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Regioselective methyl­ation of hemimellitic acid in basic MeOH yields the title 2-methyl ester, C10H8O6, of the parent acid. The asymmetric unit contains one complete mol­ecule, which packs with the methyl ester groups lying between zigzag chains produced by hydrogen bonding, utilizing the head-to-tail carboxylic acid-acid dimer motif.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103002610/bm1520sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270103002610/bm1520Isup2.hkl
Contains datablock I

CCDC reference: 208032

Comment top

Derivatives of hemimellitic acid (benzene-1,2,3-tricarboxylic acid) have been studied little using single-crystal X-ray diffraction, with only eight crystal structures in the Cambridge Structural Database (September 2002 update; Allen, 2002), of which three are determinations of the commercially available dihydrate (Fornies-Marquina et al., 1972; Takusagawa & Shimada, 1973; Mo & Adman, 1975). The successful use of many of the other members of the benzenepolycarboxylic acid family, such as trimesic and terephthalic acids, in the formation of supramolecular organic (e.g. Sharma & Zaworotko, 1996) and inorganic (e.g. Groeneman et al., 1999) networks has inspired us to investigate the relatively inexpensive hemimellitic acid as a potential supramolecular building block and metal ligand. Hemimellitic acid possesses three adjacent carboxylic acid groups, providing the opportunity for coordination to metal cations as well as the creation of extended networks through hydrogen bonding.

The reaction of hemimellitic acid with 0.5 equivalents of M2CO3 (M is Li, Na or K) in the mixed solvent MeOH:H2O (9:1) under reflux conditions affords, surprisingly, regioselective methylation at the 2-position. The title compound, (I), is produced as X-ray quality colourless crystals in almost quantitative yield from the slow evaporation of the cooled solution. In contrast, similar reactions with phthalic acid in pure H2O have been shown to yield the expected group 1 metal salts (Smith, 1975a,b). \sch

Compound (I) has previously been synthesized from the reaction of hemimellitic anhydride with MeOH and characterized only by 1H NMR spectroscopic data (Hurst & Bender, 1971), but here, both the single-crystal X-ray structure and 13C NMR data are presented. NMR spectroscopic analysis of the bulk sample indicated a single product, showing that the isomeric 1-ester and the possible di- and tri-esters (Kasina & Nematollaki, 1974; Revial et al., 1983) had not been produced.

The asymmetric unit of (I) contains one complete molecule (Fig. 1). The external carboxylic acid substituents at C1 and C3 form hydrogen bonds to one symmetry-related neighbour each, via the expected head-to-tail R22(8) carboxylic acid-acid synthon (Etter, 1990; Etter & MacDonald, 1990; Bernstein et al., 1995) (Table 2), producing zigzag chains (Fig. 2), reminiscent of the packing of isophthalic acid (Derissen, 1974). One outer Is this text change OK? carboxylic acid group of the parent acid dihydrate (Takusagawa & Shimada, 1973) adopts the R22(8) dimer motif, but, in contrast to (I), the other also forms a hydrogen bond to a water of crystallization. Protection of the central Is this text change OK? carboxylic acid group as the methyl ester prevents its involvement in strong hydrogen bonding and also modifies the angle of rotation of this carboxyl group with respect to the plane of the aromatic ring, from 86.8° in the parent acid to 76.7° in (I), allowing the Me group to lie between the chains. Weak C—H···O interactions [C···O 3.2193 (18)–3.9409 (16) Å; Desiraju & Steiner, 1999] between the zigzag chains produce sheets, and interactions between these sheets produce a loosely held three-dimensional structure.

Experimental top

Hemimellitic acid dihydrate (1 equivalent) was refluxed with M2CO3 (M is Li, Na or K, 0.5 equivalents) in a 9:1 mixture of MeOH:H2O overnight. The solutions were allowed to cool and then left to evaporate. X-ray quality colourless crystals formed (m.p. 478–482 K; literature value 478–483 K; Hurst & Bender, 1971) and single-crystal X-ray analysis indicated that compound (I) had been synthesized in all three cases. Spectroscopic analysis: IR (KBr, νmax, cm−1): 3500–2500 (br, OH), 3087, 3046 and 3006 (aromatic C—H), 2948, 2884 and 2837 (Csp3—H), 1742 (CO, ester), 1711 and 1692 (CO, acid), 1586(CC, aromatic), 1466, 1453, 1430 and 1415 (Csp3—H), 1308, 1275, 1123 and 1072 (C—O), 776 (aromatic C—H), 688; 1H NMR (400 MHz, d6-DMSO, δ, p.p.m.): 8.13 (2H, d, J = 8 Hz), 7.68 (1H, t, J = 7.6 Hz), 3.77 (3H, s, Me); 13C NMR (100 MHz, d6-DMSO, δ, p.p.m.): 167.9 (Cquat, CO, ester), 166.17 (2Cquat, CO, acid), 135.6 (Cquat, Ar), 133.4 (2CH, Ar), 129.8 (CH, Ar), 129.6 (2Cquat, Ar), 52.2 (CH3). The 1H NMR results correspond to the previously reported data (Hurst & Bender, 1971).

