Idea Transcript
Potassium permanganate is widely used as an oxidizing agent in synthetic as well as in analytical chemistry and also as a disinfectant. The reactions are governed by pH of the medium. Among six oxidation states of manganese from +2 to +7, permanganate, Mn(VII) is the most potent oxidation state in acid as well as in alkaline medium. The oxidation by permanganate ion finds extensive application in organic synthesis catalysis
3,5
1-6
especially since the advent of phase transfer
. Kinetic studies are important sources of mechanistic information on
the reaction as demonstrated by the results referring to unsaturated acids both in aqueous3-6and non-aqueous media 7. During oxidation by permanganate, it is evident that permanganate is reduced to various oxidation states in acidic, alkaline and neutral media. Furthermore, the mechanism by which the multivalent oxidant oxidizes a substrate depends not only on the substrate but also on the medium 8 used for the study. In strongly alkaline medium, the stable reduction product
9,10
of permanganate ion is
manganate ion, MnO42-. Methocarbamol is a central muscle relaxant used to treat skeletal muscle spasms. It is the carbamate of guaifenesin, but does not produce guaifenesin as a metabolite, since the carbamate bond is not hydrolyzed metabolically; metabolism is by Phase I ring hydroxylation and O-demethylation, followed by Phase II conjugation. All of the major metabolites are unhydrolyzed carbamates11. The structure of methocarbamol is shown below.
95
NH2 O
O
HO O H3C
O
The present study deals with the title reaction to investigate the redox chemistry of permanganate in basic media and to arrive at a suitable mechanism. EXPERIMENTAL
Materials All chemicals used were of analytical reagent grade and double distilled water was used throughout the work. The solution of methocarbamol (Bayer, AG) was prepared by dissolving known amount of solid sample in 100 cm3 of double distilled water. The permanganate solution was prepared and standardised against oxalic acid12. Potassium manganate solution was prepared as described by Carrington and Symons
13
. NaOH (BDH, Analar) and NaClO4 (BDH, Analar)
were employed to maintain the required alkalinity and ionic strength respectively. Instruments used a) For kinetic measurements: CARY 50 Bio UV-vis. spectrophotometer (Varian, Victoria – 3170, Australia ). b) For product analysis: GC-MS(Shimadzu 17A gas chromatograph with a Shimadzu XP -5000A mass spectrometer). c) Nicolet 5700 - FT-IR spectrometer (Thermo, USA) and 300 MHz 1H NMR spectrometer (Bruker, Switzerland).
96
Kinetic studies The oxidation of methocarbamol by permanganate was followed under pseudo-first order conditions where methocarbamol concentration was excess over permanganate concentration at 25 0.1C unless otherwise stated. The reaction was initiated by mixing the required quantities of previously thermostatted solutions of methocarbamol and permanganate, which also contained definite quantities of sodium hydroxide and NaClO4 to maintain the required alkalinity and ionic strength. The application of Beer’s law to permanganate at 526 nm had been verified between 1.0 x 10-4 - 1.0 x 10-3 under the reaction conditions and observed extinction coefficient is, = 2100 50 dm3 mol-1 cm-1 (Fig. IV (i) (p.98)). An example run is given in Table IV (i) (p.99). The first order rate constants, kobs were obtained from the plots of log (At - A∞) versus time (Fig.IV (ii) (p.100)). Where At and A∞ are absorbances of permanganate at time t and ∞ respectively. The plots were linear upto 80% completion of the reaction and good first order kinetics were observed. In the course of measurements, the solution changed from violet to blue and then to green. The spectrum of the green solution was identical to that of MnO42-. It is probable that the blue colour originated from the violet of permanganate and the green from the manganate, excluding the accumulation of hypomanganate. The formation of Mn(VI) was also evidenced by a decreasing absorbance of Mn(VII)
97
Fig. IV (i) Verification of Beer’s law for permanganate concentrations at 526 nm in 0.05 mol -
dm 3 aqueous alkali at 250C
98
