Osmium(VIII) catalysed and uncatalysed oxidation of aspirin drug by diperiodatocuprate(III) complex in aqueous alkaline medium: A mechanistic approach

Article abstract of DOI:10.1016/j.poly.2010.01.014

The kinetics of oxidation of a non-steroidal analgesic drug, aspirin (ASP) by diperiodatocuprate(III)(DPC) in the presence and absence of osmium(VIII) have been investigated at 298 K in alkaline medium at a constant ionic strength of 0.10 mol dm^-3 spectrophotometrically. The reaction showed a first-order in [DPC] and less than unit order in [ASP] and [alkali] for both the osmium(VIII) catalysed and uncatalysed reactions. The order with respect to Os(VIII) concentration was unity. The effects of added products, ionic strength, periodate and dielectric constant have been studied. The stoichiometry of the reaction was found to be 1:4 (ASP:DPC) for both the cases. The main oxidation product of aspirin was identified by spot test, IR, NMR and GC-MS. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. Activation parameters with respect to slow step of the mechanisms were computed and discussed for both the cases. The thermodynamic quantities were also determined for both reactions. The catalytic constant (K_C) was also calculated for catalysed reaction at different temperatures and the corresponding activation parameters were determined.

Full text of DOI:10.1016/j.poly.2010.01.014

Polyhedron 29 (2010) 1443–1452
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Osmium(VIII) catalysed and uncatalysed oxidation of aspirin drug
by diperiodatocuprate(III) complex in aqueous alkaline
medium: A mechanistic approach
*
Ragunatharaddi R. Hosamani, R.T. Mahesh, Sharanappa T. Nandibewoor
P.G. Department of Studies in Chemistry, Karnatak University, Dharwad 580 003, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The kinetics of oxidation of a non-steroidal analgesic drug, aspirin (ASP) by diperiodatocuprate(III)(DPC)
in the presence and absence of osmium(VIII) have been investigated at 298 K in alkaline medium at a
constant ionic strength of 0.10 mol dmꢀ3 spectrophotometrically. The reaction showed a first-order in
[DPC] and less than unit order in [ASP] and [alkali] for both the osmium(VIII) catalysed and uncatalysed
reactions. The order with respect to Os(VIII) concentration was unity. The effects of added products, ionic
strength, periodate and dielectric constant have been studied. The stoichiometry of the reaction was
found to be 1:4 (ASP:DPC) for both the cases. The main oxidation product of aspirin was identified by spot
test, IR, NMR and GC–MS. The reaction constants involved in the different steps of the mechanisms were
calculated for both reactions. Activation parameters with respect to slow step of the mechanisms were
computed and discussed for both the cases. The thermodynamic quantities were also determined for both
reactions. The catalytic constant (KC) was also calculated for catalysed reaction at different temperatures
and the corresponding activation parameters were determined.
Received 22 September 2009
Accepted 13 January 2010
Available online 18 January 2010
Keywords:
Aspirin
Os(VIII) catalysis
Diperiodatocuprate(III)
Oxidation
Mechanistic
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
and multiple equilibria between different copper(III) species are
involved, it would be interesting to know which of the species is
In recent years, the study of highest oxidation state transition
metals has intrigued many researchers. Transition metals in a
higher oxidation state can be stabilized by chelation with suitable
polydentate ligands. Metal chelates such as diperiodatocuprate(III)
[1], diperiodatoargentate(III) [2] and diperiodatonickelate(IV) [3]
are good oxidants in a medium with an appropriate pH value. Per-
iodate and tellurate complexes of copper in its trivalent state have
been extensively used in the analysis of several organic compounds
[4]. The kinetics of self-decomposition of these complexes was
studied in some detail [5]. Copper(III) is an intermediate in the cop-
per(II) catalysed oxidation of amino acids by peroxydisulphate [6].
The oxidation reaction usually involves the copper(II)–copper(I)
couple and such aspects are detailed in different reviews [7,8].
The use of diperiodatocuprate(III) (DPC) as an oxidant in alkaline
medium is new and restricted to a few cases due to its limited sol-
ubility and stability in aqueous medium. DPC is a versatile one-
electron oxidant for various organic compounds in alkaline med-
ium and its use as an analytical reagent is now well-recognized
[9]. Copper complexes have occupied a major place in oxidation
chemistry due to their abundance and relevance in biological
chemistry. When the copper(III) periodate complex is the oxidant
the active oxidant.
Aspirin (acetylsalicylic acid) (ASP) is one among the most used
drugs worldwide. It is a non-steroidal analgesic, anti-inflammatory
and anti-pyretic agent. It is used in acute conditions such as head-
ache, arthralgia, myalgia and other cases requiring mild analgesia.
It is widely studied in medicine and several methods are suggested
in literature for its determination [10].
In recent years, the use of transition metal ions such as osmium,
ruthenium and iridium, either alone or as binary mixtures, as cat-
alysts in various redox processes have attracted considerable inter-
est [11]. The role of osmium(VIII) as a catalyst in some redox
reactions has been reviewed [12]. Although the mechanism of
catalysis depends on the nature of the substrate, oxidant and on
experimental conditions, it has been shown [13] that metal ions
act as catalysts by one of these different paths such as the forma-
tion of complexes with reactants or oxidation of the substrate itself
or through the formation of free radicals. Osmium(VIII) catalysis in
redox reactions involves several complexes, different oxidation
states of osmium, etc. The literature survey reveals that there are
no reports on the oxidative mechanism of aspirin by DPC. We have
also observed that micro amounts of osmium(VIII) enhanced the
rate of oxidation of aspirin by DPC. Such oxidation studies may
throw some light on the mechanism of conversions of compounds
in biological system. In view of the complexity of the title reaction,
* Corresponding author. Fax: +91 836 2747884.
E-mail address: stnandibewoor@yahoo.com (S.T. Nandibewoor).
0277-5387/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2010.01.014

1444
R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
a detailed study of the reaction becomes important. Hence in order
to understand the active species of copper(III) species and os-
mium(VIII), and to propose the appropriate mechanisms for both
Os(VIII) catalysed and uncatalysed reactions, the title reaction
was undertaken.
No significant difference in the results was obtained under a N2
atmosphere and in the presence of air. In view of the ubiquitous
contamination of carbonate in the basic medium, the effect of car-
bonate was also studied. Added carbonate had no effect on the
reaction rates. The spectroscopic changes during the reaction are
shown in Fig. 1. It is evident from the figure that the concentration
of DPC decreases at 415 nm.
2. Experimental
3. Results and discussion
2.1. Materials and reagents
3.1. Stoichiometry and product analysis
All chemicals used were of reagent grade and double distilled
water was used throughout the work. A solution of aspirin (M/s.
