Oxidation of n-propylamine and n-butylamine by chloramine-B and chloramine-T in basic medium: A kinetic study

Article abstract of DOI:10.1080/15533171003766329

The oxidation of aliphatic primary amines, n-propylamine (PA) and [image omitted]-butylamine (BA), by chloramine-B (CAB) and chloramine-T (CAT) in aqueous alkaline medium has been kinetically studied at 318 K. The reaction follows the experimental rate law: rate [image omitted] k' [oxidant] [amine]^o [OH-]^X, where oxidant is CAT or CAB and x is fractional. Additions of chloride ions, the reduction product, sulfonamide, and sodium perchlorate, which is used for changing the ionic strength of the solvent medium, have no effect on the reaction rate. However, the rate varies with change in dielectric constant of the medium. The reaction has been studied in the temperature range, 313-323K, and the activation parameters have been evaluated. A suitable mechanism consistent with the observed kinetic data has been proposed and the rate law derived. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/15533171003766329

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 40:225–230, 2010
Copyright © Taylor & Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533171003766329
Oxidation of n-Propylamine and n-Butylamine by
Chloramine-B and Chloramine-T in Basic Medium:
A Kinetic Study
1
2
3
M. K. Veeraiah, A. S. Ananda Murthy, and Netkal M. Made Gowda
1
Department of Chemistry, Sri Siddhartha Institute of Technology, Tumkur, India
Department of Studies in Chemistry, Manasagangothri, University of Mysore, Mysore, India
Department of Chemistry, Western Illinois University, Macomb, IL, USA
2
3
been reported.[
The oxidation of aliphatic primary amines, n-propylamine (PA) ies on the oxidation of aliphatic primary amines, n-propylamine
and n-butylamine (BA), by chloramine-B (CAB) and chloramine-T
7−11]
The present paper reports the kinetic stud-
(
PA) and n-butylamine (BA) by CAT and CAB in aqueous
sodium hydroxide solutions.
(
CAT) in aqueous alkaline medium has been kinetically studied at
18 K. The reaction follows the experimental rate law: rate = k
ꢀ
3
0 − x
[
oxidant] [amine] [OH ] , where oxidant is CAT or CAB and x is
fractional. Additions of chloride ions, the reduction product, sul-
fonamide, and sodium perchlorate, which is used for changing the
ionic strength of the solvent medium, have no effect on the reaction
rate. However, the rate varies with change in dielectric constant
of the medium. The reaction has been studied in the temperature
range, 313–323K, and the activation parameters have been eval-
EXPERIMENTAL
Materials
Chloramine-T (Loba) was purified by the method of Morris
[
12]
and coworkers.
Chloramine-B was prepared by a standard
uated. A suitable mechanism consistent with the observed kinetic method.[ Approximately 0.10 mole dm stock solutions of
12]
−3
data has been proposed and the rate law derived.
CAT and CAB were prepared and standardized by iodometric
method and used. The solutions were stored in amber colored
bottles. The two amines used, n-propylamine and n-butylamine
Keywords kinetics, oxidation, amines, n-propylamine and n-
butylamine, Chloramine-T, Chloramine-B, mechanism,
rate law
(SD Fine or Sisco Research Chemicals, India), were purified
by distillation. All other reagents were of analytical grades of
purity. All aqueous solutions were prepared in triply distilled
water.
INTRODUCTION
Sodium salts of N-halo derivatives of arylsulphonamide
are N-metallo-N-Arylhalosulphonamides. The important mem-
bers of this class of haloamine compounds are: chloramine-
T (p-CH3C6H4SO2NClNa.3H2O or CAT) and chloramine-B
Kinetic Measurement
Kinetic runs were carried out under pseudo first order con-
ditions of [amine]o ꢁ [oxidant]o at a constant temperature.
[11]
C6H5SO2NClNa 1.5H2O or CAB). Bishop and Jennings[
1]
The constant temperature (e.g., 318 ± 0.1 K) was maintained
using a water bath. Requisite amounts of solutions of the amine
(PA or BA), NaOH, and perchlorate (to maintain a constant ionic
strength) were mixed in a stoppered Pyrex glass tube. Required
volume of water was added to maintain a known total volume
of the reaction mixture. The tube was thermostated at 318 K.
The reaction was initiated by adding a measured amount of pre-
equilibrated, standard CAB or CAT solution into the above tube
and the reaction mixture was shaken periodically. The progress
of the reaction was monitored by iodometric titrations of the
unreacted oxidant present in aliquots against a standardized
(
have reported some important characteristics of CAT solutions.
