Mechanistic Investigation of Osmium(VIII) Catalyzed Oxidation of Glutamic Acid With Sodium Salt of N-Chloro 4-Methylbenzenesulfonamide in Aqueous Media: A Practical Approach

Article abstract of DOI:10.1080/15533174.2013.872141

L-glutamic acid is used in the production of monosodium glutamate spices and other biochemical reagents. Its oxidation kinetics and a detailed mechanistic interaction of Os(VIII) catalyzed Glue-CAT reaction in alkaline medium have been investigated at different temperatures. It has been studied spectrophotometrically as a basic experimental approach for this study. All variables affecting the development of the color were investigated and the conditions were optimized. The effect of Glue, CAT, Os(VIII), and OH concentration on the rate of reaction has been studied. The reactions follow identical kinetics for all It is a first order reaction in both Glue and CAT, but fractional order in alkali and Os(VIII). Increasing ionic strength dielectric constant of the medium had no significant effect on the rate. The effects of added products like halide ions and toluene-p-sulfonamide have also been investigated. A mechanism involving the formation of a complex between Glue-CAT-Os(VIII) has been proposed. The stoichiometry of the reaction is found to be 1:1. The main products of Glue were identified with the help of FTIR and TLC. The reaction constants involved in the mechanism are explained. There is a good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism. The proposed methods were successfully applied for the high yield of the products and short reaction times. It is also an inexpensive, simple, and smooth method.

Full text of DOI:10.1080/15533174.2013.872141

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Mechanistic Investigation of osmium(VIII) catalyzed
oxidation of glutamic acid with sodium salt of N-chloro
4-methylbenzenesulfonamide in aqueous media A
Practical Approach
Aftab Aslam Parwaz Khanab, Anish Khanab, Abdullah M. Asiriab, Naved Azumab, Malik Abdul
Rubab, Mohammed M. Rahmanab & Sher Bhadar Khanab
a Chemistry Department, Faculty of Science, King Abdulaziz University, Jeddah 21589, P.O.
Box 80203, Saudi Arabia
b Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah
21589, P.O. Box 80203, Saudi Arabia
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Accepted author version posted online: 14 Jan 2015.
To cite this article: Aftab Aslam Parwaz Khan, Anish Khan, Abdullah M. Asiri, Naved Azum, Malik Abdul Rub, Mohammed
M. Rahman & Sher Bhadar Khan (2015): Mechanistic Investigation of osmium(VIII) catalyzed oxidation of glutamic acid with
sodium salt of N-chloro 4-methylbenzenesulfonamide in aqueous media A Practical Approach, Synthesis and Reactivity in
Inorganic, Metal-Organic, and Nano-Metal Chemistry, DOI: 10.1080/15533174.2013.872141
To link to this article: http://dx.doi.org/10.1080/15533174.2013.872141
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Mechanistic Investigation of osmium(VIII) catalyzed oxidation of glutamic acid with
sodium salt of N-chloro 4-methylbenzenesulfonamide in aqueous media: A Practical
Approach
Aftab Aslam Parwaz Khana,b,*, Anish Khana,b,Abdullah M. Asiria,b, Naved Azuma,b,Malik
Abdul Ruba,b, Mohammed M. Rahmana,b,Sher Bhadar Khana,b
a Chemistry Department,Faculty of Science,King Abdulaziz University, Jeddah 21589, P.O. Box
80203, Saudi Arabia
bCenter of Excellence for Advanced Materials Research,King Abdulaziz University, Jeddah
21589, P.O. Box 80203, Saudi Arabia
Keywords Osmium(VIII), Glutamic acid, N-chloro 4-methylbenzenesulfonamide, Kinetics and
mechanistic dicussed
*Corresponding author. E-mail address: draapk@gmail.com
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ABSTARCT
L-glutamic acid,used in the production of monosodium glutamate spices and other biochemical
reagents. Its oxidation kinetics and a detailed mechanistic interaction of Os(VIII) catalyzed Glue-
CAT reaction in alkaline medium have been investigated at different tempretures. It has been
studied spectrophotometrically as a basic experimental approach for this study. All variables
affecting the development of the color were investigated and the conditions were optimized.The
effect of Glue,CAT,Os(VIII) and OH concentration on the rate of reaction has been studied. The
reactions follow identical kinetics for all It is a first order reaction in both Glue and CAT, but
fractional order in alkali and Os(VIII). Increasing ionic strength dielectric constant of the
medium had no significant effect on the rate. The effects of added products like halide ions and
Toluene-p-sulphonamide have also been investigated. A mechanism involving the formation of a
complex between Glue-CAT-Os(VIII) has been proposed. The stoichiometry of the reaction is
found to be 1∶1. The main products of Glue were identified with the help of FTIR and TLC.The
reaction constants involved in the mechanism are explained. There is a good agreement between
the observed and calculated rate constants under different experimental conditions.
