Kinetic and mechanistic studies of some aliphatic amines' oxidation by sodium N-bromo-p-toluenesulfonamide in hydrochloric acid medium

Article abstract of DOI:10.1002/1097-4601(2000)32:12<776::AID-KIN5>3.0.CO;2-J

Oxidations of n-propyl, n-butyl, isobutyl, and isoamyl amines by bromamine-T (BAT) in HCl medium have been kinetically studied at 30°C. The reaction rate shows a first-order dependence on [BAT], a fractional-order dependence on [amine], and an inverse fractional-order dependence on [HCl]. The additions of halide ions and the reduction product of BAT, p-toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the medium has no influence on the reaction. Activation parameters have been evaluated from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data have been proposed. The protonation constant of monobromamine-T has been evaluated to be 48 ± 1. A Taft linear free-energy relationship is observed for the reaction with ρ^* = -12.6, indicating that the electron-donating groups enhance the reaction rate. An isokinetic relationship is observed with β = 350 K, indicating that enthalpy factors control the reaction rate.

Full text of DOI:10.1002/1097-4601(2000)32:12<776::AID-KIN5>3.0.CO;2-J

Kinetic and Mechanistic
Studies of Some Aliphatic
Amines’ Oxidation by
Sodium N-bromo-p-
toluenesulfonamide in
Hydrochloric Acid Medium
1
1,
2
1
3
S. ANANDA, M. B. JAGADEESHA, * PUTTASWAMY, B. M. VENKATESHA, T. K. VINOD,
3
N. M. MADE GOWDA
1
Department of Studies in Chemistry, University of Mysore Manasagangothri, Mysore-570 006, India
Department of Studies in Chemistry, Central College, Bangalore University, Bangalore-560 001, India
Department of Chemistry, Western Illinois University, One University Circle, Macomb, IL 61455, USA
2
3
ABSTRACT: Oxidations of n-propyl, n-butyl, isobutyl, and isoamyl amines by bromamine-T
(BAT) in HCl medium have been kinetically studied at 30ЊC. The reaction rate shows a first-
order dependence on [BAT], a fractional-order dependence on [amine], and an inverse frac-
tional-order dependence on [HCl]. The additions of halide ions and the reduction product of
BAT, p-toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength
of the medium has no influence on the reaction. Activation parameters have been evaluated
from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data
have been proposed. The protonation constant of monobromamine-T has been evaluated
to be 48 Ϯ 1. A Taft linear free-energy relationship is observed for the reaction with ␳* ϭ
Ϫ12.6, indicating that the electron-donating groups enhance the reaction rate. An isokinetic
relationship is observed with ␤ ϭ 350 K, indicating that enthalpy factors control the reaction
rate. ᭧ 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 776–783, 2000
INTRODUCTION
alogue, bromamine-T (BAT), is a better oxidizing
agent than CAT. However, meager information exists
in the literature on BAT reactions [3–6].
Aromatic N-halosulfonamides are mild oxidants con-
taining a strongly polarized N-linked halogen in its ϩ1
oxidation state. The prominent member of this group,
chloramine-T (CAT), is a well-known analytical re-
agent and the mechanistic aspects of many of its re-
actions have been documented [1,2]. The bromine an-
Aliphatic amines are nitrogen-containing bases that
find wide applications in industry as additives in plat-
ing complex baths, as reagents in the synthesis of dyes
and polymeric materials, and as potential ligands for
metal complexes used in heterogeneous catalysis.
They also play an important role in biological systems.
Oxidation of primary amines is of importance, as it
adds to the body of knowledge on redox chemistry.
The products of oxidation depend on the type of oxi-
dant, on the reaction medium, and on the nature of the
Correspondence to: N. M. Made Gowda or S. Ananda (GN-
Made@wiu.edu)
*
Present address: M.C.E., Hassan-573 201, Karnataka, India
᭧
2000 John Wiley & Sons, Inc.

STUDIES OF SOME ALIPHATIC AMINES’ OXIDATION
777
alkyl groups present. Because of these, amines have
been oxidized by a number of oxidizing agents under
various experimental conditions.
at a LFER through the Taft treatment and an isoki-
netic relationship with the computed activation pa-
rameters.
