Oxidation of 2-Phenylethylamine with N-Bromosuccinimide in Acid ...

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 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.
Keywords: Oxidation kinetics; N-Bromosuccinimide; Acid and alkaline media;
2-Phenylethylamine.
INTRODUCTION
2-Phenylethylamine (PEA) is a naturally occurring
endogenous amine, which is present in several mammalian
tissues 1 including the brain. 2 2-Phenylethylamine is formed
by decarboxylation of amino acid, L-phenylalanine. 3 It
crosses the presynaptic membrane and potentiates the postsynaptic
effects of dopamine. 4 PEA may act as neuromodulator
of catecholamine neurotransmission in the brain. 4
This bioactive amine is also present in certain foodstuffs
such as chocolate, cheese and wine and may cause undesirable
side effects in susceptible individuals. 5 After reviewing
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.
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
media. 6-8 This potent oxidizing agent has been used in the
oxidation of esters, 9 alcohols 10,11 and ketones. 12,13 In the
present work the kinetics of oxidation of PEA with NBS in
acid and alkaline media has been studied with a view to elucidate
the mechanism of the reaction and to identify the reactive
species of oxidant in acid and alkaline media.
RESULTS
The oxidation of PEA with NBS was kinetically investigated
at several initial concentrations of the reactants
in HCl and NaOH media. The salient features obtained in
these two media are discussed separately.
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 dependence
of rate on [NBS] o . The pseudo-first-order rate constants
(k) calculated are given in Table 1. Further, the values
of k calculated from these plots are unaltered with variation
of [NBS] o , confirming the first-order dependence on
[NBS] o . The rate increased with increase in [PEA] o (Table

1224 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
10 4 [NBS]
(mol dm -3 )
10 3 [PEA]
(mol dm -3 )
10 2 [HCl]
(mol dm -3 )
k 10 4
(s -1 )
1.0 08.0 5.0 3.62
3.0 08.0 5.0 3.70
5.0 08.0 5.0 3.56
7.0 08.0 5.0 3.42
9.0 08.0 5.0 3.67
5.0 06.0 5.0 2.69
5.0 10.0 5.0 4.60
5.0 12.0 5.0 5.98
5.0 14.0 5.0 6.81
5.0 08.0 4.0 2.50
5.0 08.0 6.0 4.79
5.0 08.0 7.0 6.20
5.0 08.0 9.0 8.87
5.0* 08.0 5.0 3.62
5.0** 08.0 5.0 3.66
*ationicstrength() = 0.5 mol dm -3 and ** at = 0.75 mol dm -3
1). A plot of log k vs. log [PEA] was linear (Fig. 1; r
0.996) with the unit slope showing first-order dependence
of the rate on [PEA] o . Similarly, the rate of reaction increased
with increase in [HCl] (Table 1). The order with respect
to [HCl], as calculated from the slope of the plot of
log k vs. log [HCl], was found to be 1.31.
The total [Cl - ] in the reaction mixture was kept constant
at 0.15 mol dm -3 by adding NaCl, then [H ] was varied
by using HCl. The rate increases with an increase in [H ]
(Table 2) and the plot of log k vs. log [H ] (Fig. 2) was
found to be linear (r 0.999) with a unit slope indicating
first order dependence on [H ]. At constant [H ], addition
Table 2. Effect of varying concentrations of H + and Cl - on the
reaction rate at 313 K
10 2 [H + ]
(mol dm -3 )
10 2 [Cl - ]
(mol dm -3 )
k 10 4
(s -1 )
3.0 15.0 03.27
5.0 15.0 05.66
7.0 15.0 08.04
9.0 15.0 10.12
10.0 15.0 11.39
5.0 06.0 04.31
5.0 08.0 04.72
5.0 10.0 05.07
5.0 12.0 05.37
5.0 14.0 05.60
[NBS] = 5 10 -4 mol dm -3 ;[PEA]=8 10 -3 mol dm -3 ; =0.25
mol dm -3
of chloride ions in the form of NaCl increases the reaction
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 reaction
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 medium
(0.25-0.75 mol dm -3 ) and addition of mercuric acetate
(0.001-0.01 mol dm -3 ) had no significant effect on the rate.
