Kinetics and mechanism of uncatalysed and ruthenium(III) catalysed oxidation of allyl alcohol by diperiodatoargentate(III) in aqueous alkaline medium

Article abstract of DOI:10.1002/poc.1126

The oxidation of allyl alcohol by diperiodatoargentate(III) (DPA) is carried out both in the absence and presence of ruthenium(III) catalyst in alkaline medium at 298 K and a constant ionic strength of 1.1 mol dm ^-3 was studied spectrophotometrically. The oxidation products in both the cases were acrolein and Ag(I), identified by spectral studies. The stoichiometry is same in both the cases, that is, [AA]/[DPA] = 1:1. The reaction shows first order in [DPA] and has less than unit order dependence each in both [AA] and [Alkali] and retarding effect of [IO₄^-] in both the catalysed and uncatalysed cases. The order in [Ru(III)] is unity. The active species of DPA is understood to be as monoperiodatoargentate(III) (MPA) in both the cases. The uncatalysed reaction in alkaline medium has been shown to proceed via a MPA-allyl alcohol complex, which decomposes in a rate determining step to give the products. In catalysed reaction, it has been shown to proceed via a Ru(III)-allyl alcohol complex, which further reacts with one molecule of MPA in a rate determining step to give the products. The reaction constants involved in the different steps of the mechanisms were calculated for both reactions. The catalytic constant (K_c) was also calculated for catalysed reaction at different temperatures. The 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. Copyright

Full text of DOI:10.1002/poc.1126

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY
J. Phys. Org. Chem. 2007; 20: 55–64
Published online in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/poc.1126
Kinetics and mechanism of uncatalysed and
ruthenium(III) catalysed oxidation of allyl alcohol by
diperiodatoargentate(III) in aqueous alkaline medium
*
Veeresh Tegginamath, Chanabasayya V. Hiremath and Sharanappa T. Nandibewoor
P.G. Department of Studies in Chemistry, Karnatak University, Dharwad-580 003, India
Received 20 June 2006; revised 17 August 2006; accepted 4 October 2006
ABSTRACT: The oxidation of allyl alcohol by diperiodatoargentate(III) (DPA) is carried out both in the absence and
presence of ruthenium(III) catalyst in alkaline medium at 298 K and a constant ionic strength of 1.1 mol dmꢀ3 was
studied spectrophotometrically. The oxidation products in both the cases were acrolein and Ag(I), identified by
spectral studies. The stoichiometry is same in both the cases, that is, [AA]/[DPA] ¼ 1:1. The reaction shows first order
in [DPA] and has less than unit order dependence each in both [AA] and [Alkali] and retarding effect of [IOꢀ4 ] in both
the catalysed and uncatalysed cases. The order in [Ru(III)] is unity. The active species of DPA is understood to be as
monoperiodatoargentate(III) (MPA) in both the cases. The uncatalysed reaction in alkaline medium has been shown to
proceed via a MPA–allyl alcohol complex, which decomposes in a rate determining step to give the products. In
catalysed reaction, it has been shown to proceed via a Ru(III)-allyl alcohol complex, which further reacts with one
molecule of MPA in a rate determining step to give the products. The reaction constants involved in the different steps
of the mechanisms were calculated for both reactions. The catalytic constant (Kc) was also calculated for catalysed
reaction at different temperatures. The 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.
Copyright # 2007 John Wiley & Sons, Ltd.
KEYWORDS: allylalcohol; diperiodatoargentate(III); Ru(III)catalysis; oxidation; kinetics
INTRODUCTION
was also observed that they did not arrive the possible
active species of DPA in alkali and on the other hand they
proposed mechanisms by generalizing the DPA as
[Ag(HL)L](x þ 1)ꢀ. However, Kumar et al.9 put an effort
to give an evidence for the reactive form of DPA in the
large scale of alkaline pH. In the present investigation, we
have obtained the evidence for the reactive species for
DPA in alkaline medium.
In recent years, the use of transition metal ions such as
osmium, ruthenium and iridium, either alone or as binary
mixtures, as catalysts in various redox processes has
attracted considerable interest.10 The ruthenium(III) acts
as a catalyst in the oxidation of many organic and
inorganic substrates.11 Ruthenium(III) catalysis in redox
reactions involve different degrees of complexity, due to
formation of different intermediate complexes, and to
different oxidation states of ruthenium. The use of
different catalysts, gave different oxidation products12 in
case of AA oxidation. We have observed that rutheniu-
m(III) catalyses the oxidation of AA by DPA in alkaline
medium in micro amounts. In order to understand the
active species of oxidant and catalyst, and to propose the
appropriate mechanisms, the title reaction is investigated
in detail, in view of various mechanistic possibilities.
Allyl alcohol (AA) finds a number of industrial
applications in the preparation of resin, plasticizers,
pharmaceuticals and many organic compounds. Kinetic
studies on the oxidation of AA with different oxidants
such as potassium permanganate, chromic acid, vana-
dium(V), chloramine-T, diperiodatonickelate(IV), and so
on have been reported.1–3 Different products were
obtained with different oxidants4,5 for the oxidation
of AA.
Diperiodatoargentate(III) (DPA) is a powerful oxidiz-
ing agent in alkaline medium with the reduction
potential6 1.74 V. It is widely used as a volumetric
reagent for the determination of various organic and
inorganic species.7 Jaya Prakash Rao et al.8 have used
DPA as an oxidizing agent for the kinetics of oxidation of
various organic substrates. They normally found that
order with respect to both oxidant and substrate was unity
and [OHꢀ] was found to enhance the rate of reaction. It
*Correspondence to: S. T. Nandibewoor, Department of Chemistry,
Karnatak University, Dharwad-580003, India.
