Oxidation of primary amines by bromamine-B catalyzed by osmium(VIII) in alkaline medium: A kinetic and mechanistic study

Article abstract of DOI:10.1002/(SICI)1097-4601(1997)29:10<737::AID-KIN2>3.0.CO;2-N

The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-butylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB), in the presence of osmium(VIII), has been studied in alkaline medium at 35 °C. In the presence of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes the form, rate = k[BAB][OsO₄][OH^-]^x, which in the absence of the catalyst changes to the form, rate = k[BAB][S][OH^-]^y, where x and y are less than unity. Additions of halide ions and the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the solvent medium have no effect on the reaction rate. Activation parameters have been evaluated. The proposed mechanism assumes the formation of a complex intermediate between the active oxidant species, PhSO₂NBr^-, and the catalyst, OSO₄, in the rate determining step. This complex then interacts with the substrate amine in fast steps to yield the end products. The average value for the deprotonation constant of monobromamine-B, forming PhSO₂NBr^-, is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as 9.80×10³ at 35 °C. The average value for the same constant for the uncatalyzed reactions is 1.02×10⁴ at 35 °C.

Full text of DOI:10.1002/(SICI)1097-4601(1997)29:10<737::AID-KIN2>3.0.CO;2-N

Oxidation of Primary
Amines by Bromamine-B
Catalyzed by Osmium(VIII)
in Alkaline Medium: A
Kinetic and Mechanistic
Study
S. ANANDA,1 T. DEMAPPA,1 N. M. MADE GOWDA2
1Department of Studies in Chemistry, University of Mysore, Manasagangothri, Mysore 570 006, India
2Department of Chemistry, Western Illinois University, 1 University Circle, Macomb, Illinois 61455
Received 25 September 1996; accepted 21 February 1997
ABSTRACT: The kinetics of oxidation of the aliphatic primary amines, n-propylamine, n-bu-
tylamine, and isoamylamine, by N-sodio-N-bromobenznesulfonamide or bromamine-B (BAB),
in the presence of osmium(VIII), has been studied in alkaline medium at 35ЊC. In the presence
of the catalyst, the experimental rate law for the oxidation of the amine substrate (S) takes
the form, rate ϭ k[BAB][OsO4][OHϪ]x, which in the absence of the catalyst changes to the
form, rate ϭ k[BAB][S][OHϪ]y, where x and y are less than unity. Additions of halide ions and
the reduction product of BAB (benzenesulfonamide), and the variation of ionic strength of the
solvent medium have no effect on the reaction rate. Activation parameters have been evalu-
ated. The proposed mechanism assumes the formation of a complex intermediate between
the active oxidant species, PhSO2NBrϪ, and the catalyst, OsO4, in the rate determining step.
This complex then interacts with the substrate amine in fast steps to yield the end products.
The average value for the deprotonation constant of monobromamine-B, forming PhSO2NBrϪ,
is evaluated for the Os(VIII) catalyzed reactions of the three amines in alkaline medium as
9.80 ϫ 103 at 35ЊC. The average value for the same constant for the uncatalyzed reactions is
1.02 ϫ 104 at 35ЊC. ᭧ 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 737–744, 1997.
INTRODUCTION
shown that the aromatic amine oxidations are inde-
pendent of changing [OH Ϫ ]. Gupta and Agrawal have
found that the kinetics of S-butylamine oxidation by
CAT shows a retarding effect of alkali [3]. However,
there is no information available in the literature on
the kinetics of oxidation of aliphatic amines by bro-
mamines. A part of our mechanistic studies on the ox-
idation of different substrates by arylsulfonyl-N-bro-
mamines [4–6] involves the reaction of amines. The
Some kinetic studies of reactions of aromatic amines
and their derivatives with chloramine-T (CAT) have
been reported by Ramaiah and Rao [1] and Radha-
krishnamurthi and Rao [2]. These investigations have
Correspondence to: S. Ananda and N. M. Made Gowda
International Journal of Chemical Kinetics, Vol. 29, 737-744 (1997)
᭧ 1997 John Wiley & Sons, Inc.