[2]
Higuchi and Coworkers have published an extensive study of
the concentrations of various species present in aqueous solu-
tions of 0.05 M CAT at different pH values. Both CAT and CAB
have been widely used in oxidation studies and mechanisms
[
3−6]
of their reactions have been investigated.
Oxidations of
amines by oxidants such as N-bromosuccinamide, bromamine,
cerium(IV), aqueous chlorine, bromamine-T and Mn(III) have
12
Na2S2O3 solution at various time periods . The pseudo-first
Received 19 November 2009; accepted 12 January 2010.
Address correspondence to M. K. Veeraiah and N. M. Made Gowda,
Department of Chemistry, Western Illinois University, Macomb, IL
|
order rate constants, k , were calculated from plots of ln [ox] vs.
time or ln (titer) vs time (where ox = CAT or CAB). Values of
|
61455, USA. E-mail: GN-Made@wiu.edu
k are accurate within ± 3%.
225

226
M. K. VEERAIAH ET AL.
RESULTS
TABLE 1
Effects of [CAT]0 and [CAB]0 on the reaction rate
Stoichiometry and Product Analysis
−2
−2
[
PA]0 = [BA]0 = 5.00 × 10 M, [NaOH] = 5.00 × 10 M,
Reaction mixtures containing varying compositions of the
amine and oxidant in 0.05 M NaOH were stirred for 24 hrs at 318
K. The unconsumed oxidant was determined iodometrically.[
Based on these data, the number of moles of CAB or CAT
consumed per mole of the amine was calculated, which showed
a mole ratio of 1:1. The following general equation represents
the reaction stoichiometry:
µ = 0.500 M, T = 318 K
11]
4
ꢀ
–1
10 k (s )
1
03[CAT]0 (M)
Or
0 [CAB]0 (M)
CAT
CAB
PA
3
1
PA
BA
BA
3
4
5.00
.00
.00
1.05
1.03
1.04
1.06
1.04
0.86
0.87
0.87
0.86
0.86
1.06
1.01
1.05
1.00
1.00
1.23
1.27
1.30
1.32
1.30
−
RCH2NH2 + ArSO2NCl + H2O
−
→
RCHO + NH3 + ArSO2NH2 + Cl
[1]
6
7
.00
.00
where R = ethyl or propyl group and Ar = C6H5 for CAB and
p-CH3C6H4 for CAT.
In each case, the oxidation products were identified as the
The rate constant increased with an increase in [NaOH] when
corresponding aldehyde (propionaldehyde or n-butyraldehyde), the other reaction conditions were kept constant (Table 3). The
ammonia, and p-toluenesulphonamide (PTS) or benzene- order of the reaction with respect to the hydroxide ion concen-
|
sulphonaminide (BSA). The aldehydes were identified by tration, calculated from the slope of the linear plot of ln k vs
−
preparing their orange 2,4-dinitrophenylhydrazone (2,4-DNP) ln [OH ], was found to be fractional, in each case. The orders
derivatives[
13,14]
and by Tollen’s reagent test.
[14]
Furthermore, obtained were: 0.35 and 0.33 for PA and BA, respectively, for
the aldehydes were characterized by melting points of 2,4-DNP the CAT reaction and 0.56 and 0.53, respectively, for the CAB
derivatives, which were consistent with the reported values for reaction.
2,4-DNP derivatives of propionaldehyde and n-butyraldehyde.
Addition of the reduction product, PTS or BSA, to the re-
Ammonia liberated during the reaction was quantitatively mea- action mixtures had no significant effect on the rate. Also, the
sured using a slightly modified micro-Kjeldahl procedure.[
13,15]
ꢀ
addition of sodium chloride and perchlorate did not affect k
The reduction products, benzenesulphonamide (BSA) and values suggesting that the chloride ions and the ionic strength
p-toluene-sulfonamide, in the reaction mixtures were isolated of the medium (µ) had no effect on the reaction rate. Varying
using solvent extraction with diethylether, recrystallized from the solvent composition using MeOH (up to 30% (v/v)) showed
the dichloromethane-petroleum ether mixture (1:1 v/v) and that the rate increased with increasing concentrations of MeOH
identified by TLC (PTS, Rf = 0.26 with a mobile phase of (i.e., decreasing dielectric constant D of the medium), as shown
ꢀ
dichloromethane; BSA, Rf = 0.88 with a mixture of petroleum in Table 4. Plots of ln k vs 1/D were linear up to 20% MeOH
ether, chloroform and n−butanol (2:2:1 – v/v/v); and iodine de- and with further increase in MeOH content the curve leveled off
veloping agent. Furthermore, mass spectra obtained on a 70 eV with CAT and decreased slightly with CAB.
