Kinetics and mechanism of the oxidation of L-α-amino-n-butyric acid in moderately concentrated sulfuric acid medium

Article abstract of DOI:10.1139/v03-181

The reaction kinetics of L-α-amino-n-butyric acid oxidation by permanganate ion have been investigated in moderately strong acid medium using a spectrophotometric technique. In all cases studied an autocatalytic effect, due to Mn⁺² ions formed as a reaction product, was observed. Both catalytic and noncatalytic processes were determined to be first order with respect to the permanganate ion and the amino acid. The overall rate equation for this process may be written as: -d[MnO₄-]/dt = k ₁′[MnO₄-] + k₂′[MnO ₄-]·[Mn⁺²] where k₂′ and k ₂′ are pseudo-order rate constants for the noncatalytic and catalytic reactions, respectively. The influence of some factors such as temperature and reactant concentration on the rate constants has been studied, and the activation parameters have been calculated. Reaction mechanisms satisfying observations for both catalytic and noncatalytic routes have been presented.

Full text of DOI:10.1139/v03-181

4
30
Kinetics and mechanism of the oxidation of -␣-
L
amino-n-butyric acid in moderately concentrated
sulfuric acid medium
Homayoon Bahrami and Mansour Zahedi
Abstract: The reaction kinetics of L-α-amino-n-butyric acid oxidation by permanganate ion have been investigated in
moderately strong acid medium using a spectrophotometric technique. In all cases studied an autocatalytic effect, due
+
2
to Mn ions formed as a reaction product, was observed. Both catalytic and noncatalytic processes were determined to
be first order with respect to the permanganate ion and the amino acid. The overall rate equation for this process may
be written as:
–
–
–
+2
–
d[MnO ]/dt = k′[MnO ] + k′ [MnO ]·[Mn ]
1 2
4 4 4
where k′ and k′ are pseudo-order rate constants for the noncatalytic and catalytic reactions, respectively. The influence
1
2
of some factors such as temperature and reactant concentration on the rate constants has been studied, and the activa-
tion parameters have been calculated. Reaction mechanisms satisfying observations for both catalytic and noncatalytic
routes have been presented.
Key words: L-α-amino-n-butyric acid, permanganate oxidation, concentrated acidic medium, autocatalysis, free radical
intermediates.
Résumé : Faisant appel à une technique spectrophotométrique, on a étudié la cinétique de la réaction d’oxydation de
l’acide L-α-aminobutyrique par l’ion permanganate dans un milieu acide relativement fort. Dans tous les cas étudiés, on
a observé un effet autocatalytique par les ions Mn+ qui se forment comme produit de la réaction. On a déterminé que
les processus tant catalytique que non-catalytique sont tous les deux du premier ordre par rapport à l’ion permanganate
et à l’acide aminé. L’équation globale de vitesse pour le processus est de la forme:
2
–
–
–
+2
–
d[MnO ]/dt = k′[MnO ] + k′ [MnO ]·[Mn ]
1 2
4 4 4
dans laquelle k′ et k′ sont les constantes de vitesse du premier ordre des réactions respectivement non-catalytique et
1
2
catalytique. On a étudié l’influence de quelques facteurs, tels que la température et la concentration, sur les constantes
de vitesse étudiées et on a calculé les paramètres d’activation. On propose des mécanismes réactionnels pour les voies
catalytique et non catalytique qui satisfont les résultats obtenus.
Mots clés : acide L-α-aminobutyrique, oxydation avec du permanganate, milieu acide concentré, autocatalyse, intermé-
diaires radicalaires.
[
Traduit par la Rédaction] Bahrami and Zahedi 436
Introduction
whereas no rigorous evidence of such an effect has been re-
ported in strong acid media. There have been just two re-
ports (10, 14) of a “double-stage” process vaguely attributed
to possible autocatalysis, with no thorough information as
far as the autocatalysis effect is concerned.
Owing to the biological importance of amino acids, the
kinetics and mechanistic study of their oxidation has re-
ceived considerable attention. The permanganate oxidation
process of amino acids in strong acid media (1–14), in neu-
tral and weak basic solutions (15–23), and in weak acid me-
dia (24–29) has been investigated. The occurrence of
autocatalysis effects in weak acid media, neutral aqueous so-
lution, and weak basic media has been extensive (15–29),
+2
In autocatalytic pathways in which Mn ions have been
determined to be responsible for the effect, a mechanism
with no free radicals involved has been suggested (28, 29).