CCC 0538-8066/97/100737-08

738
ANANDA, DEMAPPA, AND GOWDA
present article reports our studies on the kinetic and
mechanistic aspects of Os(VIII) catalyzed oxidation
of three aliphatic primary amines, n-propylamine
(nPA), n-butylamine (nBA), and iso-pentylamine or
iso-amylamine (iAA), by bromamine-B (BAB or
PhSO2NBrNa·1.5 H2O) in alkaline medium at 35ЊC.
We have previously reported the kinetic studies of the
uncatalyzed reactions of the same amines with BAB,
under similar conditions [6].
zone derivatives and by using Tollens’ and chromic
acid tests [7]. The other product, ammonia, was quan-
titatively estimated by the standard micro-Kjeldahl
procedure. The reduction product of BAB,
PhSO2NH2 , was identified by TLC using the solvent
system of petroleum ether-chloroform-1-butanol
(2 : 2 : 1 V/V) in ascending irrigation and using iodine
vapor as the developing reagent (Rf ϭ 0.88) [8].
RESULTS
EXPERIMENTAL
Stoichiometry and Product Analysis
The oxidant, BAB, was prepared and purified using
the standard methods [4,5]. Its purity was checked io-
dometrically and through IR and NMR spectral data
[4]. Aqueous solutions of BAB were prepared, stan-
dardized by the iodometric method, and preserved in
amber colored bottles. Concentrated aqueous solutions
of n-propylamine (E. Merck), n-butylamine (E.
Merck), iso-amylamine (Fluka), and NaClO4 (E.
Merck) were prepared. A solution of OsO4 (Johnson
The reaction showed that a mole of the amine substrate
was oxidized by a mole of BAB.
Kinetics
Under pseudo-first-order conditions of [amine]0 ϾϾ
[BAB]0 with known [OsO4] and [NaOH], plots of log
[BAB] vs. time were linear (r Ͼ 0.9978) indicating a
first-order dependence of the reaction rate on [BAB].
The pseudo-first-order rate constants, kЈ, obtained at
35ЊC are presented in Table I. Under the same exper-
imental conditions, an increase in [amine]0 did not af-
fect the kЈ values showing that the rate is independent
of [amine] (Table I). At constant [BAB]0 , [substrate]0 ,
[catalyst], and temperature, the rate increased with in-
crease in [NaOH] yielding linear plots of log kЈ vs.
log [NaOH] (Fig. 1; r Ͼ 0.9977). These plots with
slopes less than unity show positive fractional orders
in [NaOH] (Table II). The rate also increased with
increasing [OsO4] and plots of log kЈ vs. log [OsO4]
were linear with unit slopes, showing a first-order de-
pendence of the rate on [catalyst] (Table III) (Fig. 2;
r Ͼ 0.9987). The change in [ClϪ] and [BrϪ], effected
using their sodium salts at fixed reaction conditions,
did not affect the rate (results not shown). Addition
of the reduction product, benzenesulfonamide or
3
Matthey, UK) was prepared in 0.020 mol dmϪ
NaOH. All other chemicals used were of analytical
grade. Triply distilled water was used for preparing
aqueous solutions.
Kinetic Measurement
The kinetic runs were carried out in stoppered Pyrex
glass tubes whose outer surfaces were coated black to
eliminate photochemical effects. Requisite amounts of
the amine, NaClO4 , OsO4 , and NaOH solutions and
water (to maintain a constant total volume for all runs)
were taken in the tubes and thermally equilibrated in
a water bath set at a given temperature (e.g., 35 Ϯ
0.1ЊC). To this solution, was added a measured amount
of standard BAB solution, also preequilibrated at the
same temperature, to initiate the reaction. The reaction
mixture was shaken periodically 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.
The pseudo-first-order rate constants, kЈ, calculated
were reproducible within Ϯ3%. Regression analysis
of the experimental data was carried out on an EC-75
Statistical Calculator.
4
3
PhSO2NH2
(2.0 ϫ 10Ϫ Ϫ 8.0 ϫ 10Ϫ4 mol dmϪ
)
or the variation of ionic strength of the medium
(0.090–0.40 mol dmϪ3) had no effect on the reaction
rate. The variation of the solvent composition using
MeOH (0–15%) did not affect the rate.