Investigations at different temperatures allowed the determination of the activation parameters
with respect to the slow step of the proposed mechanism. The proposed methods were
successfully applied for the high yield of the products and short reaction times. It is also an
inexpensive simple and smooth method.
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INTRODUCTION
Oxidation of amino acids is of immense significance both from chemical view point and
from its behavior on the mechanism of amino acid metabolism. Amino acids not only act as
building blocks in protein synthesis but also play a significant role in the metabolism. They are
subjected to many reactions and can supply precursors for many endogenous substances like
hemoglobin in blood. They can undergo many kinds of reactions, depending on whether a
particular amino acid contains a polar or non-polar subtituent. L-Glutamic acid is one of the most
abundant amino acids, especially high in cereal proteins and can be oxidized by different
oxidants [1-6]. A salt of glu-e is used in the production of monosodium glutamate and nutritional
supplements. L-glutamate itself can be used as medicine and promotes oxidation process. It
combines with ammonia as a drug-free glutamine. It is mainly used for the treatment of hepatic
coma and severe liver dysfunction, but the response is not satisfactory. Racemic glutamate is
used for the production of drugs. Physiologically, it plays a role in the metabolism of amino
groups and is the precursor of neurotransmitter, gamma-amino butyric acid and L-glutamic acid.
Being acidic in nature it is important in determining 3-D conformation of proteins.
The well-known member of this group, chloramine-T(p-Me-C6H4SO2NClNa.3H2O or
CAT), is a well known analytical reagent, and the mechanistic aspects in many reactions have
been reported [7-11]. The redox potential of CAT is pH dependent and decreases with an
increase the medium of the pH [12]. The nature of active oxidizing species of CAT depends on
the pH of the medium and the reaction circumstances. Chloramine-T is a source of positive
halogen and this reagent has been exploited as oxidant for a variety of substrates in both acidic
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and alkaline media [13-18]. We have also observed that the oxidation of LF by CAT in alkaline
medium [19].
The OsO4 undergoes reduction up to +2, +4 and +6 oxidation states in acid medium.
However, in alkaline medium it undergoes reduction [20] up to +6 oxidation state only. Together
the unique nature and the moderate reduction potential, [21] Os(VIII)/(VI) of +0.85 V in acidic
and +0.30 V in aqueous medium act as a catalyst with a large number of oxidants both organic
and inorganic substrates[22]. Hence, this study is concerned with the mechanistic to setup the
oxidative paths of L-glutamic acid. with a N-chlorobenzenesulfonamide oxidant and a catalyst,
osmium(VIII), respectively.
EXPERIMENTAL
Chemicals and Solutions
Stock solution of L-Glutamic acid (Merck) was prepared by dissolving known amount of its
hydrochloride salt in distilled water. Chloramine-T ( E. Merck ) was purified by the method of
Morris et al. [23]. An aqueous solution of CAT was prepared, standardized periodically by the
iodometric titration, and stored in brown bottles to prevent its photochemical deterioration. All
other reagents were of analytical grade and their solutions were prepared by dissolving the
requisite amounts in doubly distilled water. A stock solution of Os(VIII) (BDH) was prepared in
0.50 mol dm−3 NaOH and its concentration was standardizing by titrimetric method against
ceric sulphate solution [24]. Acetonitrile (Sigma) and acrylonitrile (Sigma) were used directly as
received to study for the effect of solvent polarity in varying proportions (v/v) of water-
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acetonitrile mixtures on the reaction medium and free radical formation, respectively. NaOH and
NaClO4 were used to provide the required basicity and to maintain the ionic strength
respectively.
