Open Journal of Physical Chemistry, 2011, 1, 85-93
doi:10.4236/ojpc.2011.13012 Published Online November 2011 (
Copyright © 2011 SciRes. OJPC
Organocatalyzed Decarboxylation of Naturally
Occurring Cinnamic Acids: Po tential Role in Flavoring
Chemicals Production
Virginia Aldabalde1#, Mariela Risso1#, María Lucía Derrudi1, Federico Geymonat1, Gustavo Seoane1,
Daniela Gamenara1, Patricia Saenz-Méndez1,2*
1Grupo de Fisicoquímica Orgánica y Bioprocesos, Facultad de Química, UdelaR, Montevideo, Uruguay
2Computational Chemistry and Biology Group, Facultad de Química, UdelaR, Montevideo, Uruguay
E-mail: *
Received June 26, 2011; revised August 15, 2011; accepted September 17, 2011
The mechanism and the final outcome of the Knoevenagel-Doebner reaction are discussed. The condensation
reaction between different hydroxy-substituted aromatic aldehydes and malonic acid is performed using
piperidine as organocatalyst. The key role of the catalyst is clearly pointed out during the decarboxylation of
ferulic acid, without the use of a strong decarboxylating agent, leading to a 4-vinylphenol derivative. Based
on the results obtained, the studied pathway may be important in the understanding of vinylphenol produc-
tion during malting and brewing of wheat and barley grains. Finally, changing the solvent of the reaction
from pyridine to water in the Knoevenagel-Doebner reaction of 4-hydroxybenzaldehydes, dimerization of
resulting styrene derivatives is observed. These results can be of interest also in the field of food chemistry,
since cinnamic acids are frequently found in fruits and vegetables used for human consumption.
,β-Unsaturated Carboxylic Acids, Decarboxylation, Vinylphenols, Organocatalysis,
1. Introduction
,β-Unsaturated carboxylic acids are versatile compo-
unds which allow the access to a variety of synthetic
intermediates as well as natural products, such as lignin
related structures (Figure 1) [1].
Lignin is a component of the cell wall in vascular
plants. Its structure involves a variety of different cova-
lent bonds result of the oxidative coupling of aromatic
alcohols derived from hydroxycinnamic acids [2]. There
is an increasing interest in its structural study due to its
potential utilization as renewable raw material in the
chemical industry.
Within a research program devoted to the use of
unsaturated carboxylic acids to prepare lignans as well as
high added value building blocks, the synthesis of cin-
namic acid derivatives through a Knoevenagel-Doebner
reaction was performed [3,4]. The Knoevenagel conden-
sation of aldehydes and malonic acid is generally pro-
moted by bases, such as pyridine and piperidine, yielding
the correspondin g
,β-unsaturated carboxylic acid, under
organocatalytic conditions [5]. Organocatalysis has be-
come a field of great importance within organic synthesis,
allowing the development of widely applicable reactions
while avoiding the use of metal catalysts [6-9].
In this context, we condensed different aromatic alde-
hydes with malonic acid, using piperidine as organo-
catalyst and pyridine as solvent [10,11]. In most cases,
the reaction lead to the corresponding
carboxylic acid in very good yields (results not shown).
However, when vanillin (4-hydroxy-3-methoxybenzald-
ehyde) was employed as electrophile, the formation of
2-methoxy-4-vinylphenol 1a, instead of ferulic acid ((E)-
3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid) 2a,
was observed (Figure 2).
This useful transformation was reported in 2005 and
since then, some aspects of the outcome of the reaction
were described [12,13 ].
4-Vinylphenols are natural products widely distributed
in plants [14-17]. Moreover, such intermediates are also
employed as building blocks for the preparation of
# Both authors contributed equally.
Figure 1.
,β-Unsaturated carboxylic acids as precursors of lignin models.
Figure 2. Organocatalyzed conversion of vanillin into 2-methoxy-4-vinylphenol 1a.
polymers and bioactive compounds [18,19]. Conse-
quently, the design of synthetic strategies to prepare this
type of compounds and gaining knowledge regarding
their occurrence in nature, are of increasing importance.
Recently, a detailed computational study of the mech-
anism of the Knoevenagel-Doebner reaction was re-
ported [20], answering questions regarding the mecha-
nism of the reaction and opening the door to new ones.
