Cooxidation of Anilides and Oxalic Acid by Chromic Acid: A One-Step, Three-Electron Oxidation

Article abstract of DOI:10.1002/1097-4601(20010101)33:1<21::AID-KIN3>3.0.CO;2-R

The chromic acid oxidation of a mixture of oxalic acid and anilides proceeds much faster than that of either of the two substrates alone. The oxidation kinetics of acetanilide, p-methyl-, p-chloro-, and p-nitroacetanilides by Cr(VI) in the presence of oxalic acid in aqueous acetic acid medium follows first-order zero-order, and second-order dependence in [oxidant], [substrate], and in [oxalic acid], respectively, while the oxidation kinetics of benzanilide, p-methyl-, p-chloro-, and p-nitrobenzanilides follow first order in [oxidant] and fractional order each in [substrate] and [oxalic acid] and yields corresponding azobenzenes and benzaldehydes in the case of benzanilide and substituted benzanilides as the main products of oxidation. Aluminium ions suppress the reaction The intermediate is believed to be formed from the anilide and a chromic acid-oxalic acid complex In the proposed mechanism, the rate-limiting step involves the direct reduction of Cr(VI) to Cr(III).

Full text of DOI:10.1002/1097-4601(20010101)33:1<21::AID-KIN3>3.0.CO;2-R

Cooxidation of Anilides and
Oxalic Acid by Chromic
Acid: A One-Step,
Three-Electron Oxidation
K. A. BASHEER AHAMED1
Post Graduate and Research Department of Chemistry, Jamal Mohamed College, Tiruchirappalli-620 020, India
Received 2 June 1999; accepted 29 June 2000
ABSTRACT: The chromic acid oxidation of a mixture of oxalic acid and anilides proceeds much
faster than that of either of the two substrates alone. The oxidation kinetics of acetanilide, p-
methyl-, p-chloro-, and p-nitroacetanilides by Cr(VI) in the presence of oxalic acid in aqueous
acetic acid medium follows first-order, zero-order, and second-order dependence in [oxidant],
[substrate], and in [oxalic acid], respectively, while the oxidation kinetics of benzanilide, p-
methyl-, p-chloro-, and p-nitrobenzanilides follow first order in [oxidant] and fractional order
each in [substrate] and [oxalic acid] and yields corresponding azobenzenes and benzaldehydes
in the case of benzanilide and substituted benzanilides as the main products of oxidation.
Aluminium ions suppress the reaction. The intermediate is believed to be formed from the
anilide and a chromic acid-oxalic acid complex. In the proposed mechanism, the rate-limiting
step involves the direct reduction of Cr(VI) to Cr(III). ꢀ 2000 John Wiley & Sons, Inc. Int J Chem
Kinet 33: 21–28, 2001
INTRODUCTION
of piperidin–4-ols by Cr(VI) in the presence of oxalic
acid were nearly ten times greater than the oxidation
rates of piperidin–4-ols in the absence of oxalic acid
[4]. While studying the influence of oxalic acid on
Cr(VI) oxidation of As(III) in the presence of chloride
ion in aqueous acetic acid, it was observed that both
As(III) and oxalic acid are oxidized concertedly in
three equivalent steps [5]. In their study of the kinetics
and mechanism of oxidation of o-, p-, and m-substi-
tuted trans-cinnamic acids by pyridinium chlorochro-
mate in the presence of oxalic acid, Mohan et al. [6]
have proposed the carbanion formation for electron-
withdrawing substituents and carbonium ion forma-
tion for electron-releasing substituents in their transi-
tion state. Their study revealed that both electron-
releasing and electron-withdrawing substituents facil-
itate the rate of oxidation. The oxidation of phenoxy
acetic acid by pyridinium fluorochromate in the pres-
ence of oxalic acid proceeds through pyridinium fluo-
Enough evidences are available to show that the hex-
avalent chromium functions both as a one- and two-
electron oxidant depending on the substrate. Rocek
and Hasan [1] and Venkatasubramanian et al. [2]
showed that the system involving an alcohol-oxalic
acid-Cr(VI) behaved in a different way in that the
Cr(VI) species get reduced directly to Cr(III) species
involving three-electron transfer. Haight and Huber
[3] proposed the rate law: Rate ϭ Ϫd[Cr(VI)]/dt ϭ
Ϫ
2
2
kЈ[HCrO4 ][Mn(C2O4)2 Ϫ][C2O4 Ϫ] [Hϩ]2 for the oxi-
dation of manganese (II) by Cr(VI) in the presence of
oxalate ion. It was observed that the rates of oxidation
Correspondence to: K. A. Basheer Ahamed (sride-
vikkn@mailcity.com)
1Present address: Department of Chemistry, Rajagiri Dawood
Batcha College of Arts & Science, Rajagiri: 614207 Tamilnadu,
India.
ꢀ 2000 John Wiley & Sons, Inc.

