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(fē`nôlthăl`ēən), or 2,2-Bis(p-hydroxyphenyl) phthalide, C20H14O4, crystalline organic compound. It is used medicinally as a laxative and is widely employed in the laboratory as an indicatorindicators, acid-base,
organic compounds that, in aqueous solution, exhibit color changes indicative of the acidity or basicity of the solution. Common indicators include p-nitrophenol, which is colorless from pH 1 to 5 and yellow from p
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 of the acidity or basicity of solutions. In pure water it is insoluble, but it is soluble in basic solutions or in ethanol or acetone. In a solution with pH greater than 8 (pH 8 is mildly basic) phenolphthalein is pink to red in color, but at pH less than 8 it is colorless. Phenolphthalein is a phenol derivative of phthalic anhydride.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(also 4, 4’-dihydroxyphthalophenone), C20H1404, a colorless, odorless, and tasteless crystalline compound that is only slightly soluble in water but highly soluble in alcohol. The melting point is 259°–263°C. The compound is obtained through the condensation of phenol with phthalic anhydride.

Phenolphthalein is used in analytical chemistry as an indicator in the titration of acids and alkalies (the compound being colorless in neutral and acidic mediums and raspberry red in weakly alkaline mediums, the interval for the color change being pH 8.2–10). In medicine, the compound is used as a laxative, the therapeutic effect of which derives from increased peristalsis of the large intestine. Phenolphthalein is prescribed in tablet form as a treatment for chronic constipation, each tablet containing 0.1 g of the compound.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


(organic chemistry)
(C6H4OH)2COC6H4CO Pale-yellow crystals; soluble in alcohol, ether, and alkalies, insoluble in water; used as an acid-base indicator (carmine-colored to alkalies, colorless to acids) for titrations, as a laxative and dye, and in medicine.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.