HPLC studies on the organic subset of the oscillatory BZ reaction. 2. Two different types of malonyl radicals in the Ce4+-malonic acid reaction

Article abstract of DOI:10.1021/jp952492l

Applying combined HPLC and NMR techniques, it was found that, besides the already known 1,1,2,2-ethanetetracarboxylic acid (ETA), monomalonyl malonate (MAMA) is also a product of the Ce⁴⁺-malonic acid reaction. This is indirect evidence that two different types of organic radicals are formed in the reaction: the alkyl and the carboxylato malonyl radicals. While ETA is a recombination product of two alkyl radicals, MAMA is formed in the recombination of one alkyl and one carboxylato radical.

Full text of DOI:10.1021/jp952492l

J. Phys. Chem. 1996, 100, 3051-3055
3051
HPLC Studies on the Organic Subset of the Oscillatory BZ Reaction. 2. Two Different
Types of Malonyl Radicals in the Ce4+-Malonic Acid Reaction
Atchara Sirimungkala and Horst-Dieter Fo1rsterling*
Fachbereich Physikalische Chemie, Philipps-UniVersita¨t Marburg, D-35032 Marburg/Lahn, Germany
Zoltan Noszticzius*
Center for Complex and Nonlinear Systems and the Department of Chemical Physics, Technical UniVersity
Budapest, H-1521 Budapest, Hungary
ReceiVed: August 25, 1995; In Final Form: October 20, 1995X
Applying combined HPLC and NMR techniques, it was found that, besides the already known 1,1,2,2-
ethanetetracarboxylic acid (ETA), monomalonyl malonate (MAMA) is also a product of the Ce4+-malonic
acid reaction. This is indirect evidence that two different types of organic radicals are formed in the
reaction: the alkyl and the carboxylato malonyl radicals. While ETA is a recombination product of two
alkyl radicals, MAMA is formed in the recombination of one alkyl and one carboxylato radical.
Introduction
rather easily. To avoid this, we changed the solvent from
methanol to water after the first step of the hydrolysis, and this
In the first paper of this series Gao et al.1 reported HPLC
studies on the products of the Ce4+-malonic acid reaction. Even
before their studies it was known from ESR measurements2,3
that the very first but highly unstable intermediate of the reaction
is an alkyl malonyl radical. Nevertheless, there were no direct
experimental data available prior to Gao’s work on further
reactions of these radicals. It was generally assumed (see e.g.
Barkin et al.,4 Gyo¨rgyi et al.5) that the malonyl radicals react
with each other in a disproportionation reaction to form tartronic
and malonic acids. Gao et al. have shown that there is no
tartronic acid among the first molecular intermediates of the
Ce4+-malonic acid reaction; thus, the radical-radical reaction
cannot be a disproportionation. Two product peaks were found
in the chromatogram, the second of which was identified as
1,1,2,2-ethanetetracarboxylic acid (ETA) a recombination prod-
uct of the alkyl malonyl radicals. The first peak was not
identified, however. The aim of the present work is to identify
this unknown product to obtain more information about the
mechanism of the reaction.
way we could carry out the process at 40 °C only. (The first
step produces a mixture of potassium salts of different half
esters, which are not soluble in methanol and are consequently
difficult to hydrolyze further in methanol but readily dissolve
and hydrolyze in water.) The solid potassium salt of ETA was
precipitated from its aqueous solution with methanol. The
product can be purified if necessary by dissolving it in water
and reprecipitating with methanol. Free ETA acid in crystalline
form was produced from its potassium salt. One gram of the
potassium salt was dissolved in 5 mL of 1 M sulfuric acid
saturated with NaHSO4. This mixture was extracted with 20
mL of ether three times. The ether phases were combined, and
the ether was distilled. The remaining solid acid was dried in
vacuum at room temperature for 10 min to remove the last traces
of ether. The free ETA acid readily dissolves in acetone-d6,
which was necessary to study its H-NMR spectrum in that
solvent. The potassium salt of 1,1,2-ethanetricarboxylic acid
(ETRA) was prepared by hydrolyzing triethyl 1,1,2-ethanetri-
carboxylate (Aldrich 99%) with KOH in a similar way to the
case of ETA. A mixture of monomalonyl malonate (MAMA)
