Methyl 2,6-dicarboxybenzoate

Article abstract of DOI:10.1107/S0108270103002610

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

Full text of DOI:10.1107/S0108270103002610

organic compounds
Acta Crystallographica Section C
Crystal Structure
been shown to yield the expected group 1 metal salts (Smith,
1975a,b).
Communications
Compound (I) has previously been synthesized from the
reaction of hemimellitic anhydride with MeOH and char-
acterized only by H NMR spectroscopy (Hurst & Bender,
ISSN 0108-2701
1
1971), but here, both the single-crystal X-ray structure and 1H
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 &
Nematollahi, 1978; Revial et al., 1983) had not been produced.
The asymmetric unit of (I) contains one complete molecule
(Fig. 1). The outer 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 et al., 1990; Bernstein et al., 1995)
(Table 2), producing zigzag chains (Fig. 2) reminiscent of the
packing of isophthalic acid (Derissen, 1974). One outer
carboxylic acid group of the parent acid dihydrate (Takusa-
gawa & 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 carboxylic
Methyl 2,6-dicarboxybenzoate
Sophie H. Dale and Mark R. J. Elsegood*
Chemistry Department, Loughborough University, Loughborough, Leicestershire
LE11 3TU, England
Correspondence e-mail: m.r.j.elsegood@lboro.ac.uk
Received 23 December 2002
Accepted 30 January 2003
Online 28 February 2003
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.
Comment
Derivatives of hemimellitic acid (benzene-1,2,3-tricarboxylic
acid) have been little studied 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 metal-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 coordi-
nation to metal cations as well as the creation of extended
networks through hydrogen bonding.
Figure 1
A view of the molecule of (I), showing the atom-labelling scheme and the
selective methylation at the central position. Displacement ellipsoids are
drawn at the 50% probability level and H atoms are shown as small
spheres of arbitrary radii.
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 re¯ux conditions affords, surprisingly, regioselec-
tive methylation at the 2-position. The title compound, (I), is
produced as X-ray quality colourless crystals in almost quan-
titative yield by the slow evaporation of the cooled solution. In
contrast, similar reactions with phthalic acid in pure H2O have
Figure 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 bonded to C atoms have been omitted for clarity.
Hydrogen bonding between molecules is indicated by dashed lines.
Acta Cryst. (2003). C59, o165±o166
DOI: 10.1107/S0108270103002610
# 2003 International Union of Crystallography o165

