phenolphthaleinn.
/ˌfiːnɒlˈ(f)θeɪlɪɪn/, /ˌfiːnɒlˈ(f)θalɪɪn/, /ˌfiːnɒlˈ(f)θeɪlɪiːn/, /ˌfiːnɒlˈ(f)θalɪiːn/, U.S. /ˌfinəlˈθeɪˌli(ə)n/ Chemistry.
A crystalline solid, C20H14O4, which is the simplest phthalein and is used in alcoholic solution as an indicator in the pH range 8 (colourless) to 10 (red) and also medicinally as a laxative.
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phenolphthalein1875
phenolsulphonphthalein1898
phenol red1916
nitramine1922
1875 Jrnl. Chem. Soc. 28 67 When phenol is gently warmed with phthalic anhydride and sulphuric acid the mixture assumes a brownish yellow colour, from the formation of phenol-phthalein.
1881 J. Attfield Chem. (ed. 9) 658 In delicate experiments turmeric, ‘eosin’, ‘phenolphthalein’, etc., may be used instead of litmus.
1893 Photogr. Ann. 287 For testing the alkalinity of sulphites... The best [indicator] is phenol-phthalein in alcoholic solution.
1946 Nature 23 Nov. 744/2 Back titration of the solution.., using phenolphthalein as an indicator, indicated an apparent equivalent weight of 325.
1974 M. C. Gerald Pharmacol. ii. 31 In some laxatives, such as Ex-Lax and Feen-A-Mint, the active ingredient is phenolphthalein.
1992 Age & Ageing 21 6/2 The end-point of neutralization was indicated by a phenolphthalein colour indicator.
This entry has been updated (OED Third Edition, December 2005; most recently modified version published online March 2022).
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n.1875