Kinetic and mechanistic investigations on the oxidation of N'-heteroaryl unsymmetrical formamidines by permanganate in aqueous alkaline medium

Article abstract of DOI:10.1007/s11243-014-9811-3

Kinetic studies on the oxidation of two substituted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-N'-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dimethyl-N'-(pyridin-2-yl) formamidine (Py-F), by alkaline permanganate have been performed by spectrophotometry. The spectroscopic and kinetic evidence reveals the formation of 1:1 intermediate complexes between the oxidant and substrates. The influence of pH on the oxidation rates indicated that the reactions are base-catalyzed. The reactions show identical kinetics, being first order each in [MnO₄ ^-]₀ and [Azn-F] ₀, but with a fractional first-order dependence on [OH^-]. The effect of temperature on the reaction rate has been studied. Increasing ionic strength has no significant effect on the rate. The final oxidation products of Pym-F and Py-F were identified as 2-aminopyrimidine and 2-aminopyridine, respectively, in addition to dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate of Py-F is higher than that of Pym-F. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-limiting step of the reactions, along with thermodynamic quantities, are presented and discussed.

Full text of DOI:10.1007/s11243-014-9811-3

Transition Met Chem
DOI 10.1007/s11243-014-9811-3
Kinetic and mechanistic investigations on the oxidation
of N’-heteroaryl unsymmetrical formamidines
by permanganate in aqueous alkaline medium
•
Ahmed Fawzy Mohamed R. Shaaban
Received: 14 December 2013 / Accepted: 19 February 2014
Ó Springer International Publishing Switzerland 2014
Abstract Kinetic studies on the oxidation of two substi-
tuted azinyl formamidines (Azn-Fs), namely N,N-dimethyl-
N’-(pyrimidin-2-yl) formamidine (Pym-F) and N,N-dime-
thyl-N’-(pyridin-2-yl) formamidine (Py-F), by alkaline
permanganate have been performed by spectrophotometry.
The spectroscopic and kinetic evidence reveals the for-
mation of 1:1 intermediate complexes between the oxidant
and substrates. The influence of pH on the oxidation rates
indicated that the reactions are base-catalyzed. The reac-
tions show identical kinetics, being first order each in
[MnO4-]0 and [Azn-F]0, but with a fractional first-order
dependence on [OH-]. The effect of temperature on the
reaction rate has been studied. Increasing ionic strength has
no significant effect on the rate. The final oxidation pro-
ducts of Pym-F and Py-F were identified as 2-aminopy-
rimidine and 2-aminopyridine, respectively, in addition to
dimethyl amine and carbon dioxide. Under comparable
experimental conditions, the oxidation rate of Py-F is
higher than that of Pym-F. A reaction mechanism ade-
quately describing the observed kinetic behavior is
proposed, and the reaction constants involved in the dif-
ferent steps of the mechanism have been evaluated. The
activation parameters with respect to the rate-limiting step
of the reactions, along with thermodynamic quantities, are
presented and discussed.
Introduction
Interest in the tri-substituted formamidines of general
structure (I), shown in Scheme 1, has increased in the last
decades, due to their very broad spectrum of biological
activity. The biochemical potentialities of formamidines
include monoamine oxidase inhibitors [1, 2], adrenergic,
neurochemical receptors [3, 4] and prostaglandin E2 syn-
thesis [5]. Formamidines are also noted for their com-
plexation with transition metals [6, 7] and usage as
auxiliaries in asymmetric synthesis [8, 9] and as electro-
philes [10]. The N,N-dialkyl derivatives are highly effec-
tive acaricides, and the most rewarding of these studies
resulted in discovery of the acaricide insecticide chlor-
dimeform, structure (II), Scheme 1.
Electronic supplementary material The online version of this
article (doi:10.1007/s11243-014-9811-3) contains supplementary
material, which is available to authorized users.
The oxidative cleavage of formamidines is quite impor-
tant, since the N,N-dialkyl formamidine group is one of the
most versatile protecting groups, especially in biosynthetic
applications. The azine moiety is a common structural sub-
unit in a large number of natural products and synthetic
compounds with important biological activities [11].