and malonic acid was prepared by forming the half ester of
malonic acid with tartronic acid (the OH group of which reacts
like an alcohol), applying an excess of malonic acid. In this
reaction a twofold excess of malonic acid was applied to avoid
the formation of different byproducts. First 150 mL of ether
was stirred with 5 g of P2O5 for 5 min to remove any water
present in the ether. As P2O5 gets sticky when it absorbs water,
the procedure was performed in a 250 mL Erlenmeyer flask
equipped with a large magnetic stirrer bar. The flask was
covered with a watch glass to prevent large losses of ether due
to evaporation. (The whole procedure was carried out under
the hood.) The water free ether then was poured into another
Erlenmeyer flask containing 3 g of malonic acid and 0.5 g of
tartronic acid in solid form. When these acids were dissolved
in the ether, 5 g of P2O5 was added and the stirring was
continued at laboratory temperature for 30 min. Then the ether
phase was transferred again to a new Erlenmeyer flask contain-
ing 0.5 g of tartronic acid in solid form. When most of the
tartronic acid dissolved, another 5 g of P2O5 was added and the
stirring was continued again for 30 min. The same procedure
Experiments
Materials. Malonic acid (Fluka puriss) was recrystallized
from acetone and acetone/chloroform following the procedures
proposed by Noszticzius et al.6,7 All organic solvents applied
in our experiments were of reagent grade. Tartronic acid
(Hereaus, purum) was purified by extracting its crystals with
ethyl acetate; e.g., 2 g of tartronic acid was mixed with 20 mL
of ethyl acetate, and the mixture was stirred for 3-4 h. Then
the tartronic acid crystals were filtered, washed with chloroform,
and dried. The procedure was repeated if the product was not
pure enough. The purity of the compounds was checked by
HPLC. The potassium salt of ETA was produced by the
hydrolysis of its ethyl ester. The method of Horri et al.8 applied
previously1 was slightly modified. To facilitate hydrolysis,
Horri et al. boiled the ester in a methanol/KOH mixture. We
found, however, that ETA decarboxylates at higher temperatures
* Authors to whom correspondence should be addressed. E-mail: H.-
D.F., foersthd@PS1405.Phys-Chemie.Uni-Marburg.de; Z.N., noszti@
phy.bme.hu.
X Abstract published in AdVance ACS Abstracts, January 1, 1996.
0022-3654/96/20100-3051$12.00/0 © 1996 American Chemical Society

3052 J. Phys. Chem., Vol. 100, No. 8, 1996
Sirimungkala et al.
TABLE 1: Retention Times and H-NMR Shifts for Some Organic Acidsa
H-NMR shift (ppm)
CH2
acid
retention time (s)
CH
CH3
injection peak (strong inorganic acids)
monomalonyl malonate (MAMA)
1,1,2,2-ethanetetracarboxylic acid (ETA)b
oxalic acid (OA)
480
570
600
600
640
5.57
4.10
3.60
mesoxalic acid (MOA)
tartronic acid (TA)
800
840
965
4.73
3.77, 3.80, 3.84
5.18
1,1,2-ethanetricarboxylic acid (ETRA)b
glyoxylic acid (GOA)b
3.65, 3.72
malonic acid (MA)
succinic acid (SA)
formic acid (FA)
acetic acid (HOAc)
1040
1240
1385
1500
3.38
2.58
8.11
1.98
a Retention times were measured under the HPLC conditions applied in this work. H-NMR shifts were measured in acetone-d6 with TMS as
standard. b These acids take part in a slow reversible reaction in acetone-d6, and the characteristic NMR peaks are decreasing in time as a consequence.
Thus NMR measurements should be made within 1-2 h after the preparation of the sample. The reaction is reversible because after the acetone-d6
is evaporated and the NMR sample is dissolved in 0.01 M H2SO4, the HPLC shows no chemical change.
was then repeated with the last 0.5 g portion of tartronic acid.
(Thus the total amount of tartronic acid used in the synthesis
was 1.5 g. The stepwise addition of the tartronic acid was
necessary because of its low solubility in ether.) After 30 min
of stirring, the ether phase was separated and extracted twice
in a separatory funnel with 5 mL of 1 M H2SO4 saturated with
NaHSO4 to remove all phosphoric acid, most of the tartronic
acid, and some of the contaminating byproducts. The ether
phase was distilled, and the remaining solid mixture of MAMA
and malonic acid was dried in vacuum to remove traces of ether.
As the solid product is very hygroscopic, sample solutions for
Figure 1. Chromatogram of the products of the Ce4+-MA reaction.
