Spectral and mechanistic investigations of ruthenium(III) catalyzed oxidation of atenolol by diperiodatocuprate(III) in aqueous alkaline medium 1

Article abstract of DOI:10.1134/S0036024412030247

The kinetics of ruthenium(III) catalyzed oxidation of atenolol by diperiodatocuprate(III) in aqueous alkaline medium at a constant ionic strength of I = 0.10 M has been studied spectrophotometrically at 27°C. The reaction between diperiodatocuprate(III) and atenolol in alkaline medium in presence of ruthenium(III) exhibits 2: 1 stoichiometry (atenolol: diperiodatocuprate(III)). The main products were identified by spot test, IR, NMR, and LC-MS. The reaction is of first order in DPC concentrations and has less than unit order in both ATN and alkali concentrations. The order in ruthenium(III) was unity. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreases the rate. The oxidation reaction in alkaline medium has been shown to proceed via a ruthenium(III)-atenolol complex, which reacts with monoperiodatocuprate(III) in a rate determining step followed by other fast steps to give the products. Probable mechanism is proposed and discussed. The activation parameters with respect to the slow step of the mechanism and thermodynamic quantities were determined and discussed. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S0036024412030247

ISSN 0036ꢀ0244, Russian Journal of Physical Chemistry A, 2012, Vol. 86, No. 3, pp. 369–374. © Pleiades Publishing, Ltd., 2012.
CHEMICAL KINETICS
AND CATALYSIS
Spectral and Mechanistic Investigations of Ruthenium(III)
Catalyzed Oxidation of Atenolol by Diperiodatocuprate(III)
1
in Aqueous Alkaline Medium
R. K. Patil, S. T. Nandibewoor, and S. A. Chimatadar
P. K. Department of Studies in Chemistry, Karnatak University, Dharwad 580003, India
eꢀmail: schimatadar@gmail.com
Received March 24, 2011
Abstract—The kinetics of ruthenium(III) catalyzed oxidation of atenolol by diperiodatocuprate(III) in
aqueous alkaline medium at a constant ionic strength of
I = 0.10 M has been studied spectrophotometrically
at 27°C. The reaction between diperiodatocuprate(III) and atenolol in alkaline medium in presence of rutheꢀ
nium(III) exhibits 2 : 1 stoichiometry (atenolol: diperiodatocuprate(III)). The main products were identified
by spot test, IR, NMR, and LCꢀMS. The reaction is of first order in DPC concentrations and has less than
unit order in both ATN and alkali concentrations. The order in ruthenium(III) was unity. Intervention of free
radicals was observed in the reaction. Increase in periodate concentration decreases the rate. The oxidation
reaction in alkaline medium has been shown to proceed via a ruthenium(III)–atenolol complex, which reacts
with monoperiodatocuprate(III) in a rate determining step followed by other fast steps to give the products.
Probable mechanism is proposed and discussed. The activation parameters with respect to the slow step of
the mechanism and thermodynamic quantities were determined and discussed.
Keywords: atenolol, diperiodatocuprate(III), ruthenium(III), kinetics.
DOI: 10.1134/S0036024412030247
4
ꢀ(2ꢀHydroxyꢀ3ꢀisopropylaminopropoxy)phenylꢀ dation chemistry because of their abundance and releꢀ
acetamide, commercially known as atenolol (ATN), a vance in biological chemistry [11, 12]. Copper(III) is
ꢀadrenoreceptor blocking agent, is used as a antihyꢀ involved in many biological electron transfer reactions
β
pertensive drug [1]. It is also used for antiꢀangina [13]. When the copper(III) periodate complex is oxiꢀ
treatment to relieve symptoms, improve tolerance and dant and multiple equilibria between different copꢀ
as an antiꢀarrhythmic to help regulate heartbeat. It is per(III) species [14] are involved, it would be interestꢀ
also used in management of alcohol withdrawal, in ing to know which of the species is the active oxidant,
anxiety states, migraine prophylaxis, hyperthyroidism and to propose the appropriate mechanism, the title
and tremors [2, 3].
reaction is investigated in detail.