A. Fawzy ꢀ M. R. Shaaban
Chemistry Department, Faculty of Applied Sciences,
Umm Al-Qura University, Makkah Al-Mukarramah 13401,
Saudi Arabia Kingdom
A. Fawzy (&)
Chemistry Department, Faculty of Science, Assiut University,
Assiut 71516, Egypt
e-mail: afsaad13@yahoo.com
Although permanganate ion in alkaline media has been
used extensively as a potent oxidant for many organic mol-
ecules [12–16], to the best of our knowledge, the kinetics of
oxidation of azinyl formamidines (Azn-Fs) by permanga-
nate, or indeed by any other oxidants, have not yet been
reported. This observation prompted us to investigate the
M. R. Shaaban
Chemistry Department, Faculty of Science, Cairo University,
Cairo, Egypt
123

Transition Met Chem
CH3
CH3
Kinetic measurements
R'
R
N
N
Cl
N
N
Kinetic runs were performed under pseudo-first-order
conditions, such that in general, the Azn-Fs were present in
large excesses over permanganate at a constant ionic
strength and temperature. Some additional experiments
were conducted under second-order conditions of [Azn-F]
B [MnO4-] in order to check the data obtained from the
pseudo-first-order kinetics; the results were found to be in a
good agreement with each other within the experimental
errors, indicating the reproducibility of the measurements.
The absorbance measurements were made in a thermo-
statted cell compartment at the desired temperature on a
Shimadzu UV-1800 PC automatic scanning double-beam
spectrophotometer fitted with a program controller using
cells of path-length 1 cm. The course of the reactions was
followed up to not less than two half-lives by recording the
decrease in the absorbance of permanganate ion at
k = 525 nm, its absorption maximum, as a function of
time. It was verified that there is no interference from other
reagents at this wavelength. All experiments were studied
in triplicate, and the rate constants were reproducible to
within 3 %.
CH3
(I)
(II)
N
H
H
N
N
NMe2
N
N
NMe2
Pym-F
Py-F
Scheme 1 Structure of some azinyl formamidines
kinetics and mechanism of oxidation of two substituted Azn-
Fs, namely N,N-dimethyl-N’-(pyrimidin-2-yl) formamidine
(Pym-F) and N,N-dimethyl-N’-(pyridin-2-yl) formamidine
(Py-F), Scheme 1, by alkaline permanganate. The objectives
of the present investigation are to establish optimum condi-
tions affecting oxidation of Azn-Fs, elucidate a plausible
oxidation mechanism and characterize the oxidation
products.
Experimental
Results
Materials
Stoichiometry and product analysis
Azinyl formamidines were synthesized by heating a mixture
of 10 mmol of 2-aminopyrimidine or 2-aminopyridine in dry
benzene and dimethylformamide dimethylacetal (DMF-
DMA) (30 mmol) in dry benzene under reflux for 8 h. The
solvent was then removed in vacuo, and the crude products
were dried and purified either by chromatography or
recrystallization to afford the corresponding formamidine
derivatives Pym-F and Py-F, respectively. The identities of
Pym-F and Py-F were confirmed by their elemental analysis
Reaction mixtures containing an excess of permanganate over
Azn-Fs were mixed at [OH-] = 0.03 and I = 0.1 mol dm-3
and allowed to react in the dark for about 24 h at 25 °C. The
remaining[MnO4-] in eachcasewasanalyzedperiodicallyby
both titrimetric and spectrophotometric techniques. The
results revealed that 2.00 0.11 mol of permanganate were
consumed by 1.0 mol of Azn-F, according to the following
stoichiometric equations;
1
and spectral data. For example, the H NMR spectrum of
RꢁN ¼ CHꢁNMe2 þ 2MnOꢁ4 þ 2OHꢁ
Pym-F displayed two singlets at d 3.09–3.12 ppm due to the
N,N-dimethyl protons, a singlet at d 8.60 ppm due to the
olefinic proton, a triplet at ca. 6.76 ppm due to the pyrimi-
dine-CH-5 protons, a doublet at d 8.43 ppm assigned to
pyrimidine-CH-4 and a doublet at d 8.49 ppm for the
pyrimidine-CH-6 protons.
¼ RꢁNHðCOÞNMe2 þ 2MnO24ꢁ þ H2O
ð1Þ
ð2Þ
RꢁNHðCOÞNMe2 þ H2O
¼ RꢁNH2 þ Me2NH þ CO2
where R–N = CH–NMe2 is the Azn-F, R–NH(CO)NMe2
is 1,1-dimethyl-3-(azin-2-yl) urea as an intermediate
product and R-NH2 is the corresponding 2-amino azine.
The above stoichiometric equations are consistent with the
results of product analysis. The intermediate product 1,1-
dimethyl-3-(azin-2-yl) urea was confirmed by spectral data.