S.S. Antibiotics Pvt. Ltd., Aurangabad, India) was prepared by dis-
solving the appropriate amount of recrystallised sample in double
distilled water. The purity of ASP sample was checked by compar-
ing its IR spectrum with literature data and with its m.p. 135 °C
(literature m.p. 136 °C). The required concentration of ASP was
used from its aqueous stock solution. The osmium(VIII) solution
was prepared by dissolving OsO4 (Johnson Matthey) in
0.50 mol dmꢀ3 NaOH. The concentration was ascertained [14] by
determining the unreacted [Fe(CN)6]4ꢀ with standard Ce(IV) solu-
tion in an acidic medium. The copper(III) periodate complex was
prepared by standard procedure [15,16]. The copper(III) complex
was verified by its UV–Vis spectrum, which showed an absorption
band with maximum at 415 nm. The aqueous solution of cop-
per(III) was standardized by iodometric titration and gravimetri-
cally by thiocyanate [17] method. The copper(II) was prepared by
dissolving a known amount of copper sulphate (BDH) distilled
water. Periodate solution was prepared by weighing out the re-
quired amount of sample in hot water and used after keeping it
for 24 h to attain equilibrium. Its concentration was ascertained
iodometrically [18] at neutral pH using phosphate buffer. Since
periodate is present in excess in DPC, the possibility of oxidation
of aspirin by periodate in alkaline medium at 25 °C was tested.
The progress of the reaction was followed iodometrically. There
was no significant reaction under the experimental conditions em-
ployed compared to the DPC oxidation of aspirin. KOH and KNO3
(BDH, AR) were employed to maintain the required alkalinity and
ionic strength respectively in reaction solutions.
Reaction mixture containing different ratios of DPC to aspirin in
the presence of 5.0 ꢁ 10ꢀ5 mol dmꢀ3 KIO4 (8.0 ꢁ 10ꢀ7 mol dmꢀ3
osmium(VIII) for the catalysed reaction) were equilibrated at
298 K for 6 h in a closed vessel under nitrogen atmosphere. The
remaining concentration of DPC was estimated spectrophotometri-
cally at 415 nm. The results indicate four moles of diperiodatocup-
rate(III) consumed by one mole of aspirin as given in Scheme 1.
The main reaction products were extracted with ether, which
was identified as 1,4-benzoquinone-2-carboxylate ion by spot test
[19]. The nature of 1,4-benzoquinone-2-carboxylate ion was con-
firmed by its IR spectrum which showed a C@O stretching at
1632 cmꢀ1 indicating the presence of C@O group at 1,4-benzoqui-
none moiety, the band at 1584 cmꢀ1 and also at 1361 cmꢀ1 indicat-
ing the presence of COOꢀ group. The product was also
characterized by NMR spectra (CDCl3, d ppm) chemical shift at
6.73 (d, 1H, C6–H), 6.80 (d, 1H, C5–H) 7.78 (s, 1H, C3–H). It was fur-
ther confirmed by its melting point 206 °C (literature m.p. 205–
207 °C). Further, 1,4-benzoquinone-2-carboxylate ion was sub-
jected to GC–Mass Spectral analysis. GC–MS data was obtained
on a 17 A Shimadzu gas chromatograph with a QP-5050A Shima-
dzu mass spectrometer using the EI ionization technique. The mass
spectrum (Fig. 2) showed a molecular ion peak at 152 amu con-
firming 1,4-benzoquinone-2-carboxylate ion. All other peaks ob-
served in GC–MS can be interpreted in accordance with the
observed structure of the 1,4-benzoquinone-2-carboxylate ion. An-
other product, acetate was identified by spot test [19]. The product
Cu(II) was identified by UV–Vis spectra. The reaction products do
not undergo further oxidation under the present kinetic conditions.
2.2. Kinetic measurements
3.2. Reaction orders
The kinetic measurements were performed on a Varian CARY 50
Bio UV–Vis spectrophotometer. The kinetics was followed under
pseudo first-order conditions where [ASP] > [DPC] both in uncatal-
ysed and catalysed reactions at 25 0.1 °C, unless specified. In the
absence of catalyst the reaction was initiated by mixing the DPC to
ASP solution which also contained required concentration of KNO3,
KOH and KIO4.The reaction in the presence of catalyst was initiated
by mixing DPC to ASP solution which also contained required con-
centration of KNO3, KOH, KIO4 and Os(VIII). The progress of reac-
tion was followed spectrophotometrically at 415 nm by
monitoring the decrease in absorbance due to DPC with the molar
The kinetics of oxidation of aspirin by DPC was investigated at
several initial concentrations of reactants in alkaline medium in
absorbancy index, ‘e
’ taken as 6230 100 dm3 molꢀ1 cmꢀ1 in both
catalysed and uncatalysed reactions. It was verified that there is a
negligible interference from other species present in the reaction
mixture at this wavelength.
The pseudo first-order rate constants (kU or kt), in both the cases
were determined from the log(absorbance) versus time plots. The
plots were linear up to 80% completion of reaction and the rate
constants were reproducible within 5%. Regression analysis of
experimental data to obtain the regression coefficient, r and stan-
dard deviation, S was performed using Microsoft Excel-2003.
Kinetic runs were also carried out under N2 atmosphere in order
to understand the effect of dissolved oxygen on the rate of reaction.
Fig. 1. Spectroscopic changes occurring in the oxidation of aspirin by diperioda-
tocuprate(III)] at 25 °C, [DPC] = 1.0 ꢁ 10ꢀ4
,
[ASP] = 1.0 ꢁ 10ꢀ3
,
[OHꢀ] = 0.05 and
I = 0.10 mol dmꢀ3 with scanning time interval = 1 min.

R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
1445
O
C
6
3
O
CH3
O
-
5
4-
Os(VIII)
-
1
+
CH3COO
+
2OH
4
+ 4[Cu(OH)2(H3IO6)(H2IO6)]
-
-
2
2
COO
O
COO
3-
2-
6
+ H2IO6
7H IO
+
4Cu(OH)
+
3
Scheme 1. Stoichiometry of the reaction.
Fig. 2. GC–Mass Spectrum of 1,4-benzoquinone-2-carboxylate ion with its molecular ion peak at 152 amu.
the presence and absence of osmium(VIII). The reaction is under-
stood to occur in parallel paths with contributions from both cata-
lysed and uncatalysed paths. Thus the total rate constant (kT) is
equal to the sum of the rate constants of the catalysed (kC) and
uncatalysed (kU) reactions, so kC = kT ꢀ kU. Hence the reaction or-
ders have been determined from the slopes of log kC versus log
(concentration) plots by varying the concentrations of aspirin,
OHꢀ and catalyst Os(VIII), in turn, while keeping all other concen-
trations and conditions constant.
