Osmium(VIII)/ruthenium(III) catalysis of periodate oxidation of acetaldehyde in aqueous alkaline medium

Article abstract of DOI:10.1002/(SICI)1099-1395(199803)11:3<171::AID-POC988>3.0.CO;2-4

Os(VIII) and Ru(III) catalysis of the periodate oxidation of acetaldehyde in aqueous alkaline medium was investigated. The catalytic efficiency is Ru(III) < Os(VIII). The product of oxidation in both cases is acetate and IO₃^-. The stoichiometry is the same in both catalyzed reactions, i.e. [IO₄^-]:[CH₃CHO] = 1:1. Probable mechanisms are proposed and discussed. The reaction constants involved in the mechanisms are derived.

Full text of DOI:10.1002/(SICI)1099-1395(199803)11:3<171::AID-POC988>3.0.CO;2-4

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)
Osmium(VIII)/ruthenium(III) Catalysis of periodate
oxidation of acetaldehyde in aqueous alkaline medium
1
Dasharath L. Kamble and Sharanappa T. Nandibewoor *
1
Department of Post-Graduate Studies in Chemistry, Karnatak University, Dharwad 580 003, India
Received 23 September 1996; revised 26 August 1997; accepted 1 September 1997
ABSTRACT: Os(VIII) and Ru(III) catalysis of the periodate oxidation of acetaldehyde in aqueous alkaline medium
was investigated. The catalytic efficiency is Ru(III) < Os(VIII). The product of oxidation in both cases is acetate and
�
�
IO3 . The stoichiometry is the same in both catalyzed reactions, i.e. [IO4 ]:[CH CHO] = 1:1. Probable mechanisms
3
are proposed and discussed. The reaction constants involved in the mechanisms are derived.  1998 John Wiley &
Sons, Ltd.
KEYWORDS: acetaldehyde; oxidation; periodate; osmium (VIII) catalysis; ruthenium (III) catalysis
INTRODUCTION
Periodate is widely employed as a diol cleaving reagent.
study of the reactions is reported here with a discussion of
the mechanisms.
1
Periodate is a less potent oxidant in alkaline than in acidic
media. In an alkaline medium, periodate is known to exist
as different species involving multiple equilibria and it
EXPERIMENTAL
2
is necessary to know the active form of oxidant in the
reaction.
Reagent grade chemicals were used. Doubly distilled
water was used throughout. A 30–35% solution solution
of acetaldehyde (S.D. Fine Chemicals) was distilled
Acetaldehyde is used in the manufacture of acetic acid,
which is employed as a solvent in some mechanistic
studies. It is also used in the preparation of phenolic
resins in the manufacture of dyes and rubber. The
using a 1.3 m fractionating column and collected at 30–
6
3
2°C in ice-cold water, then standardized by mixing a
known volume of solution with hydroxylamine hydro-
chloride in 90% methanol and titrating the liberated
hydrochloric acid against standard alkali solution. A
3
oxidation of acetaldehyde by variety of oxidants such as
bromine, chromium(VI), iron(III), cerium(IV), perman-
ganate, chloramine-T and peroxodisulfate has been
studied.
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
�
stock standard solution of IO4 was prepared by
dissolving a known weight of KIO (Riedel-de Ha e¨ n) in
4
hot water and used after keeping for 24 h. Its concentra-
7
tion was ascertained iodometrically at neutral pH
maintained using phosphate buffer. A stock standard
attracted considerable interest. The role of osmium(VIII4)
solution of Os(VIII) was prepared by dissolving OsO4
as a catalyst in some redox reactions has been reviewed.
�3
(
Johnson Matthey) in 0.50 mol dm
NaOH. The
Although the mechanism of catalysis depends on the
nature of the substrate, the oxidant and other experi-
8
concentration was ascertained by determining the
unreacted [Fe(CN)6] with standard Ce(IV) solution in
4�
5
mental conditions, it has been shown that metal ions act
an acidic medium. A stock standard solution of Ru(III)
as catalysts by one of these different paths such as the
formation of complexes with reactants or oxidation of the
substrate itself or through the formation of free redicals.
Osmium(VIII) and ruthenium(III) catalysis in redox
reactions involves several complexes, different oxidation
states of osmium/ruthenium, etc. We have observed that
osmium(VIII) and ruthenium(III) catalyse the oxidation
of acetaldehyde by periodate in alkaline medium and the
was prepared by dissolving RuCl (S.D. Fine Chemicals)
3
�3
in 0.20 mol dm HCl. The concentration was deter-
9
mined by EDTA titration.
KIO3 (Reechem) was used to prepare an iodate
solution. Distilled and appropriately diluted acetic acid
was neutralized with alkali and the resulting salt solution
was used to study the effect of acetate ion on the reaction.
KOH and KCl (AnalaR, BDH) were employed to
maintain the required alkalinity and ionic strength,
respectively. The temperature was maintained constant
to within Æ0.10°C.
*
Correspondence to: Department of Post-Graduate Studies in
Chemistry, Karnatak University, Dharwad 580 003, India.