Shimadzu GCMS-QP5050 spectrometer showed parent molec-
The temperature effect on the reaction rate was studied at
ular ion peaks at m/z 157 amu and 171 amu for BSA and PTS, different temperatures (313–323 K) by keeping all other con-
ꢀ
respectively, confirming their identities.
ditions the same and the k values are listed in Table 5. Based
TABLE 2
Effects of [PA] and [BA] on the reaction rate
Kinetics
−3
−2
[
CAT]0 = [CAB]0 = 5.00 × 10 M, [NaOH] = 5.00 × 10
The reactions were studied under pseudo-first-order condi-
tions of [amine]o ꢁ [ox]o, at several initial concentrations of the
oxidant (ox = CAT or CAB) while keeping the other reaction
M, µ = 0.500 M, T = 318 K
4
ꢀ
−1
1
0 k (s )
−
conditions such as [amine]0, [OH ], ionic strength, solvent and
temperature constant.
Plots of ln [ox] vs. time were found to be linear (e.g.,
r > 0.996, plots not shown) showing a first-order dependence
CAT
CAB
PA
1
02[Amine]0 (M)
PA
BA
BA
of the reaction rate on [ox]. Pseudo-first-order rate constants
2.50
5.00
7.50
10.0
0.96
1.04
1.06
1.08
0.85
0.87
0.87
0.89
0.97
1.05
1.07
1.09
1.22
1.30
1.33
1.40
ꢀ
(
k ) obtained with varying [ox]0, which are nearly constant,
are presented in Table1. Under identical conditions, increase in
|
[
amine]0 did not affect the rate. The values of k at different
concentrations of PA and BA are given in Table 2.

OXIDATION OF N-PROPYLAMINE AND N-BUTYLAMINE
227
TABLE 3
Effect of [NaOH] on the reaction rate
PA]0 = [BA]0 = 7.50 × 10− M, [CAT]0 = [CAB]0 = 5.00 × 10 M, µ = 0.500 M, T = 318 K
2
−3
[
PA
BA
CAT
10 k (s )
CAB
10 k (s )
CAT
10 k (s )
CAB
10 k (s )
02[NaOH] (M)
4
|
–1
4
|
–1
4
|
–1
4
|
–1
1
2
5
7
.50
.00
.50
0.820
1.04
1.20
1.33
0.680
1.05
1.26
1.49
0.680
0.87
0.98
1.07
0.920
1.30
1.65
1.90
1
0.0
ꢀ
−
+
on the Arrhenius plot of ln k vs 1/T and the Eyring plot of ln
ArSO NCl + H ꢁ ArSO NHCL
[4]
2
ꢂ
2
ꢀ
(
k /T) vs 1/T, activation parameters for the composite reaction,
2
ArSO2NHCl ꢁꢂ ArSO2NH2 + ArSO2NCl2 [5]
ꢂ=
namely, energy of activation (Ea), enthalpy of activation (ꢀH ),
+
+
ArSO2NHCl + H ꢁꢂ ArSO2NH2Cl
[6]
[7]
ꢂ
and entropy of activation (ꢀS ) were calculated (Table 6).
ArSO2NHCl + H2O ꢁꢂ ArSO2NH2 + HOCl
ArSO2NCl2 + H2O ꢁꢂ ArSO2NHCl + HOCl
[8]
Test for Free Radicals
+
−
HOCl ꢁꢂ H + OCl
[9]
Alkene monomers, acrylonitrile and 10% acrylamide so-
lution, under nitrogen atmosphere, were added to the amine-
oxidant reaction mixtures in 0.0500 M NaOH to initiate poly-
merization in the presence of free radicals formed in situ in
dark.A suitable control was also run. A lack of turbidity ob-
served in the solutions indicated the absence of in situ formation
of free radicals.[
+
+
HOCl + H ꢁ H OCl
[10]
ꢂ
2
where Ar = p − CH3C6H4−
In alkaline solutions, Hardy and Johnston[3,16] have reported
the existence of equilibria (11)-(13) for CAT, which are also
applicable to CAB.