3.3. Effect of [diperiodatocuprate(III)]
The oxidant DPC concentration was varied in the range of
ꢀ
1.0 ꢁ 10ꢀ5 to 1.0 ꢁ 10ꢀ4 mol dmꢀ3 at fixed aspirin, OHꢀ and IO4
for uncatalysed and catalysed reactions. The linearity of the plots
of log [absorbance] versus time (r P 0.983, S 6 0.016) up to 80%
completion of the reaction (Fig. 3) indicates a first-order depen-
dence of the reaction rate on [DPC]. The pseudo first-order rate
constants remained unchanged with the variation of [DPC] (kU
(Table 1), kC (Table 2; Os(VIII)). This confirms the unit order in
[DPC] for both the reactions.
Fig. 3. First-order plots for the oxidation of aspirin by DPC in aqueous alkali
medium at 298 K. [DPC] ꢁ 10ꢀ4
; (1) 1.0; (2) 3.0; (3) 6.0; (4) 8.0; (5) 10.0
[ASP] = 1.0 ꢁ 10ꢀ3, [OHꢀ] = 0.05 and I = 0.10 mol dmꢀ3
.
of Os(VIII) in catalysed reaction. The substrate aspirin was varied in
the range of 1.0 ꢁ 10ꢀ4 to 1.0 ꢁ 10ꢀ3 mol dmꢀ3. The kU and kC val-
ues increased with increase in concentration of aspirin indicating
an apparent less than unit order dependence on [ASP] [order
kU = 0.50 and kC = 0.68] under the conditions of experiment (Tables
1 and 2) (r P 0.997, S6 0.009). This is also confirmed in the plots of
3.4. Effect of [aspirin]
The effect of aspirin on the rate of reaction was studied at con-
stant concentrations of alkali, DPC and a constant ionic strength of
0.10 mol dmꢀ3 uncatalysed reaction and at constant concentration

1446
R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
Table 1
Effect of [DPC], [ASP], [OHꢀ] and [IO4ꢀ] on the oxidation of aspirin by DPC in alkaline
medium at 25 °C, I = 0.10 mol dmꢀ3
.
105 [DPC]
103 [ASP]
[OHꢀ]
105 [IO4
]
104 kU (sꢀ1
Found Calculated
)
ꢀ
(mol dmꢀ3
)
(mol dmꢀ3
)
(mol dmꢀ3
)
(mol dmꢀ3
)
1.0
3.0
6.0
8.0
10.0
1.0
1.0
1.0
1.0
1.0
0.05
0.05
0.05
0.05
0.05
1.0
1.0
1.0
1.0
1.0
9.43
9.41
9.44
9.45
9.45
9.49
9.49
9.49
9.49
9.49
10.0
10.0
10.0
10.0
10.0
0.1
0.3
0.6
0.8
1.0
0.05
0.05
0.05
0.05
0.05
1.0
1.0
1.0
1.0
1.0
3.00
6.03
7.98
9.02
9.43
3.10
6.18
8.23
8.97
9.49
10.0
10.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
0.01
0.03
0.05
0.08
0.1
1.0
1.0
1.0
1.0
1.0
5.2
5.22
8.35
9.49
1.02
1.05
Fig. 4. Plot of kU vs. [ASP]0.50 and kU vs. [ASP]. In case of oxidation of aspirin by DPC.
8.63
9.43
1.01
1.05
with increasing [alkali] and the order was found to be less than
unity (Tables 1 and 2).
10.0
10.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
0.05
0.05
0.05
0.05
0.05
1.0
2.0
5.0
7.0
10.0
9.43
9.45
9.46
9.47
9.47
9.49
9.49
9.49
9.49
9.49
3.6. Effect of [periodate]
The effect of increasing concentration of periodate was studied
by varying the periodate concentration from 1.0 ꢁ 10ꢀ5 to
1.0 ꢁ 10ꢀ4 mol dmꢀ3 keeping all other reactants concentrations
constant. The added periodate had no effect on the rate of reaction
(Tables 1 and 2).
kU versus [ASP]0.50 in which it is linear rather than the direct plot of
log kU versus [ASP] (Fig. 4) similarly catalysed reaction the plots of
kC versus [ASP]0.68 in which it is linear rather than the direct plot of
log kC versus [ASP] (Fig. 5).
3.7. Effect of Ionic strength (I) and dielectric constant of the medium
(D)
3.5. Effect of [alkali]
The effect of alkali on the reaction has been studied for both the
cases in the range of 0.01– 0.1 mol dmꢀ3 at constant concentra-
The effect of ionic strength was studied by varying the potas-
sium nitrate concentration from 0.1 to 1.0 mol dmꢀ3 at constant
concentrations of all other reactants. The rate was found to in-
crease with increase in the ionic strength for both cases. A plot of
log kU or kC versus I1/2 is linear with positive slope (Figs. 6 and 7).
tions of aspirin, DPC and
a constant ionic strength of
0.10 mol dmꢀ3 in uncatalysed reaction and at constant concentra-
tion of Os(VIII) in catalysed reaction. The rate constants increased
Table 2
Effect of [DPC], [ASP], [OHꢀ] and [IO4ꢀ] on the osmium(VIII) catalysed oxidation of aspirin by DPC in alkaline medium at 25 °C, I = 0.10 mol dmꢀ3
.
