Reactivity of some products formed by the reaction of sorbic acid with sodium nitrite: Decomposition of 1,4-dinitro-2-methylpyrrole and ethylnitrolic acid

Article abstract of DOI:10.1021/jf802822y

Sorbic acid reacts with nitrite to yield mutagenic products such as 1,4-dinitro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA). In order to know the stability of these compounds, a kinetic study of their decomposition reactions was performed in the 6.0-9.5 pH range. The conclusions drawn are as follows: (i) The decomposition of NMP occurs through a nucleophilic attack by OH^- ions, with the rate equation as follows: r = k_dec ^NMP[OH^-][NMP] with k_dec^NMP (37.5 °C) = 42 ± 1 M^-1 s^-1. (ii) The rate law for the decomposition of ENA is as follows: r = k_dec^ENA[ENA] K_a/(K_a + [H⁺]), with K_a being the ENA dissociation constant and k_dec^ENA (37.5 °C) = (7.11 ± 0.04) × 10^-5 s^-1. (iii) The activation energies for NMP and ENA decomposition reactions are, respectively, E_a = 94 ± 3 and 94 ± 1 kJ mol^-1. (iv) The observed values for the decomposition rate constants of NMP and ENA in the pH range of the stomach lining cells, into which these species can diffuse, are so slow that they could be the slow determining step of the alkylation mechanisms by some of the products resulting from NMP and ENA decomposition. Thus, the current kinetic results are consistent with the low mutagenicity of these species.

Full text of DOI:10.1021/jf802822y

11824 J. Agric. Food Chem. 2008, 56, 11824–11829
Reactivity of Some Products Formed by the Reaction
of Sorbic Acid with Sodium Nitrite: Decomposition of
,4-Dinitro-2-methylpyrrole and Ethylnitrolic Acid
1
†
†
†
M. TERESA PE´REZ-PRIOR, JOSE´ A. MANSO, RAFAEL GO´MEZ-BOMBARELLI,
†
†
†
MARINA GONZA´LEZ-PE´REZ, M. PILAR GARCI´A-SANTOS, EMILIO CALLE,
‡
,†
M. CRUZ CABALLERO, AND JULIO CASADO*
Departamento de Qu ´ı mica F ´ı sica, Universidad de Salamanca, E-37008 Salamanca, Spain, and
Departamento de Qu ´ı mica Org a´ nica, Universidad de Salamanca, E-37008 Salamanca, Spain
Sorbic acid reacts with nitrite to yield mutagenic products such as 1,4-dinitro-2-methylpyrrole (NMP)
and ethylnitrolic acid (ENA). In order to know the stability of these compounds, a kinetic study of
their decomposition reactions was performed in the 6.0-9.5 pH range. The conclusions drawn are
-
as follows: (i) The decomposition of NMP occurs through a nucleophilic attack by OH ions, with the
rate equation as follows: r ) kdec [OH ][NMP] with kdec (37.5 °C) ) 42 ( 1 M s-1. (ii) The rate
NMP
-
NMP
-1
ENA
+
law for the decomposition of ENA is as follows: r ) kdec [ENA]K
a
/(K
s
a
-5 -1
+ [H ]), with K
. (iii) The activation energies for
a
being the ENA
ENA
dissociation constant and kdec (37.5 °C) ) (7.11 ( 0.04) × 10
-1
NMP and ENA decomposition reactions are, respectively, E ) 94 ( 3 and 94 ( 1 kJ mol . (iv) The
a
observed values for the decomposition rate constants of NMP and ENA in the pH range of the stomach
lining cells, into which these species can diffuse, are so slow that they could be the slow determining
step of the alkylation mechanisms by some of the products resulting from NMP and ENA
decomposition. Thus, the current kinetic results are consistent with the low mutagenicity of these
species.
KEYWORDS: Nitrite; sorbic acid; 1,4-dinitro-2-methylpyrrole; ethylnitrolic acid.
INTRODUCTION
nitrosamine chemistry, in particular the formation and reactions
of these substances. This area continues to be one of major
concern, since nitrosamines can readily be formed under acidic
conditions (e.g., in the human stomach) from many naturally
occurring amines and ingested nitrate and nitrite (15-17).
Because sorbic acid also inhibits Clostridium botulinum
growth as well as the formation of nitrosamines, it has been
proposed as a partial replacement for nitrite in meat curing.