Hence no attempt was made to keep ionic strength constant
for kinetic runs.
The effect of dielectric permittivity (D) on the reaction
rate was studied by adding various proportions of
Fig. 1. Plot of 4+logk versus 3+log[PEA].
Fig. 2. Plot of 4+logk versus (2+log[H + ]) a or (2log
[Cl - ]) b or (3log[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
10 3 [NH] (mol dm -3 ) k 10 4 (s -1 )
1.0 2.64
2.0 1.75
4.0 1.09
5.0 0.91
6.0 0.80
[NBS] = 5 10 -4 mol dm -3 ;[PEA]=8 10 -3 mol dm -3 ;[HCl]=5
10 -2 mol dm -3 ; = 0.25 mol dm -3 ; T = 313 K.
CH 3 CN (0-20 v/v) to the reacting system. It was observed
that an increase in CH 3 CN composition decreased the rate
and a plot of log k vs. log 1/D gave a straight line (r =
0.999) with a negative slope (Fig. 3). The values are reported
in Table 4. The values of permittivity for CH 3 CN-
H 2 O mixtures are taken from the literature. 16,17 Blank experiments
performed showed that CH 3 CN was not oxidized
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. Absence
of free radicals during the course of oxidation was
confirmed when no polymerization was initiated with addition
of acrylonitrile solution to the reaction mixture.
Table 4. Effect of varying dielectric permittivity of the medium
on the reaction rate at 313 K
%CH 3 CN
(v/v)
D
Acid a
k 10 4 (s -1 )
Alkaline b
0 70.8 3.56 4.11
5 69.0 2.72 3.61
10 67.3 2.17 3.23
15 65.7 1.70 2.87
20 64.2 1.35 2.56
a [NBS] = 5 10 -4 mol dm -3 ;[PEA]=8 10 -3 mol dm -3 ;[HCl]=
5 10 -2 mol dm -3 ; = 0.25 mol dm -3 .
b [NBS] = 5 10 -4 mol dm -3 ;[PEA]=8 10 -3 mol dm -3 ; [NaOH]
=3 10 -2 mol dm -3 ; = 0.25 mol dm -3 .
Kinetics of oxidation in alkaline medium
With substrate in excess at constant [NaOH] and temperature,
the [NBS] o was varied. Plots of log [NBS] vs.
time were linear (r 0.998) indicating a first-order dependence
of the rate on [NBS] o . The pseudo first-order rate constants
(k) obtained are listed in Table 6. The value of k increased
with an increase in [PEA] o (Table 6), and a plot of
log k vs. log [PEA] was linear (Fig. 1; r = 0.999) with a
slope of 0.58 indicating a fractional-order dependence of
the rate on [PEA] o . Similarly, an increase in [OH - ] increased
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 -3 ) and
NaCl (0.005 mol dm -3 ) or variation of ionic strength of the
medium using NaClO 4 solution (0.25-0.75 mol dm -3 )or
mercuric acetate (0.001-0.01 mol dm -3 ) showed no significant
effect on the rate. The rate decreased with increasing
CH 3 CN content (0-20 v/v) and the results are shown in
Table 4. Plot of log k vs. 1/D was linear (Fig. 3; r 0.999)
Fig. 3. Plot of 4+logk versus 10 2 /D.
Fig. 4. Plot of 4+logk versus 10 3 /T.

1226 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
k 10 4 (s -1 ) G (kJ mol -1 )
Temperature (K)
Acid Alkaline Acid Alkaline
303 1.59 04.11 96.3 94.0
308 2.36 05.11 96.9 95.0
313 3.56 06.60 97.5 95.9
318 5.25 08.65 98.0 96.7
321 - 11.59 - 96.9
323 7.68 - 98.6 -
E a /kJ mol -1 64.9 42.9 - -
H /kJ mol -1 62.3 40.4 - -
S /J K -1 mol -1 -112.4 -177.0 - -
[NBS] = 5 10 -4 mol dm -3 ;[PEA]=8 10 -3 mol dm -3 ; [HCl] = [NaOH] = 5 10 -2 mol dm -3 ;
= 0.25 mol dm -3 .