105 [DPC]
(mol dmꢀ3
103 [ASP]
[OHꢀ]
105 [IO4]
107 [Os(VIII)]
103 kT
(sꢀ1
104 kU
(sꢀ1
103 kC (sꢀ1
)
)
(mol dmꢀ3
)
(mol dmꢀ3
)
(mol dmꢀ3
)
(mol dmꢀ3
)
)
)
Found
Calculated
1.0
3.0
6.0
8.0
10.0
1.0
1.0
1.0
1.0
1.0
0.05
0.05
0.05
0.05
0.05
1.0
1.0
1.0
1.0
1.0
8.0
8.0
8.0
8.0
8.0
6.21
6.20
6.24
6.23
6.23
9.43
9.41
9.44
9.45
9.45
5.26
5.25
5.29
5.28
5.28
5.26
5.26
5.26
5.26
5.26
10.0
10.0
10.0
10.0
10.0
0.1
0.3
0.6
0.8
1.0
0.05
0.05
0.05
0.05
0.05
1.0
1.0
1.0
1.0
1.0
8.0
8.0
8.0
8.0
8.0
1.02
2.73
4.14
5.14
6.21
3.00
6.03
7.98
9.02
9.43
0.70
2.12
3.34
4.24
5.26
0.71
2.06
3.50
4.46
5.26
10.0
10.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
0.01
0.03
0.05
0.08
0.1
1.0
1.0
1.0
1.0
1.0
8.0
8.0
8.0
8.0
8.0
1.90
4.58
6.21
7.77
9.09
5.20
8.63
9.43
10.1
10.50
1.38
3.71
5.26
6.76
8.07
1.39
3.59
5.27
6.97
8.09
10.0
10.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
0.05
0.05
0.05
0.05
0.05
1.0
2.0
5.0
7.0
10.0
8.0
8.0
8.0
8.0
8.0
6.21
6.31
6.54
6.71
6.86
9.43
9.45
9.46
9.47
9.47
5.26
5.36
5.59
5.76
5.91
5.26
5.26
5.26
5.26
5.26
10.0
10.0
10.0
10.0
10.0
1.0
1.0
1.0
1.0
1.0
0.05
0.05
0.05
0.05
0.05
1.0
1.0
1.0
1.0
1.0
3.0
5.0
8.0
20.0
30.0
2.85
4.05
6.21
13.5
18.4
9.43
9.43
9.43
9.43
9.43
1.91
3.11
5.26
12.60
17.5
1.90
3.08
5.26
12.40
17.3

R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
1447
3.8. Effect of added products
The initially added products, 1,4-benzoquinone-2-carboxylate
and copper(II) (CuSO4) did not have any significant effect on the
rate of the reaction in both the case of uncatalysed and catalysed
reactions.
3.9. Polymerization study
The involvement of free radicals in the reaction was examined
as follows. The reaction mixture, to which a known quantity of
acrylonitrile monomer was initially added, was kept for 2 h in an
inert atmosphere. On diluting the reaction mixture with methanol,
a white precipitate was formed, indicating the involvement of free
radicals in the reaction. The blank experiments of either DPC or
aspirin alone with acrylonitrile did not induce any polymerization
under the same conditions. Initially added acrylonitrile decreased
the rate of reaction indicating free radical participation in presence
and absence of Os(VIII).
Fig. 5. Plot of kC vs. [ASP]0.68 and kC vs. [ASP]. In case of Os(VIII) catalysed oxidation
of aspirin by DPC.
I/D x 102
(
)
3.10. Effect of [Os(VIII)]
1.8
1.6
1.4
1.2
1.0
1.96
2.02
2.00
1.98
1.96
The [Os(VIII)] concentrations was varied from 3.0 ꢁ 10ꢀ7 to
3.0 ꢁ 10ꢀ6 mol dmꢀ3 range, at constant concentration of DPC,
aspirin, alkali and ionic strength. The order in [Os(VIII)] (Table 2)
was found to be unity from the linearity of the plot of kC versus
[Os(VIII)] (r = 0.9725).
1.97
1.98
1.99
2.00
3.11. Effect of temperature
The influence of temperature on the rate of reaction was studied
for uncatalysed reaction at 25, 30, 35 and 40 °C. The rate constants
(k1), of the slow step of Scheme 2 were obtained from the slopes
and the intercepts of the plots of 1/kU versus 1/[ASP] and 1/kU ver-
sus 1/[OHꢀ] plots at four different temperatures. The values are gi-
ven in Table 3. The activation parameters for the rate determining
step were obtained by the least square method of plot of log k1 ver-
sus 1/T and are presented in Table 3.
0.0
0.4
I1/2
0.8
1.2
(
)
Fig. 6. Effect of ionic strength and dielectric constant of the medium on oxidation of
aspirin by DPC in aqueous alkali medium at 298 K.
The rate constants (k2), of the slow step of Scheme 3 were ob-
tained from the slopes and the intercepts of the plots of [Os-
(VIII)]/kC versus 1/[ASP] and [Os(VIII)]/kC versus 1/[OHꢀ] plots at
four different temperatures. The values are given in Table 4. The
activation parameters for the rate determining step were obtained
by the least square method of plot of log k2 versus 1/T and are pre-
sented in Table 4.
The water-soluble copper(III) periodate complex is reported
[20] to be [Cu(HIO6)2(OH)2]7ꢀ. However, in aqueous alkaline med-
ium at high pH as employed in this study, periodate is unlikely to
4ꢀ
exist as HIO6 (as present in the complex) as is evident from its
involvement in the multiple equilibria [21] (1)–(3) depending on
the pH of the solution.
H5IO6 ꢀ H4IO6ꢀ þ Hþ
H4IO6ꢀ ꢀ H3IO62ꢀ þ Hþ
H3IO62ꢀ ꢀ H2IO63ꢀ þ Hþ
ð1Þ
ð2Þ
ð3Þ
Fig. 7. Effect of ionic strength and dielectric constant of the medium on Os(VIII)
catalysed oxidation of aspirin by DPC in aqueous alkali medium at 298 K.
ꢀ
Varying the t-butyl alcohol and water percentage varied the
dielectric constant of the medium, ‘D’. The D values were calcu-
lated from the equation D = DwVw + DBVB, where Dw and DB are
dielectric constants of pure water and t-butyl alcohol, respectively,
and Vw and VB are the volume fractions of components water and
t-butyl alcohol, respectively, in the total mixture. The decrease in
dielectric constant of the reaction medium decreases the rate and
the plot of log kU or kC versus I/D was liner with negative slope
(Figs. 6 and 7) (r P 0.9824, S 6 0.006).
Periodic acid exists as H5IO6 and as H4IO6 around pH 7. Thus,
under the conditions employed in alkaline medium, the main spe-
cies are expected to be H3IO6 and H2IO63ꢀ. At higher concentra-
2ꢀ
tions, periodate also tends to dimerise [9]. However, formation of
this species is negligible under the conditions employed for this
study. Hence, at the pH employed in this study, the soluble cop-
per(III) periodate complex exists as diperiodatocuprate(III),
[Cu(H3IO6)2(OH)2]3ꢀ, a conclusion also supported by earlier work
[22].

1448
R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
3-
K1
[Cu(OH)2(H3IO6)(H2IO6)]4-+ H2O
-
[Cu(OH)2(H3IO6)2] + OH
O
C
CH3
+
O
K2
[Cu(OH)2(H3IO6)(H2IO6)]4-
Complex (C)
-
COO
.
O
+
2-
-
k1
+
Cu(OH)
+ 2H3IO6
+
Complex (C)
CH3COO
slow
COO-
O+
.
O
fast
fast
2-
4 -
3 -
H2IO6
+
+
Cu(OH) H3IO6
+
-
[Cu(OH)2(H3IO6)(H2IO6)]
+
2
COO-
COO
O+
O
-
OH
+
-
H
-
COO
COO
OH
6
3
O
2-
O
5
4 -
fast
1
+ 4H3IO6
+2Cu(OH)2
-
+ 2[Cu(OH)2(H3IO6)(H2IO6)]
-
4
H
2
COO
O
COO
OH
Scheme 2. Detailed scheme for the oxidation of aspirin by alkaline diperiodatocuprate(III).