Radhakrishriamurthi and Rao [7] have studied the
kinetics of oxidation of aniline and substituted anilines
by CAT in alkaline medium and observed a first-order
dependence of the rate on both CAT and aniline con-
EXPERIMENTAL
Ϫ
centrations and a zero-order dependence on [OH ].
The oxidant, bromanine-T, was prepared by a standard
procedure and its purity was checked iodometrically
and through UV, IR, and 13C-NMR spectral data
[15,16]. Aqueous solutions of BAT were prepared,
standardized by the iodometric method and preserved
in amber-colored bottles until use, to prevent its pho-
tochemical deterioration.
Aqueous solutions of analar grade n-propylamine
(E. Merck), n-butylamine (E. Merck), isobutylamine
(Sisco Chem.), and isoamylamine (Fluka) were pre-
pared and used. All other chemicals used were of ac-
ceptable grades of purity. A constant ionic strength of
the reaction mixture was maintained at 0.30 M by add-
The reactivity order shows that electron-withdrawing
groups retard the reaction. A mechanism leading to the
formation of azobenzene is postulated through a rate-
determining radical formation. The kinetics of oxida-
tion of benzoyl hydrazines by CAT [8] in the alkaline
pH 8.9–11.5 have shown a first-order dependence on
both [CAT] and [substrate] and a zero-order depen-
ϩ
dence on [H ]. The reaction is accelerated by electron-
withdrawing groups. Gupta and Agarwal [9] have re-
ported the oxidation kinetics of S-butylamine by CAT
in alkaline medium and the rate is first-order in [CAT],
Ϫ
[
amine], and [OH ]. Jabbar and Rao [10] have oxi-
dized methylamine, n-butylamine, diethylamine, and
triethylamine with N-bromophthalamide (NBP) in the
ing a required amount of a concentrated NaClO so-
lution. Triply distilled water was used for preparing
aqueous solutions.
4
presence of Hg(OAc) . The reaction rate shows a first-
2
order dependence on [NBP] and a fractional-order on
ϩ
[
amine] and [H ]. Saxena et al. [11] have studied the
Kinetic Measurement
oxidation of ethylamine, diethylamine, and triethylam-
ine by N-bromosuccinimide (NBS) catalyzed by pal-
ladium(II) in perchloric acid medium. Shukla and
Upadhyay [12] have investigated the mechanism of
The kinetic runs were performed under pseudo-first-
order conditions of [amine] ϾϾ [BAT] . Requisite
amounts of solutions of the amine, NaClO , and HCl
0
0
4
the PdCl -catalyzed oxidation of amines and amino
alcohols by hexacyonoferrate(III) in alkaline medium.
were taken in stoppered Pyrex glass tubes whose outer
surfaces were coated black to eliminate photochemical
effects. A required amount of water was added to
maintain a constant total volume for all runs. The tube
was thermostated in a water bath set at a given tem-
perature (30ЊC for most runs). To this solution was
added a measured amount of preequilibrated BAT so-
lution to give a known concentration. The reaction
mixture was periodically shaken for uniform concen-
tration. The progress of the reaction was monitored
iodometrically for two half-lives by withdrawing ali-
quots of the reaction mixture at regular time intervals.
Under pseudo-first-order conditions, rate constants, kЈ,
were reproducible within Ϸ3%. The regression anal-
ysis of experimental data was carried out on an EC-
75 statistical calculator.
2
A mechanism involving [Pd(II) Ϫ A ] or [Pd(II) Ϫ
1
A ] (where A represents amines and A represents
2
1
2
amino alcohols) as the intermediate complex is pro-
posed. Ananda et al. have reported the kinetics of un-
catalyzed [13] and Os(VIII)-catalyzed [14] oxidations
of n-propyl, n-butyl, and isoamyl amines by broma-
mine-B (BAB) in alkaline medium. The rate laws for
Ϫ
x
the two paths are: rate ϭ k [BAB] [amine] [OH ] and
Ϫ
y
rate ϭ k [BAB] [Os(VIII)] [OH ] , where x and y are
less than unity.