1998 John Wiley & Sons, Ltd.
CCC 0894–3230/98/030171–06 $17.50

1
72
D. L. KAMBLE AND S. T. NANDIBEWOOR
�
Kinetic Measurements. Kinetic runs were initiated by
initial rates versus concentrations of CH CHO and IO4
3
mixing the previously thermostated reactant solutions of
showed that the order in [CH CHO] was less than unity
3
�
�
IO , CH CHO [which also contained the required
(Ca 0.8) whereas the order in [IO ] was nearly unity
4
3
4
amount of Os(VIII) or Ru(III)], KOH and KCl. Aliquots
of the reaction mixture were removed by pipette at
regular time intervals and poured into an iodine flask
containing 5% KI and a suitable amount of 5% KH PO ,
over the range of concentrations studied (Tables 1 and 2).
Hence initial rates were given for variation of acetalde-
hyde and periodate. For variation of the alkali and
catalyst, second-order rate constants (a = b) and initial
rates were determined (Table 2). The order in alkali
concentration was found to be less than unity and that in
[Os(VIII)] was unity over the range of concentrations
studied (Table 2).
2
4
just sufficient to neutralize the alkali and to bring the pH
7
of solution to 5–5.5. The liberated iodine was titrated
against Na S O solution using starch as an indicator.
2
2 3
Under these conditions, iodate had no effect on the added
�
�
iodide and the IO4 was quantitatively reduced to IO .
Initially added products, acetate and iodate, in the
3
�
2
�3
�3
Kinetic runs were carried under second-order conditions
concentration range 1.0 Â10 – 1.0 Â10 mol dm ,
did not have any significant effect on the reaction rate.
The ionic strength of the medium was varied from
at 25 Æ0.10° C unless stated otherwise.
The apparent second-order rate constant. k , was
s
�
2
�3
�3
obtained from plots of 1/(a�x) versus time from runs
1.0 Â10 to 1.0 Â10 mol dm with KCl at constant
concentrations of oxidant, reduotant, alkali and catalyst.
The results showed that ionic strength has no effect on the
reaction rate. The dielectric constant (D) of the reaction
medium was varied by varying the content of tert-butanol
(its earlier found inertness towards oxidant was con-
involving equivalent concentrations of reactants, where a
�
and x are the initial concentration of IO4 and amount
reacted at time t, respectively. The initial rates were
obtained from the slopes of concentration versus time
graphs in the initial stages of the reactions by the plane
mirror method. The rates were reproducible to within
Æ6%.
