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
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
3D model (JSmol)
97816
ChemSpider
ECHA InfoCard 100.008.979
UNII
  • C1=CC=C2C(=C1)C(=CC=C2O)C3(C4=CC=CC=C4C(=O)O3)C5=CC=C(C6=CC=CC=C65)O
Properties
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]
Insoluble
Hazards
Occupational safety and health (OHS/OSH):
Main hazards
 Irritant
GHS labelling:
[1]
Warning
H315, H319, H335[1]
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).
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Infobox references

References
  1. α-Naphtholphthalein
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