Oxidation of 2-phenylethylamine with N-bromosuccinimide in acid and alkaline media: A kinetic and mechanistic study

Article abstract of DOI:10.1002/jccs.200700173

A kinetic study of oxidation of 2-phenylethylamine (PEA), a bioactive compound, with potent oxidant, N-bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimental rate laws obtained are: -d [NBS]/dt = k[NBS][PEA][H⁺] in hydrochloric acid medium and -d [NBS]/dt = k[NBS][PEA]^x[OH^-]^y in alkaline medium where x and y are less than unity. Accelerating effect of [Cl ^-], and retardation of the added succinimide on the reaction rate have been observed in acid medium. Variation of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The reactions were studied at different temperatures and the activation parameters have been evaluated. The reaction constants involved in the proposed mechanisms were computed. The reaction was found to be faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the observed experimental results.

Full text of DOI:10.1002/jccs.200700173

Journal of the Chinese Chemical Society, 2007, 54, 1223-1232
1223
Oxidation of 2-Phenylethylamine with N-Bromosuccinimide in Acid and
Alkaline Media: A Kinetic and Mechanistic Study
Kikkeri N. Mohana* and Paanemangalore M. Ramdas Bhandarkar
Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore - 570 006, India
A kinetic study of oxidation of 2-phenylethylamine (PEA), a bioactive compound, with potent oxi-
dant, N-bromosuccinimide (NBS) has been carried out in HCl and NaOH media at 313 K. The experimen-
+
tal rate laws obtained are: -d [NBS]/dt = k[NBS][PEA][H ] in hydrochloric acid medium and -d [NBS]/dt
x
k[NBS][PEA] [OH ] in alkaline medium where x and y are less than unity. Accelerating effect of [Cl ],
- y
-
=
and retardation of the added succinimide on the reaction rate have been observed in acid medium. Varia-
tion of ionic strength of the medium shows negligible effect on rate of reaction in both media. Decrease in
dielectric permittivity of the medium decreased the rate in both media. The stoichiometry of the reaction
was found to be 1:1 in acid medium and 1:2 in the case of alkaline medium. The oxidation products of PEA
were identified as the corresponding aldehyde and nitrile in acid and alkaline medium, respectively. The
reactions were studied at different temperatures and the activation parameters have been evaluated. The
reaction constants involved in the proposed mechanisms were computed. The reaction was found to be
faster in alkaline medium in comparison with the acid medium, which is attributed to the involvement of
different oxidizing species. The proposed mechanisms and the derived rate laws are consistent with the
observed experimental results.
Keywords: Oxidation kinetics; N-Bromosuccinimide; Acid and alkaline media;
2
-Phenylethylamine.
9
oxidation of esters, alcohols
10,11
12,13
INTRODUCTION
and ketones.
In the
present work the kinetics of oxidation of PEA with NBS in
acid and alkaline media has been studied with a view to elu-
cidate the mechanism of the reaction and to identify the re-
active species of oxidant in acid and alkaline media.
2
-Phenylethylamine (PEA) is a naturally occurring
endogenous amine, which is present in several mammalian
1
tissues including the brain. 2-Phenylethylamine is formed
3
by decarboxylation of amino acid, L-phenylalanine. It
2
crosses the presynaptic membrane and potentiates the post-
4
synaptic effects of dopamine. PEA may act as neuromod-
RESULTS
4
ulator of catecholamine neurotransmission in the brain.
This bioactive amine is also present in certain foodstuffs
such as chocolate, cheese and wine and may cause undesir-
5
able side effects in susceptible individuals. After review-
The oxidation of PEA with NBS was kinetically in-
vestigated at several initial concentrations of the reactants
in HCl and NaOH media. The salient features obtained in
these two media are discussed separately.
ing the literature we found that there was no information
available on the oxidation kinetics of 2-phenylethylamine
with any oxidant. In view of its biological importance, the
present study was undertaken to deal with the oxidation
mechanism of PEA in acid and alkaline media so that the
study could throw some light on the fate of the compound
in biological systems.
