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T.L.N. Taoana et al. / Journal of Molecular Structure 694 (2004) 173–178
from Sigma-Aldrich and were used without further
purification.
Proton nuclear magnetic resonance (1HNMR) spectra
were recorded on a Bruker-300 MHz in D2O and on a
VARIAN INOVA 500 MHz in CDCl3.
diethylether ether (3 £ 30 ml). The organic layer extracts
were combined, dried over anhydrous magnesium sulfate
and filtered. The filtrate gave, after a slow evaporation, a
white powder: (2.8 g, 40%), m.p. 139 8C. Anal. Found %: C,
30.01; H, 5.40. Calcd% for C6H13O9.5 or C6H6O6·3.5 H2O
(cyclopropane-1,1,2-tricarboxylic acid hydrate): C, 30.39,
H, 5.53.
Elementary analysis was performed by the Micro-
analytical Services at the University of Cape Town (South
Africa). The instrument used is Fisons Elemental Analyser
1108 CHNS-O. The calibration compound was acetanilide.
The results were obtained in duplicate for consistency.
Fast atom bombardment (FAB) mass spectrum was
performed on VG 70 SE spectrometer (Cape Techniknon
Research Unit). The calibration compound was
perfluorokerosene.
After re-crystallization in ethanol, the decomposition
point was found to be 150 8C. The elemental analysis
showed the compound to be containing 0.25 molecule of
alcohol per formula. Anal. Found%: C, 42.56; H, 4.37.
Calcd% for C6.5H7.5O6.25 or C6H6O6·0.25 C2H5OH: C,
42.05; H, 4.04. The compound still contains traces of
alcohol as impurity. This could suggest that the solvent is
very important in stabilizing the structure of the compound.
Electrospray mass spectrum was recorded on a VG
Quattro triple quadripole spectrometer (University of
Stellenbosch, South Africa). Samples were dissolved in
100 l of 50% (v/v) acetonitrile (50% ACN). Ten liters of this
solution were diluted to 100 l with 50% ACN. Ten liters of
the final solution, were injected in the analyzer, via a
Rheodyne injection valve. The carrier solvent was a solution
of 50% ACN, at a flow rate of 20 l/min. Spectra were made
of an average of 10 scans, and were recorded using a cone
voltage of 30 V and a capillary voltage of 3.5 kV. The
calibration compound was polyethylene glycol 200.
Differential scanning calorimetric (DSC) analyses were
performed on a Perkin–Elmer DSC 7 and thermogravi-
metric (TG) analyses on a Perkin–Elmer TGA 7, using
5–10 mg powder samples at a heating rate of 5 8C min21
under a nitrogen flow rate of 20 cm3 min21. For DSC
analyses, empty aluminum pans were used as reference.
2.3. Theoretical calculations
The reported calculations were carried out at the MP2/
6-31G(d) [8,9]. Full geometry optimization was carried out
after conformational searching with smaller basis sets
identified the lowest energy conformation. All stationary
points were classified as minima by Hessian matrix
calculations. Calculations were performed using GAMESS
(March 1997 Version) [10]. Thermodynamic calculations
were performed for all stationary points. The frequencies
were scaled by a factor of 0.92 [11] for the MP2/6-31G(d)
structures. Visualization of vibrational motions derived
from the Hessian calculation was accomplished using the
MacMOLPLT software package [12].
2.2. Synthesis of cyclopropane-1,1,2-tricarboxylic acid
3. Results and discussion
A mixture of 2,3-dibromopropionic acid (9.30 g,
40 mmol) and cyanoacetic acid (3.40 g, 40 mmol) was
placed in a 500ml-flask with a magnetic stirrer. Benzyl-
triethylammonium chloride (9.10 g, 40 mmol) was added
with stirring. The reaction mixture was cooled in an ice-bath
while 50% sodium hydroxide (40 ml) with vigorous stirring
over a period of 30 min. The light brownish solution was
stirred for 1 h at room temperature. The solution was then
diluted with 100 ml of water and then extracted with ether
(2 £ 30 ml). The organic phase was discarded and the
aqueous layer was acidified with concentrated HCl (50 ml),
then extracted with diethyl ether (3 £ 30 ml). The organic
phase was washed with brine, then dried over anhydrous
sodium carbonate and was filtered. The filtrate was left
in the air for evaporation. The resulting product was
2-bromoacrylic acid (3.66 g, 60%.), m.p. 68–70 8C. Anal.
Found %: C, 24.14; H, 1.72. Calcd% for C3H3Br: C, 23.87;
H, 2.00.
The TEBA-catalyzed reaction of cyanoacetic acid and
2,3-dibromopropionic acid in 50% sodium hydroxide has
been investigated (Scheme 1). Several procedures were tried
by changing the temperature, duration of the reaction and
the order of addition of reactants in order to increase the
yield in cyclopropane-1,1,2-tricarboxylic acid. The best
The aqueous phase was concentrated to about 100 ml at
45 8C with a rotary evaporator. The residue was cooled to
0 8C and acidified to pH 1 with concentrated hydrochloric
acid. The solution was subsequently extracted with
Scheme 1.