However, this practice may lead to other toxicological problems
since sorbic acid reacts with nitrite to yield certain mutagenic
products (18) (Scheme 1). The main mutagens seem to be 1,4-
dinitro-2-methylpyrrole (NMP) and ethylnitrolic acid (ENA)
Sorbic acid (trans,trans-2,4-hexadienoic acid) and its potas-
sium, sodium, and calcium salts are used as preservatives in a
wide range of foodstuffs, such as cheese, pickles, sauces, and
wine. They inhibit the growth of fungi and yeasts and have
antibacterial activity (1). Accordingly, many analytical methods
have been proposed to determine the amount of sorbic acid and
sorbates in different types of samples (2, 3). Sorbates have been
reported to be more efficient and less toxic than benzoate (4)
and are classified as “Generally Recognized as Safe” (GRAS)
additives by the U.S. Food and Drug Administration (FDA) (5).
Nevertheless, a weak genotoxic potential of stored sorbate
solutions has been reported (6-11). In light of this, the
alkylating potential of the sorbic acid has been investigated
previously (12, 13).
(
19).
Since (i) a comparison of the alkylating capacity of NMP
and ENA with their mutagenic potential could be of interest
and (ii) knowledge of the kinetic parameters of the decomposi-
tion reactions of those species (and, hence, of their stability) is
Nitrite is widely used in the curing of meat, where, in
conjunction with sodium chloride, it inhibits the growth and
toxin production of Clostridium botulinum (14). Since the
discovery in 1956 that nitrosamines are powerful carcinogens,
there has been a noteworthy increase in studies addressing
Scheme 1. Reaction of Sorbic Acid with Sodium Nitrite
*
To whom correspondence should be addressed. E-mail: jucali@
usal.es. Tel.: +34 923 294486. Fax: +34 923 294574.
†
Departamento de Qu ´ı mica F ´ı sica, Universidad de Salamanca.
Departamento de Qu ´ı mica Org a´ nica, Universidad de Salamanca.
‡
1
0.1021/jf802822y CCC: $40.75  2008 American Chemical Society
Published on Web 11/18/2008

Reaction of Sorbic Acid with Sodium Nitrite
J. Agric. Food Chem., Vol. 56, No. 24, 2008 11825
Scheme 2. Decomposition Reaction of 1,4-Dinitro-2-methylpyrrole
Scheme 3. Decomposition Reaction of Ethylnitrolic Acid (ENA) Present
-
in Its Nondissociated (HA) and Dissociated (A ) Forms
Figure 1. Spectra showing the NMP decomposition over time: [NMP] )
o
-4
10
M; T ) 32.5 °C; pH ) 9.47 with borate buffer.
necessary as a previous step in the investigation of their
alkylating potential, here we were prompted to address this issue.
MATERIALS AND METHODS
To monitor the NMP and ENA decomposition reactions (Schemes
2
and 3), their absorbances at the wavelengths of maximum absorption
(
λ ) 269 nm and λ ) 328 nm, respectively) were followed. The
hydrolysis reaction of acetonitrile oxide (ACNO) was monitored
spectrophotometrically at λ ) 210 nm, where the product acetohy-
droxamic acid (ACH) absorbs. A Shimadzu UV-2401-PC spectropho-
tometer with a thermoelectric six-cell holder temperature control system
NMP
Figure 2. Determination of kobs (eq 3): [NMP]
°C; pH ) 9.47 with borate buffer.
-4
o
) 10 M; T ) 32.5
((0.1 °C) was used. Detailed reaction conditions are given in the figure
and table legends.
Reactions were carried out in the 6.0-9.5 pH range. Phosphate and
borate buffers were used to maintain constant pH. A Crison Micro pH
2
000 pH-meter was used for pH measurements ((0.01). The reaction
temperature was kept constant ((0.05 °C) with a Lauda Ecoline RE120
thermostat.
Titrations were performed using a pH-Stat Metrohm 718 STAT
Titrino, which releases NaOH, previously normalized with potassium
hydrogen phthalate. An QSTAR XL TOF-MS system (Applied Bio-
systems) was used for the determination of accurate masses. NMR
proton spectra were obtained with a Varian spectrometer Mod. Mercury
VS2000 (200 MHz).
Water was deionized with a MilliQ-Gradient (Millipore). Sorbic acid
and sodium nitrite were from Panreac. Nitroethane and D
were obtained from Aldrich.