Kinetics of oxidation in acid medium
Under pseudo-first-order conditions ([PEA] >> [NBS])
at constant [HCl] and temperature, plots of log [NBS] vs.
time were linear (r > 0.994) indicating a first-order depend-
o
ence of rate on [NBS] . The pseudo-first-order rate con-
N-bromosuccinimide (NBS) is a source of positive
halogen, and this reagent has been selectively used as an
oxidant for a variety of substrates in both acid and alkaline
stants (k¢) calculated are given in Table 1. Further, the val-
ues of k¢ calculated from these plots are unaltered with vari-
ation of [NBS]
o
, confirming the first-order dependence on
(Table
6
-8
media. This potent oxidizing agent has been used in the
[NBS] . The rate increased with increase in [PEA]
o
o

1
224 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Mohana and Ramdas Bhandarkar
+
-
Table 1. Effect of varying concentrations of oxidant, substrate
and HCl on the reaction rate at 313 K
Table 2. Effect of varying concentrations of H and Cl on the
reaction rate at 313 K
4
0 [NBS]
3
10 [PEA]
-3
(mol dm )
2
10 [HCl]
-3
(mol dm )
4
2
+
10 [H ]
2
-
10 [Cl ]
4
1
k ´ 10
-1
(s )
k ´ 10
-1
(s )
-
3
mol dm )
-3
(mol dm )
-3
(mol dm )
(
1
3
5
7
9
5
5
5
5
5
5
5
5
5
5
.0
08.0
08.0
08.0
08.0
08.0
06.0
10.0
12.0
14.0
08.0
08.0
08.0
08.0
08.0
08.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
4.0
6.0
7.0
9.0
5.0
5.0
3.62
3.70
3.56
3.42
3.67
2.69
4.60
5.98
6.81
2.50
4.79
6.20
8.87
3.62
3.66
3.0
5.0
7.0
9.0
10.0
5.0
5.0
5.0
5.0
5.0
15.0
15.0
15.0
15.0
15.0
06.0
08.0
10.0
12.0
14.0
03.27
05.66
08.04
10.12
11.39
04.31
04.72
05.07
05.37
05.60
-3
.0
.0
.0
.0
.0
.0
.0
.0
.0
.0
-4
-3
-3
[
NBS] = 5 ´ 10 mol dm ; [PEA] = 8 ´ 10 mol dm ; m = 0.25
.0
-3
mol dm
.0
.0*
.0**
of chloride ions in the form of NaCl increases the reaction
-
at ionic strength (m) = 0.5 mol dm and ** at m = 0.75 mol dm
3
-3
*
rate and is shown in Table 2. From the plot of log k¢ vs. log
-
Cl ] (Fig. 2; r = 0.999), the order with respect to [Cl ] is
-
[
found to be 0.32. Addition of succinimide (NH) to the reac-
tion mixture retards the rate (Table 3). Further, a plot of log
k¢ vs. log [NH] was linear (r = 0.992) with a negative slope
of 0.65 indicating an inverse fractional-order dependence
of the rate on [NH]. Variation of ionic strength of the me-
1
0
). A plot of log k¢ vs. log [PEA] was linear (Fig. 1; r =
.996) with the unit slope showing first-order dependence
o
of the rate on [PEA] . Similarly, the rate of reaction in-
creased with increase in [HCl] (Table 1). The order with re-
spect to [HCl], as calculated from the slope of the plot of
log k¢ vs. log [HCl], was found to be 1.31.
-
3
dium (0.25-0.75 mol dm ) and addition of mercuric acetate
-
3
-
(0.001-0.01 mol dm ) had no significant effect on the rate.
Hence no attempt was made to keep ionic strength constant
for kinetic runs.
