Pyrogallolphthalein
Structural formula | |||||||||||||||||||
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Surname | Pyrogallolphthalein | ||||||||||||||||||
other names |
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Molecular formula | C 20 H 12 O 7 | ||||||||||||||||||
Brief description |
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properties | |||||||||||||||||||
Molar mass | 364.30 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
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Melting point |
> 300 ° C |
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solubility |
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safety instructions | |||||||||||||||||||
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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).