22
BASHEER AHAMED
rochromate-oxalic acid complex, and the reaction
involves three-electron transfer [7]. Substituted s-
phenylmercaptoacetic acids were subjected to oxida-
tive cleavage by chromic acid in the presence of oxalic
acid, in which the formation of a ternary complex be-
tween oxalic acid, chromic acid, and s-phenylmercap-
toacetic acid in a fast step is proposed [8]. The com-
plex is then hydrolyzed in a subsequent slow
rate-limiting step, yielding the corresponding sulphox-
ides. The title investigation is projected toward the be-
havior of the ternary system involving anilide-oxalic
acid-Cr(VI) to evaluate the substituent effects, if any,
in the cooxidation process, as anilides are very slug-
gish toward Cr(VI). Detailed literature scanning re-
veals that no satisfactory work is on record about the
kinetics and mechanism of oxidation of anilide, sub-
stituted anilides, benzanilide, and substituted benzan-
ilides by Cr(VI) in the presence of oxalic acid in aque-
ous acetic acid medium. Only a few reports are
available about the oxidation kinetics of acetanilides
and substituted acetanilides with a variety of oxidizing
reagents [9–15].
adding sodium perchlorate. All the reactions were car-
ried out in 150 ml gena glass flasks coated black on
the outside to avoid any photochemical decomposi-
tion. Aliquots (5 ml) of the reaction mixture were pi-
petted out at regular intervals and quenched in ice-cold
5% KI solution (5 ml) and 2 N H2SO4 (10 ml) was
added. The reaction was monitored by estimating the
unreacted Cr(VI) at various time intervals by iodom-
etric procedure to a starch end point. Under the con-
ditions of the experiment, the solvents were not oxi-
dized. Rate constants were computed from the linear
(r Ͼ 0.98) plot of log[Cr(VI)] against time. In the eval-
uation of rate coefficients, the kinetics were followed
to nearly 75% reaction. Duplicate kinetic runs showed
that the rates were reproducible within Ϯ4%. The sec-
ond-order rate constant, k2, was obtained from the re-
lation k2 ϭ k1/[anilide], where k1 is the pseudo-first-
order rate constant. The rate constants were calculated
by the method of least squares.
Product Analysis
The product analyses were carried out separately for
acetanilide and for benzanilides under kinetic condi-
tions. Anilide (acetanilide 13.50 g, 0.1 M; benzanilide
19.70 g, 0.1 M), oxalic acid (12.60 g, 0.1 M), and
Cr(VI) (1.0 g, 0.01 M) were made up to 50 ml with
45, 50, and 60% (v/v) acetic acid in different reaction
bottles, keeping the ionic strength (0.2 M) constant.
To ensure the completion of the reaction, the re-
action mixtures were allowed to stand for 12 h and
were then diluted with water. The organic layers were
extracted with ether and dried with anhydrous sodium
sulphate. The solvents were removed under reduced
pressure. The products of oxidation were cooled well
and a small amount of cold dilute acetic acid was
added to each sample. A sufficient amount of ice-cold
bromine in acetic acid was added to each sample and
shaken vigorously for half an hour after adding
crushed ice. Bromo derivatives were separated out
from each sample, filtered, dried, weighed, and re-
crystallized from ethanol and again dried and weighed.
Comparison of the melting points of each bromo de-
rivative with that of the authentic samples confirmed
that one of the products of oxidation is azobenzene.
Sodium bicarbonate was added to each filtrate just
to neutralize the solutions. After concentrating these
solutions, ether extractions were carried out. After
evaporating the ether, an excess of the concentrated
solution of sodium bisulphite was added to each sam-
ple and shaken vigorously. The bisulphite addition
compounds formed were filtered separately and treated
with a slight excess of sodium carbonate solution. Oily
layers separated out from each sample were extracted
EXPERIMENTAL
Materials
Acetanilide (AA) and benzanilide (BA) were LR grade
and were used after recrystallization as described in
the literature [16]. Substituted acetanilides and
benzanilides like para-bromoacetanilide(p-BrA),
para-chloroacetanilide (p-ClA), para-methylacetani-
lide (p-CH3A), para-nitroacetanilide (p-NO2A), para-
chlorobenzanilide (p-ClBA), para-methylbenzanilide
(p-CH3BA), and para-nitrobenzanilide (p-NO2BA)
were prepared by the standard procedure, recrystalli-
zed as described in the literature, and their purities
checked by determining their melting points, compar-
ing with the values given in the literature [16,17] and
by IR. All other reagents used were Analar grade. Con-
ductivity water was used throughout the course of the
investigation. Acetic acid (AR) was twice distilled
over chromic oxide containing acetic anhydride (bp
118ꢁC).
Kinetic Measurements
Standard solutions of anilides and Cr(VI) prepared in
HOAc-H2O mixtures were thermostatted for 2 h be-
fore each run. The reactions were carried out under
pseudo-first-order conditions by keeping an excess of
anilide over oxidant in the presence of oxalic acid,
maintaining the ionic strength constant (0.2 M) by