The solution of potassium permanganate was prepared
and standardized as reported earlier [17]. All other chem-
icals used were of analytical grade, and double distilled
water was used throughout the work. Sodium hydroxide
solution was used to provide the required alkalinity. The
ionic strength (I) was maintained constant (0.1 mol dm-3
)
1
The H NMR spectrum displayed two singlets due to the
using NaClO4 as an inert electrolyte. The reaction tem-
methyl group protons in the range of d 3.12 ppm, a triplet
perature was controlled to within 0.1 °C.
123

Transition Met Chem
1.0
0.8
0.6
0.4
0.2
0.0
Fig. 1 a, b Spectral changes for
the oxidation of azinyl
formamidines by alkaline
permanganate.
1.0
0.8
0.6
0.4
0.2
0.0
Permanganate
Permanganate
(a)
(b)
[Azn-F] = 8 9 10-3
,
[MnO4-] = 4 9 10-4
[OH-] = 0.03 and
,
I = 0.1 mol dm-3 at 25°C.
Scanning time
intervals = 1 min
200
400
600
800
200
400
600
800
Wavelength, nm
Wavelength, nm
in the range of d 7.16 ppm for the pyrimidine-CH-5 pro-
tons, a doublet at d 8.60 ppm due to the pyrimidine-CH-4
and pyrimidine-CH-6 protons, and a broad signal at d
10.90 ppm from the NH proton. Furthermore, the IR
spectrum showed an NH band at ca. 3320 cm-1 (spectrum
not shown). The final 2-amino azine products were also
isolated after completing the reaction courses and were
Reaction orders
The orders (n) of these oxidation reactions were deter-
mined from the slopes of plots of the observed first-order
rate constants (kobs) versus concentration (C) in loga-
rithm coordinates (log kobs = n log C) by varying the
concentrations of permanganate, Azn-F and alkali in turn
while keeping all other concentrations and conditions
constant.
1
confirmed by their spectral data. The H NMR spectrum
displayed a triplet at ca. d 6.50 ppm due to the pyrimidine-
CH-5 protons and a doublet at d 8.20 ppm due to the
pyrimidine-CH-4 and pyrimidine-CH-6 protons. In addi-
tion, the IR spectrum showed two bands assigned to the
NH2 group at 3,420 and 3,380 cm-1. Dimethyl amine was
identified by a spot test [18], the intermediate MnVIO42- by
its visible spectrum and carbon dioxide by lime water [17].
Under pseudo-first-order conditions of [Azn-F]0 -
[MnO4-]0 at constant [Azn-F]0, [OH-] and temperature,
plots of ln absorbance versus time were linear, showing first-
order dependence of the rates on [MnO4-]0. The values of
k
obs remained unaffected with changes in [MnO4-]0 as listed
in Table 1, confirming the first-order kinetics in [MnO4-]0.
On the other hand, increasing [Azn-F]0 was found to
accelerate the reaction rates, Table 1. Plots of kobs versus
[Azn-F]0 gave straight lines passing through the origin,
substantiating a first-order dependence of the rates on
[Azn-F]0. Furthermore, the second-order rate constants
(k0 = kobs/[Azn-F]0) were nearly the same for the two Azn-
F, establishing the first-order dependence on [Azn-F]0 .
The influence of alkali on the rate was studied at
various [OH-], keeping all other reactant concentrations
constant. The rate constants increased with increasing
alkali concentration (Table 1), suggesting that the oxida-
tion reactions are base-catalyzed. Plots of kobs versus
[OH-] were linear with nonzero intercepts, suggesting
that these reactions are fractional first order in [OH-].
Furthermore, plots of log kobs versus log [OH-] were
linear with less than unit slopes showing fractional orders
with respect to [OH-].
Spectral changes
The spectral scans obtained during the oxidation of Azn-Fs
by alkaline permanganate are shown in Fig. 1a, b. The
-
Figure shows a gradual decay of the MnO4 band at
525 nm with corresponding growth of new intermediate
absorption maxima at wavelengths of 606 and 435 nm. The
band at 606 nm corresponds to the transient manganate(VI)
species [19]. The formation of a manganate(VI) interme-
diate was also consistent with the green color observed as
the reaction proceeded [20]. The appearance of two isos-
bestic points at 575 and 473 nm during the course of
-
reaction indicates the interconversion of MnO4 to both
MnVIO4 and MnO2, respectively [21, 22]. The yellow
2-
color persisted after completion of the oxidation reactions,
then finally, dispersed brown MnO2 sol was observed,
confirming that the hypomanganate(V) formed and subse-
quently decomposed to MnIV sol. The latter was coagulated
by aging to give a colloidal precipitate of MnIVO2. The
absence of a hypomanganate(V) intermediate band around
700 nm is explained as due to rapid disproportionation of
MnV [23, 24]. When the concentration of manganate(VI)
intermediate builds up, a slow decay of the intermediate
takes place to give rise to the final oxidation products.