In the present paper, distinct evidence of the autocatalytic in-
+2
fluence of Mn for the permanganate oxidation of L-α-
amino-n-butyric acid in strong acid medium has been pre-
Received 18 June 2003. Published on the NRC Research
Press Web site at http://canjchem.nrc.ca on 9 January 2004.
sented, and a free radical mechanism has been proposed.
1
H. Bahrami and M. Zahedi. Department of Chemistry,
Faculty of Sciences, Shahid Beheshti University, Evin, Tehran
Experimental
1
9839, Iran.
All the reagents were from Merck or Sigma. The solutions
were prepared with triply distilled and deionized water. The
1Corresponding author (e-mail: m-zahedi@cc.sbu.ac.ir).
Can. J. Chem. 82: 430–436 (2004)
doi: 10.1139/V03-181
© 2004 NRC Canada

Bahrami and Zahedi
431
–
4
–3
Fig. 1. Spectral changes in the oxidation of L-α-amino-n-butyric acid by permanganate ion. [KMnO ] = 4 × 10 mol dm , [L-abu] =
4
–
3
–3
0
.1 mol dm , [H SO ] = 3.16 mol dm , T = 318 K. Scanning time intervals = 6 min.
2 4
permanganate solutions were prepared and tested by the
Vogle method (30). The kinetic progress of the reaction was
followed by measuring the absorbance of the permanganate
ions at 525 nm with a thermostated (Shimadzu TB-85 ±
tration was determined by a calorimetric procedure using
chromotropic acid. We came to the final conclusion that
1 mol of permanganate generates 2.5 mol of aldehyde, as is
indicated by the balanced equation, eq. [1] (1, 2, 8).
0
.1 K) Shimadzu (2100 Model) UV–vis spectrophotometer
within the temperature range 25–45 °C. For the permanga-
nate molar absorption coefficient at 525 nm and in strong
acid solution, a value of 2.26 × 10 dm mol cm was ob-
Rate equation
Figure 1 illustrates the permanganate absorption vs. wave-
length curves obtained at 6 min intervals as the reaction pro-
ceeded. From previous studies (15–23), Mn(IV) ions absorb
in the region 400–650 nm. Figure 1 shows the lack of spec-
3
3
–1
–1
tained.
In all the kinetic measurements, the amino acid was used
in excess (250-fold) relative to permanganate, to insure
pseudo-first-order kinetics (28, 29).
tral changes from 400–650 nm, which means that MnO is
2
not a reaction product. Furthermore, since no rise and fall in
absorption is observed at 418 nm, it is concluded that
Mn(IV) ions do not intervene as possible oxidizing agents
unless they are short lived.
Results
Stoichiometry and product analysis
The absorbance–time plots are illustrated in Fig. 2. In all
the experiments performed, curves with a sigmoid profile
(Fig. 2a) were obtained. This characteristic suggests the ex-
istence of an autocatalytic mechanism. To demonstrate that
By employing spot tests (31, 32), the final reaction prod-
ucts were detected as ammonium ions and the corresponding
aldehyde. For carbon dioxide detection, the standard Vogle
method (33) was employed. As well, it is well known (4, 12,
+
2
Mn is the species responsible for the autocatalytic effect,
kinetic runs were carried out in the presence of the MnSO4
species at the beginning of the reaction. As the initial con-
3
4) that in the reduction process of permanganate ions in
strong acid media (as long as the reducing species is in ex-
cess), Mn+ ions are the final product.
