Gallein

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