COOXIDATION OF ANILIDES AND OXALIC ACID BY CHROMIC ACID
23
with ether. After evaporating the solvents, the samples
in different reaction bottles of different composition
were treated separately with an excess of freshly pre-
pared saturated solution of 2,4-dinitrophenylhydrazine
in 2 M hydrochloric acid. The precipitates formed
were collected separately by filtration. The difference
between the crude yield and yield determined after re-
crystallization was about 3–4%. The melting points
of 2,4-dinitrophenylhydrazones (DNP) obtained from
different samples of different composition, TLC of
DNP of the products, and that of authentic samples
and melting points confirmed that one of the products
in the case of benzanilide was benzaldehyde. In the
case of acetanilide, one of the products is acetalde-
hyde. The same procedure was adopted for benzani-
lides with different substituents. Under the specified
conditions of oxidations of benzanilides by Cr(VI) in
the presence of oxalic acid in aqueous acetic acid me-
dium, it was observed that azobenzene is the only ni-
trogen-containing major product of oxidation along
with benzaldehyde. In the case of substituted benzan-
ilides containing substituents in the aniline moiety,
substituted azobenzenes are the only nitrogen-contain-
ing major products of oxidation along with unsubsti-
tuted benzaldehydes. As there is no evidence for the
presence of benzoic acids, it can be confirmed that the
further oxidation of benzaldehydes did not take place.
In the case of acetanilide, 2,4-dinitrophenylhydrazone
was rather poor in yield.
is found to be 1.95, whereas it is 1.28 in the case
of BA, 1.39 in the case of p-CH3BA, 1.72 in the
case of p-ClBA, and 1.41 in the case of p-
NO2BA (Table I; Fig. 2)
4. Effect of varying ionic strength of the medium:
The rate of oxidation of acetanilides as well as
benzanilides remains constant when the ionic
strength of the medium is increased.
5. Effect of adding sodium chloride: There is no
change in the rates of oxidation of acetanilides
and benzanilides by the addition of sodium chlo-
ride.
6. Effect of adding sulfuric acid and perchloric
acid: The rates of oxidation of acetanilides as
well as benzanilides are not at all affected by the
addition of sulfuric acid and perchloric acid.
They remain constant and do not vary.
7. Effect of adding pyridine: An appreciable de-
crease in the rate is observed by the addition of
pyridine.
8. Effect of adding aluminium nitrate: Addition of
aluminium nitrate suppresses the oxidation of
benzanilide with Cr(VI) in presence of oxalic
acid (Table II).
9. Effect of different substituents: It is observed
that the substituents like -CH3, -Cl, -NO2 en-
hance the rate of oxidation of substituted BA by
Cr(VI) in the presence of oxalic acid in aqueous
acetic acid medium, and hence the observed
trend in rate can be given as -CI Ͼ -NO2 Ͼ
-CH3 Ͼ -H (Table I). It is to be noted that Ham-
mett relation could not be verified; even a more
refined treatment as suggested by Venkatasubra-
manian et al. [2] could not lead to the evaluation
of ␳.
RESULTS AND DISCUSSION
The oxidation of acetanilide, substituted acetanilides,
benzanilide, and substituted benzanilides by Cr(VI) in
the presence of oxalic acid in aqueous acetic acid me-
dium showed the following features.
The results of the title investigation study can be
compared with the results obtained by Rocek and
Hasan [1] and Venkatasubramanian et al. [2] except
for the fact that the oxidation of acetanilides and ben-
zanilides is very sluggish in the absence of oxalic acid.
Radharkrishnamoorti and others [9–12,14] report the
fractional order dependence on substrate in the case of
oxidation kinetics study of acetanilides and substituted
acetanilides with a variety of oxidizing agents in the
absence of oxalic acid. It is observed that in the present
study the rate increases with increasing oxalic acid
concentration (Table I; Fig. 2). As suggested by Rocek
and Hasan [1], this behavior is characteristic of the
formation of an intermediate complex. Therefore, it is
worthwhile to assume that chromic acid under the re-
action conditions forms a complex with oxalic acid.
This assumption is expressed in Eqs. (1) and (2),
where C1 is a 1:1 complex of oxalic acid and chromic
acid.
Rate Laws
1. Order with respect to oxidant: Under the con-
dition [anilide] ϾϾ [Cr(VI)] the order in [Cr(VI)]
is unity, as revealed by the linear plot of
log[Cr(VI)] vs. time (Table I)
2. Order with respect to substrates: A more than
threefold variation in the [acetanilides] has no
effect on first-order rate constant (k1) values,
suggesting an independent nature of the rate in
the [acetanilides] (Table I), whereas it follows
fractional order in [BA] and [substituted BA],
as revealed by the slopes of the plots of log k1
against log[substrates] (Table I; Fig. 1).
3. Order with respect to oxalic acid: In the case of
acetanilide, the order with respect to oxalic acid

