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Acta Cryst. (2009). E65, o317-o318    [ doi:10.1107/S1600536809001123 ]

Methyl gallate

D. Bebout and S. Pagola

Abstract top

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.

Comment top

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).

Crystallized I has intra- and intermolecular hydrogen bonding. The hydroxyl H atoms bound to O3 and O4 (donors) form intramolecular hydrogen bonds to O4 and O5 (acceptors), respectively. This is shown in Figure 1. Similar hydroxyl arrangements have been reported in other gallic acid derivatives, such as gallate ester solvates (Hitachi et al., 2005), a gallic acid monohydrate polymorph (Okabe et al., 2001) and 2,3,4-trihydroxybenzophenone monohydrate (Okabe & Kyoyama, 2002b).

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.

Related literature top

For natural extracts containing gallic acid methyl ester, see: Saxena et al. (1994); Schmidt et al. (2003); Hawas (2007). For studies concerning antioxidant activity, see: Aruoma et al. (1993); Schmidt et al. (2003); Hawas (2007). For studies concerning anticancer properties, see: Fiuza et al. (2004) and for antimicrobial properties, see: Saxena et al. (1994); Landete et al. (2007). For cocrystals containing gallic acid methyl ester, see: Sekine et al. (2003); Martin et al. (1986). Similar gallate ester conformations are found in Parkin et al. (2002); Okabe & Kyoyama (2002a); Nomura et al. (2000); Mizuguchi et al. (2005). For structures with similar hydroxyl arrangements, see: Hitachi et al. (2005); Okabe et al. (2001); Okabe & Kyoyama (2002b). For a description of the Cambridge Structural Database, see: Allen (2002).

Experimental top

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.

Refinement top

All hydrogen atoms were observed in the Fourier difference map. However, the torsion angle for the hydroxyl H was refined from the electron density and the methyl H was positioned in idealized staggered geometry. The H atoms were refined constrained to ride on their parent C or O atoms, with Uiso(H)=1.2 Ueq(C) for aromatic H, and Uiso(H)=1.5 Ueq(C or O) for methyl and hydroxyl H, respectively.

Computing details top

Data collection: APEX2 (Bruker , 2004); cell refinement: SAINT-Plus (Bruker, 2004); data reduction: SAINT-Plus (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: WinGX (Farrugia, 1999); molecular graphics: ORTEP-3 (Farrugia, 1997) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Thermal ellipsoid plot of gallic acid methyl ester with the atomic numbering scheme. Non-H atoms are represented at 50% probability level. Intramolecular hydrogen bonds are shown with dashed lines.
[Figure 2] Fig. 2. The packing of gallic acid methyl ester molecules along the a-axis showing the unit cell and the hydrogen bonded network formed (dashed lines). Symmetry codes: (i) x,y,z; (ii) 1/2 + x, 1.5 - y, -1/2 + z; (iii) -1/2 + x, 1.5 - y, 1/2 + z; (iv) -1/2 + x,1.5 - y, -1/2 + z; (v) -1/2 - x, -1/2 + y, 1.5 - z; (vi) 1/2 + x, 1.5 - y, 1/2 + z; (vii) -1/2 - x, 1/2 + y, 1.5 - z.
methyl 3,4,5-trihydroxybenzoate top
Crystal data top
C8H8O5F(000) = 384
Mr = 184.14Dx = 1.526 Mg m−3
Monoclinic, P21/nMelting point: 474 K
Hall symbol: -P 2ynCu Kα radiation, λ = 1.54178 Å
a = 7.6963 (2) ÅCell parameters from 1352 reflections
b = 9.9111 (2) Åθ = 6.1–67.0°
c = 10.5625 (2) ŵ = 1.12 mm−1
β = 95.993 (1)°T = 100 K
V = 801.29 (3) Å3Rhombic prism, colourless
Z = 40.31 × 0.23 × 0.21 mm
Data collection top
Bruker SMART APEXII CCD
diffractometer		1352 independent reflections
Radiation source: fine-focus sealed tube1311 reflections with I > 2σ(I)
graphiteRint = 0.034
ω and ψ scansθmax = 67.0°, θmin = 6.1°
Absorption correction: numerical
(SADABS; Sheldrick, 2004)		h = −8→9
Tmin = 0.723, Tmax = 0.799k = −11→11
8192 measured reflectionsl = −12→12
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033Hydrogen site location: difference Fourier map
wR(F2) = 0.093All H-atom parameters refined
S = 0.69 w = 1/[σ2(Fo2) + (0.0834P)2 + 0.9466P]
where P = (Fo2 + 2Fc2)/3
1352 reflections(Δ/σ)max = 0.004
121 parametersΔρmax = 0.23 e Å−3
0 restraintsΔρmin = −0.20 e Å−3
32 constraints
Crystal data top
C8H8O5V = 801.29 (3) Å3
Mr = 184.14Z = 4
Monoclinic, P21/nCu Kα radiation
a = 7.6963 (2) ŵ = 1.12 mm−1
b = 9.9111 (2) ÅT = 100 K
c = 10.5625 (2) Å0.31 × 0.23 × 0.21 mm
β = 95.993 (1)°
Data collection top
Bruker SMART APEXII CCD
diffractometer		1352 independent reflections
Absorption correction: numerical
(SADABS; Sheldrick, 2004)		1311 reflections with I > 2σ(I)
Tmin = 0.723, Tmax = 0.799Rint = 0.034
8192 measured reflectionsθmax = 67.0°
Refinement top
R[F2 > 2σ(F2)] = 0.033All H-atom parameters refined
wR(F2) = 0.093Δρmax = 0.23 e Å−3
S = 0.69Δρmin = −0.20 e Å−3
1352 reflectionsAbsolute structure: ?
121 parametersFlack parameter: ?
0 restraintsRogers parameter: ?
Special details top