The reaction was studied at varying temperatures,
298 K to 313 K. The activation parameters, namely
energy of activation (Ea), enthalpy of activation
Product Analysis
Þ
Þ
(⌬H ), entropy of activation (⌬S ), and free energy
Þ
The presence of the aldehydes, which are oxidation
products of the amines, in the reaction mixtures was
detected by preparing their 2,4-dinitrophenylhydra-
of activation (⌬G ), were obtained from the Arrhenius
plots of log kЈ vs. (1/T ) and the Eyring plots of
log (kЈ/T ) vs. (1/T ) which were linear. The kinetic and

OXIDATION OF PRIMARY AMINES
739
Table I Effect of Varying Reactant Concentrations on the Rate. [NaOH] ϭ 5.00 ϫ 10Ϫ3 mol dmϪ3; [OsO4] ϭ 1.20 ϫ
5
10Ϫ mol dmϪ3; ␮ ϭ 0.40 mol dmϪ3; and Temp. ϭ 35Њ Ϯ 0.1ЊCa
Ϫ
1
kЈ ϫ 104/(s
)
[BAB]0 ϫ 104
[Amine]0 ϫ 102
Ϫ
3
Ϫ3
(mol dm
)
(mol dm
)
n-propylamine
n-butylamine
iso-amylamine
6.0
7.0
8.0
7.5
7.5
7.5
7.5
7.5
7.5
2.5
5.0
7.5
15.69 (1.13)
15.65 (1.12)
15.63 (1.12)
15.60 (1.12)
15.57 (1.11)
15.53 (1.10)
15.79 (0.38)
15.68 (0.72)
15.60 (1.12)
15.56 (2.12)
15.50 (3.51)
15.41 (4.82)
16.89 (4.16)
16.86 (4.14)
16.84 (4.12)
16.81 (4.11)
16.79 (4.11)
16.77 (4.10)
16.96 (1.3)
17.31 (7.29)
17.29 (7.24)
17.26 (7.21)
17.23 (7.21)
17.21 (7.19)
17.19 (7.17)
17.41 (2.35)
17.34 (4.84)
17.23 (7.21)
17.15 (11.98)
17.01 (21.38)
— (—)
9.0
10.0
11.0
9.0
9.0
9.0
9.0
9.0
9.0
16.89 (2.7)
16.81 (4.11)
16.73 (6.90)
16.68 (10.71)
16.61 (14.92)
12.5
22.0
30.0
a Values in the parentheses are for the uncatalyzed oxidation of the amine by BAB[6].
activation parameter data obtained are presented in Ta-
ble IV.
lyte in aqueous solutions forming different species as
in eqs. (2)–(6).
Additions of the reaction mixtures to aqueous ac-
rylamide monomer solutions, in the dark, did not ini-
tiate polymerization indicating the absence of the in
situ formation of free radical species in the reaction
sequence. Proper control experiments were also run
simultaneously.
PhSO2NBrNa EF PhSO2NBrϪ ϩ Naϩ
PhSO2NBrϪ ϩ Hϩ EF PhSO2NHBr
(2)
(3)
PhSO2NHBr ϩ H2O EF PhSO2NH2 ϩ HOBr (4)
KЈ
d
2 PhSO2NHBr E
R
F PhSO2NH2 ϩ PhSO2NBr2
(KЈ ϭ 1.13 ϫ 10Ϫ2 at 25ЊC) (5)
d
MECHANISMS AND DISCUSSION
Stoichiometry and Product Analysis
HOBr ϩ Hϩ EF H2OBrϩ
(6)
In acidic medium, the probable oxidizing species are
The osmium(VIII) catalyzed reaction stoichiometry
for the oxidation of the primary amine by BAB is rep-
resented in eq. (1).
R9CH2NH2 ϩ PhSO2NBrNa ϩ H2O !:
R9CHO ϩ PhSO2NH2 ϩ NH3 ϩ Naϩ ϩ BrϪ (1)
where R ϭ CH3CH2Ϫ for n-propylamine (nPA),
CH3CH2CH2Ϫ for n-butylamine (nBA), and
(CH3)2CHCH2Ϫ for iso-amylamine (iAA).
