Structural Formula Vector Image
Title: a-Naphtholphthalein
CAS Registry Number: 596-01-0
CAS Name: 3,3-Bis(4-hydroxynaphthalenyl)-1(3H)-isobenzofuranone
Additional Names: 3,3-bis(4-hydroxy-1-naphthyl)phthalide; di-p-a-naphtholphthalide; p-a-naphtholphthalein
Molecular Formula: C28H18O4
Molecular Weight: 418.44
Percent Composition: C 80.37%, H 4.34%, O 15.29%
Literature References: Prepn: Werner, J. Chem. Soc. 113, 20 (1918). Commercial prepn contains a small amount of the isomeric 3,3-bis(2-hydroxy-1-naphthyl)phthalide.
Properties: Colorless powder when pure; usually grayish-red. mp 253-255°. Practically insol in water. Sol in alcohol.
Melting point: mp 253-255°
Use: As indicator in 0.1% or 0.04% soln in alc. pH 7.3 colorless to reddish; 8.7 greenish to blue. Particularly adapted for weak acids in strong alcoholic soln.

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