Most of the investigations reported on the oxidation
of amines with different oxidants were carried out in
alkaline medium. The literature reports are lacking on
the oxidation kinetics of amines in acid medium, es-
pecially using BAT as oxidant. For these reasons, in
the present communication we report the kinetics of
oxidation of four aliphatic primary amines, n-propyl-
amine (nPA), n-butylamine (nBA), isobutylmine
Stoichiometry and Product Analysis
Reaction mixtures containing different compositions
Ϫ2
(
(
iBA), and isopentyl or isoamylamine (iAA), by BAT
p-CH -C H -SO NBrNa · 3H O) in HCl medium. It
of amine, BAT, and 5.00 ϫ 10 M HCl were equi-
librated with occasional shaking at 30ЊC for 24 h. The
iodometric titration of unreacted BAT in the reaction
mixture showed that one mole of BAT was consumed
per mole of the amine.
3
6
4
2
2
is interesting to note that the present study involves
oxidation kinetics showing a different mechanism and
a different rate law. Attempts have been made to arrive

7
78
ANANDA ET AL.
Ϫ3
Table I Effects of Varying Reactant Concentrations on the Reaction Rate. [HCl] ϭ 0.0500 mol dm ; ␮ ϭ 0.30 mol
dm ; temp ϭ 30ЊC.
0
Ϫ3
5
Ϫ1
kЈ ϫ 10 (s )
4
2
1
(
0 [BAT]
10 [amine]
0
0
3
Ϫ
Ϫ3
mol dm )
(mol dm )
nPA
nBA
iBA
iAA
8
9
.00
.00
5.00
5.00
5.00
5.00
5.00
5.00
1.00
2.00
5.00
8.00
10.00
7.15
7.10
7.05
7.12
7.02
7.08
2.00
3.35
7.05
9.74
12.30
7.66
7.50
7.58
7.44
7.48
7.56
2.15
3.75
7.58
10.20
12.40
8.06
8.02
8.10
8.15
8.12
8.08
2.35
4.10
8.10
10.60
12.50
8.38
8.30
8.32
8.38
8.30
8.40
2.60
4.45
8.32
10.90
12.90
1
1
1
1
1
1
1
1
1
0.00
1.00
2.00
3.00
0.00
0.00
0.00
0.00
0.00
ϩ
R9CH NH ϩ TsNBrNa ϩ H O !:
[amine] were linear (r Ͼ 0.9989) with slopes of 0.74
(nPA), 0.64 (nBA), 0.62 (iBA), and 0.65 (iAA), thus
2
2
3
0
ϩ
ϩ
Ϫ
R9CHO ϩ TsNH ϩ NH4 ϩ Na ϩ Br . . .
2
(1)
indicating a fractional-order dependence on [amine].
where R ϭ CH CH2 for n-propylamine (nPA),
3
Effect of HCl
CH CH CH for n-butylamine (nBA), (CH ) CH for
3
2
2
3 2
isobutylamine (iBA), and (CH ) CHCH for isoamyl-
amine (iAA).
The presence of the corresponding aldehyde prod-
ucts of the amines in the reaction mixture was detected
by preparing their 2,4-dinitrophenylhydrazone deriv-
atives and by using Tollen’s and chromic acid tests
3
2
2
At constant [BAT] , [amine] , and temperature, the
0
0
rate of the reaction decreased with increase in [HCl]0
Table II). The plots of log kЈ vs. log [HCl] were
(
0
linear, with negative fractional slopes indicating an
inverse fractional-order of approximately Ϫ0.5 in
[acid].
[17]. The other product, ammonia, was quantitatively
estimated by the standard micro-Kjeldahl procedure.