2
O (98%)
All kinetic runs were performed in triplicate. Numerical treatment
of the data was performed using the 7.1.44 Data Fit software.
Procedures: Synthesis of 1,4-Dinitro-2-methylpyrrole and Eth-
ylnitrolic Acid. 1,4-Dinitro-2-methylpyrrole was obtained from the
reaction between sorbic acid and sodium nitrite in aqueous solution at
pH ) 3.5 (18, 20). A solution of sodium nitrite (11.0 g) was added to
a partially suspended solution of sorbic acid (2.2 g) in distilled water
Figure 3. Variation in the NMP decomposition rate constant with the
-4
acidity of the medium at T ) 37.5 °C: [NMP] ) 10 M; phosphate
o
and borate buffers.
to a solution of nitroethane (8 mL) in aqueous sodium hydroxide (4.3
g in 100 mL) at 0 °C. Simultaneously to sodium nitrite addition, a
solution of sulfuric acid (5 M) was slowly added to maintain an acidic
pH in the reaction mixture. The aqueous solution was extracted with
three 50 mL portions of ether and evaporated to dryness in vacuo to
give the product. The product was recrystallized in dichloromethane
hexane. Because of its low thermal stability, it was stored at 0 °C.
(
200 mL). Keeping the pH of the mixture constant at 3.5 with dilute
SO , the mixture was stirred at 60 °C for 2 h. The mixture was
extracted with four 50 mL portions of CH Cl . The combined extracts
were washed with water, dried over Na SO , and evaporated to dryness
H
2
4
2
2
2
4
in vacuo to give the residue. The residue was recrystallized in
chloroform ether.
-
1
-1
UV λmax in nm (ε, M cm ): 240 (4341 ( 29) in acid media and
UV λmax in nm (ε, M- cm-1): 209 (11621 ( 123), 229 (17428 (
1
1
3
3
28 (8237 ( 17) in alkaline medium. H NMR (CDCl
H, CH ), 9.3 (broad, 1H, OH).
3
): δ 2.46 (s,
1
1
(
35), 270 (13551 ( 107), 329 (8764 ( 66), 385 (1806 ( 19). H NMR
3
CDCl
CH-N-NO
94.017227; Found: 194.0187.
Ethylnitrolic acid was obtained from the nitrosation reaction of
nitroethane in acidic aqueous solution. Sodium nitrite (8.9 g) was added
3
): δ 2.64 (s, 3H, CH
3
), 7.9 (d, 1H, CH-C-NO
2
), 8.8 (d, 1H,
H N O Na (M Na):
5 5 3 4
+
2
). Accurate mass calculated for C
RESULTS AND DISCUSSION
1
Decomposition of 1,4-Dinitro-2-methylpyrrole. 1,4-Dinitro-
2-methylpyrrole undergoes decomposition, and an inverse

11826 J. Agric. Food Chem., Vol. 56, No. 24, 2008
P e´ rez-Prior et al.
Figure 4. (a) Absorption spectra of ENA at different pH’s and (b)
determination of the pK ) 1.4
of ENA in water at 25.0 °C (eq 4): [ENA]
10 M; λ ) 350 nm.
a
o
-4
Figure 5. (a) Titration curve for ENA and (b) determination of the pK
a
of
×
-3
ENA in water at 25.0 °C (eq 5): [ENA]
o
) 2 × 10 M; [NaOH] ) 9.38
-2
NMP
dec H O dec D O
NMP
× 10 M.
kinetic isotope effect, k
/k
) 0.7, was observed.
2
2
This result was interpreted in terms of a nucleophilic attack of
the OH- on the NMP molecule. Since OD is a stronger
-
-
nucleophile than OH , the direct nucleophilic attack on the
electrophilic carbon (Scheme 2) would be expected to proceed
faster in D2O (21), as was observed.
The presence of nitro groups on the pyrrole ring may play a
significant role in lowering the high π-electron density of the
ring and in favoring the attack of the nucleophilic reagent (20, 22).
This explains the formation of the Meisenheimer-type adduct
-
due to the addition of OH on the NMP molecule.
