Naphtholphthalein

α-Naphtholphthalein (C₂₈H₁₈O₄) is a phthalein dye used as a pH indicator with a visual transition from colorless/reddish to greenish blue at pH 7.3–8.7.

Naphtholphthalein (pH indicator)
below pH 7.3		above pH 8.7
7.3	⇌	8.7

Naphtholphthalein

Skeletal formula
Ball-and-stick model
Names
Preferred IUPAC name 3,3-Bis(4-hydroxynaphthalen-1-yl)-2-benzofuran-1(3H)-one
Other names 1-Naphtholphthalein, alpha-naphtholphthalein, naphtholphthalein blue
Identifiers
CAS Number	596-01-0 Y
3D model (JSmol)	Interactive image
Beilstein Reference	97816
ChemSpider	62215 N
ECHA InfoCard	100.008.979
PubChem CID	68993
UNII	2QEG1706NN Y
CompTox Dashboard (EPA)	DTXSID70208273
SMILES C1=CC=C2C(=C1)C(=CC=C2O)C3(C4=CC=CC=C4C(=O)O3)C5=CC=C(C6=CC=CC=C65)O
Properties
Chemical formula	C28H18O4
Molar mass	418.448 g·mol−1
Appearance	Colorless-reddish to blue-green solid
Melting point	238–240 °C (460–464 °F; 511–513 K)[1]
Solubility in water	Insoluble
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Irritant
GHS labelling:
Pictograms	[1]
Signal word	Warning
Hazard statements	H315, H319, H335[1]
Precautionary statements	P261, P305+P351+P338[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references