Thymolphthalein
Appearance
Names | |
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IUPAC name
3,3-bis(4-hydroxy-2-methyl-5-propan-2-ylphenyl)-2-benzofuran-1-one
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Identifiers | |
3D model (JSmol)
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ChEMBL | |
ChemSpider | |
ECHA InfoCard | 100.004.300 |
EC Number |
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PubChem CID
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CompTox Dashboard (EPA)
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Properties | |
C28H30O4 | |
Molar mass | 430.544 g·mol−1 |
Appearance | White powder |
Melting point | 248 to 252 °C (478 to 486 °F; 521 to 525 K) (decomposes) |
Hazards | |
NFPA 704 (fire diamond) | |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Thymolphthalein is an acid–base (pH) indicator. Its transition range is around pH 9.3–10.5. Below this pH, it is colorless; above, it is blue. Thymolphthalein is used as a visual indicator for the pH of swimming pools, changing the water blue when the pH increases, it can be used to detect the presence of urine being introduced into the normally neutral pH of the water. The molar extinction coefficient for the blue thymolphthalein dianion is 38,000 M−1 cm−1 at 595 nm.[1]
Thymolphthalein (pH indicator) | ||
below pH 9.3 | above pH 10.5 | |
9.3 | ⇌ | 10.5 |
Preparation
Thymolphthalein can be synthesized from thymol and phthalic anhydride by Friedel-Crafts alkylation:
References
- ^ Hahn HH; Cheuk SF; Elfenbein S; Wood WB (April 1970). "Studies on the Pathogenesis of Fever: Xix. Localization of Pyrogen in Granulocytes" (PDF). J. Exp. Med. 131 (4): 701–9. doi:10.1084/jem.131.4.701. PMC 2138774. PMID 5430784.