7244. Phenolphthalin

Nomenclature

CAS number: 81-90-3
2-[Bis(4-hydroxyphenyl)methyl]benzoic acid; decolorized phenolphthalein; phthalin; 4′,4″-dihydroxytriphenylmethane-2-carboxylic acid.
C20H16O4; mol wt 320.34.
C 74.99%, H 5.03%, O 19.98%.

Description and references

Made by boiling phenolphthalein with zinc dust in alkaline soln. Called “Kastle-Meyer reagent” when in soln. Prepd by dissolving 2 g phenolphthalin + 20 g KOH in a desired amt of doubly distd H2O and diluting with an equal vol of 95% ethanol. Detailed directions for prepn of test soln and its use: Lecoq, Bull. Soc. Chim. Belg. 54, 186-202 (1945), C.A. 41, 2346i (1947).

Chemical structure

Properties

Colorless crystals, mp 237°. Insol in water; sol in alcohol, ether, aq alkali. The alkaline solns gradually become pink on exposure to air or other oxidizing substances.

Use

As a reagent for oxidases, blood, HCN, peroxides, copper.