Since Scheme 2 is in accordance with the generally well-ac-
cepted principle of noncomplementary oxidations taking place in
sequence of one-electron steps, the reaction between the substrate
and oxidant would afford a radical intermediate. A free-radical
scavenging experiment revealed such a possibility (see infra). This
type of radical intermediate has also been observed in earlier work
[26].
4. Mechanism for uncatalysed reaction
The reaction between the aspirin and DPC complex in alkaline
media has the stoichiometry of 1:4 with first-order dependence
on the DPC concentration and apparently less than unit order in
aspirin and alkali concentrations. In most of the reports [23] on
DPC oxidation, periodate had retarding effect and OHꢀ had an a
increasing effect on the rate of reaction and monoperiodatocup-
rate(III) is considered to be active species. However in the present
kinetic study, entirely different kinetic observations have been ob-
tained. The rate of reaction increased with increase in alkalinity
(Table 1) and periodate had totally no effect on the rate of the reac-
tion. Accordingly, the deprotonated form of DPC is considered to be
the active species of copper(III). It is well known that aspirin exists
in the anionic form in basic medium [24].
The probable structure of the complex (C) is given below:
5-
O
OH
Cu
O
I
HO
HO
HO
O
OH
OH
O
O
I
O
In the first equilibrium step the [OHꢀ] deprotonates the DPC to
give a deprotonated DPC. The less than unit order in [ASP] presum-
ably results from formation of a complex (C) between the anionic
form of aspirin and the active species of DPC. This complex (C)
decomposes in a slow step to give a free radical of salicylate ion,
acetate ion and copper(II). Such type anionic free radical is avail-
able in the literature [25]. This free radical species further reacts
with three more moles of deprotonated DPC in further fast steps
to form the products such as 1,4-benzoquinone-2-carboxylate
ion, Cu(II) and periodate as given in Scheme 2.
OH
O
O
C
O
CH3
O
C
O

R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
1449
Table 3
linear (Fig. 8). From the slopes and intercepts, the values of K1
and K2 were calculated at different temperatures and these values
are given in Table 3. The van’t Hoff’s plots were made for variation
of K1 and K2 with temperature (log K1 versus 1/T (r P 0.9605,
S 6 0.005), log K2 versus 1/T (r P 0.994, S 6 0.008) and the values
Thermodynamic activation parameters for the oxidation of aspirin by DPC in alkaline
medium with respect to the slow step of Scheme 2.
Temperature (K)
103 k1 (sꢀ1
)
(A) Effect of temperature
298
303
308
313
318
1.23
2.10
3.00
3.39
3.98
of enthalpy of reaction
of reaction G, were calculated for the first and second equilibrium
steps. These values are given in Table 3. A comparison of the
value (86 kJ molꢀ1) from K1 with that of H# (42 kJ molꢀ1) of rate
DH, entropy of reaction DS and free energy
D
D
H
D
limiting step supports that the reaction before the rate determin-
ing step is fairly slow as it involves high activation energy [28]. A
Parameters
Values
high negative value of
D
S# (ꢀ158 J Kꢀ1 molꢀ1) suggests that inter-
(B) Activation parameters (Scheme 2)
Ea (kJ molꢀ1
)
44.7 2.0
42.3 2.1
mediate complex is more ordered than the reactants [29].
D
D
D
H# (kJ molꢀ1
S# (J Kꢀ1 molꢀ1
G# (kJ molꢀ1
)
)
ꢀ158
6
)
89.3 3.1
5.0 0.3
5. Mechanism for Os(VIII) catalysed reaction
log A
Temperature
(K)
K1
10ꢀ4 K2
(dm3 molꢀ1
)
Osmium(VIII) is known [30] to form different complexes at dif-
(dm3 molꢀ1
)
ferent OHꢀ concentrations, [OsO4(OH)2]2ꢀ and [OsO5(OH)]3ꢀ At
.
higher concentration of OHꢀ, [OsO5(OH)]3ꢀ is significant. At lower
concentrations of OHꢀ, as employed in the present study, and since
the rate of oxidation increased with increase in [OHꢀ], it is reason-
able that [OsO4(OH)2]2ꢀ was operative and its formation is impor-
tant in the reaction [30]. To explain all the observed orders,
Scheme 3 is proposed for osmium(VIII) catalysed reaction.
The equilibrium step 1 and stoichiometry is same as in uncatal-
ysed reaction. In second step anionic form of aspirin reacts with ac-
tive species of osmium(VIII) to form a complex (C1) in view of less
than unit order in [ASP]. The complex (C1) reacts with one mole of
deprotonated DPC in a slow step to give a free radical of salicylate
ion [25] acetate ion and copper(II) with regeneration of catalyst
Os(VIII). This free radical species further reacts with three more
moles of deprotonatad DPC in further fast steps to yield the prod-
ucts such as 1,4-benzoquinone-2-carboxylate ion, Cu(II) and perio-
date as given in Scheme 3.
(C) Effect of temperature to calculate K1 and K2 for the oxidation of aspirin by
diperiodatocuprate(III) in alkaline medium
298
303
308
313
318
2.46
6.03
9.15
17.2
21.7
3.06
1.42
0.74
0.69
0.63
Thermodynamic quantities
Values from K1
Values from K2
(D) Thermodynamic quantities using K1 and K2
D
D
D
H (kJ molꢀ1
S (J Kꢀ1 molꢀ1
G298 (kJ molꢀ1
)
86
297 20
ꢀ2.2 0.5
4
ꢀ61
3
)
)
ꢀ122 15
ꢀ25 1.5
[DPC] = 1.0 ꢁ 10ꢀ4; [ASP] = 1.0 ꢁ 10ꢀ3; [OHꢀ] = 0. 05; [IO4ꢀ] = 1.0 ꢁ 10ꢀ5 mol dmꢀ3
.
Spectroscopic evidence for the complex (C) formation between oxi-
dant and substrate was obtained from UV–Vis spectra of aspirin
(1.0 ꢁ 10ꢀ3), DPC (1.0 ꢁ 10ꢀ4), [OHꢀ] (0.05 mol dmꢀ3) and a mix-
ture of both. A bathochromic shift of about 4 nm from 242 to
246 nm in the spectra of ASP was observed. However, the Michae-
lis–Menten plot also proved the complex formation between DPC
and aspirin, which explains the less than unit order dependence
on [ASP]. Such a complex between a substrate and an oxidant has
been observed in other studies [27].
