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"phph" redirects here. For Ph-Ph, see biphenyl.
Sample of solid phenolphthalein.jpg
CAS number 77-09-8 YesY
PubChem 4764
ChemSpider 4600 YesY
DrugBank DB04824
KEGG D05456 YesY
ATC code A06AB04
Jmol-3D images Image 1
Molecular formula C20H14O4
Molar mass 318.32 g mol−1
Appearance White powder
Density 1.277 g/cm3 (32 °C)
Melting point 258–263 °C (496–505 °F; 531–536 K) [1]
Boiling point N/A
Solubility in water Insoluble
Solubility in other solvents Insoluble in benzene or hexane, very soluble in ethanol and ether, slightly soluble in DMSO
λmax 552 nm (1st)
374 nm (2nd)[1]
GHS pictograms The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[1]
GHS signal word Danger
GHS hazard statements H341, H350, H361[1]
GHS precautionary statements P201, P281, P308+313[1]
EU classification Toxic T Harmful Xn
R-phrases R22, R40, R45, R62, R68,
S-phrases S53, S45
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Phenolphthalein /ˌfnɒlfˈθln/[2] is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Often used in titrations, it turns colorless in acidic solutions and pink in basic solutions. If the concentration of indicator is particularly strong, it can appear purple. In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH. The molecule has four forms:

Species H3In+ H2In In2− In(OH)3−
Structure Phenolphthalein-very-low-pH-2D-skeletal.svg Phenolphthalein-low-pH-2D-skeletal.svg Phenolphthalein-mid-pH-2D-skeletal.svg Phenolphthalein-high-pH-2D-skeletal.svg
Model Phenolphthalein-orange-very-low-pH-3D-balls.png Phenolphthalein-colourless-low-pH-3D-balls.png Phenolphthalein-red-mid-pH-3D-balls.png Phenolphthalein-colourless-high-pH-3D-balls.png
pH <0 0−8.2 8.2−12.0 >13.0
Conditions strongly acidic acidic or near-neutral basic strongly basic
Color orange
pink to fuchsia colorless
Image Phenolphthalein-in-conc-sulfuric-acid.jpg Phenolphthalein-at-pH-9.jpg

The rather slow fading reaction that produces the colorless InOH3− ion is sometimes used in classes for the study of reaction kinetics.

Phenolphthalein is insoluble in water and usually is dissolved in alcohols for use in experiments. It is a weak acid, which can lose H+ ions in solution. The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink. When a base is added to the phenolphthalein, the molecule ions equilibrium shifts to the right, leading to more ionization as H+ ions are removed. This is predicted by Le Chatelier's principle.


Phenolphthalein is synthesized by condensation of phthalic anhydride with two equivalents of phenol under acidic conditions (hence the name). It was discovered in 1871 by Adolf von Baeyer.[3][4][5]

Synthesis of phenolphthalein


Phenolphthalein (pH indicator)
below pH 8.2 between
pH 10.0 and 13.0
colorless fuchsia

Phenolphthalein has been used for over a century as a laxative, but is now being removed from over-the-counter laxatives[6] because of concerns over carcinogenicity.[7][8]

Phenolphthalein is used in a test to identify substances thought to contain blood, commonly known as the Kastle-Meyer test. A dry sample is collected with a swab or filter paper. A few drops of alcohol, then a few drops of phenolphthalein, and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample contains hemoglobin, it will turn pink, considered a positive test and indicates the sample contains hemoglobin and, therefore, is likely blood. This test is not destructive to the sample; it can be kept and used in further tests. This test has the same reaction with blood from any animal, so further testing would be required to determine whether it originates from a human.

