Catalog classification, reference sizes, lab math links, and source-backed data. Educational use only — not medical advice.
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Also known as: 3,3-Bis(4-hydroxyphenyl)-1(3H)-isobenzofuranone, 3,3-bis(p-hydroxyphenyl)phthalide, alpha-(p-hydroxyphenyl)-alpha-(4-oxo-2,5-cyclohexadien-1-ylidene)-o-toluic acid, Phthalin, CAS 77-09-8
Phenolphthalein is a synthetic phthalein dye and acid-base indicator. It is colorless under acidic conditions and develops pink to red coloration in alkaline solution, with an indicator transition commonly reported near pH 8.2-9.8. It was formerly used in some over-the-counter laxative preparations. The International Agency for Research on Cancer classifies phenolphthalein as Group 2B, possibly carcinogenic to humans. The U.S. National Toxicology Program reported clear evidence of carcinogenic activity in male and female B6C3F1 mice and in male F344/N rats, with some evidence in female F344/N rats, under the conditions of two-year dietary studies.
Source review pending. This descriptive profile is shown from the available source material as a best-effort educational reference. It has not passed the full verification bar and is not a dosing instruction, medical claim, or treatment recommendation.
Data source: Primary literature, regulator records, trial registries, and identity-specific evidence search
Reflects preclinical/research literature context only. Not a medical claim, dosing instruction, or treatment recommendation.
No reliable compound-specific half-life, onset, storage specification, or catalog-standard common reference size was established from the authoritative sources reviewed. NTP TR-465 reported feed-based animal studies using phenolphthalein of 98%-99% purity. Historical laxative use is included only as background; no human dosing or administration guidance is provided.
Supplementary research context only. Not medical advice or a treatment recommendation.
CAS RN: 77-09-8; PubChem CID: 4764; molecular formula: C20H14O4; molecular weight: 318.33 g/mol
Phenolphthalein is used as an acid-base endpoint indicator and laboratory reagent. NTP TR-465 evaluated dietary exposure in F344/N rats and B6C3F1 mice for 14 days, 13 weeks, and 2 years. The two-year studies used 12,000, 25,000, or 50,000 ppm in rat feed and 3,000, 6,000, or 12,000 ppm in mouse feed. These animal-study exposure levels are research observations and are not human-use recommendations.
Reflects published research. Educational reference — not a recommendation for use.
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Published articles on this site that mention Phenolphthalein or one of its catalog aliases.
Research Use Only. All content is for educational and research reference only. Not medical advice, a treatment recommendation, or guidance on human use. Compounds are not FDA-approved drugs unless specifically noted.