The probable structure of the complex (C1) is given below:
3-
O
O
O H
H O
O
O s
O
The Scheme 2 leads to rate law (5)
O
ꢀd½DPCꢂ
Rate ¼
Rate
½DPCꢂ
¼ k1½Cꢂ ¼ k1K1K2½DPCꢂ½ASPꢂ½OHꢀꢂ
ð4Þ
ð5Þ
dt
O
C
k1K1K2½ASPꢂ½OHꢀꢂ
¼ kU
¼
1 þ K1½OHꢀꢂ þ K1K2½ASPꢂ½OHꢀꢂ
C H3
O
C
The rate law (5) may be verified by rearranging it in the form of
Eq. (6)
O
1
1
1
1
¼
þ
þ
ð6Þ
Spectroscopic evidence for the complex (C1) formation between os-
mium(VIII) and aspirin was obtained from UV–Vis spectra of aspirin
(1.0 ꢁ 10ꢀ3), Os(VIII) (8.0 ꢁ 10ꢀ7), [OHꢀ] (0.05 mol dmꢀ3) and a mix-
ture of both. A hypsochromic shift from 341 to 337 nm in the spectra
of aspirin was observed. This is also evident from the plot of 1/kC ver-
sus 1/[ASP], which shows a straight line with non-zero intercept.
Such type of catalyst-substrate complex formation was also ob-
served in other studies [31]. Scheme 3 leads to the rate law (8)
kU k1K1K2½OHꢀꢂ½ASPꢂ k1K2½ASPꢂ k1
According to Eq. (6), the plots of 1/kU versus 1/[OHꢀ] (r P 0.998,
S 6 0.014) and 1/kU versus 1/[ASP] (r P 0.997, S 6 0.016) should be
linear which is the case as given in Fig. 8. From the slopes and
intercepts of such plots, the reaction constants K1, K2 and k1 were
calculated as (2.46 0.05) dm3 molꢀ1
,
(3.06 0.12) ꢁ 104 dm3
molꢀ1 and (1.23 0.04) ꢁ 10ꢀ3 sꢀ1 respectively. The value of K1 is
in the neighborhood of earlier literature [27]. Using these con-
stants the rate constants were calculated and the values agreed
well with the experimental values (Table 1).
Rate ¼ k2½C1ꢂ½DPCꢂ
¼ k2K1K3½DPCꢂ½ASPꢂ½OHꢀꢂOsðVIIIÞ
ð7Þ
ð8Þ
The thermodynamic quantities for the first and second equilib-
rium steps of Scheme 2 can be evaluated as follows. The [ASP] and
[OHꢀ] (Table 1) were varied at four different temperatures. The
plots of 1/kU versus 1/[OHꢀ] and 1/kU versus 1/[ASP] should be
Rate
½DPCꢂ
k2K1K3½ASPꢂ½OHꢀꢂ½OsðVIIIÞꢂ
¼ kC ¼ kT ꢀkU ¼
1þK1½OHꢀꢂþK3½ASPꢂþK1K3½ASPꢂ½OHꢀꢂ

1450
R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
K1
3-
[Cu(OH)2(H3IO6)(H2IO6)]4-+ H2O
-
[Cu(OH)2(H3IO6)2] + OH
O
C
CH3
+ [OsO4(OH)2]
O
K3
2-
Complex (C1)
-
COO
.
O
+
4-
-
k2
+
Cu(OH)
+
CH3COO
Complex (C )
+
[Cu(OH)2(H3IO6)(H2IO6)]
1
slow
COO-
2-
2-
[OsO (OH) ]
+ 2H3IO6
+
4
2
O+
.
O
fast
fast
2-
4 -
3 -
H2IO6
+
H IO +
Cu(OH)
O
+
-
[Cu(OH)2(H3IO6)(H2IO6)]
+
2
3
6
COO-
COO
O+
-
OH
+
-
H
-
COO
COO
OH
6
O
2-
O
5
4 -
fast
1
+ 4H3IO6
+2Cu(OH)2
-
COO
+ 2[Cu(OH)2(H3IO6)(H2IO6)]
-
4
H
2
O
COO
3
OH
Scheme 3. Detailed scheme for the Os(VIII) catalysed oxidation of aspirin by alkaline diperiodatocuprate(III).
The rate law (8) may be verified by rearranging it in the form of
from K1 with that of D
H# (10 kJ molꢀ1) of rate limiting step sup-
Eq. (9)
ports that the reaction before the rate determining step is fairly
slow as it involves high activation energy [28]. In the same manner,
K3 values were calculated at different temperatures and the corre-
sponding values of thermodynamic quantities are given in Table 4.
½OsðVIIIÞꢂ
1
1
1
1
¼
þ
þ
þ
ð9Þ
kC
k2K1K3½OHꢂ½ASPꢂ k2K3½ASPꢂ k2K1½OHꢀꢂ k2
According to Eq. (9), the plots of [Os(VIII)]/kC versus 1/[OHꢀ]
and [Os(VIII)]/kC versus 1/[ASP] were linear (Fig. 9). From the inter-
cepts and slopes of such plots, the reaction constants K1, K3, and k2
were calculated as (8.70 0.2) dm3 molꢀ1, (3.9 0.1) ꢁ 102 dm3
molꢀ1, (7.78 0.20) ꢁ 104 dm3 molꢀ1 sꢀ1, respectively. The value
of K1 is in the neighborhood of earlier literature [31]. These con-
stants were used to calculate the rate constants and compared
with the experimental kC values and found to be in reasonable
agreement with each other, which fortifies the Scheme 3.
5.1. Catalytic activity
Moelwyn-Hughes [32] pointed out that catalysed and uncataly-
sed reactions proceed simultaneously and the relationship is
x
kT ¼ kU þ KC½catalystꢂ
Here kT is the observed pseudo first-order rate constant ob-
tained in the presence of osmium(VIII) catalyst, kU is that for the
uncatalysed reaction, KC is the catalytic constant and x is the order
of the relation with respect to osmium(VIII) which is found to be
unity in the present study. The value of KC was calculated using
the equation
The thermodynamic quantities for the different equilibrium
steps, in Scheme 3 can be evaluated as follows. The aspirin and
hydroxide ion concentrations (Table 2) were varied at different
temperatures. The plots of [Os(VIII)]/kC versus 1/[ASP] (r P 0.9988,
S 6 0.00132) and [Os(VIII)]/kC versus 1/[OHꢀ] (r P 0.9996,
S 6 0.00087) should be linear as shown in Fig. 9. From the slopes
and intercepts, the values of K1 are calculated at different temper-
atures. A van’t Hoff’s plot was made for the variation of K1 with
temperature [i.e., log K1 versus 1/T (r P 0.9984, S 6 0.1105)] and
x
x
KC ¼ ðkT ꢀ kUÞ=½OsðVIIIÞꢂ ¼ kC=½OsðVIIIÞꢂ
The values of KC were evaluated at different temperatures (298–
318 K) and KC was found to vary with temperature. A plot of log KC
versus 1/T was linear and the values of energy of activation and
other thermodynamic parameters for the catalyst are tabulated
in Table 5.
the values of the enthalpy of reaction
and free energy of reaction G, were calculated. These values are
also given in Table 4. A comparison of the
H value (104 kJ molꢀ1
DH, entropy of reaction DS
D
D
)

R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
1451
Table 4
Thermodynamic activation parameters for the Os(VIII) catalysed oxidation of aspirin
by DPC in alkaline medium with respect to the slow step of Scheme 3.