E-mail: stnandibewoor@yahoo.com
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 55–64

56
V. TEGGINAMATH ET AL.
EXPERIMENTAL
reaction in an atmosphere of nitrogen. No significant
difference between the results obtained under nitrogen
and in presence of air was observed. In the view of
ubiquitous contamination of CO23ꢀ, its effect was also
studied on the rate of reaction. Added carbonate had no
effect on the reaction rate.
All chemicals used were of reagent grade and double
distilled water was used throughout the work. The AA
(Koch Light) was purified by standard procedure and its
concentration in aqueous solution was checked13 by
addition of excess of chloramine-T followed by
iodometric estimation of the excess. A standard stock
solution of Ru(III) was prepared by dissolving RuCl3
(S.D. Fine Chemicals) in 0.20 mol dmꢀ3 HCl and the
concentration was ascertained14 by EDTA titration.
KNO3 and KOH (BDH) were used to maintain ionic
strength and alkalinity of the reaction, respectively.
Aqueous solution of AgNO3 was used to study the
product effect, Ag(I). A stock standard solution of IO4ꢀ
was prepared by dissolving a known weight of KIO4
(Riedel-de Haen) in hot water and used after keeping for
24 h. Its concentration was ascertained iodometrically15
at neutral pH maintained using phosphate buffer. The
temperature was maintained constant to within ꢁ0.10 8C.
Kinetics
The kinetic measurements were performed on a Varian
CARY 50 Bio UV-Vis spectrophotometer. The kinetics
was followed under pseudo first order condition where
[AA] > [DPA] both in uncatalysed and catalysed reaction
at 25 ꢁ 0.1 8C, unless specified. In the absence of catalyst
the reaction was initiated by mixing the DPA to AA
solution which also contained required concentration of
KNO3, KOH and KIO4. The reaction in the presence of
catalyst was initiated by mixing DPA to AA solution
which also contained required concentration of KNO3,
KOH, KIO4 and Ru(III) catalyst. The progress of
reaction was followed spectrophotometrically at
360 nm by monitoring decrease in absorbance due to
DPA with the molar absorbancy index, ‘e’ to be
13,900 ꢁ 100 dm3 molꢀ1 cmꢀ1 in both catalysed and
uncatalysed reaction. 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 kc’), in
both the cases were determined from the log(absorbance)
versus time plots. The plots were linear up to 85%
completion of reaction (Fig. 1 for uncatalysed). The
orders for various species were determined from the
slopes of plots of log (ku or kc) versus respective
concentration of species except for [DPA] in which
non-variation of ‘ku or kc’ was observed as expected to the
Preparation of DPA
DPAwas prepared by oxidizing Ag(I) in presence of KIO4
as described elsewhere:16 the mixture of 28 g of KOH and
23 g of KIO3 in 100 cm3 of water along with 8.5 g AgNO3
was heated just to boiling and 20 g of K2S2O8 was added
in several lots with stirring then allowed to cool. It was
filtered through a medium porosity fritted glass filter and
40 g of NaOH was added slowly to the filtrate, whereupon
a voluminous orange precipitate agglomerates. The
precipitate was filtered as above and washed three to
four times with cold water. The pure crystals were
dissolved in 50 cm3 water and warmed to 80 8C with
constant stirring thereby some solid was dissolved to give
a red solution. The resulting solution was filtered when it
was hot and on cooling at room temperature, the orange
crystals separated out and were recrystallised from water.
The complex was characterized from its U.V. spectrum,
exhibited three peaks at 216, 255 and 362 nm. These
spectral features were identical to those reported earlier
for DPA.16 The magnetic moment study revealed that the
complex is diamagnetic. The compound prepared was
analyzed17 for silver and periodate by acidifying a
solution of the material with HCl, recovering and
weighing the AgCl for Ag and titrating the iodine
liberated when excess KI was added to the filtrate for IOꢀ4 .
The aqueous solution of DPA was used for the required
[DPA] in the reaction mixture. During the kinetics a
constant concentration viz.1 ꢂ 10ꢀ5 mol dm3 of KIO4 was
used throughout the study unless otherwise stated. Thus,
the possibility of oxidation of AA by periodate was tested
and found that there was no significant interference due to
KIO4 under experimental condition. The effect of
dissolved oxygen on the rate of reaction was checked
by preparing the reaction mixture and following the
Figure 1. First order plots for the oxidation of allyl alcohol
by DPA in aqueous alkaline medium at 25 8C. 105 [DPA]
(mol dmꢀ3); (1) 1.0; (2) 3.0; (3) 5.0; (4) 8.0; (5) 10.0
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 55–64
DOI: 10.1002/poc

KINETICS AND MECHANISM OF UNCATALYSED AND Ru(III) CATALYSED
57
reaction condition. The rate constants were reproducible
to within ꢁ5%. Regression analysis of experimental
data to obtain regression coefficient r and the standard
deviation S, of points from the regression line,
was performed with the Microsoft office Excel-2003
programme.
and ꢀCH stretching at 2854 cmꢀ1 thus confirming the
presence of acrolein.