In recent years, the study of the highest oxidation
state of transition metals has intrigued many researchꢀ
ers. Transition metals in a higher oxidation state can be
stabilized by chelation with suitable polydentate
ligands. Metal chelates such as diperiodatocuꢀ
prate(III) [4], diperiodatoargentate(III) [5, 6], and
diperiodatonickelate(IV) [7] are good oxidants in a
medium with an appropriate pH value. Copper(III) is
shown to be an intermediate in the copper(II)ꢀcataꢀ
lyzed oxidation of amino acids by peroxydisulfate [8].
The oxidation reaction usually involves the copꢀ
per(II)–copper(I) couple, and such aspects are
detailed in different reviews [9, 10]. The use of diperiꢀ
odatocuprate(III) (DPC) as an oxidant in alkaline
medium is new and restricted to a few cases because its
limited solubility and stability in aqueous medium.
Copper complexes have occupied a major place in oxiꢀ
EXPERIMENTAL
All chemicals used were of reagent grade, and douꢀ
bly distilled water was used throughout the work. A
solution of atenolol (ATN) (M/s. S.S. Antibiotics Pvt.
Ltd., Aurangabad, India) was prepared by dissolving
an appropriate amount of ATN in double distilled
water. Ruthenium(III) solution was prepared by disꢀ
solving RuCl3 (S. d. fine chem.) in 0.20 M HCl. The
concentration was determined [15] by EDTA titraꢀ
tion. The copper(III) periodate complex was prepared
by standard procedure [16, 17]. The aqueous solution
of copper(III) was standardized by iodometric titraꢀ
tion and gravimetrically by the thiocyanate [18]
method. The copper(II) solution was prepared by disꢀ
solving the known amount of copper sulfate (BDH) in
double distilled water. Periodate solution was prepared
by weighing the required amount of sample in hot
1
The article is published in the original.
369

370
PATIL et al.
water and used after 24 h. Its concentration was ascerꢀ atenolol in aqueous alkaline medium proceeds with a
III
tained iodometrically [19] at neutral pH by using measurable rate in the absence of the catalyst, Ru
.
phosphate buffer. KOH and KNO3 (BDH, AR) were Hence, in the presence of catalyst the reaction is
employed to maintain the required alkalinity and ionic understood to occur via parallel paths with contribuꢀ
strength, respectively, in reaction solutions.
tions from the uncatalysed and catalysed paths. In
both cases, the pseudo first order rate constants were
obtained from log(absorbance) versus time plots and
were reproducible within ±5%. Thus, the total rate
Kinetic measurements were performed on a Varian
CARY 50 Bio UVꢀVIS spectrophotometer at its maxꢀ
imum absorption wavelength, 415 nm, as a function of
time. The kinetics was followed under pseudoꢀfirst
constant ( t
in the presence of catalyst ( c
catalyst ( u) reaction. Hence, k =k –ku.
k
) is equal to the sum of the rate constants
k
) and in the absence of
order condition where [ATN] > [DPC] at 27
± 0.1°C,
k
c
t
unless specified. The reaction was initiated by mixing
the DPC to atenolol solution which also contained
III
RESULTS AND DISCUSSION
required concentrations of Ru , KNO3, KOH, and
KIO4 and the progress of the reaction was followed
Different sets of reaction mixtures containing variꢀ
spectrophotometrically at 415 nm by monitoring the ous ratios of DPC to ATN in the presence of constant
–
decrease in absorbance of DPC. Beer’s law was verified amounts of ruthenium(III), OH , and KNO3 were
ε
under experimental conditions ( = 6230 ±
100 dm3 kept for 2 h in a closed vessel under nitrogen atmoꢀ
–1
–1
mol cm ). The kinetic runs were followed more sphere. The remaining concentration of DPC was
than 80% completion of the reaction and good first estimated by spectrophotometrically. The results indiꢀ
order kinetics was observed. The DPC oxidation of cated 1 : 2 stoichiometry as given in equation.
OH
O
CH3
CH3
O CH2 CH CH2 NH CH
O CH2 C OH
4
5
RuIII
3
2
–
+
2[Cu(H IO )(H O) ] + 2OH
2
6
2
2
6
O
1
O
(1)
CH2
C
CH2 C
NH2
OH
CH3
CH3
3–
+ 2Cu2+ + 2H IO6 + NH + 4H O.