Kinetics
Pryde and Soper [9], Morris et al. [10], and Bishop
and Jennings [11] have shown the existence of sim-
ilar equilibria in acid and alkaline solutions
of N-metallo-N-haloarylsulfonamides. Bromamine-B
(PhSO2NBrNa), which is similar to its chlorine ana-
logues like chloramine-T, behaves as a strong electro-
Figure 1 Plots of log kЈ vs. log[NaOH]: [Amine]0
ϭ
Ϫ2
Ϫ3
Ϫ4
7.50 ϫ 10 mol dm
;
[BAB]0
ϭ
9.00
ϫ
;
10 mol
␮ ϭ 0.40
Ϫ3
Ϫ
5
Ϫ3
dm
;
[OsO4]
ϭ
1.20
ϫ
10 mol dm
Ϫ
mol dm 3; and Temp. ϭ 308 K.

740
ANANDA, DEMAPPA, AND GOWDA
Table II Effect of Varying Hydroxide Concentration on the Rate. [BAB]0 ϭ 9.00 ϫ 10Ϫ4 mol
dmϪ3; [Amine]0 ϭ 7.50 ϫ 10Ϫ2 mol dmϪ3; [OsO4] ϭ 1.20 ϫ 10Ϫ5 mol dmϪ3; ␮ ϭ 0.40 mol
dmϪ3; and Temp. ϭ 35Њ Ϯ 0.1ЊCa
Ϫ
1
k ϫ 104/(s
)
[NaOH] ϫ 103
Ϫ
3
(mol dm
)
n-propylamine
n-butylamine
iso-amylamine
2.0
3.0
4.0
5.0
6.0
8.96 (0.73)
11.49
13.70
15.60 (1.12)
17.24
20.03
9.61 (2.80)
12.50
14.71
16.81 (4.11)
18.34
21.45
9.75
13.00 (5.21)
15.01 (6.38)
17.20 (7.21)
18.83 (8.18)
22.22
8.0
10.0
15.0
20.0
30.0
22.07 (1.58)
24.09 (5.36)
25.10
–
–
–
–
–
(1.93)
(2.23)
(3.28)
–
–
–
(6.92)
(8.43)
(10.2)
a Values in the parentheses are for the uncatalyzed oxidation of the amine by BAB [6].
the free acid (PhSO2NHBr), dibromamine-B (Ph-
SO2NBr2), HOBr, and H2OBrϩ. In alkaline medium,
where PhSO2NBr2 and H2OBrϩ do not exist, the ex-
pected reactive species are PhSO2NHBr, HOBr, and
PhSO2NBrϪ. Hardy and Johnston [12] have reported
the existence of the following equilibria in alkaline
solutions of BAB:
the anion, PhSO2NBrϪ, itself acts as the reactive spe-
cies responsible for the oxidation of amines.
It has been shown that OsO4 is stable as Os(VIII)
and exists in the following equilibria in alkaline me-
dium [13–15]:
OsO4 ϩ OHϪ ϩ H2O EF [OsO4(OH)(H2O)]Ϫ (9)
[OsO4(OH)(H2O)]Ϫ ϩ OHϪ EF
PhSO2NBrϪ ϩ H2O EF PhSO2NHBr ϩ OHϪ (7)
2
[OsO4(OH)2]Ϫ ϩ H2O (10)
KЈ
h
PhSO2NHBr ϩ H2O ERF PhSO2NH2 ϩ HOBr
(K Ј ϭ 4.21 ϫ 10Ϫ3 at 25ЊC) (8)
h
Neither of the two octahedral coordination species,
2
[OsO4(OH)(H2O)]Ϫ and [OsO4(OH)2]Ϫ , is likely to
As equation (8) indicates a slow hydrolysis, if HOBr
were the primary oxidizing species, a first-order retar-
dation of the rate by the added PhSO2NH2 would be
expected, which was not observed. If PhSO2NHBr
were the reactive species, a retardation of the rate by
[OHϪ] would be expected (eq. (7)), which is also con-
trary to the observed data. Therefore, it is likely that
form an effective complex with the oxidant. It is,
therefore, reasonable to postulate that OsO4 , with a
tetrahedral geometry, can effectively form a complex
with the oxidant species. Furthermore, a first-order de-
pendence of the rate on [BAB] and [Os(VIII)] each, a
fractional-order dependence on [OHϪ ], and zero-order
in [amine] suggest that the intermediate complex spe-
Table III Effect of Varying Catalyst Concentration on the Reaction Rate. [BAB]0 ϭ 9.00 ϫ
10Ϫ4 mol dmϪ3; [Amine]0 ϭ 7.50 ϫ 10Ϫ2 mol dmϪ3; [NaOH] ϭ 5.00 ϫ 10Ϫ3 mol dmϪ3; ␮ ϭ
0.40 mol dmϪ3; and Temp. ϭ 35Њ Ϯ 0.1ЊC
Ϫ
1
kЈ ϫ 103/(s
)
105[OsO4]
Ϫ
3
(mol dm
)
n-propylamine
n-butylamine
iso-amylamine
1.60
1.40
1.20
0.80
0.40
2.11
1.80
1.56
1.03
0.513
2.23
1.96
1.68
1.12
0.558
2.31
2.01
1.72
1.15
0.571

OXIDATION OF PRIMARY AMINES
741
and X, XЈ, and XЉ are complex intermediates whose
structures are shown in Scheme III.