Initial conditions: [Ce4+]0 ) 0.02 M, [MA]0 ) 0.2 M, [H2SO4]0 ) 1
M. When the reaction was over, the mixture was diluted with water
by a factor of 100 and 20 µL of this sample was injected onto the
column. A is the absorbance.
HPLC and NMR were prepared from the solid in the distilling
flask on the spot.
H2SO4 (Merck 95%), Ce(SO4)2‚4H2O (Riedel de Haen), and
changed to get a better column stability and peak resolution.
(Earlier it was a problem that the hydrodynamic impedance of
other chemicals used were of reagent grade and used without
the column was increasing continuously using the more
further purification. All aqueous solutions were prepared with
concentrated eluent.) Thus the retention times are slightly
doubly distilled water. The Ce4+-malonic acid reaction was
different from that of the previous work, and the two peaks (1
carried out excluding oxygen (by bubbling nitrogen through the
) unknown, 2 ) ETA) are better resolved. In Table 1 retention
reactants and the reaction mixture before and during the
times of some organic acids are given for the new conditions.
reaction).
PreparatiVe HPLC and Concentration of the Samples. To
Analytical Techniques. H-NMR measurements were made
identify an unknown peak in the HPLC chromatogram, the
on a Bruker ARX-200 automatic NMR spectrometer. Deuter-
separation of this component on a small scale for further
ated acetone was used as a solvent. Another choice would have
experiments was sometimes necessary. As it is known, HPLC
been D2O, but we wanted to avoid the isotope exchange of the
itself can be used to collect relatively pure but small samples
of the separated components especially if the original sample
injected onto the column is concentrated enough. To obtain
more concentrated samples, we extracted with ether a relatively
mobile hydrogens via enolization, which occurs in D2O.9
HPLC experiments were performed with a Merck Polyspher
OA KC column (length 30 cm, diameter 7.8 mm) at 45 °C.
Shimadzu HPLC equipment (LC-10AS pump, CTO-10A col-
umn oven, SPD-10A dual-wavelength UV detector working at
220 nm) was used. The output signals from the detector were
measured by two Keithley 155 microvoltmeters simultaneously.
The microvoltmeters were set to different sensitivities. One
channel was used with high sensitivity to detect small peaks,
and the other was used with low sensitivity to measure the
HPLC peaks of the main components. The outputs of the
microvoltmeters were connected to an AT 286 computer
equipped with a 12 bit AD converter. The sample was injected
using a Rheodyne 7010 injector with a 20 µL sample loop. The
0.01 M H2SO4 eluent was filtered with a membrane filter
(Sartorius, cellulose nitrate, pore size 0.2 µm) and degassed by
applying vacuum.
large reaction volume containing the products of the Ce4+
-
malonic acid reaction and accumulated them into a much smaller
volume by evaporating the ether phase. One hundred milliliters
of 0.1 M Ce4+ (in 1 M H2SO4) was added dropwise to 100 mL
of 1 M malonic acid (also in 1 M H2SO4) in a nitrogen
atmosphere. When the reaction was complete NaHSO4 was
added to the solution to make it nearly saturated with NaHSO4.
Then it was extracted four times with 200 mL of ether. After
the first extraction the 200 mL ether phase was poured into the
flask of a Bu¨chi rotavapor-R containing 5 mL of 0.01 M H2-
SO4 eluent as an aqueous phase. The ether was distilled, and
then the ether phase of the next extraction step was added. After
the distillation of the last fraction of the ether, the remaining
aqueous phase containing the concentrated sample was used for
HPLC experiments. The last traces of ether were removed from
the concentrated sample by bubbling nitrogen through it. The
same technique was used to transfer organic acids from the
aqueous phase to deuterated acetone for NMR measurements.
The only difference in the procedure was that the ether phase
We started our work by repeating the experiments of Gao et
al. but under somewhat different conditions (see Figure 1). The
main difference was that a more dilute, 0.01 M, sulfuric acid
was used as an eluent with a lower flow rate of 0.4 mL/min.
(Previously these parameters were 0.02 M and 0.5 mL/min,
respectively.) The eluent concentration and the flow rate were

Malonyl Radicals in the Ce4+-Malonic Acid Reaction
J. Phys. Chem., Vol. 100, No. 8, 1996 3053
Figure 2. Ratio A2/A1 as a function of the ratio [MA]0/[Ce4+]0. See
text for explanation of the symbols.
was evaporated to dryness without adding anything to it. Traces
of ether were removed in vacuum.