The reduction product of BAT, p-CH C H SO NH or
3
6
4
2
2
Effects of Halide Ions, TsNH , and Ionic
Strength
2
TsNH , was identified by paper chromatography using
2
benzyl alcohol saturated with water as the solvent sys-
tem using 0.5% vanillin in 1% HCl in EtOH as the
Ϫ
Ϫ
The addition of Cl or Br ions in the form of NaCl
ϩ
or NaBr at constant [H ] and ionic strength did not
spray reagent (R ϭ 0.905) [18].
f
affect the rate. Hence the dependence of the rate on
ϩ
[
HCl] reflected the effect of [H ] only on the reaction.
The variation of ionic strength of the medium using
RESULTS
NaClO (0.12–0.30 M overall) had no effect on the
4
Effects of Varying Reactant Concentrations
Table II Effect of Varying [HCl] on the Reaction Rate.
The stoichiometry of the amine-BAT reaction was
found to be of 1 : 1 ratio. The reaction performed in
the presence of HCl, under pseudo-first-order condi-
tions of [amine] ϾϾ [BAT] , gave linear plots of log
Ϫ3
Ϫ3
[
1
BAT] ϭ 1.00 ϫ 10 mol dm ; [amine] ϭ 5.00 ϫ
0 0
Ϫ2
Ϫ3
Ϫ3
0
mol dm ; ␮ ϭ 0.30 mol dm ; temp ϭ 30ЊC.
5
Ϫ1
kЈ ϫ 10 (s )
0
0
2
1
0 [HCl]
0
3
[BAT] vs. time (r Ͼ 0.9985). The linearity of these
Ϫ
(
mol dm )
nPA
nBA
iBA
iAA
plots, together with the constancy of the slope for var-
1
3
5
8
.00
.00
.00
.00
13.00
9.00
7.05
5.60
4.82
13.30
9.30
7.58
6.10
5.26
13.70
9.70
8.12
6.65
5.90
14.00
10.50
8.38
6.90
6.14
ious [BAT] , indicates a first-order dependence of the
0
reaction rate on [BAT]. The pseudo-first-order rate
constants, kЈ, obtained at 30ЊC are listed in Table I.
Under the same experimental conditions, an increase
10.00
in [amine] increased the rate. Plots of log kЈ vs. log
0

STUDIES OF SOME ALIPHATIC AMINES’ OXIDATION
779
Test for Free Radicals
The addition of the reaction mixtures to aqueous ac-
rylamide monomer solutions, in the dark, did not ini-
tiate polymerization, indicating the absence of in situ
formation of free-radical species in the reaction se-
quence. The control experiments were also performed
under the same reaction conditions.
DISCUSSION AND MECHANISM
Pryde and Soper [19], Morries et al. [20], and Bishop
and Jennings [21] have shown the existence of similar
equilibria in acid and alkaline solutions of N-metallo-
N- haloarylsulfonamides. Bromamine-T (TsNBrNa or
p-CH C H SO NBrNa), like its chlorine analog chlor-
3
6
4
2
amine-T, behaves as a strong electrolyte in aqueous
solutions, forming different species as shown in Eqs.
(2)–(6):
Figure 1 Plots of 1/kЈ vs. 1/[S]: (A) nPA, (B) nBA, (C)
Ϫ3
Ϫ3
iBA, and (D) iAA. [BAT] ϭ 1.00 ϫ 10 mol dm ;
0
Ϫ
ϩ
TsNBrNa EF TsNBr ϩ Na
(2)
(3)
(4)
Ϫ3
Ϫ3
Ϫ3
[HCl] ϭ 5.00 ϫ 10
mol dm ; ␮ ϭ 0.30 mol dm ;
temp ϭ 30ЊC.
Ϫ
ϩ
TsNBr ϩ H EF TsNHBr
TsNHBr ϩ H O EF TsNH ϩ HOBr
2
2
rate. The addition of p-toluenesulfonamide or TsNH
2
Ϫ4
Ϫ3
(2.0 ϫ 10 Ϫ 1.0 ϫ 10 M) had no effect on the
d
KЈ
rate, indicating that it is not involved in a preequi-
librium to the rate-determining step.
