Gallein
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Description
Brownish-red crystals used as a red dye. Gallein was first prepared by Baeyer in 1871 by mixing Pyrogallic acid with Phthalic anhydride. Gallein was used as a dye in the late 19th century but was soon replaced by aniline colors. It produces a bluish-red color with Alumina or iron mordants and a dark violet with lead and tin mordants. Gallein is also used as an acid-base indicator and as a detection reagent for phosphates.
Synonyms and Related Terms
3',4',5',6'-tetrahydroxyfluoran; pyrogallolphthalein; CI 45445; mordant violet 25
Risks
- Inhalation, ingestion or skin absorption may be harmful.
- Sigma Aldrich: SDS
Physical and Chemical Properties
Insoluble in cold water, benzene, chloroform. Slightly soluble in hot water, ether. Soluble in alkalis, alcohol, acetone.
As an indicator, brownish-yellow below pH=3.8; red above pH 6.6
| Composition | C20H12O7 |
|---|---|
| CAS | 2103-64-2 |
| Molecular Weight | mol. wt. = 364.31 |
Resources and Citations
- The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 4362
- F. Crace-Calvert, Dyeing and Calico Printing, Palmer & Howe, London, 1876