What is phenolphthalein 1

Phenolphthalein C.20H14O4 
White crystalline powder
molar mass 318.323 g / mol

AGWN / A, carcinogenic substance
density 1.277 g / cm3   
Melting point +262.5 ° C
Water solubility 
conc. at 20 ° C 0.092 g / l
GHS 08
Hazard classes + category  
Germ cell mutagenicity 2
Carcinogenicity 1B
Reproductive toxicity FD 2
HP rates (see also note)      
H 341, 350, 361f
P 260.264, 280.1-3.5.7, 308 + 313, 405
disposal G 3
Print a labelGerman designation 
Synonyms (German)
English designation 
CAS 77-09-8Phenolphthalein 
3,3-bis (4-hydroxyphenyl) -1 (3H)- 
3,3-bis (4-hydroxyphenyl) -1 (3H)- 
Note for schools: The current GHS marking, which results from the EC directives, applies to the solid matter and to solutions from 1% concentration. It is recommended to only work with a 0.1% solution. The 0.5%, commercially available reagent can be diluted by a factor of 5 with water. Because of its toxic potential, only diluted phenolphthalein solution should be used and stored in small quantities as a reagent for analysis purposes. A universal indicator solution or a thymolphthalein solution is recommended as a substitute for student exercises.

Pure phenolphthalein is an odorless, white powder that dissolves only slightly in water and well in ethanol and alkaline solutions. The clear, ethanolic solution is suitable as an indicator solution for determining alkaline solutions.

Phenolphthalein as powder and common solution

In the acidic and neutral range, phenolphthalein is in the lactoid form. When alkalis are added, the lactone ring opens and the quinoid form is obtained. At pH 8.2 the color changes from colorless to pink. The color change is reversed by adding acid:

Phenolphthalein: lactoid form (left) and quinoid form (right)
For this reason, phenolphthalein is suitable as an indicator. At a very high pH, ​​close to 14, it becomes colorless again. If the pH value is very low, less than zero, the indicator turns red-orange.

Phenolphthalein is produced by heating 1 mole of phthalic anhydride with 2 moles of phenol with the addition of concentrated sulfuric acid. The phthalic anhydride can be obtained from phthalic acid. In the so-called Friedel-Craft reaction, the elimination of water leads to phenolphthalein:

Phenolphthalein is an important indicator in the laboratory. 0.1% or 1% solutions in ethanol or an ethanol-water mixture are common (> manufacturing instructions). It used to be used as a laxative. Today this application is no longer allowed.