Instruments Used
The absorption spectra were obtained with UVD-2960 Double beam PC connected UV–vis
spectrophotometer. All potentiometric measurements were carried out with EL20 Education Line
pH Meter from Mettler-Toledo Inc. IR spectra of the products was scanned with Spectrum 100
FTIR spectrometer (PerkinElmer).
Kinetic Studies
All the kinetics measurements were studied under pseudo first-order conditions at a room
temperature. The reaction was initiated by mixing the previously thermostated solutions of Glu-e
and CAT, which also contained the required amount of NaOH, sodium perchlorate,
osmium(VIII) and doubly distilled water. The temperature was maintained at 25 ◦C. All
measurements were completed in glass Stoppard Pyrex boiling tubes coated black to do away
with photochemical property.The progress of the reaction was monitored estimating the amount
of unconsumed CAT by measuring the spectrophotometric method recorded by a UVD-2960
Double beam PC connected UV–vis spectrophotometer. The pH of the reaction mixture was
found to be always the same pH at the beginning and end of the runs. The pseudo-first order rate
constants, kobs obtained from the slope of the plots of log(absorbance) versus time were linear
(Fig.3). The kinetic runs were followed for more than 80% completion of the reaction and good
first order kinetics were observed. Regression analysis of the experimental data to obtain the
regression co-efficient, r was performed using origin Software.
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Stoichiometry Reaction and Product Analysis
The reaction mixtures containing an excess of CAT over Glue in the prersence of NaOH and
Os(VIII) catalyst were kept were kept at 25°C for 72 h. The amount of the residual CAT in
reaction mixture was determined spectrophotometrically. The reaction may be represented by the
following scheme 1.
From the scheme 1 showed that the ratio of one mole Glue consumed per mole of CAT in the
presence of catalysts was found to be 1:1 and the product CAT-Glue-Os mixture in the form of
stoichiometric ratio under stirred condition was satisfactory to run for 72 h at 25ºC.After
completion of the stirring the reaction products checked by TLC, and extracted with ethyl acetate
. The main reaction products 4-oxobutanoic acid and p-toluenesulfonamide (TsNH2), were
identified and characterized by FT-IR. The ν(C=O) appears at 1612 cm-1 which is the
characteristic band of aldehyde and also p-toluenesulfonamide was detected by TLC
(Rf=0.910).It does not undergo further oxidation. Ammonia was identified by Nessler’s reagent.
The CO2 liberated was detected by passing the gas into lime water.
RESULTS AND DISCUSSION
Effect of Varying oxidant Concentrations on the rate
With invariable concentration of [Glue], 2.0 × 10-4 mol dm-3, and [OH-] 1.0 × 10−3 mol
dm-3, at constant ionic strength, 0.10 mol dm-3, the CAT concentration was varied in the range of
1.0 × 10-4 –1.0 × 10-3mol dm-3. All kinetic runs exhibited identical characteristics. The linearity
of plots of log (absorbance) vs time, for different concentrations of CAT, indicates order in CAT
concentration as unity. This was also confirmed by the constant values of pseudo first order rate
constants, kobs, for variable [CAT] (Table 1).
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Effect of Varying Substrate Concentrations on the rate
The concentration of Glue was varied in the range of 5.0×10−5 to 5.0×10−4 mol dm-3 with
all other conditions being constant at 25 °C. The substrate [Glue] concentration The kobs
increased with increase in the concentration of [Glue] but it was found to be less than unity
(Table1).
Effect of Varying basicity Concentrations on the rate
The oxidation of [Glue] by CAT was studied at varying concentrations of OH- by
keeping other conditions constant. The rate of oxidation increased with increase in the
concentration of OH(Table1).
Effect of Varying Catalyst Concentrations on the rate
All parameters keeping constant with catalyst Os(VIII) concentration was varied in the range of
5.0×10−6 to 5.0×10-5 mol dm-3 draw the plots of log [Os(VIII)] versus log kobs with linear slopes
showed a rate increased with increases [Os(VIII)] that means fractional-order dependence on
[Os(VIII)] (Table 1).