Table IV (i) Oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC Example run [KMnO4] = 1.0 x 10-4; [KOH]
= 0.15
[methocarbamol] = 5.0 x 10-3 I = 0.17 / mol dm-3
;
Time
Optical density
[KMnO4] x 104
(min)
(526 nm)
(mol dm-3)
0.0
0.209
0.995
0.2
0.201
0.957
0.4
0.193
0.919
0.6
0.186
0.885
0.8
0.181
0.861
1.0
0.171
0.814
1.2
0.162
0.771
1.4
0.156
0.742
1.6
0.148
0.704
1.8
0.142
0.676
2.0
0.133
0.633
2.2
0.128
0.609
2.4
0.124
0.590
2.6
0.122
0.580
2.8
0.118
0.561
3.0
0.114
0.542
3.2
0.110
0.523
3.4
0.105
0.500
3.6
0.100
0.476
3.8
0.094
0.447
4.0
0.088
0.419
99
Fig. IV (ii) First order plots of the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC [MnO4-] x 10-4 mol dm-3 = 1) 0.50; 2) 1.0; 3) 2.0; 4) 3.0; 5) 4.0; 6) 5.0;
3.5 3.0
3+ log (A t -A ∞)
2.5 6 5 4 3 2
2.0 1.5 1.0
1 0.5 0.0 0.0
0.5
1.0
1.5
2.0 Time (min)
100
2.5
3.0
3.5
4.0
at 526 nm and an increasing absorbance of Mn(VI) at 604 nm during the course of the reaction(Fig. IV (iii)(p.102)). The effect of dissolved oxygen on the rate of reaction was verified by preparing the reaction mixture and following the reaction in an atmosphere of nitrogen. No significant difference between the results obtained in the presence and absence of nitrogen. RESULTS Stoichiometry and product characterization Different sets of reaction mixtures containing excess concentration of permanganate over methocarbamol in the presence of constant amounts of OHand NaClO4 were kept for 1 h in closed vessels under nitrogen atmosphere. The remaining concentration of permanganate was estimated spectrophotometrically at 525 nm. The result indicates , one mole of methocarbamol reacts with four moles of Mn(VII), as shown in equation 1.
O
CH3 O
O CH3
O O C NH2 + 4[MnO4(OH)]2-
O O C
OH
+
OH H HO C O NH2 C H O
101
+ 4MnO42- + 2H2O
(1)
Fig. IV (iii) Spectral change during the course of reaction between methocarbamol and alkaline permanganate
102
The acidified reaction mixture is extracted by using mixture of solvents i.e chloroform and ethyl acetate. The main reaction products were eluted in a mixture of chloroform and ethyl acetate (8 : 2), which were identified as 2-Methoxy phenoxy acetic acid (I) and Hydroxyl methyl carbamate (II). The IR spectrum of compound (I) showed the bands at 1682 cm-1 and 3443 cm-1 due to C=O and –OH stretching frequencies of carboxylic acid group respectively (Fig. IV (iv)(p.104)). Further it was confirmed by its mass spectrum, which exhibited m/z at 182 (Fig. IV (v)(p.105)). Similarly for compound (II),Hydroxyl methyl carbamate, IR spectrum bands at 3342 cm-1 and 3251 cm-1 due asymmetric and symmetric frequencies of –NH2 group, a band at 3114 cm-1 due to –OH stretching frequency was observed. The C=O stretching frequency of CONH2 group was also observed at 1603 cm-1(Fig. IV (vi) (p.106)). Further, the formation of compound was confirmed by its mass spectrum, which showed m/z at 91 (Fig. IV (vii)(p.107)). Reaction orders The reaction orders were determined from the slopes of log kobs versus log (concentration) plots by varying the concentration of the drug and alkali in turn while keeping others constant. Effect of [permanganate] The oxidant permanganate concentration was varied in the range of 0.50 x10-4 to 5.0 x 10-4 and the fairly constant kobs values (Table IV(ii)(p.109)) indicate 103
Fig. IV (iv) FT-IR spectra of the product, 2-Methoxy phenoxy acetic acid , obtained during the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
104
Fig. IV (v) GC-MS spectra of the product 2-Methoxy phenoxy acetic acid obtained during the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
105
Fig. IV (vi) FT-IR spectra of of the product Hydroxyl methyl carbamate obtained during the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
106
Fig. IV (vii) GC-MS spectra of the product Hydroxyl methyl carbamate obtained during the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
107