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
O10.14003 (11)1.05605 (9)0.77633 (8)0.0145 (2)
O20.29090 (12)0.99023 (9)0.61631 (8)0.0156 (3)
O3−0.38148 (12)0.74067 (10)0.72722 (9)0.0189 (3)
H3−0.43890.67420.69630.028*
O4−0.33530 (12)0.58249 (9)0.52444 (9)0.0167 (2)
H4−0.3140.54620.45590.025*
O5−0.05442 (13)0.61740 (10)0.39075 (9)0.0185 (3)
H50.01270.65240.34220.028*
C70.15489 (17)0.98352 (13)0.68447 (12)0.0121 (3)
C10.02736 (17)0.87858 (13)0.63777 (12)0.0126 (3)
C2−0.11958 (17)0.85957 (13)0.70290 (12)0.0126 (3)
H2−0.13780.91450.7740.015*
C3−0.23803 (17)0.75983 (13)0.66260 (12)0.0129 (3)
C4−0.21306 (17)0.67861 (13)0.55808 (12)0.0129 (3)
C5−0.06683 (17)0.69987 (13)0.49284 (12)0.0134 (3)
C60.05370 (16)0.79838 (13)0.53249 (12)0.0134 (3)
H60.15390.81160.48850.016*
C80.42258 (18)1.09026 (14)0.65644 (13)0.0182 (3)
H8A0.51611.08670.60030.027*
H8B0.47121.07150.74410.027*
H8C0.36951.18020.65210.027*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
O10.0147 (5)0.0147 (5)0.0141 (5)0.0011 (4)0.0010 (4)−0.0023 (4)
O20.0135 (5)0.0186 (5)0.0153 (5)−0.0048 (4)0.0040 (4)−0.0030 (4)
O30.0171 (5)0.0206 (5)0.0209 (5)−0.0067 (4)0.0108 (4)−0.0070 (4)
O40.0188 (5)0.0180 (5)0.0141 (5)−0.0071 (4)0.0058 (4)−0.0043 (4)
O50.0237 (5)0.0196 (5)0.0140 (5)−0.0080 (4)0.0103 (4)−0.0057 (4)
C10.0135 (6)0.0127 (6)0.0114 (6)0.0019 (5)0.0004 (5)0.0028 (5)
C20.0147 (7)0.0130 (6)0.0104 (6)0.0023 (5)0.0021 (5)−0.0002 (5)
C30.0127 (6)0.0147 (6)0.0120 (6)0.0012 (5)0.0041 (5)0.0025 (5)
C40.0137 (6)0.0123 (6)0.0124 (6)−0.0012 (5)0.0000 (5)0.0022 (5)
C50.0176 (7)0.0129 (6)0.0100 (6)0.0012 (5)0.0032 (5)0.0002 (5)
C60.0127 (6)0.0159 (7)0.0121 (6)0.0004 (5)0.0040 (5)0.0024 (5)
C70.0129 (7)0.0122 (6)0.0111 (6)0.0037 (5)0.0006 (5)0.0030 (5)
C80.0157 (7)0.0203 (7)0.0185 (7)−0.0071 (5)0.0015 (6)−0.0010 (5)
Geometric parameters (Å, °) top
O1—C71.2225 (16)C1—C61.3988 (19)
O2—C71.3327 (15)C2—C31.3815 (18)
O2—C81.4491 (16)C2—H20.95
O3—C31.3705 (15)C3—C41.3957 (18)
O3—H30.84C4—C51.3956 (18)
O4—C41.3598 (16)C5—C61.3813 (18)