Reaction orders
As the diperiodatoargentate(III) oxidation of AA in
alkaline medium proceeds with a measurable rate in the
absence of Ru(III), the catalysed reaction is understood to
occur in parallel paths with contributions from both the
catalysed 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 ¼ kT ꢀ kU. Hence the reaction orders have been
determined from the slopes of log kC versus log
(concentration)ꢀplots by varying the concentrations of
AA, IOꢀ4 , OH and catalyst (Ru(III)), in turn, while
keeping others constant. The order in DPA was unity
between the concentration was varied in the range of
1.0 ꢂ 10ꢀ5 to 1.0 ꢂ 10ꢀ4 mol dmꢀ3 at fixed AA, KOH and
KNO3 in both cases of uncatalysed and catalysed
reactions. Linearity of the plots of log (absorbance)
versus time up to 85% completion of the reaction
indicates a reaction order of unity in [DPA]. This was also
confirmed by varying of [DPA], which did not result in
any change in the pseudo first order rate constants, ku
(Table 1), kc (Table 3; Ru(III)). In case uncatalysed
reaction the AA concentration was varied in the range
1.0 ꢂ 10ꢀ3 to 1.0 ꢂ 10ꢀ2 mol dm3 at 25 8C while keeping
other reactant concentrations and conditions constant.
The ku values increased with the increase in concentration
RESULTS
Stoichiometry and product analysis
Different sets of reaction mixtures containing varying
ratios of DPA to AA in presence of constant amount
of OHꢀ, KNO3 in uncatalysed reaction and a constant
amount Ru(III) in catalysed reaction were kept for 3 h in
closed vessel under nitrogen atmosphere. The remaining
concentration of DPA was estimated by spectrophotome-
trically at 360 nm. Under the condition where
[AA] > [DPA] the unreacted AA was estimated13 as
mentioned above. The results indicate that 1:1 stoichi-
ometry for both the reactions as given in Eqn (1).
CH2 ¼ CH ꢀ CH2OH þ ½AgðH2IO6ÞðH2OÞꢃ
RuðIIIÞ
þ 2OHꢀ ꢀ! CH2 ¼ CH ꢀ CHO
(1)
þ AgðIÞ þ H2IO36ꢀ þ 4H2O
The stoichiometric ratio in both the cases suggests that
the main product was acrolein, which was identified by
spot test.18 The nature of aldehyde was confirmed by its
IR spectrum showed a carbonyl stretching at 1715 cmꢀ1
Table 1. Effect of [DPA], [AA], [OHꢀ] and [IO4ꢀ] on the oxidation of allyl alcohol by DPA in alkaline medium at 25 8C,
I ¼ 1.10 mol dmꢀ3
103ku (sꢀ1
)
105 [DPA] (mol dmꢀ3
)
102 [AA] (mol dmꢀ3
)
[OHꢀ] (mol dmꢀ3
)
105 [IOꢀ4 ] (mol dmꢀ3
)
Found
Calculated
1.0
3.0
5.0
8.0
10
1.0
1.0
1.0
1.0
1.0
0.1
0.3
0.5
0.8
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.05
0.08
0.1
0.3
0.5
0.5
0.5
0.5
0.5
0.5
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
3.0
5.0
8.0
10.0
2.70
2.72
2.81
2.70
2.72
0.73
1.60
2.10
2.54
2.81
1.47
1.79
1.96
2.52
2.81
2.81
2.30
2.01
1.70
1.51
2.71
2.71
2.71
2.71
2.71
0.69
1.55
2.05
2.51
2.71
1.44
1.79
1.95
2.55
2.71
2.71
2.23
1.90
1.62
1.45
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
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 55–64
DOI: 10.1002/poc

58
V. TEGGINAMATH ET AL.
Table 2. Thermodynamic activation parameters for the oxidation of allyl alcohol by DPA in alkaline medium with respect to the
slow step of Scheme 1
Temperature(K)
103k1 (sꢀ1
)
Parameters
Values
(A) Effect of temperature
(B) Activation parameters (Scheme 1)
298
303
308
313
4.01
5.95
8.47
11.3
Ea (kJ molꢀ1
)
53.6 ꢁ 2.3
51.1 ꢁ 2.2
ꢀ118 ꢁ 5
86.5 ꢁ 3.5
7.0 ꢁ 0.3
DH# (kJꢀm1olꢀ1
DG# (kJ mol
log A
)
DS# (JK mꢀol1ꢀ1
)
)
Temperature (K)
K1 (dm3 molꢀ1
)
104K2 (mol dmꢀ3
)
10ꢀ2K3 (dm3 molꢀ1
)
(C) Effect of temperature to calculate K1, K2 and K3 for the oxidation of allyl alcohol by diperiodatoargentate (III) in alkaline medium
298
303
308
313
0.17 ꢁ 0.008
0.13 ꢁ 0.006
0.11 ꢁ 0.005
0.10 ꢁ 0.004
2.99 ꢁ 0.12
7.29 ꢁ 0.32
15.2 ꢁ 0.60
25.3 ꢁ 1.02
3.14 ꢁ 0.13
1.40 ꢁ 0.05
0.87 ꢁ 0.04
0.65 ꢁ 0.03
Thermodynamic quantities
Values from K1
Values from K2
Values from K3
(D) Thermodynamic quantities using K1,K2 and K3
DH (kJ molꢀ1
DS (JKꢀ1 mol
DG298 (kJ mol
)
ꢀ27.4 ꢁ 1.2
ꢀ107.1 ꢁ 5.0
4.4 ꢁ 0.2
111 ꢁ 5.0
306 ꢁ 14
20.1 ꢁ 0.8
ꢀ80.6 ꢁ 3.8
ꢀ222 ꢁ 10
ꢀ14.2 ꢁ 0.5
ꢀ1
)
)
ꢀ1
[DPA] ¼ 5.0 ꢂ 10ꢀ5; [AA] ¼ 1.0 ꢂ 10ꢀ2; [OHꢀ] ¼ 0. 5;[IO4] ¼ 1.0 ꢂ 10ꢀ5 mol dmꢀ3
.
