Naphtholphthalein

  • 3,3- bis (4- hydroxy-1 -naphthyl) - 2 -benzofuran- 1-one ( IUPAC)
  • α - Naphtholphthalein

Colorless- red to blue-green ( brownish)

Fixed

253-255 ° C

  • Soluble in ethanol
  • Insoluble in water

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Naphtholphthalein is a triphenylmethane dye and belongs to the family of phthaleins. The name is composed of naphthol and phthalic anhydride. It is used as a pH indicator.

Properties

There is a color change area before:

  • PH 7.3 to 8.7: color change from colorless to reddish to bluish green

Naphtholphthalein is not soluble in water and is usually in 0.1 % alcoholic solution use. It is itself a weak acid.

Representation

In a Friedel -Crafts acylation of α -naphthol and a small amount of phthalic anhydride are reacted in the presence of concentrated sulfuric acid.

CAS registry number PubChem Digital Object Identifier
592099
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