The following rate equation was observed for NMP decom-
position,
d[NMP]
NMP
-
NMP
r ) -
) kdec [OH ][NMP] ) k [NMP]
obs
dt
Figure 6. Spectrograms showing the variation in ENA absorbance at
(1)
-4
different times: [ENA]
borate buffer.
o
) 1.3 × 10 M; T ) 32.5 °C; pH ) 9.52 with
NMP
where kobs is the pseudofirst-order rate constant:
NMP
obs
) kdec [OH-]
NMP
k
(2)
By fitting the absorbance values against those of time (eq 3),
NMP
NMP
the rate constant kobs was found to be kobs (T ) 32.5 °C) )
By designating the absorbance values of NMP as Ao, At, and
A∞ at times, respectively, zero, t, and infinity (end of the
reaction), integration of eq 1 yields eq 3:
-4 -1
(
7.22 ( 0.05) × 10
NMP
s
at pH 9.47. Using eq 2, at different
pH values, the NMP decomposition rate constant was found to
be kdec (T ) 32.5 °C) ) 22 ( 1 M
different temperatures are reported in Table 1.
-1 -1
NMP
s . The values of kdec at
NMP
-
kobs t
A ) A + (A - A )e
(3)
t
∞
o
∞
Decomposition of Ethylnitrolic Acid. Since (i) the stability
of ethylnitrolic acid decreases with increasing pH and (ii) the
dissociated acid molecule undergoes NO2- loss, this being the
limiting step (23), the mechanism shown in Scheme 3 for
the decomposition of ENA was investigated.
Because (i) all the kinetic experiences were carried out in
the pH ) 6-9.5 range and (ii) the ACH pKa ) 9.31 (24, 25)
Figure 1 depicts the variation in the absorption of NMP with
time. Figure 2 shows a typical kinetic run for the decomposition
reaction of NMP in aqueous solution.
Experiments were performed at different pH’s (Figure 3),
with the slope R ) 1 revealing first order with respect to the
concentration of OH (eq 2).
-

Reaction of Sorbic Acid with Sodium Nitrite
J. Agric. Food Chem., Vol. 56, No. 24, 2008 11827
-
[
[
A ]
AA - Aλ
-
pH ) pK + log
) pK - log
(4)
a
a
HA]
Aλ - AHA
where AHA and AA-, respectively, represent the absorbances of
the nondissociated (λ ) 350 nm, pH ≈ 2) and totally dissociated
(
λ ) 350 nm, pH ≈ 10) forms of ENA. Aλ represents the
absorbance values at pH’s between these boundary limits at λ
)
350 nm.
Figure 4b shows the good fit of the results to the
Henderson-Hasselbalch equation (λ ) 350 nm) and gives the
-8
value Ka ) (4 ( 1) × 10 M for the ENA dissociation constant
T ) 25.0 °C).
b) Titrimetric Method. By measuring the sodium hydroxide
(
(
consumed for the titration of ENA at different pH values with
a pH-Stat, the Henderson-Hasselbalch equation can be applied
in the form
V
pH ) pK + log
(5)
a
Vmax - V
where Vmax represents the volume of NaOH at the end point
and V is the volume of NaOH used at any other point during
the titration. Parts a and b of Figure 5, respectively, show the
titration curve and the Henderson-Hasselbalch plot, which gives
-8
the value Ka ) (4 ( 1) × 10 M for the ENA dissociation
constant (T ) 25.0 °C).
In light of the results of both the spectrometric and titrimetric
measurements for the ethylnitrolic acid dissociation constant,
-8
we used the value Ka ) (4 ( 1) × 10 M (variation in the Ka
value in the temperature range where the kinetic experiments
were performed is smaller than the experimental error with
which Ka was determined).
ENA ACNO
Figure 7. (a) Determination of kobs (eq 8) and (b) kobs (eq 11): [ENA]
o
-4
)
1.3 × 10 M; T ) 32.5 °C; pH ) 9.52 with borate buffer.
ENA
ACNO
Determination of the kdec and khyd
Rate Constants.
Since the ethylnitrolic acid concentration [ENA] can be
expressed as the sum of the concentration of nondissociated
-
ethylnitrolic acid (HA) plus that present as anion (A ),
-
[
ENA] ) [HA] + [A ]
(6)
-
+
and because Ka ) ([A ][H ]/[HA]), eq 7 is readily deduced
from Scheme 3,
d[ENA]
ENA
Ka
ENA
r ) -
) kdec
[ENA] ) kobs [ENA]
+
dt
K + [H ]
a
(
7)
ENA
ENA
+
-4
where kobs is the pseudofirst-order rate constant:
Figure 8. Variation of kobs with K
/(K
a a
+ [H ]) (eq 8): [ENA] ) 10
o
-
8
M; T ) 37.5 °C; K
a
) 4 × 10 M.