17]
−
−
ArSO2NCI + H2O ꢁꢂ ArSO2NHCI + OH
[11]
[12]
[13]
DISCUSSION
−
−
ArSO2NCI + H2O ꢂ
ꢁ
ArSO NH + OCI
The kinetic data show the following experimental rate law:
2
2
−
−
OCI + H2O ꢁꢂ HOCl + OH
ꢀ
− X
rate = – d[oxidant]/dt = k [oxidant][OH ]
[2]
The concentration of each species depends on the pH and
nature of the medium.[ As a result, CAB and CAT react
In aqueous acid solutions, CAB and CAT behave as elec- with a wide range of functional groups affecting an array of
3]
where oxidant = CAB or CAT and x is a fractional value.
trolytes as shown in the following equilibria [3–10][
3,12,16]
.
molecular transformations. In acid solutions, the probable ox-
idizing species are the free acid (ArSO2NHCl), dichloramine-
[3] T (ArSO2NCl2), HOCl and H2OCl . In alkaline solutions of
ArSO2NClNa ꢁꢂ ArSO2NCl + Na+
−
+
TABLE 4
Effect of dielectric constant (D) of the medium on the reaction rate
PA]0 = [BA]0 = 7.50 × 10− M, [CAT]0 = [CAB]0 = 5.00 × 10 M, [NaOH] = 5.00 × 10 M, µ = 0.500 M, T = 318 K
2
−3
−2
[
PA
BA
CAT
10 k (s )
CAB
10 k (s )
CAT
10 k (s )
CAB
10 k (s )
2
4
|
–1
4
|
–1
4
|
–1
4
|
–1
[Me OH] (%, V/V)
D
10 /D
0
.0
76.72
72.37
69.93
67.48
62.71
1.30
1.38
1.43
1.48
1.60
1.04
1.24
1.32
1.38
1.44
1.05
1.27
1.35
1.51
1.34
0.87
1.06
1.10
1.20
1.21
1.30
1.49
1.55
1.68
1.38
1
1
2
3
0.0
5.0
0.0
0.0

228
M. K. VEERAIAH ET AL.
TABLE 5
Effect of temperature on the reaction rate
PA]0 = [BA]0 = 7.50 × 10− M, [CAT]0 = [CAB]0 = 5.00 × 10 M, [NaOH] = 5.00 × 10−2 M, µ = 0.500 M
2
−3
[
PA
BA
CAT
10 k (s )
CAB
10 k (s )
CAT
10 k (s )
CAB
10 k (s )
4
|
–1
4
|
–1
4
|
–1
4
| –1
Temperature (K)
313
316
318
321
323
0.740
0.930
1.04
1.32
1.48
0.720
0.900
1.05
1.35
1.55
0.580
0.770
0.870
1.15
1.02
1.17
1.30
1.55
1.66
1.38
+
CAB or CAT, ArSO2NCl2, and H2OCl do not exist. Therefore,
K
1
NCl-
+
H O
NHCl
+
OH-
fast
(i)
ArSO
ArSO
2
2
2
−
the expected reactive species are ArSO2NHCl, HOCl, OCl
and ArSO2NCl . The species ArSO2NCl and OCl could be
transformed into more reactive oxidizing species ArSO2NHCl
and HOCl through reactions (eqs. 11–13). If HOCl and OCl
were the primary oxidizing species, as indicated by eqs. (7) and
12), a first-order retardation of the rate by the added ArSO2NH2
−
−
−
k2
ArSO NHCl + OH-
OCl-
ArSO NH2
+
slow
fast
f ast
(ii)
(iii)
(iv)
2
2
−
OCl- + amine
Complex X
Complex X
products
........
(
would be expected, which is contrary to the experimental ob-
SCH. 1.
servations. If ArSO2NHCl were the reactive species, retardation
−
of the rate by [OH ] would be expected (eq. 11), which is also trophilically attacks the amino N atom in a fast step to form an
−
contrary to the experimental observations. Hence, ArSO2NCl
N-Cl complex anion (X). In another fast step, X undergoes in-
is the first likely oxidizing species as the rate increases with the tramolecular rearrangements to give a chloramine intermediate
−
ꢀ
−
increase in [OH ]. Under the present experimental conditions, (complex X ) and OH . In the next fast step, the chloramine
ꢀ
−
the kinetic results of a first order dependence on [oxidant], zero intermediate X interacts with a nucleophile (OH ) and under-
order on [amine], and fractional order on [OH ] and zero effect goes rearrangements to form an imine intermediate (complex
of the added reduction product PTS/BSA can be explained by X ’) after eliminating H O and Cl . The hydrolysis of imine
considering Scheme1 as shown below.
−
ꢀ
−
2
ꢀ
ꢀ
(X ’) forms the intermediate (X ”), which on intramolecular re-
In Scheme 1, the oxidant species ArSO2NHCl formed in the arrangements leads to the formation of the aldehyde end-product
−
fast pre-equilibrium (step (i)) interacts with OH in the slow along with ammonia.