rate ϭ Ϫd[BAB]t /dt ϭ k2 [PhSO2NBrϪ][OsO4],
from Scheme I. (11)
The total effective concentration of BAB is given by
eq. (12) as,
[BAB]t ϭ [PhSO2NHBr] ϩ [PhSO2NBrϪ] (12)
Substitution for [PhSO2NHBr] from equilibrium (i) in
eq. (12), solving for [PhSO2NBrϪ or BAB] and sub-
stitution in eq. (11) lead to the following rate law:
Figure 2 Plots of log kЈ vs. log[OsO4]: [Amine]0 ϭ 7.50
Ϫ
2
Ϫ
Ϫ
4
Ϫ3
ϫ 10 mol dm 3; [BAB]0 ϭ 9.00 ϫ 10 mol dm
;
Ϫ3
Ϫ
Ϫ
[NaOH] ϭ 5.00 ϫ 10 mol dm 3; ␮ ϭ 0.40 mol dm 3; and
Temp. ϭ 308 K.
K1k2[BAB]t[OsO4 ][OHϪ]
Ϫd[BAB]t /dt ϭ
(13)
K1[OHϪ] ϩ [H2O]
cies formed from OsO4 and PhSO2NBrϪ serves as the
effective oxidant.
Based on the preceding discussion of the experi-
mental data, the following mechanism (Scheme I) is
proposed for the Os(VIII) catalyzed amine-BAB re-
action:
The rate law (eq. (13)) is consistent with the observed
kinetic data including a first-order each in [BAB] and
[OsO4 ], and a fractional order in [OHϪ].
Since the rate ϭ kobs [BAB]0 , eq. (13) can be trans-
formed into the following forms:
1
K1 [OHϪ] ϩ [H2O]
K1 k2[OsO4][OHϪ]
ϭ
, assuming [BAB]o
K1
kobs
(i) PhSO2NHBr ϩ OHϪ E
RF
ϭ [BAB]t
PhSO2NBrϪ ϩ H2O (fast)
k2
or
(ii)
OsO4 ϩ PhSO2NBrϪ 9
9: X
(slow)
k3
1
[H2O]
1
(iii)
(iv)
S ϩ X 9
9
: XЈ ϩ OsO4
(fast)
(fast)
ϭ
ϩ
(14)
kobs K1k2[OsO4 ][OHϪ] k2[OsO4 ]
XЈ !: XЉ ϩ PhSO2NHϪ
The double reciprocal plots of 1/kobs vs. 1/[OHϪ] at
constant [OsO4 ] and other experimental conditions,
from eq. (14), were found to be linear (r Ͼ 0.9976).
The values of k2 and K1 were calculated from the in-
tercept and the slope, respectively, of the plots for the
(v) PhSO2NHϪ ϩ H2O !:
PhSO2NH2 ϩ OHϪ (fast)
(vi) XЉ ϩ H2O ϩ OHϪ !: !: !:
products (fast)
Scheme I
3
standard runs with [BAB]o ϭ 9.00 ϫ 10Ϫ4 mol dmϪ
3
and [S or amine]0 ϭ 7.50 ϫ 10Ϫ2 mol dmϪ and
where S is the amine substrate (nPA or nBA or iAA)
[OsO4 ] ϭ 1.20 ϫ 10Ϫ5 mol dmϪ3 at 308 K (Table V).