Effect of Varying Ionic Strength and Dielectric Constant Concentrations on the rate
The effect of ionic strength was studied by varying the NaClo4 concentration from 0. 10 to 0.40
mol dm-3 at constant concentrations of CAT, Glue,Os(VIII) and alkali. Increasing ionic strength
had no effect on the rate constant. The effect of the dielectric constant (D) was studied by
varying the MeOH-water content (v/v) in the reaction mixture with all other parameters constant.
The rate of reaction decreases with increasing MeOH volume(Table 2). The plot of log kobs
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versus 1/D was linear with negative slope following a rate-limiting step with partial ionization.
Such type values of dielectric constant of MeOH-H2O mixture reportede[25] were employed
Effect of Added Product.
The effect of initially added product, Toluene-p-sulphonamide was studied in the 1.0×10-4–
1.0×10-3 mol dm-3 concentration range, keeping the ionic strength, reactant concentrations, and
other conditions constant. No significant effects on the reaction rate as observed.
Additon of halide ions Concentrations on the rate
The effect of halides ions(NaCl and NaBr) on the rate of reaction was studied at constant other
parameters concentration,the addition of did not show any effect on the rate. These results
indicate that the halide ions play no role in the reaction mixture
Free Radical Study
The intervention of free radicals was examined as follows. The reaction mixture, to which a
known quantity of acrylonitrile scavenger had been added initially, was kept in an inert
atmosphere for 1 h. When the reaction mixture was diluted with methanol, no precipitate
resulted, indicating the absence of free radicals in the reaction mixture.
Effect of Temperatures
The effect of temperature on the reaction rate was studied for all the kinetic runs at four different
temperatures (20-37°C), keeping other experimental conditions constant. The activation
parameters (Ea, ∆H# and ∆S# ) corresponding to these rate constants have been evaluated from
the Arrhenius plot of log k versus 1/T from which other activation parameters were also
obtained (Table 3)
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Reactive Species of Os(VIII)
In general, osmium is widely used as a catalysis agent where the reactions are governed by the
medium of pH. Of all the oxidation states of osmium +8 is the most potent state in alkaline
media [26-28].In strongly alkaline medium, osmium behaves different types of the complexes
such a OsO4,[OsO4(OH)(H2O)] , [OsO4(OH)2]- and [OsO5(OH)]3- coexist in fast equilibrium.
[OsO4OH(H2O)]-
OsO4 + OH - + H2O
(i)
[OsO4(OH)2]2-
-
[OsO4OH(H2O)] + OH-
+ H2O (ii)
kobs = ko + kC[catalyst]x
Both the octahedral complexes racting ineffective with an oxidant. It is realistic to assume that
OsO4 and the basic geometry of OsO4 molecules is tetrahedral. It is the active catalyst to form a
complex with this oxidant[29-31] .
Reactive species of CAT
In general, CAT undergoes a two-electron change in its reactions forming the reduction products,
TsNH2 and sodium chloride. The oxidation potential of CAT–TsNH2 varies with medium of the
pH [32]. CAT behaves different types of reactive species in solution[33-34].
TsNClNa
TsNCl− + Na+ (i)
TsNHCl (ii)
TsNCl− + H+
(CAT) (where, Ts represents CH3C6H4SO2-group).
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Thus, CAT exists as a free acid (TsNHCl) in acidic media. The dissociation constant of TsNHCl
at a pH ca. 4.5 is 2.8×10−5 reported by Morris et al. [22]. Further, TsNHCl can undergo
disproportionate or hydrolysis according to following reactions [35]:
2 TsNHCl
TsNCl2 +TsNH2
TsNH2 +HOCl
TsNH2Cl+
(iii)
(iv)
(v)
TsNHCl + H2O
TsNHCl + H+
TsNH2Cl+ +H2O
TsNH2 + (H2OCl)+ (vi)
It appears from the equilibrium (i)–(vi), that various probable oxidizing species of CAT exists in
acidic media such as TsNHCl, TsNCl2,TsNH2Cl, TsNH2, HOCl and H2OCl+.
In alkaline medium CAT exists such as TsNHCl, HOCl and TsNCl- reported by Johnston [36]
according to following equation
TsNCl- + H2O
TsNHCl + H2o
TsNHCl +OH
(vii)
TsNH2 + HOCl (Viii)
In the present work, the rate dependence on [OH+] that the TsNCl- formed from TsNHCl results
for the formation of TsNHCl, which is a probable oxidizing species involved in the oxidation of
Glue in alkaline medium Scheme 1.