The total [Cl ] in the reaction mixture was kept con-
-
stant at 0.15 mol dm by adding NaCl, then [H ] was varied
+
by using HCl. The rate increases with an increase in [H ]
3
+
+
Table 2) and the plot of log k¢ vs. log [H ] (Fig. 2) was
The effect of dielectric permittivity (D) on the reac-
tion rate was studied by adding various proportions of
(
found to be linear (r = 0.999) with a unit slope indicating
+
first order dependence on [H ]. At constant [H ], addition
+
+
Fig. 2. Plot of 4+logk¢ versus (2+log[H ]) or (2+log
a
Fig. 1. Plot of 4+logk¢ versus 3+log[PEA].
-
b
-
Cl ]) or (3+log[OH ]) .
c
[

Kinetics of Oxidation of 2-Phenylethylamine
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1225
Table 3. Effect of varying concentration of succinimide (NH) on
the reaction rate in acid medium
Table 4. Effect of varying dielectric permittivity of the medium
on the reaction rate at 313 K
3
0 [NH] (mol dm )
-3
4
k ´ 10 (s )
-1
4
k ´ 10 (s )
-1
1
%
CH CN
3
D
a
b
(
v/v)
1
2
4
5
6
.0
.0
.0
.0
.0
2.64
1.75
1.09
0.91
0.80
Acid
Alkaline
0
5
1
1
70.8
69.0
67.3
65.7
64.2
3.56
2.72
2.17
1.70
1.35
4.11
3.61
3.23
2.87
2.56
-3
0
5
-
NBS] = 5 ´ 10 mol dm ; [PEA] = 8 ´ 10 mol dm ; [HCl] = 5
4
-3
-3
-3
[
20
-
10 mol dm ; m = 0.25 mol dm ; T = 313 K.
2
-3
-3
´
a
-4
-3
-3
[
NBS] = 5 ´ 10 mol dm ; [PEA] = 8 ´ 10 mol dm ; [HCl] =
-
´ 10 mol dm ; m = 0.25 mol dm .
2
-3
-3
5
b
-4
-3
-3
-3
NBS] = 5 ´ 10 mol dm ; [PEA] = 8 ´ 10 mol dm ; [NaOH]
[
CH
that an increase in CH
and a plot of log k¢ vs. log 1/D gave a straight line (r =
.999) with a negative slope (Fig. 3). The values are re-
ported in Table 4. The values of permittivity for CH CN-
Blank ex-
CN was not oxidized
3
CN (0-20% v/v) to the reacting system. It was observed
-2
3 ´ 10 mol dm ; m = 0.25 mol dm .
-3
-3
=
3
CN composition decreased the rate
o
ence of the rate on [NBS] . The pseudo first-order rate con-
0
stants (k¢) obtained are listed in Table 6. The value of k¢ in-
3
1
6,17
creased with an increase in [PEA] (Table 6), and a plot of
o
H
2
O mixtures are taken from the literature.
log k¢ vs. log [PEA] was linear (Fig. 1; r = 0.999) with a
periments performed showed that CH
3
slope of 0.58 indicating a fractional-order dependence of
-
. Similarly, an increase in [OH ] increased
with NBS under the present experimental conditions. The
reaction was studied at different temperatures (303-323 K),
keeping other experimental conditions constant. From the
linear Arrhenius plot of log k¢ vs. 1/T (Fig. 4; r = 0.999), the
values of activation parameters for the overall reaction
were computed. The results are compiled in Table 5. Ab-
sence of free radicals during the course of oxidation was
confirmed when no polymerization was initiated with addi-
tion of acrylonitrile solution to the reaction mixture.
the rate on [PEA]
o
the rate (Table 6) and from the linear plot of log k¢ vs. log
NaOH] (Fig. 2; r = 0.998) an order of 0.76 was obtained
[
and hence showing the fractional-order dependence of rate
on [NaOH].