Results and Discussion
As a first step it was necessary to check whether or not the
unknown peak was really a first molecular intermediate
produced in the Ce4+-malonic acid reaction simultaneously
with ETA. Another possibility would have been that the
unknown compound was formed in a further oxidation of ETA
by Ce4+, that is in a consecutive reaction. To answer this
question, we measured the peak height of the unknown peak 1
(denoted by A1) and of that for ETA (A2), as a function of the
initial malonic acid concentration while keeping all other initial
reagent concentrations constant. If the unknown peak were a
product of the Ce4+-ETA reaction, then starting the Ce4+
-
malonic acid reaction with a higher malonic acid concentration
should decrease the yield of the unknown product (this is
because most of the Ce4+ would react with the excess malonic
acid to form ETA and not with the ETA to form the unknown
product). Our experiments (Figure 2), however, prove that this
is not the case.
Figure 3. (a) Chromatogram of the products of the Ce4+-MA reaction
enriched with the extraction-accumulation techniques as described in
the experimental part. (b) The chromatogram of the same products
after heating the sample. (c) Decomposition products of malonic acid,
[MA]0 ) 0.049 M, and (d) of ETA, [ETA]0 ) 4.8 × 10-4 M after the
same heating procedure.
As Figure 2 shows, the ratio A2/A1 is independent of the
malonic acid concentration if the latter is in a great enough
excess compared to Ce4+. If the [MA]/[Ce4+] ratio is above
25, then even the absolute values of the peaks themselves are
constant within the experimental error. Consequently the
unknown intermediate should be produced simultaneously with
ETA in a parallel process. This parallel process could be an
unknown route of recombination of the known alkyl malonyl
radicals or a recombination of some other type of radicals.
Anyhow, to solve this problem a chemical identification of peak
1 is necessary. This task turned out to be more difficult than
the identification of peak 2. As we know, the second peak was
identified as ETA by Gao et al. In that case, however, to assume
a recombination between the already known alkyl malonyl
radicals was a straightforward hypothesis. In addition ETA was
easy to produce from its commercially available ethyl ester.
Now, in the absence of a good working hypothesis and without
having a synthetic reference standard, it was more difficult to
solve the problem. We tried to obtain more information about
the unknown compound by heating it and trying to identify its
decomposition products with the HPLC technique again. As a
first step, a more concentrated solution of the unknown
compound was necessary. To this end a larger amount of the
reaction products was extracted with ether and accumulated into
a small volume of 0.01 M sulfuric acid solution. (The details
of the extraction-accumulation method are given in the
experimental part.) Twenty microliters of the concentrated
mixture was analyzed by HPLC. The chromatogram is shown
in Figure 3a.
that the latter is more soluble in ether than ETA. In a next step
a small part of the concentrated sample was heated to 70 °C
and was kept at this temperature for 15 min. Then a 20 µL
sample was analyzed again by HPLC. The result can be seen
in Figure 3b. As the figure shows, peak 1 (the unknown
product) and peak 2 (ETA) have disappeared and four new peaks
at 800, 840, 1240, and 1500 s appeared instead. To decide
which decomposition product is coming from which initial
component, we applied the same heating procedure to pure
malonic acid and ETA under similar conditions. HPLC
chromatograms of the decomposition products are given in
Figure 3c (starting material: malonic acid) and in Figure 3d
(starting material: ETA). From these experiments and using
the retention times of some selected organic acids listed in Table
1, we can draw the following conclusions: (i) The peak at 1500
s can be identified as acetic acid, which is a decomposition
product of malonic acid:
CH2(COOH)2 f CH3COOH + CO2
(ii) The peak at 840 s is due to 1,1,2-ethanetricarboxylic acid
(ETRA), which is a decarboxylation product of ETA:
(HOOC)2CHCH(COOH)2 f
As can be seen in Figure 3a the peak heights of the unknown
product and of ETA were increased by nearly two orders of
magnitude compared to those in Figure 1. The ratio of the two
peaks was also changed; compared to the ETA the relative
amount of the unknown product was increased. This indicates
(HOOC)2CHCH2COOH + CO2
(iii) The peak at 1240 s is succinic acid, which appears in a
further decarboxylation now from ETRA:

3054 J. Phys. Chem., Vol. 100, No. 8, 1996
Sirimungkala et al.
Figure 4. (a) Chromatogram of a fraction separated by the column
and collected after the HPLC detector between 550 and 580 s retention
time. As can be seen, this fraction contains the first peak mainly. (b)
Chromatogram of the same sample after the heating procedure.