2
TsNHBr E
R
F TsNH ϩ TsNBr2
(5)
(6)
2
ϩ
ϩ
HOBr ϩ H EF H OBr
2
Effect of Temperature on the Rate
In acid medium, the probable oxidizing species are
The reaction was studied by varying [amine] at each
temperature, in the range of 298 K to 313 K. From the
the free acid (TsNHBr), dibromamine-T (TsNBr ),
0
2
ϩ
HOBr, and H OBr . The involvement of TsNBr in
2
2
linear plots of 1/kЈ vs. 1/[S] (Fig. 1) at each tempera-
the mechanism leads to a second-order rate law ac-
cording to Eq. (5), which is contrary to the experi-
mental observations. As Eq. (4) indicates a slow hy-
drolysis, if HOBr were the primary oxidizing species,
a first-order retardation of the rate by the added TsNH2
would be expected, contrary to the observed results.
Hardy and Johnston [22], who have studied the pH-
dependent relative concentrations of the species
present in acidified haloamines’ solutions of compa-
ture, the rate constants k for the rate-determining step
3
of the reaction were obtained from the values of in-
tercept. The activation parameters, namely energy of
ꢀ
activation (E ), enthalpy of activation (⌬H ), and en-
a
ꢀ
tropy of activation (⌬S ), were obtained from the Ar-
rhenius and Eyring plots of ln k vs. 1/T and ln k /T
3
3
vs. 1/T, respectively. The kinetic and activation param-
eters obtained are presented in Table III.
Table III Temperature Dependence of k and Activation Parameters.
3
4
Ϫ1
k ϫ 10 (s )
3
ꢀ
ꢀ
⌬H
⌬S
Ea
Substrate
298 K
303 K
308 K
313 K
(kJ/mol)
(J/K mol)
(kJ/mol)
nPA
nBA
iBA
iAA
1.56
1.69
1.85
1.95
2.42
2.48
2.55
2.62
3.55
3.70
3.85
3.92
5.25
5.37
5.52
5.65
59.5
57.2
54.6
52.7
Ϫ118
Ϫ125
Ϫ134
Ϫ139
62.1
59.7
57.2
55.3

7
80
ANANDA ET AL.
ϩ
rable molarities, have shown that TsNHBr is the likely
oxidizing species in acid medium. Narayanan and Rao
species (Br ) of the oxidant at the nitrogen atom of
the substrate amine leads to the formation of an N-
bromo species, XЈ, and the reduction product TsNH2
(steps i and ii of Scheme II). In step iii, a nucleophilic
[23] and Subhashini et al. [24] have reported that
monohalomines can be further protonated at pH Ͻ 2,
as shown in the following Eqs. (7) and (8) for chlo-
ramine-T (CAT) and chlorarnine-B (CAB), respec-
tively:
Ѩϩ
attack by H O on the ␣-C atom of the C9N bond
2
of the neutral species, XЈ, and intramolecular rear-
rangements result in the formation of an imine inter-
mediate, XЉ, along with the elimination of H O and
Br . In step iv, the electrophilic ␣-C center of the im-
ϩ
3
ϩ
Ϫ
p-CH C H SO NHCl ϩ H EF
3
6
4
2
(CAT)
ϩ
ine intermediate undergoes a fast nucleophilic attack
p-CH C H SO NH Cl (7)
3
6
4
2
2
by H O followed by intramolecular rearrangements,
2
ϩ
forming an ␣-hydroxyamine intermediate. This step is
consistent with the observed negative reaction con-
stant ␳* (Ϫ0.06 and Ϫ12.6), suggesting a positive
charge development in the intermediate. This unstable
ϩ
C H SO NHCl ϩ H EF C H SO NH Cl (8)
6
5
2
6
5
2
2
(CAB)
The second protonation constants for CAT and CAB
are 102 and 61 Ϯ 5, respectively, at 25ЊC. Gupta [25]
believes that the values could be lower than those re-
ported by the above workers [23,24]. In the present
␣-hydroxyamine in the presence of acid dispropor-
tionates into the products aldehyde and ammonia,
where the latter forms an ammonium ion (step v).