A detailed mechanistic explanation of Glue–CAT-Os in alkaline medium is given in Scheme 2.
In view of the observed experimental results, (TsNHCl) is considered to be the active species.
The fractional order dependence of Pseudo first-order rate constant on OH- that means
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preequilibrium step with CAT formed anion species TsNCl- from TsNHCl, which resulted for
the oxidation of Glue by CAT in aqueous condition.
It was confirmed by varying Os(Viii) concentration which result inverse first-order rate
constants, kobs. The rate was increased with increase Os(VIII) concentration(Table 1)and the
order of the reaction was determined from a log with linearty. It indicates a unit order
dependence on Os(VIII) concentration.
Keeping all other conditions constant the concentrations of the oxidant TsNHCl, substrate
(Glue),catalyst Os(Viii) and alkali was varied. The reaction fallowed the first-order. Based on the
experimental results, a mechanism can be proposed for which all the observed orders for each
constituent such as [oxidant], substrate, catalyst and [OH‾] may be well accommodated. The
kinetics of Os(VIII)-catalysed Oxidation of Glue by TsNHCl in in aqueous alkaline medium is a
non-complementary reaction with oxidant undergoing five equivalent changes. Added
acrylonitrile did not undergo polymerization under inert atmospheres that means absence of free
radical in this reaction system.
Pseudo first-order rate constant dependent on the concentrations of both CAT and Glue and the
fractional-order dependence on the [OH- ]and inverse in [Os(VIII)] that means an intermediate
complex is formed from the [Os(VIII)] and CAT and then interacts with the substrate. In light of
these considerations, Os(VIII) catalyzed Glue-CAT oxidation mechanism was explained, as
shown in Scheme 3.
It appears that the alkali combines with TsNHCl to give anion species TsNCl- . In the second
step, TsNCl- combines with Os(VIII) to form an intermediate complex X. The variable order
with respect to Os(VIII) most probably results from the complex formation between oxidant and
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catalyst prior to the substrate step. Further evidence was obtained from the UV–vis spectra of
reaction mixtures. Spectrophotometric results can be verified of an intermediate complex A(A
hypsochromic shift, of complex A ca. 5 nm from 320 to 315 nm is observed in case of Os(VIII)-
and Os(VIII)-CAT mixture ). Analogous effects upon complex formation between a catalyst and
an oxidant have been observed in other investigations [37]. A obtained oxidant catalyst complex
react with substrate to give another intermediate Complex C. Complex C decomposes in slow
step to give the product of Glue.In a further fast step, one molecule of formed Oxidant-Catalyst
reacts with one more molecule of glu-e bring the oxidation of Glue to yields final product of
Glue as 4 oxo butonic acid (Scheme 2).The ratio can be satisfying the stoichiometry and such a
catalyst substrate complex was obtained from the spectrophotometric measurements. The
formation of this complex was proved kinetically by Michaelis–Menten plot, i.e., a non-zero
intercept plots(Fig.3).A high rate constant for the the large rate constant slow step, point out the
oxidation most probably occurs by the use of an inner-sphere mechanism [38,39]
A detailed mechanistic interaction of Os(VIII) catalyzed Glue-CAT reaction in alkaline
medium is showed in Scheme 2, in which the structures of complex intermediate species
Complex A are given.
The total effective concentration of CAT can be written from From rate detemining step (Scheme
2):
= [TsNHCl]+[TsNCl-] +[X]+[Complex (C)]
(1)
[CAT]t
which leads to the following rate law:
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K1K2K3 [CAT]t[Glue][OH-][Os(VIII)]
1+K1[OH-]+K1K2[OH-][Os(VIII)]
-d[CAT]t
dt
(2)
=
[CAT]t =
Further rate law equation (2) is in agreement with the experimental data.
Since rate = kobs = [CAT]t ( 3)
Rate law equation (2) can be substituted in equation (3) and explains all the observed rate
constant of different type Equation can be rearranged in the following form.