Ka
ENA
obs
ENA
k
) kdec
(8)
+
(
in water at 25 °C), it can be assumed that all the ACH is
protonated in the working acidity range. To determine kdec and
khyd , the value of the equilibrium constant Ka was determined
by spectrometric and titration methods.
K + [H ]
a
ENA
By designating the absorbance values of ENA as Ao, At, and
A∞ at times, respectively, zero, t, and infinity (end of the
reaction), the integration of eq 7 yields eq 9:
ACNO
Determination of the Ethylnitrolic Acid Dissociation
Constant. (a) Spectrometric Method. Figure 4a shows the
UV-vis absorption spectra for ENA at several pH’s, with a
well-defined isosbestic point at λ ) 282 nm. It may be observed
ENA
-kobs t
A ) A + (A - A )e
(9)
t
∞
o
∞
Figure 6 shows the variation in the absorption of ENA with
time.
Figure 7a represents a typical kinetic run for the decomposi-
tion reaction of ENA in aqueous solution.
By fitting the absorbance values against those of time (eq 9),
-
that the undissociated (HA) and dissociated (A ) forms of ENA
show maximum absorption at 240 and 328 nm, respectively.
Since at λ ) 350 nm the absorption of the anion is maximum
and that of the neutral ethylnitrolic acid is practically null, we
studied the equilibrium at this wavelength. Spectra were obtained
at pH 2-10, and the absorbance/pH data were fitted using the
Henderson-Hasselbalch equation (26),
ENA
the rate constant was found to be kobs (T ) 32.5 °C) ) (3.96
-
5
-1
( 0.03) × 10
s
at pH ) 9.52. Using eq 8, ENA
ENA
dec
decomposition rate constant was found to be k
(T ) 32.5
-
5 -1
°C) ) (3.99 ( 0.03) × 10
s .

11828 J. Agric. Food Chem., Vol. 56, No. 24, 2008
P e´ rez-Prior et al.
ACNO
kobs
(T ) 32.5 °C) ) (7.7 ( 0.2) × 10 s-1. With this value,
-4
Table 1. Rate Constants as a Function of Temperature for the
Decomposition Reactions of 1,4-Dinitro-2-methylpyrrole and Ethylnitrolic
Acid
ACNO
eq 11 immediately affords that of khyd (T ) 32.5 °C) ) (1.4
a
-5
-1 -1
ACNO
(
0.4) × 10
M
s
. The values of khyd
at different
temperatures are reported in Table 1.
NMP
ENA
ENA
With the previously determined Ka and kobs values, eq 8
-1 a
10 kdec (s-1
5
ENA
5 ACNO
10 khyd (M-1 s-1
)
T (°C)
kdec (M-1
NMP
s
)
)
allows one to know the value of the decomposition rate constant
ENA
25.0
27.5
30.0
32.5
35.0
37.5
9.4 ( 0.5
11.9 ( 0.9
17.2 ( 0.6
22 ( 1
1.53 ( 0.03
2.17 ( 0.05
2.86 ( 0.04
3.99 ( 0.03
5.31 ( 0.04
7.11 ( 0.04
0.6 ( 0.2
0.9 ( 0.2
1.2 ( 0.4
1.4 ( 0.4
1.8 ( 0.6
2.1 ( 0.1
kdec (see Scheme 3). Figure 8 shows the good fit of the
experimental results to that equation, with the slope of the plot
being the value of kdec .
Since the influence of the pH of the reaction medium in the
decomposition rate constants of NMP and ENA is quantitatively
ENA
32 ( 1
42 ( 1
NMP
ENA
measured by kobs and kobs , the values of these constants were
plotted against those of pH (Figure 9). Because the alkylating
potential of NMP and ENA (which is currently being investi-
gated by us) were measured at neutral pHsas in the stomach-
lining cells into which such products can diffusesthe plot
represented in Figure 9 reveals that, in the vicinity of neutral
a
Values are given within the 95% confidence interval.
NMP
ENA
pH, the values of the decomposition rate constants kobs and kobs
are small (e.g., for ENA, the reaction half-time is τ1/2 ≈ 12 h).
Although definitive conclusions cannot be drawn until later
studies allow us to know the alkylation rate constants by NMP
and ENA, the current results do show that the decomposition
reactions of these species formed in the reaction of sorbic
acid with sodium nitrite are so slow that they could be the
slow determining step of the alkylation mechanisms by some
of the mutagenic products resulting from NMP and ENA
decomposition (18, 28). Thus, the present kinetic approach
is consistent with the low mutagenicity of NMP and ENA.