Refinement top

Aromatic H atoms were placed in geometric positions (C—H distance of 0.95 Å) using a riding model, while the coordinates of Me and OH H atoms were freely refined. Uiso values were set to 1.2Ueq for aryl H atoms, and 1.5Ueq for methyl H and hydroxy H atoms.

Computing details top

Data collection: SMART (Siemens, 1994); cell refinement: SAINT (Siemens, 1994); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and local programs.

Figures top
[Figure 1] Fig. 1. A view of the molecule of (I), showing the atom-labelling scheme and the selective methylation at the 2-position. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
[Figure 2] Fig. 2. A packing plot for (I), viewed down the crystallographic a axis, showing the head-to-tail carboxylic acid-acid hydrogen-bonded dimers forming chains. H atoms not involved in the hydrogen bonding have been omitted for clarity. Hydrogen bonding between molecules is indicated by dashed lines.
Methyl 2,6-dicarboxybenzoate top
Crystal data top
C10H8O6F(000) = 464
Mr = 224.16Dx = 1.574 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3989 reflections
a = 5.0242 (3) Åθ = 2.8–28.5°
b = 14.6263 (10) ŵ = 0.13 mm1
c = 12.9024 (9) ÅT = 150 K
β = 93.835 (2)°Column, colourless
V = 946.02 (11) Å30.37 × 0.16 × 0.13 mm
Z = 4
Data collection top
Bruker SMART1000 CCD area-detector
diffractometer
2287 independent reflections
Radiation source: sealed tube1847 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.017
ω rotation with narrow frames scansθmax = 29.0°, θmin = 2.1°
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
h = 66
Tmin = 0.910, Tmax = 0.983k = 1918
8271 measured reflectionsl = 1616
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullHydrogen site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.033H atoms treated by a mixture of independent and constrained refinement
wR(F2) = 0.094 w = 1/[σ2(Fo2) + (0.049P)2 + 0.304P]
where P = (Fo2 + 2Fc2)/3
S = 1.03(Δ/σ)max < 0.001
2287 reflectionsΔρmax = 0.35 e Å3
160 parametersΔρmin = 0.19 e Å3
0 restraints
Crystal data top
C10H8O6V = 946.02 (11) Å3
Mr = 224.16Z = 4
Monoclinic, P21/cMo Kα radiation
a = 5.0242 (3) ŵ = 0.13 mm1
b = 14.6263 (10) ÅT = 150 K
c = 12.9024 (9) Å0.37 × 0.16 × 0.13 mm
β = 93.835 (2)°
Data collection top
Bruker SMART1000 CCD area-detector
diffractometer
2287 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 2001)
1847 reflections with I > 2σ(I)
Tmin = 0.910, Tmax = 0.983Rint = 0.017
8271 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0330 restraints
wR(F2) = 0.094H atoms treated by a mixture of independent and constrained refinement
S = 1.03Δρmax = 0.35 e Å3
2287 reflectionsΔρmin = 0.19 e Å3
160 parameters
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.