Hydroxycinnamic acids are ubiquitous in plants, and it
has been proposed that enzymatic decarboxylation may
be responsible for vinylphenol production [21]. Besides
the biocatalytic transformation, is it possible to perform
the same reaction employing an organocatalyst? As an
answer to this question, herein we describe a decarboxy-
lation reaction of hydroxycinnamic acids under mild
conditions. In addition, we report new experimental evi-
dence for the previously proposed mechanism as well as
the final outcome of the organocatalytic Knoevena-
gel-Do ebner condensation.
2. Experimental
2.1. General
Chemical reagents were purchased from commercial
sources and were used without further purification. Sol-
vents were purified and dried by standard procedures.
Reactions were monitored using thin layer chromatogra-
phy (TLC) on silica gel (Kieselgel HF254) and visual-
ized with UV light (254 nm) and p-anisaldehyde in
acidic ethanolic solution. Flash column chromatography
was performed using silica gel 60 (230 - 240 mesh).
NMR (1H and 13C) spectra were carried out in a Bruker
Advance DPX 400 MHz equipment, at 30˚C in the pres-
ence of TMS as internal stan dard. All produ cts were pre-
viously reported and the spectroscopic data of all com-
Copyright © 2011 SciRes. OJPC
pounds were found to correspond with literature data.
2.2. General Procedure for the Knoevenagel
Condensation in Pyridine
Malonic acid (1 g, 9.6 mmol) was dissolved in pyridine
(10 mL, 124 mmol). Then, the substituted benzaldehyde
(6.4 mmol) and piperidine (0.24 mL, 2.4 mmol) were
added. The mixture was refluxed for 2 h. After cooling,
the solution was poured into ice water and concentrated
HCl was added until pH 3. The aqueous solution was
extracted with ethyl acetate (3 × 20 mL), dried over
Na2SO4 and the solvent removed in vacuo. Purification
by column chromatography over silica gel (7:3 hex-
ane/ethyl acetate) yielded the corresponding 4-vinylph-
enol (for aldehydes 3a - 3c) or coumarin (for aldehydes
3d and 3e).
2.3. General Procedure for the Reaction in
Malonic acid (1 g, 9.6 mmol) was dissolved in water (10
mL). Pyridine (0.56 mL, 7.0 mmol), the substituted ben-
zaldehyde (6.4 mmol) and piperidine (0.24 mL, 2.4
mmol) were added. The mixture was refluxed for 2 h.
After cooling, the solution was poured into ice water and
concentrated HCl was added until pH 3. The aqueous
solution was extracted with ethyl acetate (3 × 20 mL),
dried over Na2SO4 and the solvent removed in vacuo.
Purification by column chromatography over silica gel
(7:3 hexane/ethyl acetate) yielded the
carboxylic acid, 4-vinylphenol and styrene dimer.
2.4. Products
Spectroscopic data of all compounds were found to
match those in previous reports: 1a [12,13], 1b [21], 1c
[13], 2a [12], 8d [22], 8e [23], 9a [24] .
2-Metho xy -4-viny lphenol (1a)
1H RMN (400 MHz, CDCl3) δH (ppm) 3.85 (s, 3H,
OCH3), 5.11 (dd, 1H, J1 = 10.8 Hz, J2 = 0.9 Hz, CH =
CH2), 5.57 (dd, 1H, J1 = 17.6 Hz, J2 = 0.9 Hz, CH = CH2),
5.77 (bs, 1H, OH), 6.62 (dd, 1H, J1 = 17.6 Hz, J2 = 10.8
Hz, CH = CH2), 6.89 (m, 3H, ArH). 13C RMN (100 MHz,
CDCl3) δC (ppm) 55.9, 108.0, 111.5, 114.5, 120.1, 130.3,
136.7, 145.6, 146.7.
4-Vinylp henol (1b)
1H RMN (400 MHz, acetone-d6) δH (ppm) 5.04 (dd,
1H, J1 = 10.9 Hz, J2 = 1.1 Hz, CH = CH2), 5.59 (dd, 1H,
J1 = 17.6 Hz, J2 = 1.1 Hz, CH = CH2), 6.65 (dd, 1H, J1 =
17.6 Hz, J2 = 10.9 Hz, CH = CH2), 6.81 (d, 2H, J = 6.7
Hz, ArH3, ArH5), 7.31 (d, 2H, J = 6.6 Hz, ArH2, ArH6),
8.43 (bs, 1H, OH). 13C RMN (100 MHz, CDCl3) δC (ppm)
110.0, 115.3, 127.4, 129.3, 136.6, 157.4.