2
+2
centration of Mn ions increased, a notable increase in the
Our reaction was performed in an excess of amino acid,
and we used the procedure outlined below to study the
stoichiometry of the reaction; the following equation is pro-
posed as the reaction stoichiometry:
reaction rate was seen (Fig. 2b). Further increases of initial
+
2
+2
Mn concentration and maintaining the Mn concentration
equal to the permanganate ion concentration led to a com-
plete disappearance of the sigmoid form (Fig. 2c). Taking
the Mn+ effect on the reaction rate into account, the follow-
ing rate equation has been proposed:
2
[
1]
2MnO − + 5CH -CH -CH(NH ) COO
+
−
4
3
2
3
+
+
+
11H → 5CH -CH -CHO + 5NH
−
−
−
+2
3
2
4
′
′
2
[
2]
d[MnO ]/dt = k [MnO ] + k [MnO ]⋅[Mn ]
4 1 4 4
+
2
+
5CO + 2Mn + 3H O
2 2
where k′ and k′ are pseudo-order rate constants for the
1
2
noncatalytic and catalytic processes, respectively. The amino
acid concentration, which is always kept in large excess, and
the constant acid concentration in each experiment are in-
cluded in these pseudo-order rate constants.
Procedure
Equal concentrations of known amounts of permanganate
and amino acid were mixed and kept at 45 °C temperature
for 1 h. For the permanganate concentration determination, a
known amount of reaction mixture was quenched by a stan-
dard iron(II) solution. The unreacted iron was subsequently
titrated by a standard cerium(IV) solution. Aldehyde concen-
The integrated form of this equation gives:
[
3]
ln[(k′/k′ + x)/(a – x)] = (k′+ k′ a)t – ln(k′ a/k′)
1 2 1 2 2 1
©
2004 NRC Canada

4
32
Can. J. Chem. Vol. 82, 2004
–
4
–3
Fig. 2. Effect of the added initial concentration of ions on the absorbance time plots. [KMnO ] = 4 × 10 mol dm , [L-abu] =
4
–
3
–3
+2
–3
+2
–4
–3
+2
0
.1 mol dm , [H SO ] = 3.16 mol dm , T = 313 K. (a) [Mn ] = 0 mol dm ; (b) [Mn ] = 2 × 10 mol dm ; (c) [Mn ] = 4 ×
2 4
–
4
–3
1
0
mol dm .
Fig. 3. Integrated rate-law plots for the oxidation of L-α-amino-n-butyric acid by potassium permanganate at various temperatures.
–
4
–3
–3
–3
[
KMnO ] = 4 × 10 mol dm , [L-abu] = 0.1 mol dm , [H SO ] = 3.16 mol dm .
4
2
4
where a represents the initial concentration of permanganate
and x the amount of permanganate ion consumed up to time t.
where b refers to the initial concentration of manganese sul-
fate(II). The calculated rate constants under this condition
For the correct determination of pseudo-constants k′ and
have provided a reasonable initial guess for k′ . Having pre-
1
2
k′ , the following procedure has been employed. Because the
viously determined preliminary values of k′ and k′ , eq. [3]
2
1
2
+
2
reaction is slow and the initial Mn concentration is suffi-
ciently low, initial guesses of k′ values have been obtained
has then been used for the simultaneous determination of the
kinetic data of the reaction by taking advantage of iterative
methods (18, 24–29). Figure 3 demonstrates the results of
the fitting process of rate data at various temperatures and
under the same conditions.
1
by fitting the initial portion of the rate data to a first-order
rate equation and assuming no catalytic effect in the early
stages of the reaction. Moreover, our kinetic run in the pres-
ence of manganese sulfate(II) with a concentration equal to
that of the permanganate ion satisfies the following rate
equation:
Table 1 gives the final values for k′ and k′ at various tem-
1
2
2
peratures. Almost perfect fits to the curves in Fig. 3 (R val-
ues of 0.9995–0.9998) not only corroborate the validity of
the applied kinetic method but also confirm the autocatalytic
[
4]
ln[a(b + x)/b(a – x)] = k′ (a + b)t
+2
2
effect of the Mn species.
©
2004 NRC Canada

Bahrami and Zahedi
433
Fig. 4. Effect of the amino acid concentration on the catalyzed and uncatalyzed pseudo-order rate constants. [KMnO ] = 4 ×
4
–
4
–3
–3
1
0
mol dm , [H SO ] = 3.16 mol dm , T = 313 K.