Effects of ionic strength and temperature
The effect of ionic strength was studied by varying the
concentration of NaClO4 in the reaction medium at con-
stant concentrations of alkali, Azn-F and permanganate. It
was found that variation in ionic strength had no significant
effect on the rates.
123

Transition Met Chem
To investigate the effect of temperature, the kinetic
experiments were conducted at 288, 293, 298 and 303 K,
keeping other experimental conditions constant. The
experimental results indicated that the oxidation rates are
greater at higher temperatures (Table 2). The activation
parameters associated with the oxidation reactions were
calculated using Arrhenius plots of ln k versus 1/T
according to the equation:
The activation enthalpy, DH=, and activation entropy,
DS=, can be determined from the Eyring equation;
kBT DS# DH#
ln k ¼ ln
hk
þ
ꢁ
or
h
R
RT
1
DS# DH#
ln
¼
ꢁ
kBT
R
R
T
where kB is the Boltzmann constant and h is the Planck
constant. The temperature dependence was found to fit both
the Eyring and Arrhenius equations.
Ea
ln k ¼ ln A ꢁ
RT
where R = 8.314 J mol-1 K-1
.
Polymerization study
Table 1 Influence of [MnO4-], [Azn-F] and [OH-] on the first-order
rate constants (kobs) in the oxidation of azinyl formamidines by
alkaline permanganate at 25°C
To test for the participation of the free radicals in these reac-
tions, the reactionmixturesweremixed with known quantities
ofacrylonitrilemonomer and kept for 24 h under nitrogen. On
dilution with methanol, a white precipitate was formed,
indicating the participation of free radicals in the oxidation
104 [MnO4
mol dm-3
]
103 [Azn-F]
mol dm-3
102 [OH-]
mol dm-3
105 kobs s-1
-
Pym-F
Py-F
-
reactions. Blank experiments carried out with either MnO4
2.0
3.0
4.0
5.0
6.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
4.0
8.0
8.0
8.0
8.0
8.0
4.0
6.0
8.0
10.0
12.0
8.0
8.0
8.0
8.0
8.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
1.0
2.0
3.0
4.0
5.0
111
109
110
113
108
58
291
295
290
287
288
146
208
290
355
424
161
235
290
342
421
or Azn-Fs alone with acrylonitrile did not induce polymeri-
zation under the same experimental conditions.
Discussion
It has been reported [25, 26] that permanganate ion in
aqueous alkaline medium first combines with alkali to form
an alkali-permanganate species in a pre-equilibrium step,
as described by the following equilibrium involving the
equilibrium constant K1
86
110
141
172
62
92
K1
2ꢁ
MnOꢁ4 þ OHꢁ ꢀ ½MnO4 ꢀ OHꢂ
ð3Þ
110
127
151
This is consistent with the apparent order of less than
unity in OH-. The formation of [MnO4ꢀOH]2- in alkaline
medium in the present systems is further supported by plots
Experimental error = 3%
103 [Asn] mol dm-3
102 [OH-] mol dm-3
Temperature (K)
Pym-F
Table 2 Effect of temperature
on the first-order rate constants
(105 kobs s-1) in the oxidation of
azinyl formamidines by alkaline
permanganate
Py-F
288
288
293
298
303
293
298
303
4
3
3
3
3
3
1
2
3
4
5
36
51
70
90
103
34
53
70
81
91
45
65
58
86
75
112
145
185
220
74
80
119
154
183
244
81
113
167
221
263
312
104
178
221
278
323
149
208
290
355
424
131
223
290
352
421
201
283
393
497
528
168
245
393
434
476
6
8
88
110
141
172
55
10
12
8
112
133
43
8
69
92
105
145
174
199
131
154
221
263
8
88
110
127
154
8
103
118
8
Experimental error = 4 %
123

Transition Met Chem
40
30
20
10
0
Fig. 2 a, b Double reciprocal
plots for the formation of the
intermediate complexes in the
oxidation of (a) Pym-F and
(b) Py-F by alkaline
permanganate at different
temperatures.