From Scheme I,
ϩ
case, the inverse fractional order in [H ] suggests that
ϩ
the deprontonation of TsNH Br results in the regen-
2
rate ϭ Ϫd[BAT] /dt ϭ k [X]
(9)
t
3
eration of TsNHBr, which is likely to be the active
oxidizing species involved in the mechanism of the
amine oxidation. Based on the preceding discussion,
a mechanism (Scheme I) is proposed for the re-
action.
Then
[
X]
[TsNHBr] ϭ
(10)
(11)
(12)
K [S]
2
ϩ
[
TsNHBr] [H ]
ϩ
ϩ
K
1
[TsNH
2
Br ] ϭ
ϩ
TsNH Br E
R
F TsNHBr ϩ H
(i)
K1
2
(
fast)
ϩ
[
X] [H ]
ϩ
K
2
[TsNH Br ] ϭ
2
TsNHBr ϩ S E(
R
F
X
(ii)
K K [S]
1 2
fast)
(
complex)
The total effective concentration of BAT, from
Scheme I, is given by Eq. (13):
k
3
X 9
9
:
XЈ ϩ TsNH2
complex)
(iii)
(iv)
(v)
(
slow)
(
ϩ
[
BAT] ϭ [TsNH Br ] ϩ [TsNHBr] ϩ [X] (13)
t
2
ϩ
Ϫ
XЈ ϩ H O 9
9
:
XЉ ϩ H O ϩ Br
3
2
(fast)
By substituting for [TsNHBr] from Eq. (10) and for
(
complex)
ϩ
[
TsNH Br ] from Eq. (12) into Eq. (13) and solving
2
for [X], one gets
XЉ ϩ H O 99 : 99 : 99 : products
(fast) (fast)
2
Scheme I
K
ϩ
K
1
2
[BAT]
[S]
t
[X] ϭ
(14)
[
H ] ϩ K ϩ K K [S]
1
1
2
In Scheme I, S represents the amine substrate, nPA
or nBA or iBA or iAA, and X, XЈ, and XЉ represent
the complex intermediates, which are defined in
Scheme II.
The substitution for [X] in Eq. (9) leads to the fol-
lowing rate law [Eq. (15)]:
A detailed mechanistic interpretation of the amine-
BAT reaction in hydrochloric acid medium is pre-
sented in Scheme II. An initial equilibrium involves
rate ϭ Ϫd[BAT] /dt
t
K K k [BAT] [S]
1
2
3
t
ϭ
(15)
ϩ
ϩ
deprotonation of TsNH Br , forming the active oxi-
K
1
ϩ [H ] ϩ K
1
K
2
[S]
2
dizing species of BAT, TsNHBr (step i in Scheme I,
not shown in Scheme II). In the next fast preequili-
brium, an electrophilic attack of the positive bromine
The rate law is consistent with the experimental data,
including a first-order dependence of the rate on

STUDIES OF SOME ALIPHATIC AMINES’ OXIDATION
781
Scheme II
[
BAT], fractional-order dependence on [S or amine],
or
or
and a negative fractional-order dependence on [acid].
ϩ
K ϩ [H ]
1
Since the rate ϭ kЈ [BAT] , under pseudo-first-
1
1
1
t
ϭ
ϩ
(18)
(19)
ͭ
ͮ
order conditions of [amine] ϾϾ [BAT] , the rate
equation (15) can be transformed into Eqs. (16)–(19).
0
0
kЈ K k [S]
K1
k3
2
3
K K k [S]
1
2 3
kЈ ϭ
(16)
(17)
ϩ
ϩ
K ϩ [H ] ϩ K K [S]
1
[H ]
1
1
1
1
2
ϭ
ϩ
ϩ
ͭ
ͮ
or
kЈ K K k [S]
K k [S] k3
2 3
1
2
3
ϩ
1
1
[H ]
1
Based on Eq. (18), a plot of 1/kЈ vs. 1/[S] (Fig. 1) at
ϭ
ϩ
ϩ
ϩ
kЈ K k [S] K K k [S] k3
constant [H ], [BAT] , and temperature was found to
2
3
1
2
3
0

7
82
ANANDA ET AL.