organic compounds
Table 1
Selected bond lengths (A).
acid group as the methyl ester prevents its involvement in
strong hydrogen bonding and also modi®es the angle of
rotation of this carboxyl group with respect to the plane of the
aromatic ring, from 86.8ꢁ in the parent acid to 76.7ꢁ in (I),
Ê
C7ÐO2
C7ÐO1
C8ÐO3
C8ÐO4
1.2233 (15)
O4ÐC10
C9ÐO5
C9ÐO6
1.4424 (16)
1.2256 (15)
1.3156 (15)
1.3177 (14)
1.2019 (15)
1.3359 (15)
allowing the methyl group to lie between the chains. Weak CÐ
Ê
= 3.2681 (15)±3.6564 (16) A;
HÁ Á ÁO interactions [CÁ Á ÁO
Desiraju & Steiner, 1999] between the zigzag chains produce
sheets, and interactions between these sheets produce a
loosely held three-dimensional structure.
Table 2
Hydrogen-bonding and short-contact geometry (A, ).
ꢁ
Ê
DÐHÁ Á ÁA
DÐH
HÁ Á ÁA
DÁ Á ÁA
DÐHÁ Á ÁA
Experimental
O1ÐH1Á Á ÁO5i
O6ÐH6Á Á ÁO2ii
C4ÐH4Á Á ÁO3iii
C5ÐH5Á Á ÁO1iv
C5ÐH5Á Á ÁO3iii
C5ÐH5Á Á ÁO5iii
C6ÐH6AÁ Á ÁO1iv
0.91 (2)
0.91 (2)
0.95
0.95
0.95
1.71 (2)
1.74 (2)
2.65
3.19
2.66
2.6131 (13)
2.6433 (13)
3.2681 (15)
3.6564 (16)
3.2725 (15)
3.5594 (16)
3.3627 (15)
172 (2)
173 (2)
123
112
122
Hemimellitic acid dihydrate (1 equivalent) was re¯uxed overnight
with M2CO3 (M is Li, Na and K; 0.5 equivalents) in a 9:1 mixture of
MeOH±H2O. The solutions were allowed to cool and then left to
evaporate. X-ray quality colourless crystals formed and single-crystal
X-ray analysis indicated that compound (I) had been synthesized in
all three cases (m.p. 478±482 K; literature value 478±483 K; Hurst &
Bender, 1971). Spectroscopic analysis, IR (KBr, ꢀmax, cm 1): 3500±
2500 (br, OH), 3087, 3046 and 3006 (aromatic CÐH), 2948, 2884 and
2837 (Csp3ÐH), 1742 (C O, ester), 1711 and 1692 (C O, acid),
1586 (C C, aromatic), 1466, 1453, 1430 and 1415 (Csp3ÐH), 1308,
0.95
0.95
2.65
2.58
160
140
Symmetry codes: (i) 1 ‡ x; 32 y; z 21; (ii) x 1; 32 y; 12 ‡ z; (iii) x; 21 ‡ y; 32 z; (iv)
1
x; 2 y; 1 z.
Data collection: SMART (Siemens, 1994); cell re®nement: SAINT
1
1275, 1123 and 1072 (CÐO), 776 (aromatic CÐH), 688; H NMR
(Siemens, 1994); data reduction: SAINT; program(s) used to solve
structure: SHELXTL (Bruker, 1997); program(s) used to re®ne
structure: SHELXTL; molecular graphics: SHELXTL; software used
to prepare material for publication: SHELXTL and local programs.
(400 MHz, d6-DMSO, ꢁ): 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, ꢁ): 167.9
(Cquat, C O, ester), 166.17 (2Cquat, C O, acid), 135.6 (Cquat, Ar),
133.4 (2CH, Ar), 129.8 (CH, Ar), 129.6 (2Cquat, Ar), 52.2 (CH3). The
1H NMR results above correspond to previously reported data (Hurst
& Bender, 1971).
The authors would like to acknowledge the EPSRC for the
provision of a studentship to SHD.
Crystal data
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BM1520). Services for accessing these data are
described at the back of the journal.
3
C10H8O6
Mr = 224.16
Monoclinic, P21=c
Dx = 1.574 Mg m
Mo Kꢃ radiation
Cell parameters from 3989
re¯ections
Ê
a = 5.0242 (3) A
ꢄ = 2.8±28.5ꢁ
ꢅ = 0.13 mm
T = 150 (2) K
Ê
b = 14.6263 (10) A
1
Ê
c = 12.9024 (9) A
References
ꢂ = 93.835 (2)ꢁ
V = 946.02 (11) A
Z = 4
3
Ê
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ꢄ
max = 29ꢁ
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8271 measured re¯ections
Re®nement
Re®nement on F2
R[F2 > 2ꢆ(F2)] = 0.033
wR(F2) = 0.094
S = 1.03
2287 re¯ections
160 parameters
H atoms treated by a mixture of
independent and constrained
re®nement
w = 1/[ꢆ2(Fo2) + (0.049P)2
+ 0.304P]
where P = (Fo2 + 2Fc2)/3
(Á/ꢆ)max < 0.001
3
Ê
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3
Ê
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Aromatic H atoms were placed in geometric positions (with a CÐ
Ê
H distance of 0.95 A) and re®ned using a riding model, while the
coordinates of the methyl and hydroxy H atoms were freely re®ned.
Uiso values were set at 1.2Ueq(C) for aryl H atoms and 1.5Ueq(C,O)
for methyl and hydroxy H atoms.
ꢀ
o166 Dale and Elsegood
C10H8O6
Acta Cryst. (2003). C59, o165±o166