+
H C NH CH
3
2 3 2
The reaction product was extracted with ether and with respect to [DPC] and [RuIII], was unity. The
recrystallized form aqueous alcohol and the purity was order in [ATN] and [OH] was found to be less than
checked by HPLC. This was identified as 4ꢀcarboxyꢀ unity. Periodate had a retarding effect on the rate of
methoxyphenylacetic acid by its IR spectrum, which reaction. Initially added products did not have any sigꢀ
showed a band at 1690 cm–1 due to >C=O stretching nificant effect on the rate of the reaction. The ionic
–1
of acid and a broad band at 2845 cm due to O–H strength was varied by varying the KNO3 concentraꢀ
stretching. 4ꢀCarboxymethoxyphenylacetic acid was tion. The increasing ionic strength of the medium, the
further characterized by 1HNMR spectrum (DMSO). rate of the reaction decreased. Dielectric constant of
Further, the product was subjected to LCꢀMass specꢀ the medium, D, was varied by varying tꢀbutyl alcohol
tral analysis with ESI technique (solvents: acetonitrile + and found that decrease in dielectric constant of the
water + ammonium acetate). Ammoniated peak at reaction medium, rate of the reaction increased. To
+
+
2
28 amu (M +17) was obtained, which conforms
M
test the presence of free radicals, the reaction mixture,
at 211 amu, which corresponds to 4ꢀcarboxymethoxyꢀ was mixed with acrylonitrile and kept in an inert atmoꢀ
phenylacetic acid. Ammonia was qualitatively identiꢀ sphere for 24 h. Dilution with methanol, a white preꢀ
fied using Nessler’s reagent. Nꢀisopropylmethyꢀ cipitate was formed, indicating the intervention of free
lamine, which is highly soluble in water, was identified radicals in the reaction. The added acrylonitrile
by spot test [20]. Another product copper(II) was decreased the rate of reaction also indicating freeꢀradꢀ
identified by UVꢀVis spectra. The reaction products ical intervention. Based on the above experimental
do not undergo further oxidation under the present results, the rate law can be written
kinetic conditions.
–d[DPC]/dt
= k
[DPC][Ru ][ATN] [OH–]0.40.
III
0.70
The reaction orders have been determined from the
slopes of log c versus log(concentration) plots by varyꢀ
k
The reaction between the atenolol and diperiodaꢀ
ing the concentration of DPC, atenolol, rutheꢀ tocuprate(III) complex in alkaline media in presence
nium(III), periodate, and hydroxide ion. The order of ruthenium(III) has the stoichiometry 1 : 2 with
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 3 2012

SPECTRAL AND MECHANISTIC INVESTIGATIONS
371
firstꢀorder dependence on DPC and ruthenium(III) form a complex (C). Then, this complex (C) reacts
concentrations and an apparent order of less than with MPC in a slow step to form a free radical derived
unity in substrate, alkali concentrations and negative from ATN and the product copper(II) is formed. This
fractional order dependence on periodate. No effect of freeꢀradical species further reacts with another moleꢀ
added products was observed. The less than unit order cule of MPC species in a fast step to yield the products
in ATN concentration indicates the formation of a 4ꢀcarboxymethoxyphenylacetic acid, Nꢀisopropylꢀ
complex (C) between the ruthenium(III) and atenolol methylamine, ammonia, Cu(II), and periodate. So,
prior to the formation of the products. K3 is the comꢀ the detailed mechanistic scheme for the oxidation
posite equilibrium constant comprising the equilibꢀ of ATN by diperiodatocuprate(III) is presented in
rium to bind active species of ATN to MPC species to scheme:
K1
–
–
2–
[
Cu(H IO ) ] + OH
3
[Cu(H IO )(H IO )] + H O,
2 6 3 6 2
6 2
K2
2–
2–
[
Cu(H IO )(H IO )] + 2H O
2
[Cu(H IO )(H O) ] + [H IO ] ,
2
6
3
6
2
6
2
2
3
6
OH
O CH2 CH CH2 NH CH
CH3
CH3
K3
2–
[
Ru(H O) OH]
2
+
Complex (C),
5
O
CH2
C
NH2
OH
CH3
CH3
•
O CH2 CH CH NH CH
k
slow
Complex (C) + [Cu(H IO )(H O) ]
2
6
2
2
O
CH2
C
NH2
[Ru(H O) OH] + Cu2+ + H IO6 + 2H O + H ,
2
–
3–
+
+
2
5
2
2
OH
OH
O CH2 C O
CH3
CH3
•
O CH2 CH CH NH CH
fast
–
•
+
[ Cu(H IO )(H O) ] + OH
2
6
2
2
O
O
CH2
C
CH2 C
NH2
OH
CH3
3–
+ Cu2+ + H IO6 + NH OH,
+
H C NH CH
3
2
4
CH3
fast
–
+
H + OH
H O.