24
BASHEER AHAMED
Table I Effect of Varying [Reactants] on the Reaction Rate (I ϭ 0.2 mol dmϪ3; Temp: 308 K; Solvent: HOAc (50% v/v)).
1
104 k1 (SϪ
)
102 [anilides] 103 [Cr(VI)] 102 [OxH2]
3
3
3
mol dmϪ
mol dmϪ
mol dmϪ
AA
p-CIA p-BrA p-NO2A p-CH3A
BA
p-CIBA p-NO2BA p-CH3BA
0.6
1.0
1.2
1.6
2.0
2.4
1.0
1.0
1.0
1.0
1.0
1.0
4.0
4.0
4.0
4.0
4.0
4.0
4.40
4.28
4.39
4.52
4.35
4.42
4.35
4.18
4.23
4.16
4.29
4.31
4.27
4.37
4.54
4.37
4.25
4.36
4.15
3.98
4.21
4.26
4.31
4.23
4.23
4.19
4.25
4.29
4.51
4.44
r
Slope
4.12
4.41
4.32
4.16
—
—
—
—
—
—
—
—
3.95
4.48
4.69
5.13
5.32
5.60
0.99
0.25
4.52
4.39
4.42
4.51
0.92
2.00
3.47
5.15
7.08
9.12
0.99
1.28
16.87
19.00
19.95
21.40
22.51
23.40
0.99
7.49
8.56
8.96
9.55
10.17
10.66
0.99
0.25
8.64
8.48
8.58
8.51
1.40
3.67
6.53
9.77
13.96
17.56
0.99
1.41
4.57
5.22
5.37
5.89
6.24
6.53
0.99
0.26
5.19
5.40
5.32
5.27
1.05
2.39
3.77
6.07
9.55
12.90
0.99
1.39
0.24
1.0
1.0
1.0
1.0
1.7
1.7
1.7
1.7
1.7
1.7
—
0.4
1.2
1.6
2.0
1.5
1.5
1.5
1.5
1.5
1.5
—
4.0
4.0
4.0
4.0
1.0
2.0
3.0
4.0
5.0
6.0
r
4.34
4.25
4.19
4.27
0.29
1.12
2.45
4.31
6.76
9.55
0.99
1.95
4.15
4.24
4.22
4.30
—
—
—
—
—
4.52
4.18
4.25
4.31
—
—
—
—
—
4.02
4.11
4.21
4.01
—
—
—
—
—
18.85
19.25
19.11
18.92
1.70
5.24
10.71
20.25
26.91
34.48
0.99
—
—
—
—
—
—
—
—
—
Slope
1.72
K1
(COOH)2 ϩ Cr(VI) E
R
F C1
(1)
C1 ϩ BA 9
9
k: Products
(2)
The concentration is given by Eq. (3)
K1[(COOH)2][Cr(VI)]Tot
[C1] ϭ
(3)
1 ϩ K1[(COOH)2]
Where
[Cr(VI)]Tot ϭ [Cr(VI)] ϩ [C1]
Table II Effect of Adding Aluminium Nitrate
[p-CIBA] ϭ 1.0 ϫ 10Ϫ mol dmϪ3; [Cr(VI) ] ϭ 1.0 ϫ 10Ϫ
mol dmϪ3; [OxH2] ϭ 4.0 ϫ 10Ϫ2 mol dmϪ3; I ϭ 0.2 mol
dmϪ3; Temp: 308 K; Solvent: HOAc (50% v/v).
2
3
Ϫ
1
[Aluminium Nitrate] M
104 k1 (S
)
0.00
1.00
1.50
2.00
2.50
19.00
0.77
0.46
0.31
0.22
Figure 1 Variation of benzanilides.