[MnO4-] = 4 9 10-4 and
[OH-] = 0.03 mol dm-3
16
12
8
(a)
(b)
288 K
293 K
298 K
303 K
288 K
293 K
298 K
303 K
s
s
o
ob
k
k
4
0
0
50
100
150
200
250
300
0
50
100
150
200
250
300
1/[Pym-F], dm3 mol-1
1/[Py-F], dm3 mol-1
2-
-
O
from the UV–Vis spectra, Fig. 1a, b. Also, the linearity of the
plots between 1/kobs and 1/[Azn-F], Fig. 2a, b, is considered
to provide kinetic evidence in favor of possible formation of
a transient complex between oxidant and substrate similar to
the well-known Michaelis–Menten [27] mechanism for
enzyme–substrate reactions. On the other hand, the observed
negligible effect of ionic strength on the reaction rate implies
the association of an ion and a neutral molecule [19, 28].
In view of the above arguments, the reaction mechanism
shown in Scheme 2 may be suggested. This involves attack
of the active species of permanganate, [MnO4ꢀOH]2-, on
the Azn-F substrate (S), leading to the formation of a
complex (C) in a prior equilibrium step;
O
O
OH
O
O
O
K1
O
Mn
+
OH-
Mn
O
Permanganate ion
Alkali-permanganate
2-
2-
X
O
H
OH
O
X
K2
N
O
N
NMe2
O
H
O
+
Mn
O
N
N
NMe2
Mn
O
O
OH
Alkali-permanganate
Azn-F
Complex (C)
slow
k1
[MnO4. OH]2-
fast
X
X
2-
H2O
MnVIO4
MnVIO4
OH
+
.
+
2-
N
N
NMe2
N
N
NMe2
Â
Ã
k2
S þ ½MnO4 ꢀ OHꢂ ꢀ S ꢁ MnVIO4 ꢀ OH 2ꢁðCÞ
ð4Þ
2ꢁ
.
Free radical (X )
X
X
O
OH
where K2 is the formation constant of this complex.
N
N
NMe2
H2O
N
N
H
NMe2
In this complex, one electron is transferred from the
Azn-F substrate to permanganate. Slow cleavage of the
complex leads to the formation of a free radical interme-
diate derived from the substrate (S.) and manganate(VI)
transient species
H2O
fast
X
N
NH2
+
O
Â
Ã
k1
2ꢁ
S ꢁ MnVIO4 ꢀ OH ðCÞ ꢁ! Sꢀ þ MnVIO42ꢁ þ H2O ð5Þ
HO
fast
NMe2
HNMe
slow
The intermediate (S) is rapidly attacked by another
CO2
+
2
alkali-permanganate species to yield an intermediate
product, 1,1-dimethyl-3-(azin-2-yl) urea, as follows:
where, X = N for Pym-F and X = CH for Py-F
fast
2ꢁ
S: þ ½MnO4 ꢀ OHꢂ ꢁ! Intermediate product þ MnVIO24ꢁ
Scheme 2 Mechanism of oxidation of azinyl formamidines by
alkaline permanganate
ð6Þ
of 1/kobs versus 1/[OH-] shown in Fig. 3a, b, which are
linear with positive intercepts.
In a further fast step, the intermediate product is
hydrolyzed to give the final oxidation products
Many investigators [14–16, 19, 26] have suggested that
most of the oxidation reactions by permanganate ion in
neutral and alkaline media proceed through intermediate
complex formation between the oxidant and substrate.
Spectroscopic evidence for such a complex was obtained
fast
Intermediate product þ H2O ꢁ! Final products
ð7Þ
According to this mechanism, the rate of disappearance
of the permanganate ion or the formation of the
123

Transition Met Chem
Table 3 Values of the rate constants of the slow step (k1) and the equilibrium constants (K1 and K2) in the oxidation of azinyl formamidines by
alkaline permanganate at different temperatures
Constant
Temperature (K)
Pym-F
Py-F
288
288
293
298
4.64
303
6.62
293
3.98
298
5.07
303
6.43
103 k1, s-1
K1, dm3 mol-1
K2, dm3 mol-1
2.41
3.16
17.31
8.09
3.16
21.84
19.54
18.90
8.89
15.62
7.27
13.71
6.41
20.41
18.36
18.62
15.56
15.97
13.32
Experimental error = 4 %
40
30
20
10
16
12
8
Fig. 3 a, b Plots of 1/kobs
versus 1/[OH-] for the
formation of the intermediate
complexes in the oxidation of
(a) Pym-F and (b) Py-F by
alkaline permanganate at
different temperatures. [Azn-
F] = 8 9 10-3 and
(a)
(b)
288 K
288 K
293 K
298 K
303 K
293 K
298 K
303 K
s
s
ob
ob
k
k
[MnO4-] = 4 9 10-4
mol dm-3
4
0
0
0
0
25
50
75
100
125
25
50
75
100
125
1/[OH-], dm3 mol-1
1/[OH-], dm3 mol-1
intermediate complexes can be expressed by the following
rate law:
intercept on the 1/kobs axis. The experimental results satisfy
this requirement at different temperatures as shown in
Fig. 2a, b. From the intercepts of these plots, values of the
rate constant of the slow step (k1) were evaluated and are
listed in Table 3.