4-Vinylbenzene-1,2-diol (1c)
1H RMN (400 MHz, acetone-d6) δH (ppm) 5.02 (dd,
1H, J1 = 10.9 Hz, J2 = 1.1 Hz, CH = CH2), 5.55 (dd, 1H,
J1 = 17.6 Hz, J2 = 1.1 Hz, CH = CH2), 6.60 (dd, 1H, J1 =
17.6 Hz, J2 = 10.9 Hz, CH = CH2), 6.80 (dd, 2H, J1 = 1.4
Hz, J2 = 0.9 Hz, ArH2, ArH6), 6.99 (dd, 1H, J1 = 1.4 Hz,
J2 = 0.9 Hz, Ar H5), 7.99 (bs, 1H, OH).
3-(4-Hydroxy-3-methoxyphenyl)-2-propenoic acid
(ferulic acid) (2a)
1H RMN (400 MHz, DMSO-d6) δH (ppm): 3.82 (s, 3H,
OCH3), 6.37 (d , 1H, J = 15 .9 Hz, = CH-COOH) , 6.80 (d,
1H, J = 8.1 Hz, ArH5), 7.09 (dd, 1H , J1 = 8.2 Hz, J2 = 1.9
Hz, ArH6), 7.28 (d, 1H, J = 1.9 Hz, ArH2), 7.50 (d, 1H, J
= 15.9 Hz, CH = CH-COOH), 9.57 (bs, 1H, OH). 13C
RMN (100 MHz, CDCl3) δC (ppm) 56.1, 111.6, 116.0,
123.3, 126.2, 145.0, 148.4, 149.5, 168.5.
2H-Chromen-2-o n e ( 8d)
1H RMN (400 MHz, acetone-d6) δH (ppm) 6.44 (d, 1H,
J = 9.6 Hz, CH = CH-C(O)O), 7.36 (m, 2H, ArH6, ArH7),
7.62 (m, 1H, ArH5), 7.71 (m, 1H, ArH8), 8.01 (d, 1H, J =
9.6 Hz, CH = CH-C(O)O).
8-Methoxy-2H-c hromen-2-one (8e)
1H RMN (400 MHz, CDCl3) δH (ppm) 3.97 (s, 3H,
OCH3), 6.45 (d, 1H, J = 9.6 Hz, CH = CH-C( O)O), 7.08
(m, 2H, ArH5, ArH7), 7.22 (m, 1H, ArH6), 7.71 (d, 1H, J
= 9.6 Hz, CH = CH-C(O)O). 13C RMN (100 MHz,
CDCl3) δC (ppm) 56.2, 113.7, 116.9, 119.3, 124.3, 143.7,
147.2, 160.3, 191.0.
1H RMN (400 MHz, CDCl3) δH (ppm) 1.43 (d, 3H, J =
7.0 Hz, CH3), 3.55 (td, 1H, J1 = 7.0 Hz, J2 = 6.6 Hz,
CH-CH3), 3.88 (s, 6H, 2xCH3), 5.52 (s, 1H, OH), 5.59 (s,
1H, OH), 6.19 (dd, 1H, J1 = 15.8 Hz, J2 = 6.5 Hz, CH =
CH-CH(CH3)), 6.31 (dd, 1H, J1 = 15.9 Hz, J2 = 1.0 Hz,
CH = CH-CH(CH3)), 6.76 (m, 2H, ArH); 6.92 (m, 4H,
ArH). 13C RMN (100 MHz, CDCl3) δC (ppm) 21.4, 42.2,
55.9, 108.0, 109.9, 114.2, 114.3, 119.8, 128.0, 130.2,
133.3, 137.8, 143.9, 145.0, 146.4, 146.6.
3. Results and Discussion
3.1. Knoevenagel Condensation: Mechanistics
A detailed proposed mechanism that agrees with experi-
mental information is shown in Figure 3. This mecha-
nism, based on previously suggested ones [12,13], in-
cludes new information, such as the role of the organo-
catalyst in the entire process. In particular, the contribut-
ing effect of the catalyst to the key decarboxylation step.