−
step to form the most reactive species OCl , which then re-
Based on the slow/rate determining step (ii), the rate law
acts with the substrate-amine in several fast steps to form the obtained is as follows:
end products as shown in Scheme 2. Scheme 2 shows the de-
−
tailed electron-pushing mechanism of oxidation of amines. The
rate = −d[oxidant]/dt = k [ArSO NHCl][OH ]
[14]
2
2
−
reactive oxidant species OCl formed in the slow step elec-
The total effective concentration of the oxidant is given by,
TABLE 6
−
[
oxidant]tot = [ArSO2Cl ] + [ArNSO2HCl]
Activation parameters for the oxidation of PA and BA by CAT
∗
and CAB in NaOH medium
where
Or
CAT
CAB
PA
[
oxidant]tot = [CAB]tot or [CAT]tot
Activation parameter
PA
BA
BA
−
1
Ea/kJ mol
ꢀ
58.7
56.1
5.66
72.3
69.7
7.82
65.3
62.6
6.74
42.2
39.6
3.04
−
After substitution for [ArNSO2Cl ] from step (i) of Scheme
and after proper rearrangements, one gets the derived rate law
ꢂ
=
−1
H /kJ mol
1
[
log A
eq. (15)].
ꢂ=
−1
−1
ꢀ
ꢀ
S /JK mol
G /kJ mol
−137.1
−95.8
−117. −187
ꢂ
=
−1
99.7
100.
99.6 99.1
−
[
ArNSO2HCl][OH]
[
oxidant]tot =
+ [ArNSO2HCl]
∗
Conditions are as shown in Table 5.
K1[H2O]

OXIDATION OF N-PROPYLAMINE AND N-BUTYLAMINE
229
-
Cl
O
H
H
R-CH -N
+
ClO
R-CH -N
2
H
2
H
(amine)
(reactive ox)
(complex X)
-
Cl
O
Cl
H
R-CH -N
H
OH-
2
R-CH -N
+
2
H
(
complex X')
(
complex X)
OH-
H
Cl
R
C
H
+ H O + Cl-
NH
2
R
(
C
H
N
H
(complex X'')
complex X')
FIG. 1. Double reciprocal plots for the amine-chloramine reactions at 318 K
H
H
O
Or
O
H
H
R
C
H
NH
R
C
H
N-H
1
1
1
=
+
−
[16]
|
(complex X''')
k
k2[OH ]
K1k2[H2O]
(
complex X'')
|
−
Thus plots of 1/k vs 1/[OH ], derived from data in Table 3,
were found to be linear, as seen in Figure 1. The values of k2
−1 −1
R
C
H
O
+ NH3
(M
6
s ) evaluated form the slope and intercept are found to be
−4
−4
.63 × 10 and 5.73 × 10 for PA and BA, respectively, with
−4
−4
CAT as oxidant and 3.8 × 10 and 5.45 × 10 , respectively,
(aldehyde)
with CAB as oxidant.
SCH. 2. Mechanism of the amine oxidation by CAB or CAT in basic medium.
The zero effect of BSA or PTS and ionic strength on the
reaction rate also supports Scheme 1. The effect of varying
[18]
solvent composition on the rate has been described by Laidlar
Or
[19]
[20]
and Benson.
Amis and Jaffe
have derived a relationship
for the variation of the rate constant as a function of the dielectric
constant (D) of the medium for the interaction between an ion
and a dipolar molecule as
−
[
ArNSO2HCl][OH ] + K1[H2O][ArNSO2HCl]
[
oxidant]tot =
K1[H2O]
|
|
2
Or
log k = log k + (Zeµ/2.303 k T r D)
[17]
D
∞
K1[oxidant]tot[H2O]
K1[H2O] + [OH−]
It is evident from equation (17) that the rate constant will
increase on decreasing D. In the present case, it is found that
the rate increases with decrease in D as expected for an ion-
dipole interaction in the rate determining step (step (ii)). The
values of energy of activation and other activation parameters
also support Scheme 1. A probable mechanism of oxidation is
given in Scheme 2.
[
ArNSO2HCl] =
Or
−
K1k2[oxidant]tot[OH ][H2O]
rate =
[15]
K1[H2O] + [OH−]
The rate law [eq. 15] derived from Scheme 1 is thus in agree-
ment with the experimental rate law (eq. (2)). It is also possible
to transform eq. (15) into the following equations:
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1
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6
97; ibid, 1962, 9, 581,593.
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−
3. Campbell, M.M., and Johnston, G. Chem. Rev. 1978, 78, 65.
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K1k2[OH ][H2O]
|
k =
K1[H2O] + [OH−]
4
6, 65–76.

230
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