Â
Ã
ꢁd MnOꢁ4
þd½S ꢁ MnVIO4 ꢀ OH2ꢁꢂ
Rate ¼
¼
dt
dt
Â
Ã
¼ k1 S ꢁ MnVIO4 ꢀ OH2ꢁ
ð8Þ
Equation (11) can be rearranged to
ꢀ
ꢁ
ꢀ
ꢁ
1
1
1
1
1
1
The variation in the rate of complex formation with the
substrate, hydroxyl ion and oxidant concentrations can be
deduced (‘‘Appendix’’) to give the following equation
¼
þ
þ
ð12Þ
kobs
k1K1K2½S] ½OHꢁꢂ
k1K2 ½S] k1
Regarding Eq. (12), plots of 1/kobs against 1/[OH-] at
constant [S] also should give straight lines with positive
intercepts on the 1/kobs axis, as was experimentally
observed, Fig. 3a, b. Values of the first and second equi-
librium constants K1 and K2 at different temperatures were
calculated from the slopes and intercepts of Fig. 3a, b (and
the obtained k1 values) and are also listed in Table 3. The
obtained values of K1 are in a good agreement with those
reported in the literature [15, 16].
Â
Ã
k1K1K2½Sꢂ½OHꢁꢂ MnO4ꢁ
Rate ¼
ð9Þ
1 þ K1½OHꢁꢂ þ K1K2½S]½OHꢁꢂ
Under pseudo-first-order conditions the rate law can be
expressed by Eq. (10)
Â
Ã
ꢁd MnOꢁ4
Â
Comparing Eqs. (9) and (10), after rearrangement we
Ã
Rate ¼
¼ kobs MnOꢁ4
ð10Þ
dt
The activation parameters for the rate constants of the
slow step (k1) were calculated using Eyring and Arrhenius
plots, as given in Table 4. Furthermore, the thermodynamic
parameters of the equilibrium constants were also deter-
mined using a Van’t Hoff’s plot and are listed in Table 5.
From Table 4, the obtained large negative values of DS=
suggest that the reactants give transition states which are more
ordered than the reactants, due to loss of degrees of freedom.
obtain
ꢀ
ꢁ
1
¼
1 þ K1½OHꢁꢂ
1
1
þ
ð11Þ
kobs
k1K1K2½OHꢁꢂ ½S] k1
According to Eq. (11), the relationship between 1/kobs
and 1/[S] at constant [OH-] should be linear with positive
123

Transition Met Chem
Table 4 Activation parameters associated with the slow step (k1) in the oxidation of azinyl formamidines by alkaline permanganate
Substrate
Parameter
DS=
DH=
DG=
Ea=
kJ mol-1
A
J mol-1 K-1
kJ mol-1
kJ mol-1
mol-1 s-1
Pym-F
Py-F
-131.19
-181.66
47.20
31.81
86.24
85.34
43.66
34.28
2.30 9 103
5.16 9 103
Experimental error = 4 %
Table 5 Thermodynamic parameters associated with the equilibrium
constants (K1 and K2) in the oxidation of azinyl formamidines by
alkaline permanganate
From reaction (3)
Â
Ã
MnO4 ꢀ OH2ꢁ
Â
Ã
K1 ¼
ðA2Þ
ðA3Þ
MnOꢁ4 ½OHꢁꢂ
Substrate
Equilibrium
constant
Parameter
DH°
DG°
298
kJ mol-1
DS°
kJ mol-1
J mol-1 K-1
Â
Ã
Â
Ã
Therefore; MnO4 ꢀ OH2ꢁ ¼ K1 MnO4ꢁ ½OHꢁꢂ
Pym-F
Py-F
K1
K2
K1
K2
-15.39
-15.74
-14.82
-19.85
-6.80
-4.91
-7.24
-6.80
-28.83
-36.34
-25.42
-43.79
From reaction (4)
½S ꢁ MnVIO4 ꢀ OH2ꢁꢂ
½Sꢂ½MnO4 ꢀ OHꢂ
K2 ¼
ðA4Þ
2ꢁ
Experimental error = 4 %
Â
Ã
Â
Ã
Therefore; S ꢁ MnVIO4 ꢀ OH2ꢁ ¼ K2½Sꢂ MnO4 ꢀ OH2ꢁ
This is also supported by the very small frequency factors A
[29]. The experimental values of DH= and DS= were both
favorable for electron transfer processes. Again, the positive
valuesofbothDH= and DG= indicate endothermic formation
of the intermediate. The observed modest values of DH= and
the higher rate constants for the slow step indicate that the
reactions occur via an inner-sphere mechanism [30]. This
accords with the suggested transition states which are con-
sistent with formation of intermediatecomplexes via an inner-
sphere electron transfer mechanism. This mechanism is also
consistent with the proposition made by Stewart and co-
workers [19, 28] for ionic transition states in oxidation of
many organic substrates by permanganate. They reported that
the entropy of activation tends to be more positive for reac-
tions with outer-sphere mechanisms, whereas it is more neg-
ative for reactions of the inner-sphere type. On the other hand,
comparison of the thermodynamic parameters listed in
Table 5 with those obtained for the slow steps of the reactions
show that the reactions before the rate-determining steps are
fairly fast and involve low activation energies [31].
