Title: Digallic Acid
CAS Registry Number: 536-08-3
CAS Name: 3,4-Dihydroxy-5-[(3,4,5-trihydroxybenzoyl)oxy]benzoic acid
Additional Names: gallic acid 5,6-dihydroxy-3-carboxyphenyl ester; 4,5-dihydroxybenzoic acid monogallate; gallic acid 3-monogallate; m-digallic acid; m-galloylgallic acid
Molecular Formula: C14H10O9
Molecular Weight: 322.22
Percent Composition: C 52.18%, H 3.13%, O 44.69%
Literature References: Isoln from Aleppo gallotannin and Chinese gallotannin: Nierensten, Ber. 43, 628 (1910). Synthesis: Fischer, Freudenberg, Ber. 46, 1128 (1913). Structure: Nierenstein et al., J. Am. Chem. Soc. 47, 846 (1925). Determn by HPLC: P. Delahaye, M. Verzele, J. Chromatogr. 265, 363 (1983); in tannic acids: M. Verzele et al., Bull. Soc. Chim. Belg. 92, 181 (1983). Role in corrosion inhibition: A. M. Beccaria, E. D. Mor, Br. Corrosion J. 11, 156 (1976).
Properties: Hydrated needles from alc + water, anhydr at 110°; dec 280°. Sol in 1900 parts water at 25°; in 50-60 parts boiling water; sol in methanol, ethanol, acetone; sparingly sol in ether, glacial acetic acid. Upon addn of KCN to an aq soln a transitory pink color appears, which returns on shaking.
NOTE: In pharmaceutical literature the name digallic acid is frequently confused with tannic acid. |