6389. α-Naphtholphthalein

Nomenclature

CAS number: 596-01-0
3,3-Bis(4-hydroxynaphthalenyl)-1(3H)-isobenzofuranone; 3,3-bis(4-hydroxy-1-naphthyl)phthalide; di-p-α-naphtholphthalide; p-α-naphtholphthalein.
C28H18O4; mol wt 418.44.
C 80.37%, H 4.34%, O 15.29%.

Description and 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.

Chemical structure

Properties

Colorless powder when pure; usually grayish-red. mp 253-255°. Practically insol in water. Sol in alcohol.

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.