firmed). The results showed that the plot of log k versus
S
1/D was linear with a positive slope. The dielectric
constants were calculated from values of pure liquids as
11
Stoichiometry and product analysis. Different sets of
given earlier.
�
reactions containing excess IO4 over CH CHO with
3
�
constant concentrations of Os(VIII) or Ru(III) and OH
were kept for 24 h at 298 K and then analyzed. The
unreacted oxidant was assayed iodometrically as men-
Test for free radicals
7
tioned earlier. Other product acetate was found by a spot
To test for free radicals, the reaction mixture containing
acrylonitrile was kept for 24 h in an inert atmosphere. On
dilution with methanol no precipitate resulted, indicating
the absence of intervention of free radicals in the
reaction.
1
0
test.
There was no perceptible reaction between
periodate and acetate in alkaline medium under the
conditions employed. The results showed 1:1 stoichio-
metry according to the equation
�
CH CHO ‡IO ‡KOH
3
4
Table 1. Effect of variation of [periodate] and [acetaldehyde]
on osmium(VIII)-catalyzed oxidation of acetaldehyde by
periodate in aqueous alkaline medium at 25°C, with
Os(VIII)/Ru(III)
�
�
����������!CH COOK ‡IO ‡H O ꢀ1†
3
3
2
�
�6
�3
[
OH ] = 0.05, [Os(VIII)] = 2.0 Â10 and I = 0.06 mol dm
(
error Æ6%)
7
Rate Â10
RESULTS
�3 �1
�
3
3
(mol dm
s )
[
(
IO4 ] Â10
[CH CHO] Â10
3
�
3
�3
a
mol dm
)
(mol dm
)
Exptl Calcd
Osmium(VIII) catalysis
0
0
0
1
2
.30
.60
.80
.00
.00
1.00
1.00
1.00
1.00
1.00
1.00
0.50
0.80
1.00
2.00
3.00
5.00
1.16
2.33
3.03
3.80
6.89
9.08
2.00
2.80
3.80
6.73
8.80
12.20
1.09
2.16
2.90
3.63
7.26
10.96
1.96
2.99
3.63
6.30
8.35
11.28
The reaction orders were obtained from log–log plots of
initial rates versus concentration. The reaction was
carried out varying the concentration of oxidant,
reductant, catalyst and alkali in turn while keeping all
other conditions constant (Tables 1 and 2). The Os(VIII)-
3.00
.00
1.00
1
�
catalyzed oxidation of acetaldehyde by IO4 was shown
1
1
1
.00
.00
.00
�
to be nearly second order as the plot of 1/[IO ] versus
4
time was linear beyond two half-lives of completion of
�
the reaction when [CH CHO] = [IO ]. However, when
1.00
3
4
�
[
CH CHO] ≠ [IO ] while varying the CH CHO and
3 4 3
a
�
Calculation of rate constants are on the basis of rate law (5) using
3 3
1
IO4 concentrations, it was found that the k values were
�1
�1 �1
�1
S
K = 24.8 Æ0.5 dm mol , K = 325 Æ12 dm mol and k = 1.19
3
1
3
3
not constant. Under such conditions, the log–log plots of
Â10 Æ50 dm mol
s .