COOXIDATION OF ANILIDES AND OXALIC ACID BY CHROMIC ACID
25
The first term represents the cooxidation process
and is responsible for the observed rate increase of
anilides oxidation by Cr(VI) in the presence of oxalic
acid. At lower concentrations, the second term of the
Eq. (6) can be neglected.
kobs ϭ k1[BA]0.25[OxH2]1.28
kobs
[BA]0.25
ϭ k1[OxH2]1.28
(7)
According to Eq. (7), a linear relationship should be
obtained between kobs/[BA] and [OxH2] and between
kobs/[OxH2] and [BA]. In practice, straight-line graphs
are obtained, but k values obtained from the slopes of
these straight lines could not fit in Hammett equation.
If we consider the scheme
K1
OxH2 ϩ H2CrO4 ERF C1
K2
C1 ϩ BA ERF C2
k3
C2 ERF Products
Rate ϭ k3 [C2] ϭ kobs [Cr(VI)]
C1 ϭ K1[OxH2][H2CrO4]
C2 ϭ K2[C1][BA]
Figure 2 Variation of oxalic acid.
Since
[Cr(VI)]T ϭ [H2CrO4] ϩ K1[OxH2][H2CrO4]
V ϭ k[C1][BA]
V ϭ kexptI[Cr(VI)]Tot
ϩ K2K1[OxH2][H2CrO4][BA]
(4)
(5)
[BA]/kexptI ϭ 1/k ϩ 1/kK1[(COOH)2]
The validity of the Eq. (5) is tested by plotting
[BA]/kexptI versus the reciprocal value of the oxalic
acid concentration. A very good straight-line plot is
obtained, which supports the assumption of the com-
plex formation (Table I; Fig. 3).
The oxidation of the ternary system can be regarded
as consisting of two independent reactions occurring
simultaneously since the oxidation of anilides with
Cr(VI) is very sluggish. Therefore, the following rate
law can be given:
Ϫd[Cr(VI)]
ϭ k1[BA]0.25[OxH2]1.28[Cr(VI)]
dt
ϩ k2[OxH2]2[Cr(VI)]
ϭ kobs[Cr(VI)]
kobs ϭ k1 [BA]0.25[OxH2]1.28
ϩ k2[OxH2]2
(6)
Figure 3 Plot of [benzanilides]/k vs 1/[OxH2].

26
BASHEER AHAMED
Rearranging, we get
k3[C2] ϭ kobs[H2CrO4] {1 ϩ K1[OxH2]
ϩ K2K1[OxH2][BA]}
ϭ k3K2K1[OxH2][H2CrO4][BA]
[OxH2]
1
[OxH2]
1
[OxH2]
ϭ
ϩ
ϩ
ͩ ͪͩ ͪ
kobs
k3K2K1
K2K1
[BA]
k3
This equation is similar to the equation obtained by
Venkatasubramanian et al [2]. Therefore, [OxH2] re-
maining constant, a linear relationship should exist be-
tween [OxH2]/kobs and 1/[BA], the intercept being
[OxH2]/k3 (Fig. 4). But even in this case, Hammett
relationship could not be verified. Considering all the
kinetic factors, Scheme I is proposed for the oxidation
of acetanilides by chromic acid in the presence of ox-
alic acid, which explains the independent nature of rate
in the [acetanilides]. Scheme II and Scheme III are
Figure 4 Plot of [OxH2/k vs. 1/[benzanilides] at constant
[OxH2].
hydrogen ion is hindered due to the addition of sulfuric
acid and perchloric acid.
Scheme I
proposed for the oxidation of benzanilides by chromic
acid in presence of oxalic acid. Both the schemes in-
volve the formation of ternary complexes (oxalic
acid–chromic acid–benzanilides). They undergo con-
certed intramolecular electronic rearrangement to
yield the products in one step. Scheme III is preferred
over Scheme II since it adequately explains the effect
of sulfuric acid and perchloric acid on the rate of ox-
idation. Scheme II involves the shift of hydride ion,
while Scheme III involves the shift of hydrogen ion.
But in the kinetic results that the addition of sulfuric
acid or perchloric acid bring out, no change in the rate
constant values supports Scheme III, since the shift of
Scheme II

