Metal phthalein
Structural formula | |||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
General | |||||||||||||||||||
Surname | Metal phthalein | ||||||||||||||||||
other names |
|
||||||||||||||||||
Molecular formula | C 32 H 32 N 2 O 18 | ||||||||||||||||||
Brief description |
beige, odorless, crystalline powder |
||||||||||||||||||
External identifiers / databases | |||||||||||||||||||
|
|||||||||||||||||||
properties | |||||||||||||||||||
Molar mass | 636.62 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
||||||||||||||||||
Melting point |
186 ° C |
||||||||||||||||||
solubility |
almost insoluble in water |
||||||||||||||||||
safety instructions | |||||||||||||||||||
|
|||||||||||||||||||
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . |
Metal phthalein is a triphenylmethane dye and belongs to the group of phthaleins. The analogous sulfonphthalein is xylenol orange . It is used as an indicator in complexometry .
Chemical properties
Metal phthalein contains a lactone ring , four carboxy , two amino and two hydroxyl groups , each of which can be protonated or deprotonated. Furthermore, the lactone ring can also be cleaved in a strongly acidic or basic environment. At pH ≈ 12–13, metal phthalein is pink in color. In this form, metal phthalein now forms a weak purple-colored complex with some divalent metal ions , which is destroyed again by adding a stronger complexing agent such as EDTA .
use
In addition to eriochrome black T , metal phthalein is used as an indicator in complexometry for the determination of Ba 2+ , Ca 2+ , Cd 2+ , Mg 2+ and Sr 2+ .
Individual evidence
- ↑ a b c d e data sheet metal phthalein (PDF) from Merck , accessed on December 25, 2019.
- ↑ M. Hübel, Ciba Geigy et al .: Laborpraxis. Volume 4, 5th edition, Birkhäuser-Verlag, Basel 1996, p. 123 ( limited preview in the Google book search)
- ↑ Entry on metal phthalein. In: Römpp Online . Georg Thieme Verlag, accessed on September 25, 2017.
- ↑ aprentas (ed.): Laborpraxis . 6th edition. tape 4 : Analytical methods . Springer-Verlag, 2017, ISBN 978-3-0348-0972-6 , pp. 29 ( limited preview in Google Book search).