2
Since scheme is in accordance with the generally
wellꢀaccepted principle of nonꢀcomplementary oxiꢀ
dations taking place in sequence of oneꢀelectron steps,
the reaction between the substrate and oxidant would
afford a radical intermediate. A freeꢀradical scavengꢀ
ing experiment revealed such a possibility. This type of
radical intermediate has also been observed in earlier
literature [21, 22]. The probable structure of the comꢀ
plex (C) is given below:
2+
OH
CH3
CH3
O CH2 CH CH2 NH CH
OH2
O
OH2
OH
CH2
C
Ru
NH2
OH2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 3 2012

372
PATIL et al.
1
/[OH−]
×
10 , dm mol
8
−2
3
−1
12
4
0
0
1.6
1.2
0.8
0.4
0
2
1
0
.4
.6
.8
0
0.4
0.8
1.2
1.6
12
0
2
4
/[ATN]
6
8
10 , dm mol
10
5
−4
3
−1
1
×
×
0
1
2
3
10 , mol dm
4
6
4
−3
[
H IO62−]
3
Verification of rate law (2) in the form of (3) for the ruthenium(III) catalysed oxidation of atenolol, by diperiodatocuprate(III) at
27°C.
Spectroscopic evidence for the complex formaꢀ plot also proved the complex formation between DPC
tion between oxidant and substrate was obtained and ATN, which explains the less than unit order
–
4
from UVꢀVis spectra of ATN (5.0
×
10 M), DPC dependence on ATN concentrations. Such a complex
–5
–
–2
(5.0
×
10
M), OH (4.0
×
10 M) and mixture of between a substrate and catalyst has also been observed
both. A hypsochromic shift from 298 to 292 nm in the in the literature [23]. The above mechanism leads the
spectra of ATN was observed. The Michaelis–Menten following rate law:
–
III
Rate
DPC]
kK K K [DPC][ATN][OH ][Ru ]
1 2 3
ꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ = k = k – k = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀ.
(2)
c
t
u
2
6
–
–
2–
–
–
[
[
H IO ] + K [OH ][H IO ] + K K [OH ] + K K K [OH ][ATN]
3
1
3
6
1
2
1
2
3
The Eq. (2) can be rearranged to equation:
is far greater than K2. This may be attributed to the
greater tendency of DPC to undergo hydrolysis comꢀ
pared to the dissociation of hydrolyzed species in alkaꢀ
line medium.
III
2–
2–
6
Ru
k
[H
3
IO
6
]
[H
3
IO
]
ꢀ
ꢀꢀꢀꢀꢀꢀꢀꢀ = ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ ꢀꢀ + ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
c
–
kK K [ATN]
2 3
kK K K [ATN][OH ]
1
2
3
(3)
1
1
k
The effect of ionic strength on the rate of reaction
is not in accordance with proposed mechanism, which
might be due to the high ionic strength used in the
+
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ + ꢀ,
kK [ATN]
3
which is suitable for verification.
According to Eq. (3), other conditions being conꢀ
stant, plots of [Ru(III)]/kc versus 1/[ATN],
reaction. Increase in the content of tꢀbutanol,
increases the rate of reaction, which seems to be conꢀ
trary to the expected interaction between ion and neuꢀ
tral species.