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
C10.1473 (2)0.85643 (8)0.57870 (9)0.0185 (3)
C20.0190 (2)0.80717 (8)0.64147 (9)0.0171 (2)
C30.1562 (2)0.85413 (8)0.71625 (9)0.0187 (3)
C40.1256 (3)0.94863 (9)0.72779 (9)0.0219 (3)
H40.22290.98030.77720.026*
C50.0458 (3)0.99649 (9)0.66769 (10)0.0228 (3)
H50.06951.06050.67710.027*
C60.1823 (2)0.95049 (9)0.59374 (9)0.0214 (3)
H6A0.30080.98310.55290.026*
C70.2753 (2)0.81085 (8)0.49142 (9)0.0187 (2)
O10.4629 (2)0.86057 (6)0.45225 (8)0.0281 (2)
H10.527 (4)0.8315 (13)0.3967 (15)0.042*
O20.20699 (17)0.73548 (6)0.45825 (7)0.0219 (2)
C80.0442 (2)0.70463 (8)0.63100 (9)0.0178 (2)
O30.12083 (18)0.65121 (6)0.66524 (7)0.0240 (2)
O40.27597 (17)0.68290 (6)0.58015 (7)0.0212 (2)
C100.3313 (3)0.58629 (9)0.57218 (12)0.0283 (3)
H10A0.207 (4)0.5573 (13)0.5293 (14)0.043*
H10B0.509 (4)0.5815 (12)0.5400 (14)0.043*
H10C0.324 (4)0.5587 (13)0.6419 (15)0.043*
C90.3305 (2)0.80378 (9)0.78586 (9)0.0190 (2)
O50.31048 (19)0.72128 (6)0.80112 (7)0.0251 (2)
O60.50342 (19)0.85625 (7)0.82979 (7)0.0264 (2)
H60.605 (4)0.8211 (13)0.8697 (14)0.040*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
C10.0178 (6)0.0192 (6)0.0186 (6)0.0002 (4)0.0028 (4)0.0005 (4)
C20.0161 (5)0.0178 (6)0.0173 (5)0.0007 (4)0.0011 (4)0.0001 (4)
C30.0181 (6)0.0210 (6)0.0172 (5)0.0010 (4)0.0034 (4)0.0000 (4)
C40.0247 (6)0.0215 (6)0.0201 (6)0.0004 (5)0.0056 (5)0.0036 (5)
C50.0276 (6)0.0168 (6)0.0245 (6)0.0017 (5)0.0043 (5)0.0016 (5)
C60.0225 (6)0.0208 (6)0.0213 (6)0.0035 (5)0.0056 (5)0.0016 (5)
C70.0187 (6)0.0191 (6)0.0187 (6)0.0008 (4)0.0045 (4)0.0027 (5)
O10.0336 (5)0.0216 (5)0.0317 (5)0.0051 (4)0.0206 (4)0.0032 (4)
O20.0230 (5)0.0217 (5)0.0216 (4)0.0025 (3)0.0072 (3)0.0032 (3)
C80.0190 (6)0.0196 (6)0.0155 (5)0.0014 (4)0.0075 (4)0.0002 (4)
O30.0225 (5)0.0218 (5)0.0281 (5)0.0029 (3)0.0051 (4)0.0047 (4)
O40.0229 (4)0.0169 (4)0.0239 (4)0.0024 (3)0.0014 (3)0.0013 (3)
C100.0315 (7)0.0177 (6)0.0357 (8)0.0050 (5)0.0017 (6)0.0031 (5)
C90.0184 (6)0.0220 (6)0.0170 (5)0.0013 (4)0.0035 (4)0.0022 (4)
O50.0297 (5)0.0206 (5)0.0264 (5)0.0017 (4)0.0130 (4)0.0000 (4)
O60.0289 (5)0.0241 (5)0.0280 (5)0.0034 (4)0.0158 (4)0.0038 (4)
Geometric parameters (Å, º) top
C1—C61.3989 (17)C7—O21.2233 (15)
C1—C21.4014 (16)C7—O11.3177 (14)
C1—C71.4911 (16)O1—H10.91 (2)
C2—C31.4024 (16)C8—O31.2019 (15)
C2—C81.5104 (17)C8—O41.3359 (15)
C3—C41.3976 (17)O4—C101.4424 (16)
C3—C91.4902 (16)C10—H10A0.960 (19)
C4—C51.3862 (17)C10—H10B0.96 (2)
C4—H40.9500C10—H10C0.984 (19)
C5—C61.3861 (17)C9—O51.2256 (15)
C5—H50.9500C9—O61.3156 (15)
C6—H6A0.9500O6—H60.907 (19)
C6—C1—C2119.99 (11)O2—C7—O1123.67 (11)
C6—C1—C7119.20 (11)O2—C7—C1122.81 (11)
C2—C1—C7120.71 (11)O1—C7—C1113.50 (10)
C1—C2—C3119.04 (11)C7—O1—H1110.1 (12)
C1—C2—C8120.56 (10)O3—C8—O4125.67 (11)
C3—C2—C8120.38 (10)O3—C8—C2124.12 (11)
C4—C3—C2120.12 (11)O4—C8—C2110.20 (10)
C4—C3—C9119.31 (11)C8—O4—C10115.18 (10)
C2—C3—C9120.55 (11)O4—C10—H10A110.1 (11)
C5—C4—C3120.53 (11)O4—C10—H10B105.8 (11)
C5—C4—H4119.7H10A—C10—H10B109.9 (15)
C3—C4—H4119.7O4—C10—H10C110.0 (11)
C6—C5—C4119.62 (12)H10A—C10—H10C111.0 (15)
C6—C5—H5120.2H10B—C10—H10C110.1 (15)
C4—C5—H5120.2O5—C9—O6123.68 (11)
C5—C6—C1120.63 (11)O5—C9—C3122.56 (11)
C5—C6—H6A119.7O6—C9—C3113.76 (11)
C1—C6—H6A119.7
C6—C1—C2—C32.39 (17)C6—C1—C7—O2162.62 (12)
C7—C1—C2—C3173.89 (10)C2—C1—C7—O213.69 (18)
C6—C1—C2—C8175.86 (11)C6—C1—C7—O115.70 (16)
C7—C1—C2—C87.87 (17)C2—C1—C7—O1167.99 (11)
C1—C2—C3—C40.26 (17)C1—C2—C8—O376.86 (16)
C8—C2—C3—C4177.99 (11)C3—C2—C8—O3101.36 (14)
C1—C2—C3—C9178.75 (11)C1—C2—C8—O4104.08 (12)
C8—C2—C3—C90.50 (17)C3—C2—C8—O477.69 (13)
C2—C3—C4—C51.79 (18)O3—C8—O4—C103.45 (17)
C9—C3—C4—C5176.72 (12)C2—C8—O4—C10175.59 (10)
C3—C4—C5—C61.69 (19)C4—C3—C9—O5158.93 (12)
C4—C5—C6—C10.48 (19)C2—C3—C9—O519.58 (18)
C2—C1—C6—C52.53 (18)C4—C3—C9—O620.24 (16)
C7—C1—C6—C5173.80 (11)C2—C3—C9—O6161.26 (11)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O5i0.91 (2)1.71 (2)2.6131 (13)172 (2)
O6—H6···O2ii0.91 (2)1.74 (2)2.6433 (13)173 (2)
C4—H4···O3iii0.952.653.2681 (15)123
C5—H5···O1iv0.953.193.6564 (16)112
C5—H5···O3iii0.952.663.2725 (15)122
C5—H5···O5iii0.952.653.5594 (16)160
C6—H6A···O1iv0.952.583.3627 (15)140
C10—H10B···O6v0.96 (2)2.86 (2)3.2975 (18)108 (2)
C10—H10C···O6vi0.98 (2)3.11 (2)3.7083 (17)120 (2)
Symmetry codes: (i) x+1, y+3/2, z1/2; (ii) x1, y+3/2, z+1/2; (iii) x, y+1/2, z+3/2; (iv) x+1, y+2, z+1; (v) x, y+3/2, z1/2; (vi) x1, y1/2, z+3/2.