Even though the Knoevenagel reaction has been em-
Copyright © 2011 SciRes. OJPC
Copyright © 2011 SciRes. OJPC
Figure 3. Proposed mechanism for the preparation of ferulic acid and 2-methoxy-4-vinylphenol.
ployed to obtain cinnamic acid and derivatives, both the
reaction and work-up conditions previously reported are
different than those described in this work. Simpson and
coworkers stated that the styrene formation took place
only when a proper substrate (2- or 4-hydroxybenzalde-
hyde) was used jointly with toluene for removing the
pyridine by distillation in vacuo [12]. In this work, we
found that quenching the reaction with acid works as
well. Therefore, contrary to previously described mecha-
nism, we demonstrate that styrene formation does not
depend on the work-up conditions, and took place before
the work-up.
We analyzed the outcome of the Knoevenagel-Doeb-
ner condensation of 2-hydroxy- and 4-hydroxy substi-
tuted benzaldehydes (Figure 4 and Table 1), employing
a lower load of catalyst (ten times) than previously de-
scribed one and quenching the reaction with HCl.
The load of catalyst was evaluated, and we found that
1:0.4 corresponds to the optimum vanillin:piperidine
ratio (results not shown).
From these results it is evident that only 4-hydroxy-
substituted aldehydes lead to the correspon ding vinylph-
enol. Presumably, a quinone methide intermediate can be
obtained for both 2-hydroxy and 4-hydroxy substituted
benzaldehydes (Figure 5). In spite of that, the stability
and reactivity of ortho- and para-quinone methides are
not exactly the same.
Quinone methides are common reactive intermediates
extensively employed by nature, particularly in the
mechanism of action displayed by a variety of bioactive
compounds [25,26]. The stability of such intermediates is
essential to evaluate the outcome of the reaction. Or-
tho-quinone methides are less stable (ca. 2 times) than
the corresponding para- isomers [27], and thus the for-
mation of the latter can be favored. Taking this into ac-
count, subsequent decarboxylation reaction is also fa-
vored, and the 4-vinylphenol is then afforded. When the
reactant aldehyde is 2-hydroxy substituted, a lower en-
ergy pathway than the formation of the quinone methide
intermediate is available, and a different ou tcome for the
reaction is observed. 2-Hydroxybenzaldehyde (entry 4,
Table 1) and 2-hydroxy-3-methoxybenzaldehyde (entry
5, Table 1) afforded a coumarin derivative.
Coumarin (1,2-benzopyrone) is a secondary plant me-
tabolite with a pleasant flavor, which use as food flavoring
Table 1. Products obtained for the Knoevenagel-Doebner
condensation of aromatic aldehy de s and malonic acid.
Product distributiona
EntryAldehydeCinnamic acid (2) (%) Styrene (1) (%)
1 3a 0 80
2 3b Traces 60
3 3c 0 59
4 3d 0 1d (0%) + 8d (15%)
5 3e Traces 1e (Traces) + 8e (20%)
aRemaining percentage corresponds to starting material.
Figure 4. Conversion of 2- and 4-hydroxy-substituted aromatic aldehydes into cinnamic acids, styrene derivatives and cou-
Figure 5. Quinone methide intermediates in the double decarboxylative Knoevenagel-Doebner reaction.
substance was prohibited due to the discovery of its
hepatotoxic properties in laboratory animals. Is has been
described that coumarin is present in cinnamon, and
therefore is of interest to identify factors influencing
coumarin levels in this important spice [28]. Cinnamon
contains also other volatile constitu ents such as cinnamic
acids and cinnamaldehyde among others. The reaction
reported herein may be of importance for understanding
observed changes in coumarin levels during storage.
The fact that only 4-hydroxybenzaldehydes undergo a
second decarboxylation yielding the corresponding
4-vinylphenol reinforces the idea that a quinone methide
is a key intermediate in this reaction. As shown in Fig-
ure 3, when using piperidine as organocatyst, the Kno-
evenagel reaction is initiated by formation of iminium
ion 4. This has been proposed as an activation mode for
reactions organocatalyzed by secondary amines (such as
piperidine, pyrrolidine or proline) [29]. According to
route 1 in Figure 3, the β-amino acid 6 can undergo a
β-elimination reaction leading to ferulic acid. Also, as
shown in Route 2, 1,6-elimination of piperidine leads to
the quinone methide 7. In the presence of a base, the
quinone methide is afforded upon deprotonation of the
phenol group. The formation of this key intermediate is
the driving force for the second decarboxylation leading
to the product 1a after a final protonation during the
work-up. When the phenolic group is absent or protected,
the quinone methide cannot be ob tained and thus no fur-
ther decarboxylation takes place, and the α,β-unsaturated
carboxylic acid is obtained through Route 1.