2 4
Table 2. Variation of k′ and k′ vs. the concentration of butyric
Table 1. Effect of temperature on k′ and k′ ; [KMnO ] = 4 ×
2
1
1
–3
2
4
–
4
–3
–3
–4
–3
–3
acid; [KMnO ] = 4 × 10 mol dm ; [H SO ] = 3.16 mol dm ;
10
mol dm ; [L-abu] = 0.1 mol dm ; [H SO ] = 3.16 mol dm .
4
2
4
2
4
T = 313 K.
5
–1
2
3
–1 –1
T (K)
k′ ×10 (s )
k′ ×10 (dm mol s )
1
2
–
3
3
–1 –1
4
–1
[
L-abu] (mol dm )
k′ (dm mol s )
k′ ×10 (s )
2
1
2
3
3
3
3
98
03
08
13
18
4.12 (±0.02)
6.16 (±0.04)
9.12 (±0.09)
12.78 (±0.09)
17.79 (±0.09)
27.72 (±0.05)
49.98 (±0.11)
81.05 (±0.19)
142.24 (±0.2)
239.8 (±0.2)
0
0
0
0
0
.1
.2
.3
.4
.5
1.43
2.81
4.35
5.67
7.05
1.28
2.51
3.83
5.17
6.33
Note: Values in parenthesis are estimated errors on each of k ′ and k ′.
1
2
Table 3. Effect of Mn(II) on k′ at 313 K; [L-abu] =
Dependence of the kinetic parameters
Dependence of reaction rate on [amino acid], [MnO ],
2
–
3
–3
0
.1 mol dm ; [H SO ] = 3.16 mol dm ; [KMnO ] = 4 ×
2
4
4
–
–4
–3
10 mol dm .
4
2
+
and [Mn ]
[
Mn(II)]
0
0.0002
1.41
0.0004
1.34
0.0006
1.19
The pseudo-order rate constants obtained at various amino
acid concentrations are summarized in Table 2. Figure 4
shows these results. The plots of 1/k′ and 1/k′ against 1/[L-
3
–1 –1
k′ (dm mol s )
1.43
2
1
2
abu] (L-abu = L-α-amino-n-butyric acid) (not shown) gave
straight lines that both pass through the origin. These obser-
vations confirm first order with respect to the amino acid for
both the noncatalytic and catalytic pathways (12).
ries of experiments carried out at various sulfuric acid con-
centrations. As Fig. 5 indicates, k′ increases when the acid
1
concentration is raised, whereas k′ initially decreases and
2
–3
To investigate the effect of permanganate concentration on
then shows a sharp increase. The region of 3–4 mol dm
–
4
the reaction rate, its concentration was varied from 4 × 10
sulfuric acid shows the least variation for k′ . Thus, this con-
2
–
4
–3
to 6 × 10 mol dm at 313 K, which caused k′ and k′ values
centration region was determined to be the most appropriate
region for the rest of our kinetic studies.
1
2
to be decreased by 14% and 31%, respectively.
Table 3 summarizes the data that have been obtained for
+
2
k′ with increasing Mn ion concentration. From these re-
Determination of activation parameters
2
+
2
sults it is evident that when Mn concentration is raised, k′
As a further justification of the method that has been ap-
plied to determine the pseudo-order rate constants k′ and k′
2
values decrease. This observation, and the fact that the very
1
2
slow reaction of Mn with MnO4– (35, 36) switches to a
fast reaction when the amino acid is present, suggest that in
the process of permanganate consumption some intermediate
complex has probably been formed between Mn+ and the
amino acid (24–29).
+
2
at various temperatures, calculated values of these parame-
ters have been evaluated by the Eyring equation. Figure 6
demonstrates the agreement of both k′ and k′ with the
1
2
2
Eyring equation. The thermodynamic activation parameters
obtained, energy, enthalpy, and entropy, are reported in Ta-
ble 4.
Dependence of reaction rate on sulfuric acid
concentration
Acrylonitrile addition
The presence of free radicals as intermediates was con-
+
The effect of [H ] has been investigated by means of a se-
©
2004 NRC Canada

4
34
Can. J. Chem. Vol. 82, 2004
Fig. 5. Effect of the sulfuric acid concentration on the uncatalyzed and catalyzed pseudo-order rate constants. [KMnO ] = 4 ×
4
–
4
–3
–3
1
0
mol dm , [L-abu] = 0.1 mol dm , T = 313 K.