COOXIDATION OF ANILIDES AND OXALIC ACID BY CHROMIC ACID
27
Table III Activation Parameters [Anilides] ϭ 1.0 ϫ
3
10Ϫ2 mol dmϪ3; [Cr(VI)] ϭ 1.0 ϫ 10Ϫ3 mol dmϪ
;
[OxH2] ϭ 4.0 ϫ 10Ϫ mol dmϪ3; I ϭ 0.2 mol dmϪ
;
2
3
Solvent; HOAc (50% v/v).
⌬H‡
(kJ mol
Ϫ⌬S‡
(J deg mol
⌬G‡
(kJ mol )
Ϫ1
Ϫ1
Ϫ1
Ϫ1
Anilides
)
)
AA
p-CIA
44.62
47.36
44.31
45.57
37.76
37.60
19.65
29.87
125.36
118.95
128.90
118.62
150.16
149.41
188.70
170.20
84.62
84.00
84.01
84.25
84.01
83.61
77.77
82.30
p-CH3A
p-NO2A
BA
p-CH3BA
p-CIBA
p-NO2BA
●
of carbon dioxide and COOH species, thus avoiding
the formation of the energetically unfavorable Cr(IV)
Ϫ
и
[1]. The fate of CO2 is explained as
Fast
Ϫ
и
CO2 ϩ Cr(VI) 9
9
: Cr(V) ϩ CO2
Fast
Scheme III
Cr(V) ϩ (COOH)2 99: 2CO2 ϩ Cr(III)
Earlier studies lend strong support for this scheme
[20]. The activation enthalpies and entropies of the
The fact that the methyl, chloro, and nitro groups
enhance the rate of oxidation of benzanilides and that
the enhancement is more pronounced due to the pres-
ence of chloro and nitro groups supports the schemes.
Addition of aluminium nitrate suppresses the oxida-
tion of benzanilides with Cr(VI) in the presence of
oxalic acid (Table II). Chatterjee and coworkers [18]
have reported that the chromic acid oxidation of oxalic
acid can be effectively prevented by the addition of
aluminum nitrate. This effect is probably due to the
ability to complex rather firmly with oxalic acid, and
thus the formation of the oxalic acid–chromic acid
complex, which is an intermediate in the oxidation re-
action, is hindered. Rocek and Hasan [1] also report
that the rate-accelerating effect of oxalic acid is almost
canceled by the addition of aluminum nitrate. These
results are in good agreement with the conclusion that
the chromic acid–oxalic acid complex is an interme-
diate in the cooxidation reaction. The unusual high
reactivity of the complex composed of a molecule of
chromic acid and oxalic acid and a molecule of sub-
strate is explained in this way [1]: that a complex con-
taining both components offers the reaction a more
favorable pathway than the oxidation of a single mol-
ecule. The presence of the molecule of oxalic acid
within the complex facilitates the reduction of Cr(VI)
directly to Cr(III), a direct three-electron reduction
coupled with the formation of a very stable molecule
Figure 5 Exner plot.

28
BASHEER AHAMED
7. Nagarajan, S.; Gopalakrishnan, M. Oxid Commun
1995, 18, 162.
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oxidation of benzanilides by Cr(VI) in the presence of
oxalic acid in aqueous acetic acid medium are linearly
related (Table III). The correlation is tested and found
genuine by applying Exner’s criterion [19] (Fig. 5).
The isokinetic temperature computed from these plots
is 454 K. However, the values of activation enthalpies
and values of free energy of activation of acetanilides
remain constant.
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The author thanks the authorities of Jamal Mohamed Col-
lege for providing facilities.
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