Table IV Temperature Dependence and Activation Parameters for the Oxidation of Primary Amines by BAB in the
Presence of OsO4 catalyst. [BAB]0 ϭ 9.00 ϫ 10Ϫ4 mol dmϪ3; [Amine]0 ϭ 7.50 ϫ 10Ϫ2 mol dmϪ3; [OsO4] ϭ 1.20 ϫ
5
3
10Ϫ mol dmϪ3; and ␮ ϭ 0.40 mol dmϪ
Ϫ
1
kЈ ϫ 104/s
Þ
Þ
Þ
⌬H
⌬S
⌬G
Ea
Ϫ
1
Ϫ
Ϫ
1
Ϫ
1
Ϫ1
Substrate
298 K
303 K
308 K
313 K
(kJ mol
)
(JK 1 mol
)
(kJ mol
)
(kJ mol )
n-Propylamine
n-butylamine
iso-amylamine
8.31
9.14
9.68
11.72
12.73
13.24
15.60
16.81
17.21
21.92
23.38
23.49
44.9
43.4
40.8
Ϫ153.1
Ϫ156.1
Ϫ165.6
91.7
91.1
91.4
47.4
45.9
43.3

742
ANANDA, DEMAPPA, AND GOWDA
Table V Equilibrium and Rate Constant Data from Eqs. (14)a and (16)b
k2 ϫ 104/
k2Ј ϫ 103/
Ϫ
4
Ϫ
Ϫ
1
Ϫ
Ϫ1
Substrate
K1 ϫ 10
(dm3 mol 1 s
)
(dm3 mol 1 s
)
n-Propylamine
n-butylamine
iso-amylamine
1.01 (1.03)
0.98 (0.98)
0.95 (1.05)
2.80
3.00
3.20
3.1
13.6
19.7
a Calculated from the plots of 1/kobs vs. 1/[OHϪ ] for OsO4 catalyzed reaction.
b Values in the parentheses were calculated from the plots of 1/kobs vs. 1/[OHϪ ] for the uncatalyzed reaction.
The constancy of K1 values and the near constancy of
k2 values (Table V) support the proposed mechanistic
Scheme I for the Os(VIII) catalyzed amine oxidation
by BAB.
Furthermore, the values of K1 for the present
Os(VIII) catalyzed primary amine oxidation by BAB
were compared with those of K1 obtained for the same
reaction in alkaline medium in the absence of the
Os(VIII) catalysis, which were previously reported by
us [6]. The mechanism and the rate law for the un-
catalyzed reaction of the amine (S) and BAB in alka-
line medium are given in Scheme II and eq. (15), re-
spectively, [6].
1
[H2O]
1
ϭ
ϩ
(16)
kЈ
obs
K1kЈ[S][OHϪ] kЈ[OsO4 ]
2
2
The values of K1 (1.03 ϫ 104 for nPA; 0.98 ϫ 104 for
nBA; and 1.05 ϫ 104 for iAA) calculated for the un-
catalyzed reactions compare well with the values of
K1 (1.01 ϫ 104 for nPA; 0.98 ϫ 104 for nBA; and
0.98 ϫ 104 for iAA) for the Os(VIII) catalyzed reac-
tions, under similar conditions. The constancy of K1
values and the near constancy of k2 (or k2Ј) values sup-
port the proposed mechanisms (Schemes I and II) for
both the uncatalyzed and the Os(VIII) catalyzed pri-
mary amine-BAB reactions.
A
detailed mechanistic interpretation of the
K1
Os(VIII) catalyzed oxidation of the primary amine by
BAB in NaOH medium is presented in Scheme III. An
anion of the oxidizing species, (PhSO2NBr)Ϫ, coor-
dinates through the sulfonamido nitrogen atom to
OsO4 activating BAB by stabilizing the charge on its
nitrogen atom and polarizing the N9Br bond in the
complex species X in the slow step (step i). In the fast
step ii, an electrophilic attack by the positive bromine
of the complex X at the amino nitrogen of the substrate
forms the intermediate complex species XЈ and regen-
erates the catalyst OsO4 . In the next fast step iii, the
intermediate XЈ disproportionates into an N-broma-
mine species XЉ and (PhSO2NBH)Ϫ which on hy-
drolysis can form the reduction product PhSO2NH2 .