–
3
–4
–3
Fig. 6. Eyring plots for the uncatalyzed and catalyzed processes. [L-abu] = 0.1 mol dm , [KMnO ] = 4 × 10 mol dm , [H SO ] =
4
2
4
–
3
3
.16 mol dm .
Table 4. Activation parameters; [KMnO ] = 4 × 10 mol dm–3;
–
4
presented and taking into account the previous literature ref-
erences, two separate mechanisms for the catalyzed and
uncatalyzed pathways are proposed to describe the reaction
pathway. Since the existence of intermediate free radicals
was confirmed, their involvement in the reaction mechanism
has also been considered.
4
–
3
–3
[
L-abu] = 0.1 mol dm ; [H SO ] = 3.16 mol dm .
2
4
Uncatalyzed
process
Catalyzed
process
#
–1
–1
∆
S (J mol K )
∆
–144 (±3)
55 (±1)
58 (±1)
19 (±4)
82 (±1)
84 (±1)
#
–1
H (kJ mol )
–
1
E (kJ mol )
a
Reaction mechanism for the uncatalyzed process
Note: Values in parenthesis are estimated errors on each thermodynam-
All the experiments were performed in strong acid media.
With the evidence presented pointing to no involvement of
other manganese oxidation states, Mn(VII) is the most prob-
able reactive species. Reaction rate enhancement observed
by increasing acid concentration suggests the formation of a
more powerful oxidant, namely permanganic acid, by the
following equilibrium:
ical parameter.
firmed by addition of acrylonitrile, which led to polymeriza-
tion, both in the presence and in the absence of manganese
sulfate(II).
Discussion
In agreement with the experimental results that have been
[5]
MnO4– + H+
HMnO4
©
2004 NRC Canada

Bahrami and Zahedi
435
At the high acid concentration used, protonation of the
zwitterionic form of amino acid gives
in the overall reaction with the stiochiometry satisfied. In
agreement with the above scheme, assuming a steady state
+
approximation for X , the rate equation obtained for the
1
[
6]
uncatalyzed process is
–
[
[
14] –d[Mn(VII)]/dt = k′[MnO ]
1
4
+
2
α [H ] [L −abu]
β (1 + β [H ] + β [H ] ) + α [H ] [MnO ]
0
t
15] k1′ =
+
+ 2
+ 2
0
1
2
1
4
A mechanism consistent with the observed kinetic data
includes the following steps.
where [L-abu] represents the total concentration of amino
t
acid; [Mn(VII)] represents the total concentration of per-
manganate; and where
In agreement with the experimental results, the formation
of an addition complex between the permanganic acid and
the cationic form of the amino acid is proposed (11, 12, 28).
α = K K k k
0
1
2
3
4
[
7]
α = K K k
1
1
2
3
β0 = k–3 + k4
β = K + K
1
1
2
β = K K
2
1
2
This complex may rupture according to the following equa-
tion:
The rate law obtained above corresponds to that mecha-
nism explaining the observed experimental behavior: the
first-order reaction with respect to both permanganate and
[
8]
amino acid and the change in k′, the uncatalyzed pseudo-
1
order rate constant, when the permanganate concentration
varies.
Reaction mechanism for the catalyzed process
Addition of Mn+ ions led to an increase in the reaction
rate, while the evidence presented also suggests that an
adduct might be formed between Mn+ and the protonated L-
α-amino-n-butyric acid in a fast step before it is oxidized by
permanganic acid in a slow step (15, 16).
2
Based on the radical involvement in the reaction mechanism,
the iminium cation (24–29) is possibly formed via three
steps
2
[
9]
[
16]
[
[
10]
11]
As the rate determining step, slow attack of
permanganic acid on complexes has been proposed (28–
2
9)
[
17]
By hydrolysis of the iminium cation, the corresponding alde-
hyde is obtained (28)
[
12]
The remaining steps, leading to the final products, resemble
those presented for the uncatalyzed pathway above. Again,
multiplying eqs. [5], [6], [7], [16], [17], [9], [10], [11], and
[
12] by a factor of five and summing them up with eq. [12]
results in the overall reaction with the correct stoichiometry.