of AA indicating an apparent less than unit order
dependence on [AA] (Table 1). In case catalysed reaction
the AA concentration was varied in the range 5.0 ꢂ 10ꢀ4
to 5.0 ꢂ 10ꢀ3 mol dmꢀ3 at 25 8C while keeping other
reactant concentrations and conditions constant. The kc
values increased with the increase in concentration of AA
indicating an apparent less than unit order dependence on
[AA] (Table 3). The effect of alkali on the reaction has
Table 3. Effect of [DPA], [AA], [OHꢀ] and [IO4ꢀ] on the ruthenium(III) catalysed oxidation of allyl alcohol by DPA in alkaline
medium at 25 8C, I ¼ 1.10 mol dmꢀ3
105 [DPA]
103 [AA]
[OHꢀ]ꢀ
105 [IO4]
106 [Ru(IꢀII)]
(mol dm 3)
102 kT
(sꢀ1
103 kU
(sꢀ1
(mol dmꢀ3) (mol dmꢀ3) (mol dm 3) (mol dmꢀ3)
)
)
102 kC Found 102 kC Found
1.0
3.0
5.0
8.0
10
1.0
1.0
1.0
1.0
1.0
0.5
0.8
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
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.05
0.08
0.1
0.3
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
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
0.8
1.0
3.0
5.0
1.0
1.0
1.0
1.0
1.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
3.0
0.8
1.0
3.0
5.0
8.0
1.10
1.10
1.08
1.09
1.09
0.68
0.93
1.08
1.51
1.70
0.41
0.55
0.63
0.92
1.08
1.22
1.11
1.08
0.78
0.60
0.38
0.48
1.08
1.55
2.36
1.08
1.15
1.16
1.17
1.18
0.55
0.88
1.16
1.40
1.85
0.65
0.78
0.86
0.95
1.16
1.45
1.25
1.16
0.98
0.95
1.16
1.16
1.16
1.16
1.16
0.99
0.98
0.96
0.97
0.97
0.62
0.84
0.96
1.37
1.52
0.34
0.47
0.54
0.82
0.96
1.08
1.00
0.96
0.68
0.50
0.27
0.36
0.96
1.43
2.24
0.95
0.95
0.95
0.95
0.95
0.64
0.85
0.95
1.42
1.58
0.34
0.47
0.53
0.84
0.95
1.06
0.99
0.95
0.68
0.52
0.27
0.35
0.95
1.42
2.23
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
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 55–64
DOI: 10.1002/poc

KINETICS AND MECHANISM OF UNCATALYSED AND Ru(III) CATALYSED
59
K1
[Ag(H IO6)(H3IO6)]2-
-
-
[Ag(H IO6)2] + OH
+ H2O
2
3
K2
K3
+ [H3IO6]2-
[Ag(H IO6)(H2O)2]
[Ag(H2IO6)(H3IO6)]2-
2H2O
2
+
CH2=CH-CH2OH + [Ag(H2IO6)(H2O)2]
k1
Complex (C) + H2O
3-
+ 2H+ + H2O
Complex (C)
CH2=CH CHO + Ag(I) + H2IO6
slow
fast
2H+ + 2OH-
2H2O
Scheme 1. Detailed scheme for the oxidation of allyl alcohol by alkaline diperiodatoargentate(III)
been studied for both the cases in the range of
0.05–0.50 mol dmꢀ3 at constant concentrations of AA,
DPA and a constant ionic strength of 1.10 mol dmꢀ3 in
uncatalysed reaction and at constant concentration of
Ru(III) in catalysed reaction. The rate constants increased
with increasing [alkali] and the order was found to be less
than unity (Tables 1 and 3 Ru(III)) for both the cases.
Effect of ionic strength (I) and dielectric
constant of the medium (D)
It was found that ionic strength and dielectric constant of
the medium have no significant effect on the rate of
reaction in both the case of uncatalysed and catalysed
reaction.
Effect of periodate
Effect of temperature
In case of uncatalysed reaction periodate was varied
from 1.0 ꢂ 10ꢀ5 to 1.0 ꢂ 10ꢀ4 mol dmꢀ3 at constant
[DPA], [AA] and ionic strength. It was observed that the
rate constants decreased by increasing [IOꢀ4 ] (Table 1).
In case of catalysed reaction periodate was varied from
5.0 ꢂ 10ꢀ6 to 5.0 ꢂ 10ꢀ5 mol dmꢀ3 at constant [DPA],
[AA] and ionic strength. It was observed that the rate
constants also decreased by increasing [IOꢀ4 ] (Table 3).
The influence of temperature on the rate of reaction was
studied for uncatalysed reaction at 25, 30, 35 and 40 8C.
The rate constants, (k1), of the slow step of Scheme 1 were
obtained from the slopes and the intercepts of the plots
of 1/ku versus 1/[AA], 1/ku versus [H3IO26ꢀ] and 1/ku
versus 1/[OHꢀ] plots at four different temperatures. The
values are given in Table 2. The activation parameters for
the rate determining step were obtained by the least
square method of plot of log k1 versus 1/T and are
presented in Table 2.
Effect of added products
The influence of temperature on the rate of reaction
was studied for catalysed reaction at 25, 30, 35 and 40 8C.
The rate constants, (k2), of the slow step of Scheme 2 were
obtained from the slopes and the intercepts of the plots of
[Ru(III)]/kC versus 1/[AA], [Ru(III)]/kC versus 1/[OHꢀ]
Initially added products, Ag (I) and acrolein did not have
any significant effect on the rate of reaction (for both the
cases).