ðA5Þ
Substituting Eq. (A3) into Eq. (A5) leads to
Â
Ã
Â
Ã
S ꢁ MnVIO4 ꢀ OH2ꢁꢂ¼ K1K2½S ½OHꢁꢂ MnOꢁ4
ðA6Þ
Substituting Eq. (A6) into Eq. (A1) yields
Â
Ã
Rate ¼ k1K1K2½Sꢂ½OHꢁꢂ MnO4ꢁ
ðA7Þ
The total concentration of the substrate is given by
Â
Ã
½SꢂT¼ ½SꢂFþ S ꢁ MnVIO4 ꢀ OH2ꢁ
ðA8Þ
where [S]T and [S]F stand for total and free concentrations
of the substrate.
Substituting Eq. (A6) into Eq. (A8) gives
Â
Ã
½SꢂT¼ ½SꢂFþK1K2½SꢂF½OHꢁꢂ MnO4ꢁ
ðA9Þ
À
Â
ÃÁ
½SꢂT¼ ½SꢂF 1 þ K1K2½OHꢁꢂ MnO4ꢁ
ðA10Þ
Appendix
Therefore,
According to the suggested mechanism,
Â
Ã
Â
Ã
ꢁd MnOꢁ4
þd S ꢁ MnVIO4 ꢀ OH2ꢁ
½SꢂT
½SꢂF ¼
Rate ¼
¼
ðA11Þ
1 þ K1K2½OHꢁꢂ½MnO4ꢁꢂ
dt
dt
Â
Ã
¼ k1 S ꢁ MnVIO4 ꢀ OH2ꢁ
ðA1Þ
123

Transition Met Chem
Similarly,
Equation (A21) can be rearranged to be
ꢀ
ꢁ
ꢀ
ꢁ
Â
MnOꢁ4 ꢂT ¼½MnO4ꢁꢂFþ½MnO4 ꢀ OH2ꢁꢂ
1
1
1
1
1
1
¼
þ
þ
ðA22Þ
ðA12Þ
Ã
k1K1K2½Sꢂ ½OHꢁꢂ
k1K2 ½S] k1
þ½S ꢁ MnVIO4 ꢀ OH2ꢁ
kobs
References
Substituting Eqs. (A3) and (A6) into Eq. (A12) gives
Â
Â
1. Beeman RW, Matsumura F (1973) Nature 242:273
2. Aziz SA, Knowles CO (1973) Nature 242:417
3. Leung VSK, Chan TYK, Yeung VTF (1999) Clin Toxicol 37:513
4. Nakayama A, Sukekawa M, Eguchi Y (1997) Pestic Sci 51:157
5. Yim GKW, Holsapple MP, Pfister WR, Hollingworth RM (1978)
Life Sci 23:2509
MnOꢁ4 ꢂT ¼½MnO4ꢁꢂF þ 1 þ K1½OHꢁꢂ
Â
Ã
ðA13Þ
þK1K2½Sꢂ½OHꢁꢂ MnO4ꢁ
F
Â
Ã
MnOꢁ4
Ã
MnOꢁ4
¼
ðA14Þ
ðA15Þ
ðA16Þ
T
1 þ K1½OHꢁꢂ þ K1K2½S]½OHꢁꢂ
F
6. Arnold DI, Cotton FA, Matonic JH, Murillo CA (1997) Polyhe-
dron 16:1837
7. Mitzi DB, Liang K (1997) J Solid State Chem 134:376
8. Meyers AI, Hutchings R (1996) Heterocycles 42:475
9. Matulenko M, Meyers AI (1996) J Org Chem 61:573
10. Benkovic SJ, Barrows TH, Farina PR (1973) J Am Chem Soc
95:8414
11. Lagoja IM (2005) Chem Biodivers 2:1
12. Vogel AI (1973) A text book of practical organic chemistry, 3rd
edn. ELBS Longman, London
Â
Ã
And OHꢁꢂT ¼½OHꢁꢂEþ½MnO4 ꢀ OH2ꢁ
½OHꢁꢂT
½OHꢁꢂF¼
Â
Ã
1 þ K1 MnOꢁ4
Substituting Eqs. (A11), (A14) and (A16) into Eq. (A7)
(and omitting ‘T’ and ‘F’ subscripts), we get
13. Ahmed GA, Fawzy A, Hassan RM (2007) Carbohydr Res
342:1382
Â
Ã
k1K1K2½Sꢂ½OHꢁꢂ MnO4ꢁ
À
Â
ÃÁÂ