Knowing the fact that the species Mn(V) is very unstable in
strong acidic media, it will be converted into Mn(II) and
Mn(VII) by means of a rapid disproportionation.
3
+
Assuming a steady-state approximation for the X2 complex
in the above mechanism, the following rate equation (28) is
derived:
[
13] 5HMnO42– + 11H → 3MnO4– + 2Mn2+ + 3H O
+
2
2
+
–
[
18] –d[Mn(VII)]/dt = k′ [Mn ][MnO ]
2
4
Multiplying eqs. [5], [6], [7], [8], [9], [10], [11], and [12] by
a factor of five and then summing them with eq. [13] results
©
2004 NRC Canada

4
36
Can. J. Chem. Vol. 82, 2004
+
2
β δ [L −abu] [H ]
0
0
t
[
19] k′2 =
+
+ 2
+
−
+
+2
+ 2+
+2
β (1 + β [H ] + β [H ] ) + α [H ][MnO ] + β δ [H ][Mn ] + β δ [H ] [Mn ]
0
1
2
1
4
0 1
0 2
where the notation employed in eq. [14] is conserved, and in
addition
7. L.M. Bharadwaj and P.C. Nigam. Ind. J. Chem. Ser. A(8), A,
793 (1981).
8
9
. V.S. Rao, B. Sethuram, and T.N. Rao. Int. J. Chem. Kinet. 11,
165 (1979).
. V.S. Rao, B. Sethuram, and T.N. Rao. Oxid. Commun. 9, 11
δ = K K K k
0
1
2
5
6
δ = K K
1
2
5
(
1986).
1
0. U.D. Mudaliar, V.R. Chourey, R.S. Verma, and V.R. Shastry.
δ = K K K
2
1
2
5
Ind. J. Chem. Soc. 60, 561 (1983).
This rate law, along with the one proposed for the
uncatalyzed process, is in accord with all experimental re-
sults presented in this article; namely, first-order dependence
11. H.M. Girgis, R.M. Hassan, and A.S. El-Shahawy. Bull. Fac.
Sci. Univ. 16(1), 41 (1987).
1
2. R.M. Hassan, M.A. Mousa, and M.H. Wahdan., J. Chem. Soc.
on Mn+ ions, permanganate ions, and the amino acid and
2
Dalton. Trans. 3, 605 (1988).
13. H. Iloukani and H. Bahrami. Int. J. Chem. Kinet. 31, 95 (1999).
+
2
inverse dependence of k′ on permanganate and Mn ion
2
1
1
1
1
1
1
4. B.R. Sahu, V.R. Chourey, S. Pandey, L.V. Shastry, and V.R.
concentrations, as shown in the k′ expression.
2
Shastry. Ind. J. Chem. Soc. 76, 131 (2000).
5. F.J. Andrés Ordax, A. Arrizabalaga, and J.I. Martinez de
Ilarduya. An. Quim. 80, 531 (1984).
6. F.J. Andrés Ordax, A. Arrizabalaga, and R. Martinez Perez de
mendiola. Studia Chemica, 11, 303 (1986).
7. F.J. Andrés Ordax, A. Arrizabalaga, and K. Ortega. An. Quim.
Owing to the complexity of the proposed mechanism,
evaluation of the values of the rate constants corresponding
to the reaction rate-determining steps for both processes has
not been possible. Thus, the activation parameters reported
are associated with reaction pseudo-rate constants k′ and k′ ,
1
2
and these values cannot be attributed to any particular reac-
tion step.
8
5, 218 (1989).
8. J.F. Perez Benito, F. Mata Perez, and E. Brillas. Can. J. Chem.
5(10), 2329 (1987).
6
9. E. Brillas, J.A. Garrido, and J.F. Perez Benito. Collect. Czech.
Conclusions
Chem. Comun. 53, 479 (1988).
The kinetics of the permanganate oxidation process of L-
α-amino-n-butyric acid in strong acid media was investigated
using a spectrophotometric technique. Addition of manga-
nese sulfate(II) to the reaction mixture raised the reaction
rate. The sigmoid profile observed for permanganate absorp-
tion variation at 525 nm vs. time was completely trans-
20. J.A. Garrido, J.F. Perez Benito, R.M. Rodrigouez, J. De
Andrés, and E. Brillas. J. Chem. Res. 11, 380 (1987).