O4—H40.84C6—H60.95
O5—C51.3644 (16)C8—H8A0.98
O5—H50.84C8—H8B0.98
C7—C11.4790 (19)C8—H8C0.98
C1—C21.3965 (17)
C7—O2—C8116.16 (10)O4—C4—C5123.25 (11)
C3—O3—H3109.5O4—C4—C3117.52 (11)
C4—O4—H4109.5C5—C4—C3119.22 (12)
C5—O5—H5109.5O5—C5—C6124.25 (11)
O1—C7—O2122.91 (12)O5—C5—C4115.24 (12)
O1—C7—C1124.36 (11)C6—C5—C4120.51 (11)
O2—C7—C1112.72 (11)C5—C6—C1119.62 (12)
C2—C1—C6120.47 (12)C5—C6—H6120.2
C2—C1—C7118.29 (11)C1—C6—H6120.2
C6—C1—C7121.24 (12)O2—C8—H8A109.5
C3—C2—C1119.15 (12)O2—C8—H8B109.5
C3—C2—H2120.4H8A—C8—H8B109.5
C1—C2—H2120.4O2—C8—H8C109.5
O3—C3—C2119.06 (11)H8A—C8—H8C109.5
O3—C3—C4119.91 (12)H8B—C8—H8C109.5
C2—C3—C4121.03 (12)
C8—O2—C7—O1−0.42 (18)C2—C3—C4—O4179.88 (11)
C8—O2—C7—C1−179.68 (10)O3—C3—C4—C5179.65 (11)
O1—C7—C1—C2−0.53 (19)C2—C3—C4—C5−0.7 (2)
O2—C7—C1—C2178.71 (11)O4—C4—C5—O50.45 (19)
O1—C7—C1—C6−179.44 (12)C3—C4—C5—O5−178.97 (11)
O2—C7—C1—C6−0.19 (17)O4—C4—C5—C6−179.37 (11)
C6—C1—C2—C30.47 (19)C3—C4—C5—C61.21 (19)
C7—C1—C2—C3−178.44 (11)O5—C5—C6—C1179.28 (12)
C1—C2—C3—O3179.52 (11)C4—C5—C6—C1−0.92 (19)
C1—C2—C3—C4−0.17 (19)C2—C1—C6—C50.07 (19)
O3—C3—C4—O40.19 (18)C7—C1—C6—C5178.95 (11)
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O40.842.252.7075 (13)115
O4—H4···O50.842.292.7247 (12)112
O4—H4···O1i0.842.152.9470 (13)159
O3—H3···O1ii0.841.992.7007 (12)142
O5—H5···O3iii0.841.862.6859 (12)166
Symmetry codes: (i) x−1/2, −y+3/2, z−1/2; (ii) −x−1/2, y−1/2, −z+3/2; (iii) x+1/2, −y+3/2, z−1/2.
Table 1
Hydrogen-bond geometry (Å, °) top
D—H···AD—HH···AD···AD—H···A
O3—H3···O40.842.252.7075 (13)115
O4—H4···O50.842.292.7247 (12)112
O4—H4···O1i0.842.152.9470 (13)159
O3—H3···O1ii0.841.992.7007 (12)142
O5—H5···O3iii0.841.862.6859 (12)166
Symmetry codes: (i) x−1/2, −y+3/2, z−1/2; (ii) −x−1/2, y−1/2, −z+3/2; (iii) x+1/2, −y+3/2, z−1/2.
Acknowledgements top

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 College of William and Mary for funding and ICDD GIA 08–04.

references
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