| | | |
HO V ---O--- V OH
OH OH
[Illustration: Purpuro Tannin.]


3. Ellagic Acid

Ellagic acid was discovered in 1831 by Braconnot, who named it "acide
ellagique." Its presence in the vegetable kingdom was not quite
comprehended for some time, and Nierenstein [Footnote: _Chem. Ztg._,
1909, 87.] was the first to prepare this substance from algarobilla,
dividivi, oak bark, pomegranate, myrabolarms, and valonea. The acid is
obtained by precipitating it with water from a hot alcoholic extraction
of the plants referred to, and recrystallising the precipitate from hot
alcohol. Another method of preparation consists in boiling the
disintegrated plants with dilute hydrochloric acid, washing the residue,
and extracting with hot alcohol, from which the acid will then
crystallise. According to Lowe, [Footnote: _Zeits. f. analyt. Chem._,
1875, 35.] it may be obtained from dividivi, an aqueous extract of
which is heated to 110 C. in a tube closed at both ends, when
crystalline ellagic acid is deposited. Heinemann [Footnote: Ger. Pat.,
137,033 and 137,934.] obtained ellagic acid by simply boiling
repeatedly aqueous tannin solutions.

Lowe [Footnote: _Jour. f. prakt. Chem._, 1868, 103, 464.] first
synthesised ellagic acid by heating gallic acid with arsenic acid or
silver oxide. Herzig [Footnote: _Monatshefte fur Chemie_, 1908, 29,
263.] states that ellagic acid is deposited when air is conducted
through a mixture of the ethyl or methyl ester of gallic acid and