3.2. Organocatalyzed Decarboxylation of Ferulic
As shown in Table 1, the corresponding 4-hydroxy-
substituted cinnamic acid is not obtained. One possible
explanation is that Route 2 corresponds to the favored
pathway under employed conditions, and therefore 2 is
simply not obtained. On the other side, if the 4-hydroxy-
substituted cinnamic acid 2 is produced through a re-
versible reaction (Route 1), the second decarboxylation
reaction can take place even if the acid is afforded. It has
been argued that the formation of the trans-cinnamic
acid is effectively non-reversible [12]. However, high-
level theoretical calculations showed that under emp-
loyed condition s , Route 1 is essen tially reversible [20].
Copyright © 2011 SciRes. OJPC
To this end, we envisioned an experiment that can
demonstrate the role of a secondary amine in the decar-
boxylation leading to 4-vinylphenol. When using the
Knoevenagel conditions mentioned before, with ferulic
acid as reactant, 2-methoxy-4-vinylphenol 1a was ob-
tained as a single product. Moreover, if this reaction is
performed under the same conditions but without piperi-
dine, unchanged ferulic acid is recovered. Herein we
report the decarboxylation of ferulic acid 2a to vinyl-
phenol 1a under mild conditions, involving a 1,4-addi-
tion of piperidine yielding intermediate 6. Most of avail-
able protocols for decarboxylation of cinnamic acid de-
rivatives involve the use of strong conditions, such as
toxic quinoline-metal salts [30].
Intermediate 6 suffer a 1,6-elimination of piperidine
affording the key quinone methide 8, which undergoes a
decarboxylation reaction leading to the styrene derivative
1a (Figure 6).
This result agrees with the mechanistic role proposed
for piperidine, suggesting that intermediate 6 facilitates
the final decarboxylation reaction leading to the 4-vi-
nylphenol 1a.
We also propose that this reaction is relevant in food
chemistry. Phenolic styrenes have strong flavours and
because of that, their presence sometimes is a limitation
for the use of the product in foods or beverages. Barley
and wheat malts are the most important raw materials for
beer production. In those grains, ferulic acid is present
and it is known that during brewing, 2-methoxy-4-
vinylphenol 1a is produced [31-33].
Until now, thermal or enzymatic decarboxylation of
ferulic acid, were proposed as the responsible mecha-
nisms for the production of 4-vinylphenol derivatives.
We suggest that 4-vinylphenol is produced also through
the pathway showed in Figure 6, using a readily avail-
able secondary amine, such as proline, which is present
in wheat and barley [34].
Thus, under malting and brewing condition, proline
(organocatalyst) adds to ferulic acid affording the corre-
sponding β-amino acid. Further amine and CO2 elimina-
tion leads to 2-methoxy-4-vinylphenol production. In
fact, when attempting the decarboxylation of ferulic acid
employing proline as organocatalyst, the reaction was
complete, leading to 2-methoxy-4-vinylphenol as a sin-
gle product.
Such processes in natural environments are actually
performed in aqueous media. Therefore, the choice of
solvent may be critical. The Knoevenagel-Doebner reac-
tion of aromatic aldehydes has been performed employ-
ing different solvents or even under solvent-free condi-
tions [3,1 2].
3.3. Vinylphenol Dimerization in Water
Both the elimination step to get ferulic acid and the de-
carboxylation leading to 4-vinylphenol, are expected to
be affected by solvent properties, such as polarity. Thus,
we performed the reaction in water. One can expect that
increasing the dielectic constant will raise both the global
conversion and th e 2-methoxy-4-vinylphenol/f erulic acid
ratio. Contrary to these assumptions, when performing
the reaction in water (dielectric constant of water = 80.1,
dielectric constant of pyridine = 13.26) [35] a totally
different result was obtained.
Ferulic acid and 2-methoxy-4-vinylphenol were ob-
tained, but in different amounts than those obtained in
pyridine (18% and 8% of yield, respectively). In addition,
during the reaction we observed the formation of a new
compound 9a (6 7% of yield), w ith a 1H NMR showing a
clear ABX system and a trans double bond (Figure 7).