-
Addition of succinimide (0.001-0.005 mol dm ) and
3
-
NaCl (0.005 mol dm ) or variation of ionic strength of the
3
-
3
4
medium using NaClO solution (0.25-0.75 mol dm ) or
-
mercuric acetate (0.001-0.01 mol dm ) showed no signifi-
3
cant effect on the rate. The rate decreased with increasing
Kinetics of oxidation in alkaline medium
3
CH CN content (0-20% v/v) and the results are shown in
With substrate in excess at constant [NaOH] and tem-
Table 4. Plot of log k¢ vs. 1/D was linear (Fig. 3; r = 0.999)
o
perature, the [NBS] was varied. Plots of log [NBS] vs.
time were linear (r > 0.998) indicating a first-order depend-
3
Fig. 4. Plot of 4+logk¢ versus 10 /T.
2
Fig. 3. Plot of 4+logk¢ versus 10 /D.

1
226 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Mohana and Ramdas Bhandarkar
Table 5. Effect of varying temperature on the reaction rate and activation parameters for the
oxidation of PEA
4
k ´ 10 (s )
-1
¹
DG (kJ mol )
-1
Temperature (K)
Acid
Alkaline
Acid
Alkaline
3
3
3
3
3
3
03
08
13
18
21
23
1.59
2.36
3.56
5.25
-
04.11
05.11
06.60
08.65
11.59
-
96.3
96.9
97.5
98.0
-
94.0
95.0
95.9
96.7
96.9
7.68
64.9
62.3
-112.4
98.6
-
-
-
1
E /kJ mol
a
42.9
-
¹
DH /kJ mol
-1
40.4
-
-
¹
-1
DS /J K mol
-1
-177.0
-
-
-
4
-3
-3
-3
-2
-3
NBS] = 5 ´ 10 mol dm ; [PEA] = 8 ´ 10 mol dm ; [HCl] = [NaOH] = 5 ´ 10 mol dm ;
[
-
m = 0.25 mol dm .
3
Table 6. Effect of varying concentrations of oxidant, substrate
and alkali on the reaction rate at 313 K
DISCUSSION
It has been shown
+
of NBS in acid solution are NBS itself or Br or protonated
+
NBS viz., N BSH, and the reactive species in alkaline solu-
4
k ´ 10 (s )
-1
18-20
4
0 [NBS] 10 [PEA] 10 [NaOH]
3
2
that probable reactive species
1
-
3
mol dm ) (mol dm ) (mol dm )
-3
-3
(
Experimental Calculated
1
3
5
7
1
5
5
5
5
5
5
5
5
5
5
5
5
5
.0
08.0
08.0
08.0
08.0
08.0
02.0
04.0
06.0
10.0
12.0
08.0
08.0
08.0
08.0
08.0
08.0
08.0
08.0
05.0
05.0
05.0
05.0
05.0
05.0
05.0
05.0
05.0
05.0
01.0
03.0
07.0
10.0
05.0
05.0
05.0
05.0
06.61
06.58
06.60
06.64
06.59
02.89
04.29
05.45
07.22
08.18
01.46
04.11
07.78
10.67
06.71
06.69
06.71
06.72
6.40
6.40
6.40
6.40
6.40
2.61
4.13
5.41
7.20
7.96
1.48
4.28
7.60
9.98
-
-
tions are NBS, HOBr or OBr . It may be pointed out that all
.0
.0
kinetic studies have been made in the presence of mercuric
acetate in order to avoid any possible bromine oxidation,
which may be produced as follows:
.0
0.0
.0
.0
O
O
.0
.0
NBr
+
HBr
NH
+
Br
2
(1)
.0
.0
.0
O
O
.0
-
Mercuric acetate acts as a capture agent for any Br
2
formed in the reaction and exists as HgBr 4 or unionized
.0
-
.0*
.0**
-
HgBr
NBS.
and ensures that oxidation takes place purely through
1,22
2
2
a
.0
-
b
.0
-
-
At m = 0.5 mol dm and ** at m = 0.75 mol dm
3
-3
-3
*
a
Mechanism and rate law in acid medium
NBS is known to exist in acid medium in the follow-
ing equilibria:
-3 b
[
NH] = 0.002 mol dm . [NH] = 0.006 mol dm .
with a negative slope. Blank experiments performed indi-
cated that CH CN was not oxidized with NBS under the ex-
>
NBr + H O
NH + HOBr
(2)
(3)
(4)
(5)
3
2
+
NHBr
+
perimental conditions employed. Kinetic and thermody-
namic parameters were calculated by studying the reaction
at different temperatures (303-321 K). A plot of log k¢ vs.