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)

Os AND Ru CATALYSIS OF PERIODATE OXIDATION OF ACETALDEHYDE
173
Table 2. Effect of variation of [alkali] and [osmium(VIII)] on osmium(VIII)-catalyzed oxidation of acetaldehyde by periodate in
�
�3
�3
�3
aqueous alkaline medium at 25°C, with [IO4 ] = 1.0 Â10 , [CH CHO] = 1.0 Â10 and I = 0.06 mol dm (error Æ6%)
3
7
�3 �1
�
1
6
Rate Â10 (mol dm
s )
[
(
OH ] Â10
[Os(VIII)] Â10
Rate constant, k
3
s
)
�
3
�3
�1 �1
mol dm
)
(mol dm
)
Exptl
Calcd
(dm mol
s
0.20
0.50
0.70
1.00
1.50
2.00
0.50
0.50
0.50
0.50
0.50
0.50
2.00
2.00
2.00
2.00
2.00
2.00
1.00
2.00
3.00
4.00
5.00
10.00
2.29
3.80
4.10
4.43
4.90
5.51
1.73
3.80
4.66
9.01
12.01
18.00
1.09
3.63
4.06
4.46
4.85
5.83
1.81
3.63
5.45
9.08
12.71
18.16
0.15
0.45
0.54
0.69
1.00
1.10
0.25
0.45
0.69
1.19
2.41
3.05
The rate constants (k ) of the slow step of Scheme 1 (see
since the initial rates were independent of the initial
concentration of IO4 and the concentration versus time
1
�
Discussion) were obtained from intercept of [Os(VIII)]
�
�1
[
IO ]/rate versus [CH CHO] plots at four different
plots were linear and parallel. The order in [CH CHO]
4
3
3
temperatures and were used for the calculation of
was found to be nearly unity from the plot of log k (zero-
0
3
�1
activation parameters. The values of k (dm mol
order rate constant) versus log [CH CHO] over the range
1
3
�
1
3
3
3
s ) are 1.19 Â10 , 1.30 Â10 , 1.46 Â10 and
of concentrations studied. The order in Ru(III) was unity
whereas the order in [alkali] was less than unity
{concentrations as given in Table 4}.
Initial addition of products (iodate and acetate) and
ionic strength did not have any significant effect on the
reaction. Regarding the effect of dielectric constant on
3
1
.68 Â10 at 298, 302, 308 and 315 K, respectively.
≠
≠
≠
These data led to values of DH , DG and DS of 15 Æ1
�
1
�1
�1
�1
kJ mol , 54 Æ3 kJ mol and �137 Æ6 J K mol ,
respectively.
the reaction, it was found that the plot of log k versus 1/D
0
Ruthenium(III) catalysis
was linear with a negative slope. The test for free radicals
was negative.
�
The Ru(III)-catalyzed oxidation of CH CHO by IO4
The rate constants (k
2
) of the slow step of Scheme 1
CHO] [Ru(III)]/
3
was followed by varying the concentrations of oxidant,
substrate, alkali, ruthenium(III) and KCl; one at a time
while all the others were kept constant (Tables 3 and 4).
were obtained from intercept of [CH
3
�
�1
rate versus [OH ] plots at four different temperatures.
3
�1 �1
2
The values of k
(dm mol
s ) are 2.77 Â10 ,
2
�
2
2
2
The order in IO4 concentration was found to be zero,
5.0 Â10 , 8.33 Â10 and 18.18 Â10 at 298, 304, 308
Table 3. Effect of variation of [periodate] and [acetaldehyde]
on ruthenium(III)-catalyzed oxidation of acetaldehyde by
periodate in aqueous alkaline medium at 25°C, with
Table 4. Effect of variation of [alkali] and [ruthenium(III)] on
ruthenium(III)-catalyzed oxidation of acetaldehyde by period-
ate in aqueous alkaline medium at 25°C, with
�
�6
�
�3
�3
[
OH ] = 0.10, [Ru(III)] = 5.0 Â10
and I = 0.11 mol
[IO4 ] = 1.0 Â10
[CH CHO] = 1.0 Â10
and I = 0.11
3
�
3
�3
dm (error Æ6%)
mol dm (error Æ6%)
7
�3 �1
7
�3 �1
�
3
3
k
0
Â10 (mol dm
s
�
1
6
k
0
Â10 (mol dm
s )
[
(
IO4 ] Â10 [CH CHO] Â10
[OH ] Â10
[Ru(III)] Â10
3
�
3
�3
�3
�3
mol dm
)
(mol dm
)
Exptl
Calcd
(mol dm
)
(mol dm
)
Exptl.
Calcd.
0
0
0
1
1
2
1
1
1
1
1
1
.30
.50
.80
.00
.50
.00
.00
.00
.00
.00
.00
.00
1.00
1.00
1.00
1.00
1.00
1.00
0.50
0.80
1.00
2.00
3.00
5.00
10.32
10.46
10.43
10.45
10.50
10.24
04.91
08.12
10.46
21.00
28.83
51.33
10.50
0.10
0.30
0.50
0.70
0.90
1.00
1.00
1.00
1.00
1.00
1.00
1.00
5.00
5.00
5.00
5.00
5.00
5.00
1.00
1.50
2.00
3.00
5.00
10.00
03.30
06.88
08.41
09.00
10.41
10.46
02.24
03.30
04.33
05.92
10.46
19.66
03.33
06.70
08.46
09.50
10.25
10.50
02.10
03.14
04.20
06.30
10.50
21.01
10.50
10.60
10.50
10.50
10.50
05.23
08.37
10.50
21.00
30.00
51.75

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)