K1
[Ag(H2IO6)(H3IO6)]2-
+ H2O
-
-
[Ag(H IO6)2] + OH
3
K2
K4
+ [H3IO6]2-
[Ag(H2IO6)(H2O)2]
[Ag(H2IO6)(H3IO6)]2-
2H2O
+
+ [Ru(H2O)5OH]2+
Complex (C)
CH2=CH CH2OH
3-
k2
slow
Complex (C) + [Ag(H2IO )(H O)2]
+ 2H+
+ Ag(I) + H2IO
CHO
CH =CH
6
6
2
2
+ 2H2O + [Ru(H2O)5(OH)]2+
fast
+ 2OH-
2H+
2H2O
Scheme 2. Detailed scheme for the Ru(III) catalysed oxidation of allyl alcohol by alkaline diperiodatoargentate(III)
Copyright # 2007 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2007; 20: 55–64
DOI: 10.1002/poc

60
V. TEGGINAMATH ET AL.
Table 4. Thermodynamic activation parameters for the ruthenium(III) catalysed oxidation of allyl alcohol by DPA in aqueous
alkaline medium with respect to the slow step of Scheme 2
Temperature (K)
10ꢀ3 k2 (dm3 molꢀ1 sꢀ1
)
Parameters
Values
(A) Effect of temperature
(B) Activation parameters (Scheme 2)
298
303
308
313
6.11
8.55
10.2
Ea (kJ molꢀ1
)
36.9 ꢁ 1.4
DH# (kJꢀm1olꢀ1
)
34.4 ꢁ 1.3
ꢀ56.5 ꢁ 2.4
51.3 ꢁ 2.3
10.2 ꢁ 0.4
DS# (JK mꢀo1lꢀ1
)
12.7
DG# (kJ mol
log A
)
Temperature (K)
K1 (dm3 molꢀ1
)
105K2 (mol dmꢀ3
)
10ꢀ3K4 (dm3 molꢀ1
)
(C) Effect of temperature to calculate K1, K2 and K3 for the Ru(III) catalysed oxidation of allyl alcohol
by diperiodatoargentate (III) in alkaline medium
298
303
308
313
0.34 ꢁ 0.014
0.45 ꢁ 0.020
0.52 ꢁ 0.022
0.64 ꢁ 0.028
7.2 ꢁ 0.3
3.8 ꢁ 0.2
2.2 ꢁ 0.1
1.4 ꢁ 0.04
2.11 ꢁ 0.09
1.89 ꢁ 0.08
1.52 ꢁ 0.06
1.22 ꢁ 0.05
Thermodynamic quantities
Values from K1
Values from K2
Values from K4
(D) Thermodynamic quantities using K1,K2 and K4
DH (kJ molꢀ1
DS (JKꢀ1 mol
DG298 (kJ mol
)
30.7 ꢁ 1.2
94.9 ꢁ 4.2
2.6 ꢁ 0.11
ꢀ83.7 ꢁ 3.8
ꢀ28.8 ꢁ 1.2
ꢀ33.1 ꢁ 1.4
ꢀ18.9 ꢁ 0.7
ꢀ1
)
)
ꢀ361 ꢁ 14
23.6 ꢁ 1.0
ꢀ1
[DPA] ¼ 5.0 ꢂ 10ꢀ5; [AA] ¼ 1.0 ꢂ 10ꢀ3; [OHꢀ] ¼ 0.5; [Ru(III)] ¼ 3.0 ꢂ 10ꢀ6 mol dmꢀ3; [IO4] ¼ 1.0 ꢂ 10ꢀ5 mol dmꢀ3
.
and [Ru(III)]/kC versus [H3IO26ꢀ] 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 presented in Table 4.
reactions proceed simultaneously, so that
x
kT ¼ KU ꢀ KC½catalystꢃ
(2)
Here kT is the observed pseudo first-order rate constant
in the presence Ru(III) catalyst, kU the pseudo first-order
rate constant for the uncatalysed reaction, KC the catalytic
constant and ‘x’ the order of the reaction with respect to
[Ru(III)]. In the present investigations, x values for the
standard run were found to be unity for Ru(III). Then the
value of KC is calculated using the equation,
Test for free radicals (polymerisation study)
To test the intervention of free radicals, for both
uncatalysed and catalysed reactions, the reaction mixture
was mixed with acrylonitrile monomer and kept for 8 and
2 h, respectively, under nitrogen atmosphere. On dilution
with methanol no precipitate resulted, suggesting the AA
dehydrogenation is faster than a hypothetic radical
interception.
kT ꢀ kU
kC
KC ¼
¼
ðWhere; kT ꢀ kU ¼ kCÞ
x
x
½Catalystꢃ
½Catalystꢃ
(3)
The values of KC were evaluated for Ru(III) catalyst at
different temperatures and found to vary at different
temperatures. Further, plots of log KC versus 1/T were
linear and the values of energy of activation and other
activation parameters with reference to catalyst were
computed. These results are summarized in Table 5. The
value of KC is 7.98 ꢂ 102 at 298 K.
Effect of [Ru(III)]
The [Ru(III)] concentrations was varied from 8.0 ꢂ 10ꢀ7 to
8.0 ꢂ 10ꢀ6 mol dmꢀ3 range, at constant concentration of
diperiodatoargentate(III), AA, alkali and ionic strength.
The order in [Ru(III)] was found to be unity from the
linearity of the plots of log kC versus log [Ru(III)].