>
>
NBr + H
+
NH + Br+
NBr
Br+
+
+
H
+
(H OBr)
2
H O
2
1
/T was linear (Fig. 4; r = 0.993). These results are given in
Table 5. Absence of free radicals in the reaction mixture
has been demonstrated by the acrylonitrile test.
+
In the present studies the positive effect of [H ] on the

Kinetics of Oxidation of 2-Phenylethylamine
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1227
reaction rate observed allows us to assume either protonated
+
Scheme II
+
+
2
NBS i.e., N BSH or Br or (H OBr) as active oxidizing
+
K5
+
species, and negative effect of the initially added product,
+
succinimide restricts us to take Br as the oxidizing species.
NBS
H
Br
fast
fast
(i)
(ii)
+
NH +
X
k6
+
Br + S
On the basis of the above discussions and observed kinetic
data, a probable mechanism (Scheme I) is proposed for the
oxidation of PEA.
-
k
7
6
-
'
(iii)
(iv)
X + Cl
X
slow and rds
fast
k8
'
X + H O
Products
2
Scheme I
K
1
+
Br+
+
fast
(i)
(ii)
From slow step in Scheme II,
NBS +
H
S
NH
X
k2
-
[X] [Cl ]
Br+
fast
slow and rds
fast
rate = k
7
(10)
+
k_
2
k3
(iii)
(iv)
X
X'
Applying steady state approximation for the species X, and
by solving [X], one obtains,
k4
X'
+
H2O
Products
+
K k [NBS][H ][S]
1
2
[
X] =
(11)
-
k [NH]+ k [Cl ][NH]
-
2
3
+
In Scheme I, S is the substrate, X is a Br -S complex
By substituting [X] from equation (11) into equation (10),
the following rate law (equation 12) is obtained:
species and X¢ is another intermediate complex species
whose structures are shown in Scheme III, where a detailed
mechanistic interpretation of PEA oxidation by NBS in
acid medium is proposed.
+
-
K k k [NBS][H ][S][Cl ]
2
3
1
rate
(12)
=
-
k [NH] + k3[Cl ][NH]
-
2
Step (iii) of Scheme I determines the overall rate,
The rate law (12) clearly demonstrates the fractional
-
order dependence of the rate on [Cl ] and retardation of the
rate = k
3
[X]
(6)
rate by added succinimide and is also in good agreement
with the experimental results.
Applying steady state condition for X, it can be shown that,
Since rate = k¢ [NBS], equation (12) can be trans-
ferred into equation (13).
+
K k [NBS][H ][S]
1
2
[
X] =
(7)
k [NH] + k [NH]
+
K k k [H ][S][Cl ]
-
-
2
3
1
2
3
k' =
(13)
-
k [NH] +k [Cl ][NH]
On substituting equation (7) in equation (6), the following
rate law [equation (8)] is obtained:
-2
3
23
Laidler and Eryings have described the effect of
varying solvent composition on the reaction kinetics in de-
tail. For the limiting case of zero angle of approach be-
+
K k k [NBS][H ][S]
1
2
3
rate =
(8)
k [NH]+ k [NH]
-2
3
2
4
tween two dipoles or an ion-dipole system, Emis has
shown that a plot of log k¢ vs. 1/D gives a straight line with
a positive slope for a reaction involving a positive ion and a
dipole and a negative slope for a negative ion-dipole or di-
pole-dipole interactions. In the present investigations, a
plot of log k¢ vs 1/D was linear with a negative slope. This
observation indicates the ion-dipole nature of the rate-de-
termining step in the reaction sequence and also points to
the extending of the charge in the transition state. The inhi-
bition of succinimide on the rate suggests its involvement
Since rate = k¢ [NBS], rate law (8) can be transferred into
equation (9).