1
74
D. L. KAMBLE AND S. T. NANDIBEWOOR
reasonable to assume that equilibrium (2) was operative.
The main osmium(VIII) species is likely to be
2�
OsO (OH)2 and its formation by equilibrium (2) is of
4
importance in the reaction. This conclusion is in
4,13
agreement with earlier work.
The results of our study on the osmium(VIII)-
catalyzed reaction suggest the formation of a complex
between the catalyst and substrate followed by its
�
reaction with IO4 in the rate-determining step to give
the products. Attempts to obtain UV–visible spectral
evidence for the intermediate complex of CH CHO and
3
Os(VIII) were not successful. However, the interaction
may be weak and such complex formation between the
catalyst and substrate has also been observed in earlier
4
studies. The evidence for complex formation is
restricted to kinetic data. The order of less than unity in
[acetaldehyde] reveals the possibility of the involvement
of complex formation between the substrate and catalyst
in the reaction system in the pre-equilibrium step. All the
experimental results are in agreement with Scheme 1.
K1
�
�
2�
2
OsO (OH) ‡OH „OsO (OH) ‡H O
3
3
4
2
K3
2
�
OsO (OH) ‡CH CHO „complex (C)
C ‡IO �!IO ‡CH COOH ‡Os(VIII)
4
2
3
ks
�
�
4
3
3
slow
Scheme 1.
Figure 1. Veri®cation of rate laws (5) and (6). Conditions as
given in Tables 1±4
The probable structure of complex (C) may be
H
≠
and 313 K, respectively. These data led to values of DH ,
≠
≠
�1
DG and DS of the slow step of 100 Æ4 kJ mol ,
[CH3 ��C ˆO ��OsO4(OH)2Š�
Scheme 1 leads to the following rate law:
2
�
1
�1
�1
5
6 Æ2 kJ mol and 147 Æ6 J K mol , respectively.
�
�
�
k K K [Os(VIII)][IO ][CH CHO][OH ]
s
1
3
4
3
DISCUSSION
rate ˆ
ꢀ4†
�
1
‡K [OH ] ‡K K [CH CHO][OH ]
1
1
3
3
Osmium (VIII)-catalyzed reaction
For verification of this rate law, it is necessary to
rearrange equation (4) to
�
�
�
The reaction has 1:1 stoichiometry and acetate and IO3
�
[Os(VIII)][IO ]
1
4
are the main products of the reaction. The order in [IO ]
4
ˆ
�
rate
k K K [OH ][CH CHO]
and [Os(VIII)] is unity and that in [CH CHO] and [OH ]
s
1
3
3
3
is fractional (Tables 1 and 2). The uncatalyzed reaction is
very slow under the experimental conditions used.
Osmium(VIII) is known to form different complexes at
1
1
‡
‡
ꢀ5†
ksK3[CH3CHO] ks
�
different OH concentrations, as shown in equations (2)
From the slopes and intercepts of the linear plots of the
left-hand side of equation (5) versus 1/[CH CHO] and 1/
and (3), where the equilibrium constants K and K have
1
2
3
�1
12
3
values of 24 and 6.8 dm mol respectively.
�
[
OH ], the values of K , K and k at 298 K were
1
3
S
3
�1
3
K1
calculated to be 24.8 Æ0.5 dm mol , 325 Æ12 dm
�
�
2�
OsO (OH) ‡OH „OsO (OH) ‡H O ꢀ2†
�1
3
3
�1 �1
3
3
4
2
2
mol and 1.19 Â10 Æ50 dm mol s , respectively
13
K2
2
2
�
�
3�
(Fig. 1). The value of K was found to be in good
1
OsO (OH) ‡OH „OsO (OH) ‡H O ꢀ3†
At higher concentration of OH i.e. >0.15 mol dm ,
4
5
2
agreement with that reported earlier. These values of
�
�3
K , K and k were utilized for the calculation of rates
1
3
S
equilibrium (3) is significant. At lower concentrations of
under various experimental conditions and were found to
be in reasonable agreement with the experimental rates
(Table 1).
�
OH , as employed in the present study, and since the rate
�
of oxidation increased with increase in [OH ], it is

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)