(HOOC)2CHCH2COOH f
HOOCCH2CH2CH2COOH + CO2
(iv) As we could see the new peaks at 840, 1240, and 1500 s
discussed above were decomposition products of components
which were already known before. The peak is 800 s is an
exception, however; thus, it should be a decomposition product
of the unknown compound. According to Table 1 this
decomposition product is most probably tartronic acid.10
Figure 5. (a) Chromatogram of a mixture containing the synthesized
MAMA, malonic acid, tartronic acid, and an unknown byproduct.
Preparation of the sample: after the synthesis (see the experimental
part) and evaporation of the ether, about 10 mg of the dry mixture was
dissolved in 5 mL of 0.01 M H2SO4 and 20 µL was injected onto the
column. (b) Proton NMR of the same mixture. Preparation of the
sample: about 10 mL of the ether phase containing the mixture after
the synthesis was evaporated to dryness and was dissolved in 1 mL of
acetone-d6. (c) Proton NMR of the first unknown peak. Preparation
of the sample: 5 HPLC fractions between 550 and 580 s were collected
(the total volume was about 1 mL). This volume was extracted with
20 mL of ether four times. Before the extraction the aqueous phase
was made 1 M for H2SO4 and saturated for NaHSO4. The ether phase
was evaporated to dryness and was dissolved in 1 mL of acetone-d6.
At this point of the investigation we still had no idea about
the chemical identity of peak 1, but we had a strong hint that at
least one of its decomposition products is tartronic acid. We
could not be sure, however, that this is the only decomposition
product, as some other could hide under the huge peak of
malonic acid (see Figure 3b). Thus we decided to use the HPLC
as a preparative device to separate the unknown compound and
get rid of most of the malonic acid. Such a separation, however,
causes dilution, which means a loss in sensitivity. To avoid
such problems, we used again the concentrated sample for this
separation. Two hundred microliters of the eluent containing
the first peak was collected right after the detector of the HPLC
apparatus. To check the purity of the collected sample, 20 µL
of it was reinjected onto the column. The resulting chromato-
gram in Figure 4a shows that most of the ETA and the malonic
acid were really removed and the main component remaining
in the sample was the unknown compound. In the next step
such a separated sample was heated with the same method as
before to observe its decomposition products. The chromato-
gram of these products is shown in Figure 4b. It is an important
feature of the chromatogram that, besides the expected appear-
ance of tartronic acid, the originally small peak of malonic acid
was increased considerably. Assuming that the products are
really tartronic and malonic acids, we could calculate from the
peak heights the ratio of these decomposition products. This
ratio was 1:1 within the experimental error.
known alkyl malonyl radical, the other is a carboxylato malonyl
radical. Thus
Consequently, if our working hypothesis holds, the unknown
compound should be monomalonyl malonate (MAMA). MAMA
is a half ester of malonic acid, where tartronic acid plays the
role of an alcohol. When heated, a hydrolysis of 1 mol MAMA
should give 1 mol of TA and 1 mol of MA, just as expected.
Without heating, a hydrolysis with KOH at room temperature
gave the same products:
At this point of our research enough data have been
accumulated to make some working hypotheses. First, we can
assume that one molecule of the unknown compound gives one
molecule of malonic acid and one molecule of tartronic acid.
Another piece of information is that the unknown compound
should be produced in a radical-radical recombination process.
In addition it is known from the work of Gao et al. that 1 mol
of Ce4+ consumes 1 mol of malonic acid. A working hypothesis
compatible with all this information is that the unknown
compound is formed in a recombination reaction between two
different types of malonyl radicals. While one is the already
The next step was to prove our hypothesis. To this end we
had to synthesize the ester MAMA. (As we were not able to
find any reference to MAMA in the chemical literature, there
was no other possibility. Our method of synthesis is given in
the experimental part.) A mixture containing MAMA and
malonic acid as main components was produced. The HPLC

Malonyl Radicals in the Ce4+-Malonic Acid Reaction
J. Phys. Chem., Vol. 100, No. 8, 1996 3055
chromatogram of this mixture is shown in Figure 5a. The
retention time of this synthetic MAMA was the same within
experimental error as the retention time of the unknown product
found in the Ce4+-malonic acid reaction. To obtain a final
piece of evidence, a H-NMR spectrum of the above mixture
(Figure 5b) was compared to the H-NMR spectrum of the
unknown peak separated by preparative HPLC (Figure 5c). From
these spectra it is straightforward that the unknown peak can
be really identified as MAMA. In the H-NMR spectrum of
MAMA the peak at 3.60 ppm close to the 3.43 ppm peak of
the malonic acid can be assigned to the CH2 protons of MAMA,
while the peak at 5.57 ppm is due to the CH proton11 of MAMA.
