Phenolphthalein

Phenolphthalein
Names
	Preferred IUPAC name 3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one
	Other names 3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3H)-one
Identifiers
CAS Number	77-09-8 ;
3D model (JSmol)	Interactive image;
ChEMBL	ChEMBL63857 ;
ChemSpider	4600 ;
DrugBank	DB04824 ;
ECHA InfoCard	100.000.914
KEGG	D05456 ;
PubChem CID	4764;
UNII	6QK969R2IF ;
CompTox Dashboard (EPA)	DTXSID0021125 ;
	InChI InChI=1S/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H Key: KJFMBFZCATUALV-UHFFFAOYSA-N ; InChI=1/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H Key: KJFMBFZCATUALV-UHFFFAOYAH;
	SMILES O=C1OC(C2=C1C=CC=C2)(C3=CC=C(C=C3)O[H])C4=CC=C(C=C4)O[H];
Properties
Chemical formula	C20H14O4
Molar mass	318.328 g·mol−1
Appearance	White powder
Density	1.277 g/cm3 (32 °C (90 °F))
Melting point	258–263 °C (496–505 °F; 531–536 K)
Solubility in water	400 mg/l
Solubility in other solvents	Insoluble in benzene and hexane; very soluble in ethanol and ether; slightly soluble in DMSO
UV-vis (λmax)	552 nm (1st); 374 nm (2nd)
Pharmacology
ATC code	A06AB04 (WHO)
Hazards
	GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H341, H350, H361
Precautionary statements	P201, P281, P308+P313
NFPA 704 (fire diamond)	2 3 0
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Phenolphthalein (/fɛˈnɒl(f)θəliːn/ feh-NOL(F)-thə-leen) is a chemical compound with the formula C₂₀H₁₄O₄ and is often written as "HIn", "HPh", "phph" or simply "Ph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions. It belongs to the class of dyes known as phthalein dyes.

Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols in experiments. It is a weak acid, which can lose H⁺ ions in solution. The nonionized phenolphthalein molecule is colorless and the double deprotonated phenolphthalein ion is fuchsia. Further proton loss in higher pH occurs slowly and leads to a colorless form. Phenolphthalein ion in concentrated sulfuric acid is orange red due to sulfonation.