Os AND Ru CATALYSIS OF PERIODATE OXIDATION OF ACETALDEHYDE
175
The negligibly small effect of ionic strength on the
reaction is consistent with reaction between neutral and
charged species as in Scheme 1. The effect of dielectric
constant on the reaction is also as expected for a reaction
1
4
between an ion and a neutral molecule. The sizeable
negative value of the entropy of activation indicates
complex formation during the reaction.
Ruthenium(III)-catalyzed reaction
In the ruthenium(III)-catalyzed reaction, the order in
[
[
(
[
CH CHO] and [Ru(III)] is unity in each and that in
3
�
IO ] is zero, unlike the case with Os(VIII) catalysis
4
see above) (Table 3). The rate increased with increasing
�
�
OH ] (Table 4). The products are acetate and IO3 and
stoichiometry is 1:1 as in the Os(VIII)-catalysed reaction.
No product effect was observed.
The spectrum of Ru(III) in alkaline medium (Fig. 2) is
15
different to those in aqueous neutral and acidic media.
It is also observed that the absorbance of Ru(III)
�
increases with increase in [OH ] and finally remains
constant. This indicates the predominance of one species
2‡
of Ru(III), presumably [Ru(H O) OH] . For this reason
2
5
and the fact that the rate increases with increase in
�
�
�
[
OH ], with less than unity order in [OH ], the main
Figure 2. Spectra of Ru(III) at various [OH ]. Ruthenium(III)
catalysis of oxidation of acetaldehyde by periodate in
aqueous alkaline medium at 25°C, (1) in aqueous medium,
2‡
Ru(III) species is likely to be [Ru(H O) OH] and its
2
5
formation in the following equilibrium is of importance
in the reaction:
�
�3
�
�2
(
2) at [OH ] = 5.0 Â10 , (3) at [OH ] = 1.0 Â10 , (4) at
�
�2
�
�2
[
OH ] = 5.0 Â10
and (5) at [OH ] = 10.0 Â10
mol
�
3
3
‡
�
2‡
dm
[
Ru(H O) Š ‡OH „[Ru(H O) OH] ‡H O
2
6
2
5
2
Also, as seen from the spectra of Ru(III), the existence
of one or more isobestic points in a system is a good
indication of an equilibrium between the two species.
Ruthenium(III) is known to form complexes with
hydroxide in basic media, such as Ru(OH) , Ru(OH)
2‡
‡
2
16–18
This conclusion is in agreement with earlier work
and Ru(OH) . However, for the reasons already given,
3
and the value of the equilibrium constant obtained for
such an equilibrium for this reaction also agrees with
the main active species of Ru(III) is understood to be
2‡
1
8
Ru(OH) at the hydroxide concentrations studied in this
work. The slow step (k step) involves interaction of
hydroxylated species with acetaldehyde resulting in the
formation of Ru(I) and acetic acid product. However, in
view of the very low concentration of Ru(III) used, no
kinetic evidence could be obtained for the formation of
Ru(I). The formation of Ru(I) is in accordance with
earlier work.
Electronic spectra of Ru(III)
The weak band observed around 530 nm is assigned to
4
2
the spin-forbidden T1g � T2g transition. The band
2
5
�
around 390 nm is attributed to spin-allowed A2g
�
earlier work. The thus formed Ru(I) is oxidized by IO
4
2
2
2
�
T2g and T1g � T2g transitions, which have similar
in the fast step to regenerate Ru(III) and to form IO .
3
energies. The bands observed near 225 and 280 nm are
charge-transfer bands.
The above mechanism leads to the rate law
�
�
�
d[IO ] kK[CH CHO][Ru(III)][OH ]
4
3
All the experimental results are in agreement with
Scheme 2.
rate ˆ
ˆ
ꢀ6†
dt
1 ‡K[OH�]
Rearrangement of equation (6) gives
K
3
‡
�
2‡
[
Ru(H O) Š ‡OH „[Ru(H O) OH] ‡H O
2
6
2
5
2
[CH CHO][Ru(III)]
1
1
3
ˆ
‡k
ꢀ7†
k
�
2
‡
rate
kK[OH ]
[
Ru(H O) OHŠ ‡CH CHO�!Ru(I) ‡CH COOH
2
5
3
3
slow
According to equation (7), the plots of [CH CHO]
3
‡
�
�
2
H ‡Ru(I) ‡IO �!Ru(III) ‡IO ‡H O
�
4
3
2
[Ru(III)]/rate versus 1/[OH ] should be linear, and they
fast
were found to be so (Fig. 1). From the slope and intercept,
3
�1
Scheme 2.
1998 John Wiley & Sons, Ltd.
the values of K and k were derived as 31 Æ2 dm mol

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)