In any case, further experimental work is necessary to check
the possible existence of a correlation between the chemical
reactivity of NMP/ENA and their mutagenicity, as has been
demonstrated with other alkylating agents such as lactones
NMP
ENA
Figure 9. Variation in kobs (2) and kobs (b) decomposition rate constants
-
4
(
see Schemes 2 and 3) with pH: [NMP]
o
) [ENA] ) 10 M; T ) 37.5
o
°C.
According to the above mechanism, the rate equation for the
formation of acetohydroxamic acid (ACH) is given by eq 10:
(
29-31).
NMP ENA
ACNO
With the kdec , kdec , and khyd values reported in Table 1,
the following energies of activation were obtained for the
d[ACH]
ACNO
ACNO
obs
r )
) khyd [ACNO][H O] ) k
[ACNO]
(
2
respective reactions: Ea (decomposition of NMP) ) 94 ( 3 kJ
dt
-
1
-1
mol ; Ea (decomposition of ENA) ) 94 ( 1 kJ mol ; and Ea
10)
-1
(
hydrolysis of ACNO) ) 73 ( 5 kJ mol
From the present study, the following conclusions may be
drawn:
1) The decomposition of NMP occurs through a nucleophilic
.
[
ACNO] is the acetonitrile oxide concentration at time t and
is the pseudofirst-order hydrolysis rate constant, defined
as follows:
ACNO
kobs
(
-
attack by OH ions, with the rate equation being the following:
ACNO
obs
ACNO
k
) khyd [H O]
(11)
NMP
-
NMP
-1
2
r ) kdec [OH ][NMP] with kdec (37.5 °C) ) 42 ( 1 M
-1
s
.
According to the general kinetic scheme for consecutive first-
order reactions (27) and the boundary condition [ACNO]o ) 0,
the concentration of acetonitrile oxide at time t is given by eq
(
2) The rate law for the decomposition of ENA is as follows:
ENA
+
r ) kdec [ENA]Ka/(Ka + [H ]), with Ka being the ENA
ENA
dissociation constant and kdec (37.5 °C) ) (7.11 ( 0.04) ×
1
2:
-
5 -1
1
0
s .
ENA
obs
k
[ENA]o
(3) The activation energies for NMP and ENA decomposition
-kENAt
obs
-kACNOt
obs
-1
[
ACNO] )
(e
- e
)
(12)
reactions are, respectively, Ea ) 94 ( 3 and 94 ( 1 kJ mol
.
ACNO
obs
ENA
k
- kobs
(4) The observed values for the decomposition rate constants
Integration of eq 10 and expression of the result in terms of
absorbance leads to the following,
of NMP and ENA in the pH range of stomach-lining cells, into
which these species can diffuse, are so slow that they could be
the slow determining step of the alkylation mechanisms by some
of the products resulting from NMP and ENA decomposition.
Thus, the current kinetic results are consistent with the low
mutagenicity of these species.
ACNOt
ACNO -kobs t
ENA
ENA
obs
e-kobs - kobs
k
e
At ) ε
ACH
l[ENA] 1 +
o
(
ACNO
obs
ENA
)
k
- kobs
(13)
ACKNOWLEDGMENT
where At is the absorbance of acetohydroxamic acid at time t,
εACH is the absorption coefficient of this species, and l is the
light path.
We thank the Spanish Ministerio de Ciencia e Innovaci o´ n
(CTQ2007-63263), as well as the Spanish Junta de Castilla y
Le o´ n (Grant SA040 A08) for supporting the research reported
in this article. M.T.P.P., J.A.M., and M.G.P. thank the Junta de
Castilla y Le o´ n, for Ph.D. grants. R.G.B. thanks the Ministerio
Figure 7b shows the good fit of the experimental results to
ENA
eq 13, which allows, with the above calculated value of kobs ,
the pseudofirst-order hydrolysis rate constant to be determined:

Reaction of Sorbic Acid with Sodium Nitrite
J. Agric. Food Chem., Vol. 56, No. 24, 2008 11829
de Ciencia e Innovaci o´ n for Ph.D. grant. Thanks are also given
for the valuable comments made by the referees.
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Received for review September 11, 2008. Revised manuscript received
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