Temperature (K)
10ꢀ4 k2 (dm3 molꢀ1 sꢀ1
)
(A) Effect of temperature
298
303
308
313
318
7.78
8.12
8.68
9.83
10.4
Parameters
Values
(B) Activation parameters (Scheme 3)
Ea (kJ molꢀ1
D
D
D
)
12
10
1
1
H# (kJ molꢀ1
S# (J Kꢀ1 molꢀ1
G# (kJ molꢀ1
)
)
ꢀ119
8
)
45
2
log A
7.0 0.3
Temperature
(K)
K1
K3 ꢁ 10ꢀ2
Fig. 9. Verification of rate law (9) of Os(VIII) catalysed oxidation of aspirin by
diperiodatocuprate(III) at 298 K.
(dm3 molꢀ1
)
(dm3 molꢀ1
)
(C) Effect of temperature to calculate K1 and K3 for the oxidation of aspirin by
diperiodatocuprate(III) in alkaline medium
298
303
308
313
318
8.70
34.5
58.0
106
132
3.9
3.4
3.0
2.8
2.4
Table 5
Values of catalytic constant (KC) at different temperatures and activation parameters
calculated using KC values.
Temperature (K)
KC ꢁ 10ꢀ3 (dm3 molꢀ1 sꢀ1
)
298
303
308
313
318
4.47
8.25
12.6
17.4
Thermodynamic quantities
Values from K1
Values from K3
(D) Thermodynamic quantities using K1 and K3
D
D
D
H (kJ molꢀ1
S (J Kꢀ1 molꢀ1
G298 (kJ molꢀ1
)
104 08
372 35
ꢀ3.5 1.0
ꢀ17 0.8
ꢀ10 0.2
ꢀ15 1.0
[IO4ꢀ] = 1.0 ꢁ 10ꢀ5
21.2
)
)
Ea (kJ molꢀ1
)
40.4 2.1
37.9 1.5
ꢀ47.4 5.0
52.0 2.5
10.7 0.5
D
D
D
H# (kJ molꢀ1
S# (J Kꢀ1 molꢀ1
G# (kJ molꢀ1
)
[DPC] = 1.0 ꢁ 10ꢀ4
;
[ASP] = 1.0 ꢁ 10ꢀ3
;
[OHꢀ] = 0.05;
;
)
[Os(VIII)] = 8.0 ꢁ 10ꢀ7; I = 0.10 mol dmꢀ3
.
)
log A
[DPC] = 1.0 ꢁ 10ꢀ4; [ASP] = 1.0 ꢁ 10ꢀ3; [OHꢀ] = 0.05 mol dmꢀ3; [IO4ꢀ] = 1.0 ꢁ 10ꢀ5
mol dmꢀ3; [Os(VIII)] = 8.0 ꢁ 10ꢀ7 mol dmꢀ3; I = 0.10 mol dmꢀ3
.
rate constant for the slow step indicate that the oxidation presum-
ably occurs via an inner-sphere mechanism. This conclusion is sup-
ported by earlier observation [35]. The activation parameters
evaluated for the catalysed and uncatalysed reaction explain the
catalytic effect on the reaction. The catalyst, Os(VIII) form the com-
plex (C1) with substrate which enhances the reducing property of
the substrate than that without catalyst, Os(VIII). Further the cata-
lyst Os(VIII) modifies the reaction path by lowering the energy of
activation.
6. Conclusion
Fig. 8. Verification of rate law (6) for the oxidation of aspirin by diperiodatocup-
rate(III) at 298 K.
Among the various species of Cu(III) in alkaline medium, depro-
tonated form of diperiodatocuprate(III)(DPC)[Cu(OH)2(H3IO6)
(H2IO6)]4ꢀ is considered as the active species. The active species
of osmium(VIII) is found to be [OsO4(OH)2]2ꢀ. Thermodynamic
quantities of individual steps in the mechanisms were evaluated.
Activation parameters with respect to slow step were also com-
puted. The overall sequence is consistent with the observed prod-
uct, mechanistic and kinetic study.
The increases in the rate, with increasing ionic strength, is in fa-
vor of reaction between charged species of reactants, as present in
Schemes 2 and 3. The effect of solvent on the reaction rate is de-
scribed in detail in the literature [33]. For the limiting case of a zero
angle approach between two dipoles or anion dipole system, Amis
[34] has shown that log kobs versus 1/D gives a straight line, with a
negative slope for a reaction between negative ion and a dipole or
between two dipoles, while a positive slope is obtained for positive
ion-dipole reactions. In the present investigations, plot of log kU or
kC versus 1/D were linear with negative slopes, which supports the
involvement of negative ions as in Schemes 2 and 3.
Appendix A
According to Scheme 2
ꢀd½DPCꢂ
Rate ¼
¼ k1½Cꢂ
D
S# suggests that the intermediate com-
dt
The negative value of
plex is more order than the reactants [29]. The observed higher
¼ k1K1K2½DPCꢂ½ASPꢂ½OHꢀꢂ
ðA:1Þ

1452
R.R. Hosamani et al. / Polyhedron 29 (2010) 1443–1452
The total concentration of DPC is given by (where T and f stands
And,
for total and free, respectively)
½OSðVIIIÞꢂT ¼ ½OSðVIIIÞꢂf þ ½C1ꢂ ¼ ½OsðVIIIÞf ꢂð1 þ K3½ASPꢂÞ
½DPCꢂ ¼ ½DPCꢂ þ ½CuðOHÞ ðH3IO6ÞðH2IO6Þꢂ4ꢀ þ ½Cꢂ
½OsðVIIIÞꢂT
T
f
2
½OSðVIIIÞꢂf ¼
ðB:5Þ
¼ ½DPCꢂ f1 þ K1½OHꢀꢂ þ K1K2½ASPꢂ½OHꢀꢂg
1 þ K3½ASPꢂ
f
Substituting Eqs. (B.2)–(B.5) in Eq. (B.1) and omitting T and f we
get
Therefore,
½DPCꢂT
½DPCꢂf ¼
ðA:2Þ
k2K1K3½ASPꢂ½OHꢀꢂ½OsðVIIIÞꢂ
1 þ K1½OHꢀꢂ þ K1K2½ASPꢂ½OHꢀꢂ
Rate
¼ kC ¼ kT ꢀ kU
¼
½DPCꢂ
1 þ K1½OHꢀꢂ þ K3½ASPꢂ þ K1K3½ASPꢂ½OHꢀꢂ
Similarly,
½ASPꢂT ¼ ½ASPꢂf þ ½Cꢂ
References
½ASPꢂT
½ASPꢂf ¼
1 þ K1K2½DPCꢂ½OHꢀꢂ
[1] K.B. Reddy, B. Sethuram, T. Navaneeth Rao, Indian J. Chem. 23A (1984) 593.