Table 6. Effect of varying concentrations of oxidant, substrate
and alkali on the reaction rate at 313 K
10 4 [NBS]
(mol dm -3 )
10 3 [PEA]
(mol dm -3 )
10 2 [NaOH] k 10 4 (s -1 )
(mol dm -3 ) Experimental Calculated
1.0 08.0 05.0 06.61 6.40
3.0 08.0 05.0 06.58 6.40
5.0 08.0 05.0 06.60 6.40
7.0 08.0 05.0 06.64 6.40
10.0 08.0 05.0 06.59 6.40
5.0 02.0 05.0 02.89 2.61
5.0 04.0 05.0 04.29 4.13
5.0 06.0 05.0 05.45 5.41
5.0 10.0 05.0 07.22 7.20
5.0 12.0 05.0 08.18 7.96
5.0 08.0 01.0 01.46 1.48
5.0 08.0 03.0 04.11 4.28
5.0 08.0 07.0 07.78 7.60
5.0 08.0 10.0 10.67 9.98
5.0* 08.0 05.0 06.71 -
5.0** 08.0 05.0 06.69 -
5.0 a 08.0 05.0 06.71 -
5.0 b 08.0 05.0 06.72 -
*At =0.5moldm -3 and ** at = 0.75 mol dm -3
a [NH] = 0.002 mol dm -3 . b [NH] = 0.006 mol dm -3 .
with a negative slope. Blank experiments performed indicated
that CH 3 CN was not oxidized with NBS under the experimental
conditions employed. Kinetic and thermodynamic
parameters were calculated by studying the reaction
at different temperatures (303-321 K). A plot of log k vs.
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.
DISCUSSION
It has been shown 18-20 that probable reactive species
of NBS in acid solution are NBS itself or Br + or protonated
NBS viz., N + BSH, and the reactive species in alkaline solutions
are NBS, HOBr or OBr - . It may be pointed out that all
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:
O
O
NBr
+ HBr NH
+ Br2
Mercuric acetate acts as a capture agent for any Br -
formed in the reaction and exists as HgBr 4 2 or unionized
HgBr 2 and ensures that oxidation takes place purely through
NBS. 21,22
Mechanism and rate law in acid medium
NBS is known to exist in acid medium in the following
equilibria:
>NBr + H2 O NH + HOBr
+
+
>NBr + H
NHBr
>NBr + H + NH +
+
Br
Br+ + HO 2
( HOBr) +
(1)
(2)
(3)
(4)
(5)
In the present studies the positive effect of [H + ]onthe
2
O
O

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
NBS i.e., N + BSH or Br + or (H 2 OBr) + as active oxidizing
+
K5
species, and negative effect of the initially added product,
+
NBS + H NH + Br fast
(i)
K k k
+
dipole and a negative slope for a negative ion-dipole or dipole-dipole
interactions. In the present investigations, a
k'
1 2 3 [H ][S]
= (9)
k-2 + k 3 [NH]
succinimide restricts us to take Br + as the oxidizing species.
+ k6
On the basis of the above discussions and observed kinetic Br + S X
fast
(ii)
- 6
data, a probable mechanism (Scheme I) is proposed for the
- k
X + Cl
7
X
oxidation of PEA.