ꢀ
ꢀ
ϩ
Figure 3 (a) A plot of ⌬H vs ⌬S and (b) an Exner plot
of log k (308 K) vs. log k (298 K).
Figure 2 Plots of 1/kЈ vs. [H ]: (A) nPA, (B) nBA, (C)
Ϫ3
Ϫ3
3
3
iBA, and (D) iAA. [BAT] ϭ 1.00 ϫ 10 mol dm ;
0
Ϫ2
Ϫ3
[
S or amine] ϭ 5.00 ϫ 10
mol dm ; ␮ ϭ 0.30 mol
Ϫ3
dm ; temp ϭ 30ЊC.
E were made by plotting log (k Ϫ E ) vs. ␴*, log k
3
s
3
s
vs. ␴*, and log k vs. E . The following regression
3
s
equations were found:
be linear (r Ͼ 0.9989) for each amine. Similarly, from
Eq. (19), a plot of 1/kЈ vs. [H ] (Fig. 2) at constant [S]
ϩ
log(k Ϫ E ) ϭ Ϫ12.6␴* Ϫ 5.2 (r ϭ 0.8987) (20)
3
s
or [amine] , [BAT] , and temperature was linear for
0
0
log k ϭ Ϫ1.8␴* Ϫ 3.6
(r ϭ 0.8567) (21)
each amine. The values of K , K , and k were cal-
3
1
2
3
culated from the slopes and intercepts of the plots. The
log k ϭ Ϫ0.06E Ϫ 3.6 (r ϭ 0.9976) (22)
3
s
protonation constant, Kp ϭ 1/K , of TsNHBr can be
1
evaluated from Eqs. (18) and (19); the data of K , K ,
A good correlation of log k with E in Eq. (22)
3 s
1
2
k3 , and Kp are presented in Table IV. The constancy
implies that steric effects play a dominant role in de-
termining the reaction rate. The implication of the
electronic effects on the rate is not clear from Eq. (21).
However, a reasonable correlation in Eq. (20) shows
that both steric and electronic factors have a synergis-
tic effect in determining the rate. The negative values
of the reaction constant ␳* (Ϫ0.06 and Ϫ12.6) suggest
that the presence of electron-donating groups in the
amine substrate increases the reaction rate.
of Kp or K values forms strong indirect evidence for
1
ϩ
the existence of the reactive species TsNH Br of the
2
oxidant, supporting the proposed mechanism of oxi-
dation of amines by BAT (Scheme I).
The existence of a linear free-energy relationship
for the oxidation of primary amines by BAT has been
evaluated [26]. Tests of the complete Taft equation as
well as single-parameter correlations with polar sub-
stitution constant ␴* and steric substitution constant
The data in Tables I and II show that the rate of
Table IV The Equilibrium and Protonation Constants Calculated from Eqs. (18) and (19).
1
02 ϫ K1
1/K ϭ Kp
(dm /mol)
1
3
3
(mol/dm )
4
k ϫ 10
(s )
K
2
3
Ϫ
1
3
Substrate or S
(dm /mol)
a
b
a
b
nPA
nBA
iBA
iAA
2.42
2.48
2.55
2.62
32.0
31.6
31.2
30.8
2.07
2.12
2.13
2.14
2.04
2.11
2.12
2.12
48.3
47.2
47.0
46.7
49.0
47.4
47.2
47.2
a
The values of K and Kp calculated from the plot of 1/kЈ vs. 1/[S].
1
b
ϩ
The values of K and Kp calculated from the plot of 1/kЈ vs. [H ].
1

STUDIES OF SOME ALIPHATIC AMINES’ OXIDATION
783
oxidation of the amines by BAT increases in the order
nPA Ͻ nBA Ͻ iBA Ͻ iAA, indicating a combined
effect of the electronic and steric factors of the alkyl
groups in amines.