[2] A. Kumar, P. Kumar, P. Ramamurthy, Polyhedron 18 (1999) 773.
[3] R.S. Shetter, S.T. Nandibewoor, J. Mol. Catal. A 234 (2005) 137.
[4] W. Niu, Y. Zhu, K. Hu, C. Tong, H. Yang, Int. J. Chem. Kinet. 28 (1996) 899.
[5] G.I. Rozovoskii, A.K. Misyavichyus, A.Y. Prokopchik, Kinet. Catal. 16 (1975) 337.
[6] M.G. Ramreddy, B. Sethuram, T. Navaneeth Rao, Indian J. Chem. 16 (1978) 313.
[7] K.D. Karlin, Y. Gultneh, in: S.J. Lipard (Ed.), Progress in Inorganic Chemistry,
vol. 35, Wiley, New York, 1997, p. 220.
In view of low concentration of [DPC] used,
½ASPꢂf ¼ ½ASPꢂT
Similarly,
½OHꢀꢂf ¼ ½OHꢀꢂT
ðA:3Þ
ðA:4Þ
[8] W.B. Tolman, Acc. Chem. Res. 30 (1997) 227.
[9] B. Sethuram, Some Aspects of Electron Transfer Reactions Involving Organic
Molecules, Allied Publishers (P) Ltd., New Delhi, 2003. p. 78.
[10] S.M. Sultan, Analyst 112 (1987) 1331.
[11] Z.D. Bugarcic, S.T. Nandibewoor, M.S.A. Hamza, F. Heinemann, R.V. Eldik,
Dalton Trans. (2006) 2984.
[12] M.C. Agrawal, S.K. Upadhyay, J. Sci. Ind. Res. 42 (1983) 508.
[13] P. Veerasomaiah, K.B. Reddy, B. Sethuram, T. Navaneeth Rao, Indian J. Chem.
26A (1987) 402.
Substituting Eqs. (A.2)–(A.4) in Eq. (A.1) and omitting T and f we
get
Rate
½DPCꢂ
k1K1K2½ASPꢂ½OHꢀꢂ
¼ kU
¼
1 þ K1½OHꢀꢂ þ K1K2½ASPꢂ½OHꢀꢂ
[14] O.C. Sexena, Microchem. J. 12 (1967) 609.
[15] K.P. Jaiswal, K.L. Yadava, Indian J. Chem. 11 (1973) 837.
[16] C.P. Murthy, B. Sethuram, T. Navaneeth Rao, Z. Phys. Chem. 262 (1981) 336.
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Quantitative Chemical Analysis, fifth ed., ELBS, Longman, Essex, UK, 1996. p.
455.
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[19] F. Feigl, Spot Tests in Organic Analysis, Elsevier, New York, 1975. pp. 333, 455.
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[21] J.C. Bailar Jr., H.J. Emeleus, S.R. Nyholm, A.F. Trotman-Dikenson,
Comprehensive Inorganic Chemistry, vol. 2, Pergamon Press, Oxford, 1975.
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[23] K.B. Reddy, B. Sethuram, T.N. Rao, Indian J. Chem. 20A (1981) 395.
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Ltd., New Delhi, 2000. p. 158.
Appendix B
According to Scheme 3
Rate ¼ k2½C1ꢂ½DPCꢂ
¼ k2K1K3½DPCꢂ½ASPꢂ½OHꢀꢂ½OsðVIIIÞꢂ
ðB:1Þ
The total concentration of DPC is given by (subscripts T and f
stands for total and free, respectively)
4ꢀ
½DPCꢂT ¼ ½DPCꢂf þ ½CuðOHÞ2ðH3IO6ÞðH2IO6Þꢂ
¼ ½DPCꢂ þ K1½DPCꢂ½OHꢀꢂ
f
½DPCꢂ ¼ ½DPCꢂ ð1 þ K1½OHꢀꢂÞ
[26] M. Jaky, M. Szeverenyi, L.I. Simandi, Inorg. Chem. Acta 186 (1991) 33.
[27] D.C. Hiremath, T.S. Kiran, S.T. Nandibewoor, Int. J. Chem. Kinet. 39 (2007) 236.
[28] K.S. Rangappa, M.P. Raghavendra, D.S. Mahadevappa, D. Channegouda, J. Org.
Chem. 63 (1998) 531.
T
f
Therefore,
[29] A. Weissberger, in: E.S. Lewis (Ed.), Investigations of Rates and Mechanism of
Reactions in Techniques of Chemistry, vol. 4, Wiley, New York, 1974, p. 421.
[30] D.L. Kamble, S.T. Nandibewoor, J. Phys. Org. Chem. 11 (1998) 171.
[31] T.S. Kiran, D.C. Hiremath, S.T. Nandibewoor, Catal. Lett. 122 (2008) 144.
[32] E.A. Moelwyn-Hughes, Kinetics of Reactions in Solutions, Oxford University
Press, London, 1947. p. 297.
[33] E.A. Moelwyn-Hughes, Physical Chemistry II, Pergamon Press, New York, 1961.
[34] E.S. Amis, Solvents Effect on Reaction Rates and Mechanisms, Academic Press,
New York, 1966.
½DPCꢂT
½DPCꢂf ¼
½ASPꢂf ¼
ðB:2Þ
1 þ K1½OHꢀꢂ
Similarly,
½ASPꢂT
½OHꢂT
½OHꢂf ¼
1 þ K3½OsðVIIIÞꢂ
1 þ K3½DPCꢂ
In view of low concentration of [Os(VIII) and [DPC] used,
[35] M. Martinez, M.A. Pitarque, R.V. Eldik, J. Chem. Soc., Dalton Trans. (1996) 2665.
½ASPꢂf ¼ ½ASPꢂT
½OHꢀꢂf ¼ ½OHꢀꢂT
ðB:3Þ
ðB:4Þ