+
K k k [H ][S]
1
2
3
k' =
(9)
k [NH] + k [NH]
-
2
3
Rate law (8) is in good agreement with the experimental re-
sults observed.
+
In the presence of chloride ion at constant [H ],
Scheme II is proposed for the reaction mechanism.

1
228 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Mohana and Ramdas Bhandarkar
Scheme III
in a fast equilibrium prior to the rate-determining step. The
fairly high positive values of Gibbs energy of activation
and enthalpy of activation indicate that the transition state
Mechanism and rate law in alkaline medium
NBS is a two equivalent oxidant, which oxidizes many
2
5-27
substrates through NBS itself, or hypobromite anion.
¹
is highly solvated. The large negative DS suggests the for-
The reaction exhibits 1:2 stoichiometry of PEA and NBS
with unit order dependence on [NBS]. Increase in rate with
- 27
increasing [OH ] can be well-explained by the formation
mation of a compact activated complex with a reduction in
the degrees of freedom of molecules.

Kinetics of Oxidation of 2-Phenylethylamine
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1229
-
of oxidant species such as OBr in the following equilib-
results observed.
t
Since rate = k¢ [NBS] , equation (19) can be trans-
rium:
ferred into equations (20) and (21).
-
NBS + OH ƒ NH + OBr
-
(14)
-
k
K K10 11[S][OH ]
9
k' =
(20)
(21)
-
-
[
H O]+K
2
9
[OH ]+K
K
10 [S][OH ]
9
Insignificant effect of the added succinimide on the rate can
be attributed to the involvement of the reactive species,
-
OBr in the equilibrium below,
1
=
k'
[H O]
2
1
1
k
+
-
+
K
9
K
10
k
11[S][OH ]
K
10
k
11[S]
11
-
HOBr + OH ƒ OBr + H
-
2
O
(15)
According to equation (21), the plots of 1/k¢ vs. 1/[S]
-
r = 0.995) and 1/k¢ vs. 1/[OH ] (r = 0.999) should be linear
(
-
Hence, OBr reacts with the substrate (S) to form a complex
which is verified (Fig. 5). From the slopes and intercepts of
-
3
(
X), which decomposes in a rate-limiting step to give an in-
2 9
such plots and [H O] = 55.56 mol dm , the values of K ,
termediate (X¢). This intermediate reacts with one more
molecules of the active species of oxidant in the fast step to
give the products shown in Scheme IV. A detailed mecha-
nistic interpretation is shown in Scheme V.
K10 and k11 were calculated. Using these values in rate
equation (20), the rate constants under different conditions
were calculated and compared with experimental values
given in Table 6. There is a reasonable agreement between
calculated and experimental rate constants.
Scheme IV
The negligible influence of the ionic strength of the
medium and of the added halide ions is consistent with the
proposed mechanism. The negative dielectric effect ob-
served in the alkaline medium shows charge dispersal in
the transition state, indicating a negative ion-dipole inter-
action in the rate-limiting step. The sign and magnitude of
K
9
-
-
OBr
+
H2O
fast
fast
(i)
(ii)
HOBr
OBr
+
+
OH
S
K10
-
X
k11
(iii)
(iv)
X'
slow and rds
fast
¹
DS as observed suggested that the activated complex is
X
k12
more compact than the ground state. The positive free en-
ergy of activation shows that the transition state is highly
solvated.
X'
+
HOBr
Products
From the slow step of Scheme IV,
rate = k11 [X]
(16)
The total effective concentration of NBS is [NBS]
t
, then
(17)
-
= [OBr ] + [HOBr] + [X]
[
NBS]
t
-
Solving for [HOBr] and [OBr ] from steps (i) and (ii), one
obtains,
-
K K10[NBS] [S][OH ]
9
t
[
X] =
(18)
-
-
[
H O]+K
2
9
[OH ] +K K10[S][OH ]
9
By substituting [X] from equation (18) into equation (16)
one obtains the following rate law:
-
K
9
K
10
k
11[NBS]t[S][OH ]
-
rate
=
(19)
-
[
H O] +K
2
9
[OH ] +K K10 [S][OH ]
3
2
Fig. 5. Plot of 10 /k¢ versus (10 /[PEA]) or (10 /
a
2
9
-
OH ]) .