DISCUSSION
In the later period of 20th century the kinetics of oxidation
of various organic and inorganic substrates have been
studied by Ag(III) species which may be due to its strong
versatile nature of two electrons oxidant. Among the
Catalytic activity
It has been pointed out by Moelwyn–Hughes19 that in
presence of the catalyst, the uncatalysed and catalysed
various species of Ag(III), Ag(OH)ꢀ4 diperiodatoargen-
,
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KINETICS AND MECHANISM OF UNCATALYSED AND Ru(III) CATALYSED
61
Table 5. Values of catalytic constant (KC) at different tem-
peratures and activation parameters calculated using KC
values
number of protons and ‘HL’ is a protonated periodate of
uncertain number of protons. This can be ruled out by
considering the alternative form22 of IO4ꢀ at pH > 7 which
is in the form H3IO62ꢀ or H3IO36ꢀ. Hence, DPA could be as
[Ag(H3IO6)2]ꢀ or [Ag(H2IO6)2]3ꢀ in alkaline medium.
Therefore, under the present condition, diperiodatoar-
gentate(III), may be depicted as [Ag(H3IO6)2]ꢀ. The
similar speciation of periodate in alkali was proposed24
for diperiodatonickelate(IV).
Temperature (K)
10ꢀ2KC
298
303
308
313
7.98
10.9
14.0
16.0
36.2
33.7
ꢀ75
56
Ea (kJ molꢀ1
)
DH# (kJ molꢀ1
)
DS# (JKꢀ1 molꢀ1
)
DG# (kJ molꢀ1
log A
)
9.2
Mechanism for uncatalysed reaction
[DPA] ¼ 5.0 ꢂ 10ꢀ5
;
[AA] ¼ 1.0x10ꢀ3;[OHꢀ] ¼ 0.5 mol dmꢀ3
;
[IO4] ¼
1.0 ꢂ 10ꢀ5 mol dmꢀ3; [Ru(III)] ¼ 3.0 ꢂ 10ꢀ6 mol dmꢀ3
.
The reaction between DPA and AA in alkaline medium
presents a 1:1 stoichiometry of oxidant to reductant.
Since, the reaction was enhanced by [OHꢀ], added
periodate retarded the rate and first order dependency
in [DPA] and fractional order in [AA] and [OHꢀ],
the following mechanism has been proposed which
also explains all other experimental observations
(Scheme 1).
Monoperiodatoargentate(III) (MPA) is considered to
be the active species in view of the observed experimental
results. In the prior equilibrium step 1, the [OHꢀ]
deprotonates the DPA to give a deprotonated diperioda-
toargentate(III); in the second step, displacement of a
ligand, periodate from deprotonated DPA takes place to
give free periodate which is evidenced by decrease in the
rate with increase in [periodate] (Table 1). It may be
expected that lower Ag (III) periodate species such as
MPAwill be more important in the reaction than the DPA.
The inverse fractional order in [H3IO26ꢀ] might also be
due to this reason. In the pre rate determining stage, MPA,
combines with a molecule of AA molecule to give a
complex, which decomposes in a slow step to form the
products, acrolein and Ag(I). Thus, all these results
indicate a mechanism of the type as in Scheme 1.
On the basis of square planar structure of DPA, the
structure of MPA and complex may be proposed as below:
tate(III) and ethylenebis (biguanide), (EBS), silver(III)
are of maximum attention to the researchers due to their
relative stability.20 The stability of Ag(OH)ꢀ4 is very
sensitive towards traces of dissolved oxygen and other
impurities in the reaction medium whereupon it had not
drawn much attention. However, the other two forms of
Ag(III)8,9,21 are considerably stable; the DPA is used in
highly alkaline medium and EBS is used in highly acidic
medium.
The literature survey16 reveals that the water soluble
diperiodatoargentate(III) (DPA) has
a
formula
[Ag(IO6)2]7ꢀ with dsp2 configuration of square planar
structure, similar to diperiodatocopper(III) complex with
two bidentate ligands, periodate to form a planar
molecule. When the same molecule is used in alkaline
medium, it is unlike to be existed as [Ag(IO6)2]7ꢀ as
periodate is known to be in various protonated forms22
depending on pH of the solution as given in following
multiple equilibria (4–6).
H5IO6 Ð H4IOꢀ6 þ Hþ
H4IO6ꢀ Ð H3IO62ꢀ þ Hþ
(4)
(5)
OH
OH
I
OH
OH
O
O
OH
O
O
2
O
O
O
OH
O
O
O
O
OH2
AA
O
O
I
Ag
I
Ag
I
Ag
OH
HO
2
O
OH
OH
OH
OH
Spectroscopic evidence for the complex formation
between oxidant and AA was obtained from UV-Vis
H3IO26ꢀ Ð H2IO63ꢀ þ Hþ
(6)
spectra of AA ((1.0 ꢂ 10ꢀ2), [OHꢀ] ¼ 0.50 mol dmꢀ3
)
Periodic acid exists as H5IO6 in acid medium and
as H4IOꢀ6 at pH 7. Thus, under the present alkaline
conditions, the main species are expected to be H3IO62ꢀ
and H2IO36. At higher concentrations, periodate also tends
to dimerise.23 On contrary, the Jayaprakash Rao et al.8 in
their recent past studies have proposed the DPA as
[Ag(HL)2]xꢀ in which ‘L’ is a periodate with uncertain
and a mixture of both. A hypsochromic shift of about
6 nm from 307 to 301 nm in the spectra of DPA to mixture
of DPA and AA was observed. The Michaelis–Menten
plot proved the complex formation between oxidant and
substrate, which explains less than unit order in [AA].
Such a complex between a oxidant and a substrate has
also been observed in other studies.25
Copyright # 2007 John Wiley & Sons, Ltd.
