds derived from phthalic anhydride, used as dyes, indicators, and pigments in industrial and laboratory applications.
Usage: chemistry; technical term; often used in compound form (e.g., phenolphthalein, phthalein dyes)

Examples

• Phenolphthalein, a common phthalein, is widely used as a pH indicator in chemistry labs.
• The phthalein family of compounds includes many important industrial dyes.
• Phthalein pigments are valued for their brightness and stability in paints.
• The chemist selected a phthalein derivative for the titration experiment.
• Phthalein-based indicators change color at specific pH levels, making them useful for analytical work.