b
[
Rate law (19) is in good agreement with the experimental

1
230 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007
Mohana and Ramdas Bhandarkar
Scheme V
EXPERIMENTAL
An aqueous solution of NBS was prepared afresh
der pseudo first-order conditions by taking a known excess
o o
of [PEA] over [NBS] at 313 K. Appropriate amounts of
PEA, HCl or NaOH solutions, mercuric acetate, sodium
perchlorate and water to keep the total volume constant
were equilibrated at constant temperature (± 0.1 °C). A
measured amount of NBS solution also pre-equilibrated at
the same temperature was rapidly added to the mixture. The
progress of the reaction was monitored by estimating the
amount of unconsumed NBS at regular time intervals iodo-
metrically. The course of reaction was studied for at least
two half lives. The pseudo first-order rate constants (k¢),
calculated from the linear plots of log [NBS] vs. time were
reproducible within ± 4%. Regression analysis of the ex-
perimental data to obtain the regression co-efficient, r, was
performed using an fx-570 MS scientific calculator.
each day from a G. R. Merck sample of the reagent, and its
6
strength was checked by the iodometric method. Analar
grade 2-phenylethylamine (Himedia) was used as received.
All other reagents, namely hydrochloric acid, sodium per-
chlorate, mercuric acetate, succinimide and sodium hy-
droxide, were of Analar grade. Doubly distilled water was
used throughout the investigations.
Kinetic Measurements
All kinetic measurements were performed in glass
stoppered Pyrex boiling tubes coated black to eliminate
photochemical effects. The reactions were carried out un-

Kinetics of Oxidation of 2-Phenylethylamine
J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1231
Stoichiometry and Product Analysis
the two media are responsible for the difference in activity.
Hence, the kinetics of oxidation of PEA with NBS is more
facile in alkaline medium in comparison with acid medium.
Reaction mixtures containing varying ratios of NBS
-
3
and PEA in the presence of 0.05 mol dm HCl or NaOH at
13 K were kept aside for 24 h, so that the substrate was
3
completely converted into products. Estimation of the un-
reacted NBS showed that one mole of substrate utilized one
mole of oxidant in acid medium and one mole of substrate
reacted with two moles of oxidant in alkaline medium. The
observed stoichiometry may be represented by the equa-
tions (1) and (2).
ACKNOWLEDGEMENTS
The authors are thankful to University of Mysore,
Mysore for financial support.
RNBr + R¢CH
R¢CH CHO + RNH + NH
RNBr + R¢CH CH NH
R¢CH CN + 2RNH + 2H + 2Br
2
CH
2
NH
2
+ H
2
O ®
Received November 30, 2006.
+
-
2
3
+ H + Br
(22)
(23)
2
2
2
2
®
+
-
2
REFERENCES
where
R = (CH
The reduction product of NBS, succinimide (NH),
1. Nakajima, T.; Kakimoto, Y.; Sano, I. J. Pharmacol. Exp.
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2
. Henry, D. P.; Russell, W. L.; Clemens, J. A.; Plebus, L. A. In
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2
2 6 5
CO) ; R¢ = C H .
1
4
was detected by the method reported elsewhere. The reac-
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3
. Dyck, L. E.; Yang, C. R.; Boulton, A. A. J. Neurochem. Res.
1
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1
4
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1
5
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. Filler, R. Chem. Rev. 1963, 63, 21.
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-
1
-1
1
2
720 cm (C=O stretch), 2850 cm (aldehydic C-H stretch)
-
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1
-1
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1
1
1
1
1
1
CONCLUSION
1
In conclusion, the stoichiometry and products of oxi-
4
dation of 2-phenylethylamine with NBS in acid and alka-
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+
veal that Br as active oxidant species oxidizes the sub-
1
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-
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1
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medium. The different active oxidizing species involved in
1
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