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62
V. TEGGINAMATH ET AL.
The rate law for Scheme 1 could be derived as
d½DPAꢃ
dt
k1K1K2K3½DPAꢃ½AAꢃ½OHꢀꢃ
Rate ¼ ꢀ
ku ¼
¼
(7)
(8)
½H3IO26ꢀꢃ þ K1½OHꢀꢃ½H3IO62ꢀꢃ þ K1K2½OHꢀꢃ þ K1K2K3½OHꢀꢃ½AAꢃ
k1K1K2K3½AAꢃ½OHꢀꢃ
½H3IO26ꢀꢃ þ K1½OHꢀꢃ½H3IO62ꢀꢃ þ K1K2½OHꢀꢃ þ K1K2K3½OHꢀꢃ½AAꢃ
which explains all the observed kinetic orders of different
species.
The rate law (8) can be rearranged into the following
form which is suitable for verification.
to the greater tendency of DPA to undergo deprotonation
compared to the formation of hydrolysed species in
alkaline medium.
The thermodynamic quantities for the different equi-
librium steps, in Scheme 1 can be evaluated as follows.
The AA and hydroxide ion concentrations (Table 1) were
varied at different temperatures. The plots of 1/ku versus
1/[AA] (r ꢄ 0.9982, S ꢅ 0.00122) and 1/ku versus 1/
[OHꢀ] (r ꢄ 0.9997, S ꢅ 0.00084) should be linear as
shown in Fig. 2. From the slopes and intercepts, the values
of K1 were calculated at different temperatures. A van’t
Hoff’s plot was made for the variation of K1 with
temperature [i.e. log K1 versus 1/T (r ꢄ 0.9894,
S ꢅ 0.1108)] and the values of the enthalpy of reaction
DH, entropy of reaction DS and free energy of reaction
DG, were calculated. These values are given in Table 2. A
comparison of the latter values with those obtained for the
slow step of the reaction shows that these values mainly
refer to the rate limiting step, supporting the fact that the
reaction before the rate determining step is fairly slow and
involves high activation energy.27 In the same manner, K2
and K3 values were calculated at different temperatures
and the corresponding values of thermodynamic
quantities are given in Table 2.
1
½H3IO26ꢀꢃ
½H3IO26ꢀꢃ
¼
þ
ku k1K1K2K3½OHꢀꢃ½AAꢃ k1K1K2K3½AAꢃ
(9)
1
1
þ
þ
k1K3½AAꢃ k1
The plots of 1/ku versus 1/[AA], 1/ku versus [H3IO26ꢀ],
1/ku versus 1/[OHꢀ] and were linear with an intercept
supporting the MPA-AA complex, as verified in Fig. 2.
From the intercept and slope of such plots, the reaction
constants K1, K2, K3 and k1 were calculated as
(0.17ꢁ 0.008) dm3 molꢀ1, (2.99 ꢁ 0.12) ꢂ 10ꢀ4 mol dmꢀ3,
(3.14ꢁ 0.13) ꢂ 102 dm3 molꢀ1
,
(4.01 ꢁ 0.2) ꢂ 10ꢀ3 sꢀ1
,
respectively. The K1 value is in near agreement with
earlier work.26 These constants were used to calculate the
rate constants and compared with the experimental values
and found to be in reasonable agreement with each other
(Table 1) which fortifies the Scheme 1.The equilibrium
constant K1 is far greater than K2 which may be attributed
A high negative value of DS# (ꢀ118 JKꢀ1 molꢀ1
)
suggests that intermediate complex is more ordered than
the reactants.28
Mechanism for Ru(III) catalysed reaction
It is interesting to identify the probable ruthenium(III)
chloride species in alkaline media. Electronic spectral
studies29 have confirmed that ruthenium chloride exists in
hydrated form as [Ru(H2O)5OH]2þ. In the present study,
it is quite probable that the [Ru(III)(OH)x]3 ꢀ X, the
x-value would always be less than six because there are no
definite reports of any hexahydroxy ruthenium species.
The remainder of the coordination sphere would be filled
by water molecules. Hence, under the conditions
employed, for example, [OHꢀ] >> [Ru(III)], rutheniu-
m(III) is mostly present as the hydroxylated species,30
[Ru(H2O)5OH]2þ
.
Figure 2. Verification of rate law (8) in the form of (9) for
the oxidation of allyl alcohol by diperiodatoargentate(III) at
25 8C
Since, the reaction was enhanced by [OHꢀ], added
periodate retarded the rate and first order dependency in
Copyright # 2007 John Wiley & Sons, Ltd.
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KINETICS AND MECHANISM OF UNCATALYSED AND Ru(III) CATALYSED
63
[DPA] and catalyst (Ru(III)) and fractional order in [AA]
and [OHꢀ], the following Scheme 2 has been proposed,
which also explains all other experimental observations.
In the prior equilibrium step 1, the [OHꢀ] deprotonates
the DPA to give a deprotonated diperiodatoargentate(III);
in the second step displacement of a ligand, periodate takes
place to give free periodate which is evidenced by decrease
in the rate with increase in [periodate] (Table 3). It may be
expected that lower Ag (III) periodate species such as MPA
is more important active species in the reaction than the
DPA. The inverse fractional order in [H3IO26ꢀ] might also
be due to this reason. In the pre rate determining stage, the
hydroxylated species of Ru(III) combines with a molecule
of AA to give an intermediate complex, which further
reacts with 1 mole of MPA in a rate determining step to
give the products as given in Scheme 2.