21. J. De Andrés, E. Brillas, J.A. Garrido, and J.F. Perez Benito. J.
Chem. Soc. Perkin Trans. 2, 107 (1988).
22. R.M. Rodrigouez, J. De Andrés, E. Brillas, J.A. Garrido, and
J.F. Perez Benito. New J. Chim. 2(2–3), 143 (1988).
2
2
2
2
2
2
2
3
3
3
3
3
3. J. De Andrés, E. Brillas, J.A. Garrido, and J.F. Perez Benito.
Gazz. Ital. 118, 203 (1988).
4. F.J. Andrés Ordax, A. Arrizabalaga, J. Casado, and R. Peche.
React. Kinet. Cattal. Lett. 44, 293 (1991).
5. F.J. Andrés Ordax, A. Arrizabalaga, R. Peche, and M.A.
Quintana. An. Quim. 87, 828 (1992).
formed to a linear one under conditions of [KMnO ] =
4
[
Mn(II)]. In the presence of manganese sulfate(II), by in-
creasing the amino acid concentration, the reaction rate was
increased. Thus, we report the first conclusive evidence of
an autocatalytic oxidation process of an amino acid in strong
+
2
acid media in which Mn species are responsible for the ef-
fect. The pseudo-order rate constants obtained for both the
catalytic and noncatalytic pathways when the amino acid
was in excess obeyed the Eyring relation. The presence of
free radicals was confirmed, and mechanisms satisfying ex-
perimental observations for both catalytic and noncatalytic
pathways were presented.
6. F.J. Andrés Ordax, A. Arrizabalaga, R. Peche, and M.A.
Quintana. An. Quim. 88, 440 (1992).
7. M.J. Insausti, F. Mata-pèrez, and M.P. Alvarez-macho. Int. J.
Chem. Kinet. 27, 507 (1995).
8. A. Arrizabalaga, F.J. Andrés Ordax, M.Y. Fernández Aránguiz,
and R. Peche. Int. J. Chem. Kinet. 28, 799 (1996).
9. A. Arrizabalaga, F.J. Andrés Ordax, M.Y. Fernández Aránguiz,
and R. Peche. Int. J. Chem. Kinet. 29, 181 (1997).
0. A.I. Vogel. Quimica analitica cuantitative. Vol. I. Kapelusz,
Buenos Aires. 1960. p. 382.
1. F. Felig. Spot tests in inorganic analysis. Elsevier, Amster-
dam.1972. p. 334.
2. F. Felig. Spot tests in inorganic analysis. Elsevier, Amster-
dam.1976. p. 199.
3. A.I. Vogel. Quimica analitica cuantitative. Vol. I. Kapelusz,
Buenos Aires. 1953. p. 250.
4. K.K. Banerji and P. Nath. Bull. Chem. Soc. Jap. 42, 2038
References
1
2
3
4
5
6
. R.S. Verma, M.J. Reddy, and R. Shastry. J. Chem. Soc. Perkin
Trans. 2, 469 (1976).
. A.A. Frost and R.G. Pearson. Kinetic and mechanisms. Wiley,
New York. 1961. p. 152.
. C.S. Ameta, P.N. Pande, H.L. Gupta, and H.C. Chowhhry.
Acta Phys. Chem. 26, 89 (1980).
. C.S. Ameta, P.N. Pande, H.L. Gupta, and H.C. Chowhhry. Z.
Phys. Chem. (Leipzig), 261, 1222 (1980).
. C.S. Ameta, P.N. Pande, H.L. Gupta, and H.C. Chowhhry. Z.
Phys. Chem. (Leipzig), 261, 802 (1980).
. C.S. Ameta, P.N. Pande, H.L. Gupta, and H.C. Chowhhry.
(
1969).
3
3
5. W.A. Waters. Q. Rev. Chem. Soc. 12, 277 (1958).
6. P.S. Radhakrishnanurti and M.D. Rao. Indian J. Chem. Soc. A,
1
5, 524 (1977).
Acta. Chim. Acad. Sci. Hung. 110, 7 (1982).
©
2004 NRC Canada