–
[
Ru(III)]/kc
versus 1/[OH ], and [Ru(III)]/ c
k
versus
2
−
[
H IO ] should be linear and are found to be so (figꢀ
ure). The slopes and intercepts of such plots lead to the
3
6
H#, and S# are obtained and are
The values of Ea
found to be 33.43
and –51.33 ±
son of value (27.05
30.9 0.6) of rate limiting step supports that the first
,
±
Δ
Δ
–1
–1
0.2 kJ mol , 30.93
±
0.6 kJ mol ,
–1
values of
0
5
K1
K
1, K2
,
K3, and
k
as 1.76
±
3
0.03 M , 1.69
±
–1
–1
4 J K mol , respectively. A compariꢀ
.30
.24
×
±
,
10–
0.40
K3, and
3
M
×
, 1.44
±
0.10
10 s , respectively 27
values, the rate constants were calcuꢀ
×
10 dm mol , and
3
–1
#
Δ
Δ
H
±
1.4) from K1 with that of H
4
–1
°C
. Using these
(
±
,
K2
k
step of scheme is fairly fast since it involves low activaꢀ
lated and compared with experimental data (table). tion energy with those obtained for the slow step of the
This fortifies the scheme. The equilibrium constant K1 reaction [24, 25].
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A
Vol. 86
No. 3 2012

SPECTRAL AND MECHANISTIC INVESTIGATIONS
373
–
III
Effect of variation of [DPC], [ATN], [OH ], and [Ru ] on the ruthenium(III) catalysed oxidation of atenolol by diperiꢀ
= 0.10 M
odatocuprate(III) in aqueous alkaline medium at 27
°
C,
I
2
–1
–
IO4
5
104,
[OH–],
4
III
106, kt
ꢀ2
–3
kc
× 10 , s
[
DPC]
×
10 , [ATN]
×
[
]
M
×
10 , [Ru ]
×
×
s
10 ,
ku
×
s
10 ,
–
1
–1
M
M
M
M
found
calc.
1
3
5
7
.0
.0
.0
.0
5.0
5.0
5.0
5.0
5.0
1.0
3.0
5.0
7.0
10.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.01
0.02
0.04
0.08
0.10
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
0.04
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
0.7
1.0
3.0
5.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
2.0
4.0
8.0
10.0
1.72
1.71
1.73
1.74
1.71
0.50
1.23
1.73
2.43
3.20
0.89
1.34
1.73
2.20
2.40
0.89
1.08
1.27
1.54
1.73
2.37
2.01
1.73
1.16
0.78
3.32
3.40
3.35
3.38
3.26
0.92
2.29
3.35
4.07
4.86
1.57
2.55
3.35
4.71
5.16
4.33
3.82
3.35
2.25
1.15
3.35
3.35
3.35
3.35
3.35
1.39
1.37
1.39
1.40
1.38
0.40
1.00
1.40
2.02
2.71
0.74
1.01
1.40
1.73
1.84
1.90
1.62
1.40
0.94
0.65
0.55
0.74
0.93
1.20
1.40
1.39
1.39
1.39
1.39
1.39
0.35
0.94
1.35
1.94
2.78
0.69
1.06
1.32
1.81
1.89
1.97
1.57
1.32
0.86
0.59
0.50
0.79
0.86
1.25
1.36
1
0.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
5.0
The values of
electron transfer processes. The negative value of S
indicates that the complex (C) is more ordered than
the reactants [26]. The value of S within the range
Δ
H# and
Δ
S# were both favorable for
REFERENCES
#
Δ
1
. M. White, A. Fourney, E. Mikes, and F. H. H. Leenen,
Am. J. Hypertens. 12, 151 (1999).
. D. G. McDevitt and J. K. Nelson, Br. J. Clin. Pharmaꢀ
#
Δ
2
for radical reaction has been ascribed [27] to the
nature of electron pairing and unpairing processes and
to the loss of degrees of freedom formerly available to
the reactants upon the formation of rigid transition
state. The observed modest enthalpy of activation and
a relatively low value of the entropy of activation as
well as a higher rate constant of the slow step indicate
that the oxidation presumably occurs via innerꢀsphere
mechanism. This conclusion is supported by earlier
observation [28, 29]. The catalyst ruthenium(III)
forms the complex (C) with the substrate, which
enhances the reducing property of the substrate than
that without the ruthenium(III) catalyst. Further, the
ruthenium(III) catalyst modifies the reaction path by
lowering the energy of activation.
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