Spectroscopic data is in agreement with the proposed
The structure of 9a immediately suggests that this
product can be obtained through a dimerization of
2-methoxy-4-vinylphenol. Dimerization of styrene de-
rivatives has been reported by sever a l authors [36-40].
In order to confirm this hypothesis, we performed the
reaction in water under the same conditions as before,
but employing 2-methoxy-4-vinylphenol 1a as substrate.
After 2 hours of refluxing, the product 9a was obtained
as a single product. If the reaction time is extend ed, polar
polymeric products are formed, while 9a is consumed.
When considering the relative amounts of acid (malo-
nic acid) and bases (pyridine/piperidine) employed, one
can see that malonic acid is present in a small excess.
ferulic acid, 2a
Figure 6. Organocatalyzed decarboxylation of ferulic acid.
Copyright © 2011 SciRes. OJPC
Figure 7. 2-Methoxy-4-vinylphenol dimer obtained in wa-
Consequently, we proposed an acid catalyzed mecha-
nism for the formation of vinylphenol dimer. 2-Methoxy-
4-vinylphenol is first protonated affording a stabilized
carbocation, which undergo cationic dimerization with a
second vinylphenol molecule. Finally, elimination of a
proton yields the dimer 9a.
In order to confirm this proposal, we performed the
reaction employing only vinylphenol 1a (1 eq.) and
malonic acid (0.02 eq.) in water. Such conditions repro-
duce the relative excess of malonic acid in the original
Figure 8. Knoevenagel condensation of 4-hydroxyaldehydes in wate r.
reaction. Under these conditions, dimer 9a was obtained
after 2 hours under reflux. When changing malonic acid
(pKa = 2.85) [35] for salicylic acid (pKa = 2.98) [35] the
same reaction was observed. Therefore, in the presence
of a weak organic acid, 3-methoxy-4-vinylphenol dimer-
Finally, attempting to extend the scope of the styrene
dimerization process, we performed the same reaction
employing those aldehydes different from vanillin, which
in the first place lead to vinylphenol derivatives (i.e.
4-hydroxy substituted aldehydes) (Figure 8 and Table
After two hours of refluxing, styrene dimer was ob-
tained, though in a lower yield than that observed when
vanillin was the reactant aldehyde. Therefore, this reac-
tion becomes more important in the latter case.
To summarize, during the Knoevenagel condensation
of vanillin and malonic acid in water, ferulic acid is first
obtained. Subsequent decarboxylation of ferulic acid
leads to vinylphenol 1a. Once the styrene derivative is
afforded, a self-addition reaction takes place producing
the dimer 9a. This reaction is also of importance in food
chemistry. Cinnamic acid derivatives are frequently
found in fruits and vegetables. Heat treatment can trigger
cinnamic acids decarboxylation to vinylphenols, and di-
merization of vinylphenol can further modify organole-
ptic properties of juices, fruits and beverages, even when
obtained in small amounts [41].
4. Conclusions
In this work we delineate the mechanism of the organo
Table 2. Products o btained for the Knoeve nagel condensa tion
of 4-hydroxy-substituted aldehydes and malonic acid in water.
Product distributiona
EntryAldehydeStyrene (1) (%) Styrene dimer (9) (%)
1 3b 15 5
2 3c 5 2
aremaining percentage corresponds to starting material.
catalyzed Knoevenagel-Doebner reaction, based on ex-
perimental evidences on the role of catalyst and solvent.
Also, we report for the first time the decarboxylation of
ferulic acid under mild conditions and the dimerization
of vinylphenol in water. This insight on the mechanism
allows to tuning the outcome of Knoevenagel reaction.
Even though dimerization of styrene derivatives has
been reported, in all cases the dimer was obtained when
treating styrene either with strong Brönsted or Lewis
acids. Here, we report the dimerization under totally dif-
ferent conditions. It is important to take into account that
several natural amines and amino acids can catalyze the
decarboxylation of cinnamic acids into vinylphenol de-
rivatives, and the subsequent dimerization of the latter
can take place. This has to be considered in food chemis-
try to avoid obtaining undesired products.
5. Acknowledgements
Lindbergh Foundation (USA), PEDECIBA (Uruguay)
and ANII (Uruguay) are gratefully acknowledged for
financial support.
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