Experimental details

Crystal data
Chemical formulaC10H8O6
Mr224.16
Crystal system, space groupMonoclinic, P21/c
Temperature (K)150
a, b, c (Å)5.0242 (3), 14.6263 (10), 12.9024 (9)
β (°) 93.835 (2)
V3)946.02 (11)
Z4
Radiation typeMo Kα
µ (mm1)0.13
Crystal size (mm)0.37 × 0.16 × 0.13
Data collection
DiffractometerBruker SMART1000 CCD area-detector
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 2001)
Tmin, Tmax0.910, 0.983
No. of measured, independent and
observed [I > 2σ(I)] reflections
8271, 2287, 1847
Rint0.017
(sin θ/λ)max1)0.683
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.033, 0.094, 1.03
No. of reflections2287
No. of parameters160
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.35, 0.19

Computer programs: SMART (Siemens, 1994), SAINT (Siemens, 1994), SAINT, SHELXTL (Bruker, 1997), SHELXTL and local programs.

Selected bond lengths (Å) top
C7—O21.2233 (15)O4—C101.4424 (16)
C7—O11.3177 (14)C9—O51.2256 (15)
C8—O31.2019 (15)C9—O61.3156 (15)
C8—O41.3359 (15)
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O1—H1···O5i0.91 (2)1.71 (2)2.6131 (13)172 (2)
O6—H6···O2ii0.91 (2)1.74 (2)2.6433 (13)173 (2)
C4—H4···O3iii0.952.653.2681 (15)123
C5—H5···O1iv0.953.193.6564 (16)112
C5—H5···O3iii0.952.663.2725 (15)122
C5—H5···O5iii0.952.653.5594 (16)160
C6—H6A···O1iv0.952.583.3627 (15)140
C10—H10B···O6v0.96 (2)2.86 (2)3.2975 (18)108 (2)
C10—H10C···O6vi0.98 (2)3.11 (2)3.7083 (17)120 (2)
Symmetry codes: (i) x+1, y+3/2, z1/2; (ii) x1, y+3/2, z+1/2; (iii) x, y+1/2, z+3/2; (iv) x+1, y+2, z+1; (v) x, y+3/2, z1/2; (vi) x1, y1/2, z+3/2.
 

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