Phenolphthalein

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Phenolphthalein
Phenolphthalein-low-pH-2D-skeletal.svg
Sample of solid phenolphthalein.jpg
Identifiers
CAS number77-09-8 YesY
PubChem4764
ChemSpider4600 YesY
DrugBankDB04824
KEGGD05456 YesY
ChEMBLCHEMBL63857 YesY
ATC codeA06AB04
Jmol-3D imagesImage 1
Properties
Molecular formulaC20H14O4
Molar mass318.32 g mol−1
AppearanceWhite powder
Density1.277 g/cm3 (32 °C)
Melting point258–263 °C (496–505 °F; 531–536 K) [1]
Boiling pointN/A
Solubility in waterSoluble
Solubility in other solventsInsoluble in benzene or hexane, very soluble in ethanol and ether, slightly soluble in DMSO
λmax552 nm (1st)
374 nm (2nd)[1]
Hazards
GHS pictogramsThe health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[1]
GHS signal wordDanger
GHS hazard statementsH341, H350, H361[1]
GHS precautionary statementsP201, P281, P308+313[1]
EU classificationToxic T Harmful Xn
R-phrasesR22, R40, R45, R62, R68,
S-phrasesS53, S45
NFPA 704
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
 
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"phph" redirects here. For Ph-Ph, see biphenyl.
Phenolphthalein
Phenolphthalein-low-pH-2D-skeletal.svg
Sample of solid phenolphthalein.jpg
Identifiers
CAS number77-09-8 YesY
PubChem4764
ChemSpider4600 YesY
DrugBankDB04824
KEGGD05456 YesY
ChEMBLCHEMBL63857 YesY
ATC codeA06AB04
Jmol-3D imagesImage 1
Properties
Molecular formulaC20H14O4
Molar mass318.32 g mol−1
AppearanceWhite powder
Density1.277 g/cm3 (32 °C)
Melting point258–263 °C (496–505 °F; 531–536 K) [1]
Boiling pointN/A
Solubility in waterSoluble
Solubility in other solventsInsoluble in benzene or hexane, very soluble in ethanol and ether, slightly soluble in DMSO
λmax552 nm (1st)
374 nm (2nd)[1]
Hazards
GHS pictogramsThe health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[1]
GHS signal wordDanger
GHS hazard statementsH341, H350, H361[1]
GHS precautionary statementsP201, P281, P308+313[1]
EU classificationToxic T Harmful Xn
R-phrasesR22, R40, R45, R62, R68,
S-phrasesS53, S45
NFPA 704
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. Phenolphthalein is often used as an indicator in titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.

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.

Synthesis[edit]

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

Uses[edit]

Indicator[edit]

Phenolphthalein's most common use is as an indicator in acid-base titrations. It also serves as a component of universal indicator, together with methyl red, bromothymol blue, and thymol blue.[6]

Phenolphthalein (pH indicator)
below pH 8.2between
pH 10.0 and 13.0
colorlessfuchsia


Phenolphthalein adopts four different states in aqueous solution: Under very strongly acidic conditions, it exists in protonated form, providing an orange coloration. Under strongly acidic conditions, the lactone form is colorless. The singly deprotonated phenolate form gives the familiar pink color. In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH. The rather slow fading reaction that produces the colorless InOH3− ion is sometimes used in classes for the study of reaction kinetics.

SpeciesH3In+H2InIn2−In(OH)3−
StructurePhenolphthalein-very-low-pH-2D-skeletal.svgPhenolphthalein-low-pH-2D-skeletal.svgPhenolphthalein-mid-pH-2D-skeletal.svgPhenolphthalein-high-pH-2D-skeletal.svg
ModelPhenolphthalein-orange-very-low-pH-3D-balls.pngPhenolphthalein-colourless-low-pH-3D-balls.pngPhenolphthalein-red-mid-pH-3D-balls.pngPhenolphthalein-colourless-high-pH-3D-balls.png
pH<00−8.28.2−12.0>13.0
Conditionsstrongly acidicacidic or near-neutralbasicstrongly basic
Colororange
colorless
pink to fuchsiacolorless
ImagePhenolphthalein-in-conc-sulfuric-acid.jpgPhenolphthalein-at-pH-9.jpg

Phenolphthalein's pH sensitivity is exploited in other applications: Concrete has naturally high pH due to the calcium hydroxide formed when Portland cement reacts with water. As the concrete reacts with carbon dioxide in the atmosphere, pH decreases to 8.5-9. When a 1% phenolphthalein solution is applied to normal concrete, it turns bright pink; if it remains colorless, it shows that the concrete has undergone carbonation. In a similar application, spackling used to repair holes in drywall contains phenolphthalein. When applied, the basic spackling material retains a pink coloration; when the spackling has cured by reaction with atmospheric carbon dioxide, the pink color fades.[7]

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.[8]

Medical uses[edit]

Phenolphthalein has been used for over a century as a laxative, but is now being removed from over-the-counter laxatives[9] because of concerns over carcinogenicity.[10][11]

Despite concerns regarding its carcinogenicity, the use of phenolphthalein as a laxative is unlikely to cause ovarian cancer.[12] 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.[13]

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.

See also[edit]

References[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. ^ "Universal Indicator". ISCID Encyclopedia of Science and Philosophy. [dead link]
  7. ^ US 6531528, Ronald D. Kurp, "Ready to use spackle/repair product containing dryness indicator" 
  8. ^ Toystore
  9. ^ 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. PMID 12708936. 
  10. ^ 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. 
  11. ^ 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. PMID 9544189. 
  12. ^ 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. 
  13. ^ 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]