slow and rds (iii)
k8
X' + HO
(iv)
2 Products fast
Scheme I
NBS +
+
H
K1
NH +
+
Br fast (i) From slow step in Scheme II,
+
Br + S
k2
k_ 2
X
fast (ii) rate = k 7 [X] [Cl - ] (10)
X
k
3
X' slow and rds (iii) Applying steady state approximation for the species X, and
k
by solving [X], one obtains,
4
X' + H O
Products fast (iv)
2
+
K k
1 2[NBS][H ][S]
[X] =
(11)
k-2 + k 3 [Cl
-
][NH]
In Scheme I, S is the substrate, X is a Br + -S complex
By substituting [X] from equation (11) into equation (10),
species and X is another intermediate complex species
the following rate law (equation 12) is obtained:
whose structures are shown in Scheme III, where a detailed
+
mechanistic interpretation of PEA oxidation by NBS in
K k [NBS][H ][S][Cl - ]
1 2k rate
3
=
(12)
acid medium is proposed.
k-2 + k 3 [Cl
-
][NH]
Step (iii) of Scheme I determines the overall rate,
rate = k 3 [X] (6)
The rate law (12) clearly demonstrates the fractional
order dependence of the rate on [Cl - ] and retardation of the
rate by added succinimide and is also in good agreement
Applying steady state condition for X, it can be shown that,
with the experimental results.
Since rate = k [NBS], equation (12) can be transferred
into equation (13).
+
K k [NBS][H ][S]
[X]
1 2
=
(7)
k-2 + k 3 [NH]
+
Kk [Cl
-
2 k 3 [H][S] ]
k'
1
=
(13)
On substituting equation (7) in equation (6), the following
k -2 [NH] + k 3 [Cl
-
][NH]
rate law [equation (8)] is obtained:
Laidler and Eryings 23 have described the effect of
K1k 2k 3[NBS][H ][S]
varying solvent composition on the reaction kinetics in detail.
For the limiting case of zero angle of approach be-
rate = (8)
k
2[NH] k
3[NH]
tween two dipoles or an ion-dipole system, Emis 24 has
Since rate k [NBS], rate law (8) can be transferred into
shown that a plot of log k vs. 1/D gives a straight line with
equation (9).
a positive slope for a reaction involving a positive ion and a
plot of log k vs 1/D was linear with a negative slope. This
Rate law (8) is in good agreement with the experimental results
observed.
observation indicates the ion-dipole nature of the rate-determining
step in the reaction sequence and also points to
In the presence of chloride ion at constant [H + ],
the extending of the charge in the transition state. The inhibition
of succinimide on the rate suggests its
Scheme II is proposed for the reaction mechanism.
involvement
k

1228 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
is highly solvated. The large negative S suggests the formation
of a compact activated complex with a reduction in
the degrees of freedom of molecules.
Mechanism and rate law in alkaline medium
NBS is a two equivalent oxidant, which oxidizes many
substrates through NBS itself, or hypobromite anion. 25-27
The reaction exhibits 1:2 stoichiometry of PEA and NBS
with unit order dependence on [NBS]. Increase in rate with
increasing [OH - ] can be well-explained 27 by the formation

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 equilibrium:
results observed.
Since rate = k [NBS] t , equation (19) can be transferred
into equations (20) and (21).
-
NBS+OH - NH + OBr - (14)
K [S][OH k'
9K 10 k 11 ]
=
Insignificant effect of the added succinimide on the rate can
[H O]+ [OH
-
2 K9 ] + K 9 K 10 [S][OH ]
K [NBS] [S][OH ]
rate
9K10k 11 t
=
(19)
[H O] + [OH
-
2 K9 ] + K 9 K 10 [S][OH ]
be attributed to the involvement of the reactive species,
1
OBr - in the equilibrium below,
k' = [H2O]
K [S][OH]
1
+ +
9K 10k 11
K 10 k 11 [S]
1
HOBr + OH - OBr - +H 2 O (15)
Hence, OBr - reacts with the substrate (S) to form a complex
(X), which decomposes in a rate-limiting step to give an intermediate
(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 mechanistic
interpretation is shown in Scheme V.
