Pyrogallolphthalein

Structural formula
General
Surname	Pyrogallolphthalein
other names	3 ′, 4 ′, 5 ′, 6′-Tetrahydroxyspiro [2-benzofuran-3,9′-xanthene] -1-one ( IUPAC ); 4,5-dihydroxyfluorescein; Bile; Alizarin violet;
Molecular formula	C 20 H 12 O 7
Brief description	red-brown powder (hydrate); red powder (anhydrous);
External identifiers / databases
EC number	218-272-6
ECHA InfoCard	100.016.611
PubChem	73685
ChemSpider	66334
Wikidata	Q2119993
properties
Molar mass	364.30 g mol −1
Physical state	firmly
Melting point	> 300 ° C
solubility	soluble in ethanol and acetone; insoluble in water, benzene and chloroform;
safety instructions
GHS labeling of hazardous substances	no GHS pictograms
	no GHS pictograms
H and P phrases	H: no H-phrases
	P: no P-phrases
	As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Pyrogallolphthalein is a triphenylmethane dye and belongs to the phthaleine family. The name is composed of pyrogallol and phthalic anhydride . It is used as a pH indicator . The corresponding sulfonphthalein is pyrogallol red .

presentation

In a Friedel-Crafts acylation , pyrogallol and phthalic anhydride are reacted in the presence of small amounts of concentrated sulfuric acid.

properties

Pyrogallolphthalein is used as a pH indicator [transition range pH 3.8 (brown-yellow) - 6.6 (pink-red)]; in a strongly alkaline medium it changes from purple back to yellow. It is also used in complexometric titration to determine bismuth and zirconium .

Pyrogallolphthalein is not soluble in water and is mostly used in 0.1% alcoholic solution. It is a weak acid itself.

Individual evidence

↑ ^a ^b ^c ^d David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 89th edition. (Internet version: 2009), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-266.
↑ ^a ^b entry on Gallein. In: Römpp Online . Georg Thieme Verlag, accessed on November 19, 2017.
↑ ^a ^b ChemYQ
↑ ^a ^b Entry on Gallein at TCI Europe, accessed on February 25, 2013.
↑ ^a ^b R. W. Sabnis: Handbook of Acid-Base Indicators . CRC Press, 2007, ISBN 978-0-8493-8219-2 , pp. 167 ( limited preview in Google Book search).
↑ Peter Waldvogel: Metal indicators of the pyrocatechol violet type and novel deep-colored quinones resulting from it . Zurich 1959, p. 32 , doi : 10.3929 / ethz-a-000090489 (dissertation, ETH Zurich).

[CRC89-1] David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 89th edition. (Internet version: 2009), CRC Press / Taylor and Francis, Boca Raton, FL, Physical Constants of Organic Compounds, pp. 3-266.

[RÖMPP-2] try on Gallein. In: Römpp Online . Georg Thieme Verlag, accessed on November 19, 2017.

[chemyq-3] ChemYQ

[TCI-4] Entry on Gallein at TCI Europe, accessed on February 25, 2013.

[R._W._Sabnis-5] R. W. Sabnis: Handbook of Acid-Base Indicators . CRC Press, 2007, ISBN 978-0-8493-8219-2 , pp. 167 ( limited preview in Google Book search).

[6] Peter Waldvogel: Metal indicators of the pyrocatechol violet type and novel deep-colored quinones resulting from it . Zurich 1959, p. 32 , doi : 10.3929 / ethz-a-000090489 (dissertation, ETH Zurich).