The step iv involves a nucleophilic attack by H2O,
followed by intramolecular rearrangements, forming
an N-protonated amine intermediate and BrϪ. In the
last steps, the protonated amine intermediate is at-
tacked by OHϪ to form the aldehyde, NH3 , and H2O.
The kinetic data in Tables I–III show that the rate
of oxidation of the three amines by BAB, in the pres-
ence of the Os(VIII) catalyst, slightly increases in the
order: nPA Ͻ nBA Ͻ iAA, indicating the effects of
the alkyl groups in the amines. There is a very small
inductive effect. However, the steric effect is domi-
nant, judging from the small (relative) increase in the
rate of the catalyzed reaction as compared to the uncat-
alyzed reaction [6]. In fact, the uncatalyzed rates vary as
(i) PhSO2NHBr ϩ OHϪ E
RF
PhSO2NBrϪ ϩ H2O (fast)
kЈ
2
(ii)
PhSO2NBrϪ ϩ S 9
9: Y
(slow)
(fast)
(iii)
Y !: YЈ ϩ PhSO2NHϪ
(iv) PhSO2NHϪ ϩ H2O !:
PhSO2NH2 ϩ OHϪ (fast)
(v) YЈ ϩ H2O ϩ OHϪ !: !: !:
products (fast)
Scheme II
where S represents nPA or nBA or iAA and Y and YЈ
are complex intermediates [6].
The Scheme II leads to the following rate law:
K1kЈ[BAB]t[S][OHϪ]
K1[OHϪ] ϩ [H2O]
2
Ϫd[BAB]t /dt ϭ
(15)
The rate law (eq. (15)) derived for the uncatalyzed
reaction, which is consistent with the observed kinetic
data including a first-order each in [BAB] and [S], and
a fractional- order in [OHϪ], is similar to the rate law
(eq. (13)) of the catalyzed reaction.
The eq. (15) can be transformed into eq. (16) and
k2Ј and K1 calculated from the plots of 1/kЈ vs.
1/[OHϪ] (Table V).
obs
rate(nPA) /rate(nBA) Х
13 and rate(nBA) /rate(iAA) Х 21.

OXIDATION OF PRIMARY AMINES
743
The relative magnitudes of Ea for the oxidation of
the three amines support the above trend (Table IV)
and indicate that the reactions are enthalpy controlled.
mation of a rigid transition state, in each case.
The constant ⌬G values indicate that the three
primary amines react with BAB via the same mecha-
nism.
Þ
Þ
The fairly negative values of ⌬S indicate the for-
Ϫ
O
O
Ϫ
N
ии
(i)
OsO4 ϩ Br
S
Ph
Br
N
S
Ph
(slow)
ии
O
O
H
(OsO4)
(catalyst)
(oxidant)
(X)
Ϫ
Ϫ
O
S
H
H
H
H
␦
ϩ
ии
(ii)
R
C
N
ии
ϩ Br
N
Ph
R
C
N
(fast)
H
H
␦
O
O
O
H
Ϫ
(OsO4)
ии
Br
N
S
Ph
ии
(X)
ϩ OsO4
(substrate)
(XЈ)
Ϫ
H
H
H
H
␦
ϩ
R
C
N
R
C
N
ϩ PhSO2NHϪ
(iii)
(fast)
H
Br
O
O
ϩH2O
␦
H
H
Ϫ
ϪOHϪ
ии
Br
N
S
Ph
ии
PhSO2NH2
(XЈ)
(XЉ)
H
H
O
H
H
ϩ
(iv)
(v)
R
C
N
R
C
H
N
H ϩ BrϪ
(fast)
Br
H
H
ии
OH2
ии
H
H
O
H
ϩ
R
C
H
N
H
ϩ OHϪ
R
C
ϩ NH3 ϩ H2O
(fast)
(fast)
H
O
(aldehyde)
–
–
–
Here Ph ϭ C6H5 and R ϭ CH3CH2 for nPa, CH3CH2CH2 for nBa, and (CH3)2CHCH2
for iAA as in eq. (1).
Scheme III
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744
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