Scheme IV
HOBr + OH
K9
OBr - + HO 2 fast (i)
OBr - K 10
+ S
X
fast (ii)
X' +
X
HOBr
k11
k12
X'
Products
slow and rds
fast
(iii)
(iv)
From the slow step of Scheme IV,
rate = k 11 [X] (16)
The total effective concentration of NBS is [NBS] t , then
[NBS] t = [OBr - ] + [HOBr] + [X] (17)
Solving for [HOBr] and [OBr - ] from steps (i) and (ii), one
obtains,
K [NBS][S][OH 9K 10 t ]
[X] =
[H O] + K [OH
-
2 9 ] + K 9 K 10 [S][OH ]
(18)
By substituting [X] from equation (18) into equation (16)
one obtains the following rate law:
Rate law (19) is in good agreement with the experimental
(20)
(21)
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
which is verified (Fig. 5). From the slopes and intercepts of
such plots and [H 2 O] 55.56 mol dm -3 , the values of K 9 ,
K 10 and k 11 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.
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 observed
in the alkaline medium shows charge dispersal in
the transition state, indicating a negative ion-dipole interaction
in the rate-limiting step. The sign and magnitude of
S as observed suggested that the activated complex is
more compact than the ground state. The positive free energy
of activation shows that the transition state is highly
solvated.
Fig. 5. Plot of 10 3 /k versus (10 2 /[PEA]) a or (10 2 /
[OH - ]) b .
k 11

1230 J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 Mohana and Ramdas Bhandarkar
Scheme V
EXPERIMENTAL
An aqueous solution of NBS was prepared afresh
each day from a G. R. Merck sample of the reagent, and its
strength was checked by the iodometric method. 6 Analar
grade 2-phenylethylamine (Himedia) was used as received.
All other reagents, namely hydrochloric acid, sodium perchlorate,
mercuric acetate, succinimide and sodium hydroxide,
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 under
pseudo first-order conditions by taking a known excess
of [PEA] o over [NBS] o 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 iodometrically.
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 experimental
data to obtain the regression co-efficient, r, was
performed using an fx-570 MS scientific calculator.

Kinetics of Oxidation of 2-Phenylethylamine J. Chin. Chem. Soc., Vol. 54, No. 5, 2007 1231
Stoichiometry and Product Analysis
Reaction mixtures containing varying ratios of NBS
and PEA in the presence of 0.05 mol dm -3 HCl or NaOH at
313 K were kept aside for 24 h, so that the substrate was
completely converted into products. Estimation of the unreacted
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 equations
(1) and (2).
where
RNBr + RCH 2 CH 2 NH 2 +H 2 O
RCH 2 CHO+RNH+NH 3 +H + +Br - (22)
2RNBr + RCH 2 CH 2 NH 2
RCH 2 CN+2RNH+2H + + 2Br - (23)
R = (CH 2 CO) 2 ;R =C 6 H 5 .
The reduction product of NBS, succinimide (NH),
was detected by the method reported elsewhere. 14 The reaction
mixture was extracted with ether and the oxidation
product of PEA was found to be 2-phenylacetaldehyde in
acid medium and 2-phenylacetonitrile in the case of alkaline
medium. The aldehyde was detected by conventional
spot tests 14 and also by 2,4-DNP derivatives. The nitrile
was identified by its colour reactions 15 with hydroxylamine
and ferric chloride. Furthermore, the presence of aldehyde
and nitrile was confirmed by their IR absorption bands
1720 cm -1 (C=O stretch), 2850 cm -1 (aldehydic C-H stretch)
2274 cm -1 (CN stretch) and 3025 cm -1 (aromatic C-H
stretch).
CONCLUSION
In conclusion, the stoichiometry and products of oxidation
of 2-phenylethylamine with NBS in acid and alkaline
media are different. Kinetic studies in acid medium reveal
that Br + as active oxidant species oxidizes the substrate
to the corresponding aldehyde. In alkaline medium
the reaction takes place between the substrate and OBr - to
form the corresponding nitrile. The magnitude of the two
activation energies (Table 4) indicates that the PEA-NBS
oxidation is faster in alkaline medium compared to acid
medium. The different active oxidizing species involved in
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.
ACKNOWLEDGEMENTS
The authors are thankful to University of Mysore,
Mysore for financial support.
Received November 30, 2006.
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