Methyl gallate

The crystal structure of the title compound (systematic name: methyl 3,4,5-trihydroxybenzoate), C8H8O5, is composed of essentially planar molecules [maximum departures from the mean carbon and oxygen skeleton plane of 0.0348 (10) Å]. The H atoms of the three hydroxyl groups, which function as hydrogen-bond donors and acceptors simultaneously, are oriented in the same direction around the aromatic ring. In addition to two intramolecular hydrogen bonds, each molecule is hydrogen bonded to six others, creating a three-dimensional hydrogen-bonded network.

The crystal structure of the title compound (systematic name: methyl 3,4,5-trihydroxybenzoate), C 8 H 8 O 5 , is composed of essentially planar molecules [maximum departures from the mean carbon and oxygen skeleton plane of 0.0348 (10) Å ]. The H atoms of the three hydroxyl groups, which function as hydrogen-bond donors and acceptors simultaneously, are oriented in the same direction around the aromatic ring. In addition to two intramolecular hydrogen bonds, each molecule is hydrogen bonded to six others, creating a three-dimensional hydrogen-bonded network.
We are indebted to the NSF (CHE-0443345) and The College of William and Mary for the purchase of X-ray equipment. This work was supported in part by the US National Science Foundation (CHE-0315934). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author and do not necessarily reflect the views of the National Science Foundation. SP gratefully acknowledges the Physics Department of the Methyl gallate D. Bebout and S. Pagola Comment Gallic acid methyl ester (I) is a polyphenolic compound present in grape seeds and other natural substrates (Saxena et al., 1994;Schmidt et al., 2003;Hawas, 2007). Like other polyphenols, I shows antioxidant activity (Aruoma et al., 1993;Schmidt et al., 2003;Hawas, 2007). Formerly used as an astringent and in opthalmology, its anticancer (Fiuza et al., 2004) and antimicrobial properties (Saxena et al., 1994;Landete et al., 2007) have also been studied. The molecular structure of I is shown below.
The molecular geometry is as expected from chemical bond rules ( Figure 1) and it shows an almost planar conformation, with maximum departures from the mean carbon and oxygen skeleton plane of 0.0343 (9) and 0.0348 (10) Å for O4 and C8, respectively. The relative positions of the carbonyl and the three hydroxyls were also observed in a cocrystal of I and 5-chloro-2-methyl-4-isothiazoline-3-one (Sekine et al., 2003). Four other compounds containing a gallic acid ester moiety have crystallized in an analogous conformation (Parkin et al., 2002;Okabe & Kyoyama, 2002a;Nomura et al., 2000;Mizuguchi et al., 2005). Three other planar conformations of gallic acid esters are found in the Cambridge Structural Database (Allen, 2002). I has one of these other conformations in a cocrystal with caffeine (Martin et al., 1986).
Gallic acid methyl ester forms a three-dimensional H-bonded network lacking significant aromatic ring stacking interactions. There is one molecule of I in the asymmetric unit. The H-bonded network is shown in Figure 2. Using the carbonyl ester oxygen O1 (acceptor) and the hydroxyl O3 and O4 (donors), each molecule is linked to another four through two O1···H3-O3, and two O1···H4-O4 H-bonds. These H-bonds are likely relatively weak due to the spacial orientation of the H atoms with respect to the lone electron pairs of O1. In addition, there are two other O5-H5···O3 H-bonds. The three hydroxyl sites are used as hydrogen bond donors and acceptors simultaneously. In the ester group, only the carbonyl oxygen is used as an H-bond acceptor.

Experimental
Gallic acid methyl ester was commercially obtained from Sigma-Aldrich (98% purity) and used as received. The crystal structure determination was carried out from a crystal with rhombic prismatic habit selected from the powder.