Thymolphthalein

Thymolphthalein

Names
IUPAC name 3,3-bis(4-hydroxy-2-methyl-5-propan-2-ylphenyl)-2-benzofuran-1-one
Identifiers
CAS Number	125-20-2
ChEMBL	ChEMBL587849
ChemSpider	29054
EC Number	204-729-7
Jmol 3D model	Interactive image
PubChem	31316
InChI InChI=1S/C28H30O4/c1-15(2)20-13-23(17(5)11-25(20)29)28(22-10-8-7-9-19(22)27(31)32-28)24-14-21(16(3)4)26(30)12-18(24)6/h7-16,29-30H,1-6H3 Key: LDKDGDIWEUUXSH-UHFFFAOYSA-N InChI=1/C28H30O4/c1-15(2)20-13-23(17(5)11-25(20)29)28(22-10-8-7-9-19(22)27(31)32-28)24-14-21(16(3)4)26(30)12-18(24)6/h7-16,29-30H,1-6H3 Key: LDKDGDIWEUUXSH-UHFFFAOYAV
SMILES O=C1OC(c2ccccc12)(c3cc(c(O)cc3C)C(C)C)c4cc(c(O)cc4C)C(C)C
Properties
Chemical formula	C28H30O4
Molar mass	430.54 g·mol^−1
Appearance	White powder
Melting point	248 to 252 °C (478 to 486 °F; 521 to 525 K) (decomposes)
Hazards
R-phrases	4, 10
S-phrases	S22 S24/25
NFPA 704	0 1 0
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

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 38000 M⁻¹cm⁻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

1. 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.