-
K K K [ G lu e ] [ O H ] [ O s ( V I I I ) ]
1
2
3
k o b s
=
( 4 )
-
-
1 + K [ O H ] + K K [ O H ] [ O s ( V I I I ) ]
1
1
2
1
1
1
1
kobs
+
(5)
+
=
3 [G lue][OH-][O s(VIII)]
K3[G lue]
K1K2K
K2K3[G lue][O s(VIII)]
1
1
1
1
1
=
+
6
+
[ OH- ]
-
kobs
K K K [ Glue]
[ Os VIII ]
1
2
3
K K [ Glue]
K3[ Glue]
[ OH ]
2
3
1
1
1
1
1
=
+
+
7
K1K2K3[ Glue] [ OH- ]
K3[ Glue]
kobs
[ Os VIII ]
K2K3[ Glue]
A plot of 1/kobs versus 1/[OH] from the equation ( 6) gives
1
1
Slope
Slope
=
=
K1K2K3[ Glue]
K1K2K3[ Glue]
[ Os VIII ]
[ Os VIII ]
1
1
+
Intercept =
K2K3[ Glue] [ OH- ]
K3[ Glue]
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Similarly, a plot of 1/kobs versus 1/[Os(VIII)] from the equation (7 ) gives
1
1
+
Slope =
K1K2K3[ Glue] [ OH- ]
K2K3[ Glue]
.
1
Intercept =
K3[ Glue]
According to Eqs. the values of K1, K2, and K3 are calculated from the slope and intercept of such
plot (Fig3) the reaction constants values obtained are K1=19.12×10-2 s-1, K2=12.4×105 dm3 mol-1,
and K3 =8.12×10-3 dm3 mol-1.
It was reasonable consideration to compare the reactivity of Glue by CAT with catalyst
under the same conditions monitored at different temperatures. A demonstrate the Arrhenius plot
of log kC versus 1/T and the calculated activation parameters for the catalyzed reaction (Table
3). Moelwyn-Hughes [40] pointed out that in presence of the catalyst, the uncatalyzed and
catalyzed reactions considred at the same time given the equation below
kobs = ko + kC[catalyst]x
Here kobs is the observed pseudo first-order rate constant for the catalyst, k0 is the pseudo first-
order rate constant for the uncatalyzed reaction, kC is represent the catalytic constant and x is the
order of the reaction with respect to catalyst and x value was found to be unity. The values of kC
were calculated using the following equation.
kobs = ko + kC/[Ru(III)]
The proposed mechanisms is also supported by the observed values of the enthalpy of reaction
∆H #and free energy of reaction ∆G# were calculated obtain a high positive values of the free
energy of activation and of the enthalpy of activation support the formation of highly solvated
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transition state. The large negative value of ∆S# indicates that complex (C) is more ordered than
the reactants [41]. Further, the experimental observation shows had no effect and ionic strength
on the rate of reaction, which also substantiates for the plausible mechanism.
CONCLUSION
The simplified kinetic model is consistent and gives a reasonable response to experimental data.
Among various species of CAT in alkaline medium, anion species TsNCl- from TsNHCl is
considered as active species for the title reaction.In the present work we have studied the rates of
oxidation of Glue by CAT catalyzed by Os(VIII) and their mechanistic pathway has been
proposed. The results presented here clearly demonstrate that the oxidizing agent CAT was used
for the oxidation of Glue catalyzed by Os(VIII) with complex formation which is more effective
and inexpensive. The oxidation products are confirmed, 4-oxobutanoic acid and p-
toluenesulfonamide (TsNH2) by spot test and and FTIR and a possible reaction path for their
formation is proposed. Activation parameters and the reaction constants were calcuated.The
observed results have been explained from proposed mechanism and the rate law has been
investigated
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ACKNOWLEDGEMENT
This project was funded by (SABIC) and the Deanship of Scientific Research (DSR), King
Abdulaziz University, Jeddah, under grant no. (14/299/1433). The authors, therefore,
acknowledge with thanks SABIC and DSR technical and financial support.
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N
H
2
Na
Cl
O
O
O
CH
S
2
N
OH
CH
2
CH
NH
2
O
CH
2
O
S
OsO
4
CH
2
2H O
2
CH
O
- HCl
- NaOH
HO
O
HO
O
CH
3
CH
3
CO2 + NH3 OsO
4
SCH. 1.