Phenolphthalein is used in toys, for example as a component of disappearing inks, or disappearing dye on the Hollywood Hair Barbie hair. In the ink, it is mixed with sodium hydroxide, which reacts with carbon dioxide in the air. This reaction leads to the pH falling below the color change threshold as hydrogen ions are released by the reaction:

OH(aq) + CO2(g)CO32−(aq) + H+(aq)

To develop the hair and "magic" graphical patterns, the ink is sprayed with a solution of hydroxide, which leads to the appearance of the hidden graphics by the same mechanism described above for color change in alkaline solution. The pattern will eventually disappear by the reaction with carbon dioxide. Thymolphthalein is used for the same purpose and in the same way, when a blue color is desired.[9]

Phenolphthalein is used as an acid or base indicator where, in contact or presence of acid, it will turn colorless and with a base, it will turn into a fuchsia color. It is also a component in universal indicator, a solution consisting of a mixture of pH indicators (usually phenolphthalein, methyl red, bromothymol blue, and thymol blue).[10]

The acid-base indication abilities of phenolphthalein also make it useful for testing for signs of carbonation reactions in concrete. Concrete has naturally high pH due to the calcium hydroxide formed when Portland cement reacts with water. The pH of the ionic water solution present in the pores of fresh concrete may be over 14. Normal carbonation of concrete occurs as the cement hydration products in concrete react with carbon dioxide in the atmosphere, and can reduce the pH to 8.5 to 9, although that reaction usually is restricted to a thin layer at the surface. When a 1% phenolphthalein solution is applied to normal concrete, it turns bright pink. If the concrete has undergone carbonation, no color change will be observed.


Despite concerns regarding its carcinogenicity, the use of phenolphthalein as a laxative is unlikely to cause ovarian cancer.[11] Phenolphthalein has been found to inhibit human cellular calcium influx via store-operated calcium entry (SOCE) by inhibiting thrombin and thapsigargin, two activators of SOCE that increase intracellular free calcium.[12]

See also[edit]


  1. ^ a b c d e "Phenolphthalein". Retrieved 7 October 2014. 
  2. ^ "phenolphthalein". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. 
  3. ^ Baeyer, A. (1871). "Ueber eine neue Klasse von Farbstoffen". Berichte der Deutschen Chemischen Gesellschaft 4 (2): 555–558. doi:10.1002/cber.18710040209. 
  4. ^ Baeyer, A. (1871). "Ueber die Phenolfarbstoffe". Berichte der Deutschen Chemischen Gesellschaft 4 (2): 658–665. doi:10.1002/cber.18710040247. 
  5. ^ Baeyer, A. (1871). "Ueber die Phenolfarbstoffe". Polytechnisches Journal 201 (89): 358–362. 
  6. ^ Spiller, H. A.; Winter, M. L.; Weber, J. A; Krenzelok, E. P.; Anderson, D. L.; Ryan, M. L. (May 2003). "Skin Breakdown and Blisters from Senna-Containing Laxatives in Young Children". The Annals of Pharmacotherapy 37 (5): 636–639. doi:10.1345/aph.1C439. ISSN 1060-0280. PMID 12708936. 
  7. ^ Dunnick, J. K.; Hailey, J. R. (1996). "Phenolphthalein Exposure Causes Multiple Carcinogenic Effects in Experimental Model Systems" (pdf). Cancer Research 56 (21): 4922–4926. PMID 8895745. 
  8. ^ Tice, R. R.; Furedi-Machacek, M.; Satterfield, D.; Udumudi, A.; Vasquez, M.; Dunnick, J. K. (1998). "Measurement of Micronucleated Erythrocytes and DNA Damage during Chronic Ingestion of Phenolphthalein in Transgenic Female Mice Heterozygous for the p53 Gene". Environmental and Molecular Mutagenesis 31 (2): 113–124. doi:10.1002/(SICI)1098-2280(1998)31:2<113::AID-EM3>3.0.CO;2-N. ISSN 0893-6692. PMID 9544189. 
  9. ^ Toystore
  10. ^ "Universal Indicator". ISCID Encyclopedia of Science and Philosophy. [dead link]
  11. ^ Cooper, G. S.; Longnecker, M. P.; Peters, R. K. (2004). "Ovarian Cancer Risk and Use of Phenolphthalein-Containing Laxatives". Pharmacoepidemiology and Drug Safety 13 (1): 35–39. doi:10.1002/pds.824. PMID 14971121. 
  12. ^ Dobrydneva, Y.; Wilson, E.; Abelt, C. J.; Blackmore, P. F. (2009). "Phenolphthalein as a Prototype Drug for a Group of Structurally Related Calcium Channel Blockers in Human Platelets". Journal of Cardiovascular Pharmacology 53 (3): 231–240. doi:10.1097/FJC.0b013e31819b5494. PMID 19247192. 

External links[edit]