Gallic acid is found in its free state and combined with the tannin molecule,
from which it can be extracted by the hydrolysis of tannic acid with sulfuric
acid. Since one molecule of gallic acid has a carboxylic acid group and
hydroxyl groups, it can react with another molecule of gallic acid to form an
ester, digallic acid. When heated above 200oC, gallic acid loses carbon dioxide
to form pyrogallol (1,2,3-trihydroxybenzene, C6H3(OH)3), which is used in the
production of azo dyes, photographic developers, and in laboratories for
absorbing oxygen.
Lab name:
Common molecules
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Obtained courtesy of the Cambridge Structural Database
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