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H
Na
Cl
Cl
N
N
O
O
O
O
S
S
K1
H O
2
NaOH
CH
3
CH
3
Cl
H
Cl
N
S
N
S
O
O
O
K2
O
O
O
Os
O
OsO
4
+
O
- H
CH
3
CH
3
x
OH
NH
2
CH
2
K3
CH
2
x
CH
O
Compl ex C
N
H
2
HO
O
O
O
S
O
CH
2
CH
2
C
H
Compl ex C
CO2 + NH3 OsO
4
- HCl
HO
O
CH
3
Cl
OH
NH
2
O
CH
2
CH
N
S
2
N
O
O
CH
2
Fast
HO
H
2
CH
O
CH
2
CH
O
Os
O
O
O
S
O
O
HO
O
O
CO2 + NH3 OsO
4
CH
3
SCH. 2. A detailed mechanistic scheme for the Os(VIII) catalyzed oxidation of Glue with CAT
in alkaline medium
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H
O
O
O
O
O
H
H
H
OH
H
HO
NH
2
H
FIG. 1. (a)Chemical Strucure of Glue (b) The main product of 4-oxobutanoic acid
FIG. 2. (a)Optimized structure of Glue (b) Optimized structure of 4-oxobutanoic acid
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1.7
1.5
1.3
1.1
0.9
0.7
0.5
A
B
C
D
0
0.5
1
1.5
2
2.5
Time (min)
3
3.5
4
4.5
5
FIG. 3.The log of the absorbance of oxidant plotted as a function of time for first order reactions
at various CAT × 10-5 mol/dm3: (A) 1.0, (B) 3.0,(C) 5.0, (D) 8.0.
1 / [OH- ] (mol•dm3)
2
4
6
8
10
12
14
16
18
20
0.7
0.6
0.5
0.4
0.3
0.2
0.5
0.45
0.4
0.35
0.3
0.25
0.2
10
30
50
70
90
110
1 / [Glue] × 10-3 (mol•dm3)
FIG. 4.Verification of rate law for the oxidation of Glue by CAT in the presence of catalyst.
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TABLE 1
Effect of varying CAT, Glue,OH-and Os(VIII)concentrations on the rate of reaction at 25°C
(Scheme.1)
Kobs (×104s- Os(VIII)(×105mold
)
[OH-]
[Glue]
[CAT]
1
m-3)
(×103moldm-3) (×104moldm-3) (×103moldm-3)
6.21
6.20
6.21
6.21
6.20
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
3.0
4.0
1.0
2.0
5.0
7.0
10.0
4.18
5.12
6.21
6.18
6.16
0.5
0.6
0.1
2.0
3.0
1.0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
3.0
4.0
5.0
5.0
5.0
5.0
5.0
3.18
4.89
5.31
6.21
8.34
1.0
1.0
1.0
1.0
1.0
0.5
0.6
0.8
1.0
2.0
2.0
2.0
2.0
2.0
2.0
5.0
5.0
5.0
5.0
5.0
2.38
4.22
6.21
12.15
18.42
0.5
0.6
0.1
2.0
3.0
1.0
1.0
1.0
1.0
1.0
0.5
1.0
2.0
3.0
4.0
5.0
5.0
5.0
5.0
5.0
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TABLE 2
Effect of varying dielectric constant (D) of the medium on the rate of reaction at 25°C
kobs × 10 4
D
Percentage of
MeOH (v/v)
8.45
7.65
5.88
4.56
76.5
70.0
65.2
60.7
0
10
20
30
[CAT] = 5.0 × 10−3 mol dm−3; [Glue]o = 2 × 10−4mol dm−3; [OH] = 1.0 × 10−3 mol dm−3;
[Os(VIII)] = 1.0 × 10−5 mol dm−3.
TABLE 3 Values of the catalytic constant (kc) and activation parameters at different
temperatures
kC ×104(s-1)
1/T ×103
Temperature (K)
4.52
6.21
7.35
8.32
3.413
3.356
3.300
3.246
293
298
303
308
Activation parameters
52.3
Ea (kJ mol-1)
88.5
-142.8
89.6
ΔH± (kJ mol-1)
ΔS±(J K-1 mol-1)
ΔG± (kJ mol-1)
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