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