The intensity ratio of the CH2 and CH proton peaks is very
close to the theoretical 2:1 ratio. (Peaks due to some known
and unknown contaminants are also marked in the NMR
spectra.)
Fonds der Chemischen Industrie for financial support. A.S. was
supported by the German Academic Exchange Service (DAAD).
Z.N is grateful for the support of OTKA Grant No. TO17041
and acknowledges an EC Copernicus grant. The authors thank
Y. Gao for some data, H. Schreiber for discussions, and R.
Wagner for his help in evaluating NMR spectra.
References and Notes
(1) Gao, Y.; Fo¨rsterling, H. D.; Noszticzius, Z.; Meyer, B. J. Phys.
Chem. 1994, 98, 8377.
(2) Brusa, M. A.; Perissinotti, L. J.; Colussi, A. J. Phys. Chem. 1985,
89, 1572.
(3) Fo¨rsterling, H. D.; Noszticzius, Z. J. Phys. Chem. 1989, 93, 2740.
(4) Barkin, S.; Bixon, M.; Noyes, R. M.; Bar-Eli, K. Int. J. Chem.
Kinet. 1978, 10, 619.
(5) Gyo¨rgyi, L.; Turanyi, T.; Field, R. J. J. Phys. Chem. 1990, 94,
7162.
(6) Noszticzius, Z.; McCormick, W. D.; Swinney, H. L. J. Phys. Chem.
1987, 91, 5129.
(7) Gyo¨rgyi, L.; Field, R. J.; Noszticzius, Z.; McCormick, W. D.;
Swinney, H. L. J. Phys. Chem. 1992, 96, 1228.
Conclusion
(8) Horri, Z.; Tamura, Y.; Kugita, H.; Okumura, K. J. Pharm. Soc.
Jpn. 1954, 74, 150.
According to the experimental evidence presented here, the
first molecular intermediates of the Ce4+-malonic acid reaction
are recombination products of two different types of malonyl
radicals. Our HPLC and NMR studies on the reaction products
show that two alkyl malonyl radicals form one molecule of ETA
and that one alkyl and one carboxylato malonyl radical form
one molecule of MAMA. An important consequence of these
results is that, besides the already known alkyl malonyl radicals,
carboxylato type malonyl radicals are also produced in the
Ce4+-malonic acid reaction. We estimate that in the present
experiments about 15% of the malonyl radicals were carboxylato
type while the rest were alkyl radicals. The importance of these
findings to the whole BZ mechanism, however, is not clear
presently. The ratio of alkyl and carboxylato type radicals for
different variants of the BZ reaction is not known either. Further
research is planned to answer these questions.
(9) Hansen, E.; Ruoff, P. J. Phys. Chem. 1988, 92, 2641.
(10) The measured retention times were very reliable and reproducible
within a few seconds or sometimes less; thus, they could be used for
chemical identification rather well. Nevertheless, a retention time alone is
usually not enough to identify an unknown compound with absolute
certainty; e.g., as Table 1 shows, retention times for ETA and oxalic acid
are the same within experimental error. Therefore some chemical reactions
of the unknown compounds, like the decarboxylation reactions applied here,
or the spectrophotometric measurements applied by Gao et al. can be very
helpful to provide additional information in critical cases. In addition to
the hydrolysis and decarboxylation reactions, we used H-NMR for this
purpose.
(11) High Resolution NMR Spectra Catalog; Bhacca, N. S., Hollins, D.
P., Johnson, L. F., Eds.; Varian Assoc. and National Press: Palo Alto, CA,
1963; Vol. 2, spectrum 546. This is a H-NMR spectrum of the diethyl
ester of the tartronic acid, where the alcoholic hydroxyl group of the tartronic
acid is esterified by acetic acid. Thus the CH proton in this compound is
in a very similar environment to that of the CH proton in MAMA. The
assignment for this proton according to the reference book is 5.52 ppm in
CDCl3, while for the CH group of MAMA this is 5.57 ppm in acetone-d6
according to our measurements.
Acknowledgment. The authors thank the Deutsche Fors-
chungsgemeinschaft, the Stiftung Volkswagenwerk, and the
JP952492L