The probable structure of the complex (C) is given
below:
Figure 3. Verification of rate law (11) in the form of (12) for
the Ru(III) catalysed oxidation of allyl alcohol by diperioda-
toargentate(III) at 25 8C
2+
HO
H2O
H2O
The plots of [Ru(III)]/kc vrersus 1/[AA], 1/[OHꢀ] and
[H3IO26ꢀ], were linear (Fig. 3). From the intercepts
and slopes of such plots, the reaction constants K1, K2,
Ru
H2O
O
CH2
CH=CH2
H2O
H2O
K4 and k2 were calculated as (0.34 ꢁ 0.014) dm3 molꢀ1
,
(7.23 ꢁ 0.36) ꢂ 10ꢀ5 mol dmꢀ3, (2.11 ꢁ 0.10) ꢂ 103 dm3
molꢀ1, (6.11 ꢁ 0.30) ꢁ 103 dm3 molꢀ1 sꢀ1, respectively.
These constants were used to calculate the rate constants
and compared with the experimental kc values and found
to be in reasonable agreement with each other (Table 3),
which fortifies the Scheme 2.
Spectroscopic evidence for the complex formation
between catalyst and substrate was obtained from UV-Vis
spectra of AA (1.0 ꢂ 10ꢀ3), Ru(III) (3.0 ꢂ 10ꢀ6
,
[OHꢀ] ¼ 0.50 mol dmꢀ3) and mixture of both. A bath-
ochromic shift of about 5 nm from 313 to 318 nm in the
spectra of ruthenium(III) was observed and hyperchro-
micity was observed at 318 nm. The Michaelis–Menten
plot also proved the complex formation between catalyst
and reductant, which explains less than unit order in
[AA]. The rate law for the Scheme 2 could be derived as,
The thermodynamic quantities for the different equi-
librium steps, in Scheme 2 can be evaluated as follows.
The AA and hydroxide ion concentrations (Table 3)
were varied at different temperatures. The plots of
[Ru(III)]/kC versus 1/[AA] (r ꢄ 0.9993, S ꢅ 0.00132),
[Ru(III)]/kC versus 1/[OHꢀ](r ꢄ 0.9995, S ꢅ 0.00088)
ꢀd½DPAꢃ
dt
k2K1K2K4½DPAꢃ½AAꢃ½OHꢀꢃ½RuðIIIÞꢃ
Rate ¼
¼
(10)
½H3IO26ꢀꢃ þ K1½OHꢀꢃ½H3IO62ꢀꢃ þ K1K2½OHꢀꢃ þ K1K2K4½OHꢀꢃ½AAꢃ
Rate
k2K1K2K4½AAꢃ½OHꢀꢃ½RuðIIIÞꢃ
¼ kC ¼ kT ꢀ kU ¼
(11)
½H3IO26ꢀꢃ þ K1½OHꢀꢃ½H3IO62ꢀꢃ þ K1K2½OHꢀꢃ þ K1K2K4½OHꢀꢃ½AAꢃ
½DPAꢃ
Equation (11) can be rearranged to Eqn (12), which is
suitable for verification.
and [Ru(III)]/kC versus [H3IO26ꢀ] (r ꢄ 0.9992, S ꢅ
0.00131), should be linear as shown in Fig. 3. From
the slopes and intercepts, the values of K1 are calculated at
different temperatures. A van’t Hoff’s plot was made for
the variation of K1 with temperature [i.e. log K1 versus 1/T
(r ꢄ 0.9993, S ꢅ 0.1105)] and the values of the enthalpy of
reaction DH, entropy of reaction DS and free energy of
reaction DG, were calculated. These values are also given
½RuðIIIÞꢃ
½H3IO26ꢀꢃ
½H3IO26ꢀꢃ
¼
þ
kC
k2K1K2K4½AAꢃ½OHꢀꢃ k2K2K4½AAꢃ
(12)
1
1
þ
þ
k2K4½AAꢃ k2
Copyright # 2007 John Wiley & Sons, Ltd.
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DOI: 10.1002/poc

64
V. TEGGINAMATH ET AL.
in Table 4. A comparison of the latter values with those
obtained for the slow step of the reaction shows that these
values mainly refer to the rate limiting step, supporting
the fact that the reaction before the rate determining step
is fairly slow and involves a high activation energy.27 In
the same manner, K2 and K4 values were calculated at
different temperatures and the corresponding values of
thermodynamic quantities are given in Table 4.
Negligible effect of ionic strength and dielectric
constant in both uncatalysed and catalysed reaction
might be due to involvement of neutral substrate in the
reaction (Schemes 1 and 2). The negative value of DS#
suggests that the intermediate complex is more ordered
than the reactants.28 The observed higher rate constant for
the slow step indicate that the oxidation presumably
occurs via an inner-sphere mechanism. This conclusion is
supported by earlier observation.31 The activation
parameters evaluated for the catalysed and uncatalysed
reaction explain the catalytic effect on the reaction. The
catalyst, Ru(III) form the complex (C) with substrate
which enhances the reducing property of the substrate
than that without catalyst, Ru(III). Further the catalyst
Ru(III) modifies the reaction path by lowering the energy
of activation.
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CONCLUSION
The comparative study of uncatalysed and ruthenium(III)
catalysed oxidation of AA by diperiodatoargentate(III)
was studied. Oxidation products were identified. Among
the various species of Ag(III) in alkaline medium, MPA is
considered to be the active species for the title reaction.
Active species of Ru(III) is found to be [Ru(H2O)5OH]2þ
.
Activation parameters were evaluated for both uncata-
lysed and catalysed reactions with respect to slow step of
reaction schemes. Catalytic constants and activation
parameters with respect to catalyst were also computed.
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