1
76
D. L. KAMBLE AND S. T. NANDIBEWOOR
2
3
�1 �1
and 2.8 Â10 Æ10 dm mol s , respectively. Using
2. F. A. Cotton and G. Wilkinson. Advanced Inorganic Chemistry, A
Comprehensive Text, 5th Ed., p. 569, Wiley-Interscience, New
York (1988).
these values, the calculated rate constants (k ) are in
reasonable agreement with the experimental values
Tables 3 and 4). The value of K obtained kinetically is
in the neighbourhood of an earlier reported value and a
0
3
. G. H. Hugar. PhD Thesis, Karnatak University, Dharwad, 1993, p.
55.
4. M. C. Agrawal and S. K. Upadhyay. J. Sci. Ind. Res. 42, 508
1983); G. H. Hugar and S. T. Nandibewoor. Transition Met.
(
2
1
8
1
9
(
value obtained conductometrically.
Chem. 19, 215 (1994).
The negligible effect of ionic strength might be due to
the presence of neutral molecules in the reaction.
However, the effect of the dielectric constant is not easy
to interpret. The positive value of the entropy of
activation suggests that the transition state is less rigid
than the reactants and no complex is involved in the
mechanism (Scheme 2).
5
. P. Veerasomaiah, K. Bal Reddy, B. Sethuram and T. Navaneeth
Rao. Indian J. Chem. 26A, 402 (1987).
6. J. Mitchell Jr, M. I. Kolthoff, E. S. Proskauer and A. Wiessberger.
Organic Analysis, Vol. I, p. 246, Interscience, New York (1953).
7
. G. P. Panigrahi and P. K. Misro. Indian J. Chem. 15A, 1066
1977).
. O. C. Saxena. Microchem. J. 12, 609 (1967).
(
8
9. C. S. Reddy and T. Vijaya Kumar. Indian J. Chem. 34A, 615
1995); D. L. Kamble, R. B. Chougale and S. T. Nandibewoor.
Indian J. Chem. 35A, 865 (1996).
0. F. Feigl. Spot Tests in Organic Analysis, p. 456. Elsevier, New
York (1975).
(
The enthalpy and free energy of activation indicate that
Os(VIII) is more efficient than Ru(III) as a catalyst for the
1
�
oxidation of acetaldehyde by IO . The Ru(III)-catalyzed
4
reaction is slower probably owing to the inability of
Ru(III) to act across a double bond. The Os(VIII)-
catalysed reaction, however, is reasonably fast in view of
the readiness of Os(VIII) to act across a double bond.
11. S. T. Nandibewoor and V. A. Morab. J. Chem. Soc., Dalton Trans.
483 (1995).
1
2. L. Bhatt, P. D. Sharma and Y. K. Gupta. Indian J. Chem., 23A, 560
1984); M. Devendra and Y. K. Gupta. J. Chem. Soc., Dalton
(
Trans. 1085 (1977); P. L. Timmanagoudar, G. A. Hiremath and S.
T. Nandibewoor. Indian J. Chem. 35A, 1084 (1996).
1
1
1
3. S. C. Pati and G. Sriramulu. Proc. Indian Acad. Sci. 87(4), 87
(1978).
Acknowledgment
4. A. A. Frost and R. G. Pearson. Kinetics and Mechanism, p. 149.
Wiley Eastern, New Delhi (1970).
5. Z. Harzion and G. Navon. Inorg. Chem. 19, 2236 (1980).
The authors thank Dr V. K. Revankar, Reader, Depart-
ment of Chemistry, Karnatak University, Dharwad, for
valuable discussions.
16. P. S. Radhakrishnamurthy and H. P. Panda. Bull. Soc. Kinet. Ind.
(1), 6 (1980).
7. A. M. Balado, B. C. Galan and F. J. P. Martin. An. Quim. 88, 170
1992).
2
1
1
(
8. F. A. Cotton and G. Wilkinson. Advanced Inorganic Chemistry, p.
885. Wiley Eastern, New York (1988); P. L. Timmanagoudar, G.
A. Hiremath and S. T. Nandibewoor. J. Indian Chem. Soc. 74, 296
(1997).
REFERENCES
1
. C. A. Bunton. in Oxidation in Organic Chemistry, Part A, edited
by K. B. Wiberg, p. 368, Academic Press, New York (1965).
19. P. Ballinger and F. A. Long. J. Am. Chem. Soc. 81, 1050 (1959).

1998 John Wiley & Sons, Ltd.
JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, VOL. 11, 171–176 (1998)