7. Radhakrishnamurthi, P. S.; Prasad Rao, M. D. Indian J
Chem 1976, 14B, 790.
8
. Ramaiah, A. K.; Rao, P. V. K. Indian J Chem 1980,
9A, 1120.
. Gupta, J.; Agrawal, M. C. Indian J Chem 1989, 28A,
100.
0. Jabbar, S. F. A.; Rao, V. S. Indian J Chem 1994, 33A,
9.
1
9
The relative magnitudes of activation energies for
the oxidation of the amines, in Table III, which support
the preceding trend, indicate that the reactions are en-
thalpy controlled. This is verified by calculating the
isokinetic temperature (␤) from the slope of a linear
1
1
1
6
1. Sexena, R.; Shukla, A.; Upadhyay, S. K. Transition Met
Chem 1994, 19, 91.
12. Shukla, A.; Upadhyay, S. K. Indian J Chem 1995, 34A,
130.
3. Ananda, S.; Demappa, T.; Mahadevappa, D. S.; Made
Gowda, N. M. Int J Chem Kinet 1996, 28, 873.
4. Ananda, S.; Demappa, T.; Made Gowda, N. M. Int J
Chem Kinet 1997, 29, 737.
ꢀ
ꢀ
plot of ⌬H vs. ⌬S (Fig. 3, r ϭ 0.9999). The ␤ value
of 350 K, which is higher than the experimental range
used in the present study, implies that the substrate
oxidation is enthalpy controlled. A further confirma-
tion of the existence of the isokinetic relationship was
inferred from the Exner criterion [27], by plotting log
k (308 K) vs. log k (298 K), which yielded a linear
1
1
1
5. Ahmed, M. S.; Mahadevappa, D. S. Talanta 1980, 27,
3
3
669.
plot (r ϭ 0.9973). The Exner slope gave a value of ␤
1
1
6. Nair, C. G. R.; Indrasenan, P. Talanta 1976, 23, 239.
7. Feigl, F. Spot Tests in Organic Analysis; Elsevier; Am-
sterdam, 1975.
ꢀ
3
47 K. The fairly negative values of ⌬S indicate the
formation of a rigid associative transition state in each
case.
18. Mahadevappa, D. S.; Made Gowda, N. M. Talanta 1975,
2, 771.
2
1
2
9. Soper, F. G. J Chem Soc Trans 1924, 125, 1899.
0. Marris, J. C.; Salazar, J. A.; Wineman, M. A. J Am
Chem Soc 1948, 70, 2036.
BIBLIOGRAPHY
2
1. Bishop, E.; Jennings, V. J. Talanta 1958, 1, 197.
1
2
. Campbell, M. M.; Johnson, G. Chem Rev 1978, 78, 65.
. Banerji, K. K.; Jayanam, B.; Mahaderappa, D. S. J Sci
Ind Res 1987, 46, 65.
22. Hardy, F. E.; Johnston, J. P. J Chem Soc, Perkin Trans
2 1973, 742.
23. Narayanan, S. S.; Rao, V. R. S. Radiochem Acta 1983,
32, 211.
24. Subhashini, M.; Subramanian, M.; Rao, V. R. S. Talanta
1985, 32, 1082.
25. Gupta, Y. K. Jodhpur University, Jaipur, India, Private
Communications 1988.
3
4
5
. Ruff, F.; Kucsman, A. J Chem Soc, Perkin Trans 2
1
982, 1075.
. Mahadevappa, D. S.; Puttaswamy, Bull Chem Soc Ja-
pan 1988, 61, 543.
. Rangappa, K. S.; Ramachandra, H.; Mahadevappa,
D. S.; Made Gowda, N. M. Int J Chem Kinet 1996, 28,
26. Gillion, R. D. Introduction to Physical Organic Chem-
istry; Addison-Wesley: London, 1970; pp 156–160,
264.
2
65.
6
. Puttaswamy, Ramachandrappa, R. Transition Met
Chem 1999, 24, 326.
27. Exner, O. Coll Czech Chem Commun 1964, 29, 1095.