Â
ÃÃ
Rate ¼
ðA17Þ
1 þ K1K2½OHꢁꢂ MnOꢁ4 1 þ K1 MnO4ꢁ ð1 þ K1½OHꢁꢂ þ K1K2½S]½OHꢁꢂÞ
In view of the low concentration of [MnO4-] used, both
the first and second terms in the denominator of Eq. (A17)
approximate to unity. Therefore, Eq. (17) becomes
14. Fawzy A, Ashour SS, Musleh MA (2013) React Kinet Mech Cat
(in press)
15. Jose TP, Nandibewoor ST, Tuwar SM (2005) E J Chem 2:75
16. Hosahalli RV, Savanur AP, Nandibewoor ST, Chimatadar SA
(2010) Trans Met Chem 35:237
17. Vogel AI (1978) A text book of quantitative inorganic analysis,
4th edn. ELBS and Longman, New York, p 352
18. Feigl F (1975) Spot tests in organic analysis. Elsevier, New York p 195
19. Stewart R (1965) In: Wiberg KB (ed) Oxidation in organic
chemistry, Part A. Academic press, New York, p 48
20. Cotton FA, Wilkinson G (1976) Advanced inorganic chemistry.
Wiley, New York
Â
Ã
k1K1K2½Sꢂ½OHꢁꢂ MnO4ꢁ
Rate ¼
ðA18Þ
1 þ K1½OHꢁꢂ þ K1K2½S]½OHꢁꢂ
Under pseudo-first-order conditions, the rate law can be
expressed as
Â
Ã
21. Hassan RM (1993) Polym Inter 30:5
ꢁd MnOꢁ4
Â
Ã
Comparing Eqs. (A18) and (A19), the following rela-
Rate ¼
¼ kobs MnOꢁ4
ðA19Þ
22. Hassan RM (1993) J Polym Sci Part A 31:51; 31:1147
23. Carrington A, Symons MCR (1956) J Chem Soc 3373
24. Zimmerman CL (1949) PhD Thesis, University of Chicago
25. Panari RG, Chougale RB, Nandibewoor ST (1998) J Phys Org
Chem 11:448
dt
tionship is obtained
26. De Oliveira LA, Toma HE, Giesbrecht E (1976) Inorg Nucl
Chem Lett 2:195
27. Michaelis L, Menten ML (1918) Biochem Z 49:333
28. Stewart R, Moden RV (1960) Disc Faraday Soc 29:211
29. Weissberger A, Lewis ES (eds) (1974) Investigation of rates and
mechanism of reactions in techniques of chemistry. Wiley, In-
terscience publishers, Inc, New York, p 421
30. Bugarcic ZD, Nandibewoor ST, Hamza MSA, Heimemann F,
Eldik RV (2006) Dalton Trans 29:84
31. Rangappa KS, Raghavendra MP, Mahadevappa DS, Chan-
negowda D (1988) J Org Chem 63:531
k1K1K2½Sꢂ½OHꢁꢂ
kobs
¼
ðA20Þ
ðA21Þ
1 þ K1½OHꢁꢂ þ K1K2½S]½OHꢁꢂ
and with rearrangement it becomes
ꢀ
ꢁ
1
1 þ K1½OHꢁꢂ
1
1
¼
þ
kobs
k1K1K2½OHꢁꢂ ½S] k1
123