that order with respect to permanganate concentration was unity. This was also confirmed by linearity of the plots of log [At - A∞] versus time(Fig. IV (ii)(p.100)) up to 80% completion of the reaction. Effect of [methocarbamol] The substrate methocarbamol concentration was varied in the range of 0.6 x 10-3 to 6.0 x 10-3 mol dm-3 at 298K keeping all other reactants concentration and conditions constant. As the methocarbamol concentration increases the rate of reaction also increases (Table IV(ii)(p.109)) and from the plot of log kobs versus log[methocarbamol], an apparent less than unit order dependence on methocarbamol concentration was observed(Fig. IV (viii)(p.110)). Effect of [alkali] The effect of alkali on the reaction rate was studied in the range of 0.2 x 10-1 to 2.0 x 10-1 at constant concentration of methocarbamol and permanganate . The rate constants increased with the increase in alkali concentration (Table IV(ii)(p.109))and the order in OH- concentration was less than unity(Fig. IV (viii)(p.110)). Effect of ionic strength and dielectric constant of the medium The effect of ionic strength was studied by varying the sodium per chlorate concentration from 0.15 to 0.27 mol dm-3 at constant concentrations of permanganate, methocarbamol and alkali. It was found that the rate constant
108
Table IV (ii) Effect of variation of permanganate, methocarbamol and alkali concentrations on the oxidation of methocarbamol by alkaline permanganate at 25C I = 0.17 mol dm-3 [MnO4-] x 104
[MET] x 103
[OH-] x 101
kobs x103
(mol dm-3)
(mol dm-3)
(mol dm-3)
(s-1)
0.5
5.0
1.5
3.32
1.0
5.0
1.5
3.34
2.0
5.0
1.5
3.35
3.0
5.0
1.5
3.36
4.0
5.0
1.5
3.36
5.0
5.0
1.5
3.34
1.0
0.6
1.5
0.99
1.0
1.5
1.5
1.75
1.0
2.0
1.5
2.22
1.0
3.0
1.5
2.64
1.0
5.0
1.5
3.69
1.0
6.0
1.5
4.45
1.0
5.0
0.2
0.95
1.0
5.0
0.7
1.92
1.0
5.0
1.0
2.46
1.0
5.0
1.5
3.59
1.0
5.0
1.7
3.91
1.0
5.0
2.0
4.31
109
Fig. IV (viii) Order with respect to methocarbamol and hydroxyl ion concentrations on the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
3.0 2.5
5+log kobs
2.0 1.5 1.0 0.5 0.0 1.0
1.5
2.0
2.5
3.0
5+log[MET]
2.0
4+log kobs
1.6 1.2 0.8 0.4 0.0 2.0
2.5
3.0
4+log[OH -] 110
3.5
decreased with increasing concentration of NaClO4(Table IV(iii)(p.112)). The plot of log kobs versus √I was found to be linear with negative slope (Fig. IV(ix)(p.113)). Dielectric constant of the medium, D was studied by varying the tert-butyl alcohol at constant concentration of permanganate, methocarbamol and alkali. It was found that dielectric constant of the medium had no significant effect on the rate of reaction. Polymerisation study The intervention 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 intervention of free radicals in the reaction. The blank experiments of either permanganate or methocarbamol alone with acrylonitrile did not induce any polymerisation under the same condition as those induced for reaction mixture. Effect of temperature The kinetics was studied at three different temperatures, 15, 25 and 350C, under varying concentrations of methocarbamol and alkali , keeping other conditions constant. The rate constants were found to increase with increase in temperature. The rate constants (k) of the slow step of Scheme 1 were obtained from the slopes and intercepts of 1/kobs versus 1/[methocarbamol] and 1/[OH-] plots at three different temperatures (Table IV (iv)(p.116)and were used to
111
Table IV (iii) Effect of variation of ionic strength (I) on the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25o C [permanganate] = 1.0 x 10-4
[MET] = 5.0 x 10-3
[OH-] = 0.15 mol dm-3 kobs x 10-2
I √I -3
(s-1)
(mol dm ) 0.15
0.3872
0.43
0.17
0.4123
0.39
0.20
0.4472
0.36
0.23
0.4795
0.33
0.25
0.5000
0.32
0.27
0.5196
0.31
112
Fig. IV (ix) Effect of ionic strength on the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25oC
0.65
3 + logk obs
0.60
0.55
0.50
0.45
0.40 0.35
0.40
0.45
√I mol dm-3
113
0.50
0.55
calculate the activation parameters. The energy of activation was evaluated from the plot of log k(y*calc) versus 1/T as shown in Fig. IV (x)(p.115), from which the activation parameters were calculated and are tabulated in Table IV (iv)(p.116). DISCUSSION The permanganate ion is a powerful oxidant in aqueous alkaline medium. Diode array rapid scan spectrophotometric studies have shown that at pH[12], Mn(VII) is reduced to Mn(VI), and no further reduction has been observed. The permanganate in alkaline medium exhibits various oxidation states, such as Mn(VII), Mn(V) and Mn(VI). The colour of the solution changed from violet to blue and further to green excluding the accumulation of hypomanganate. The violet colour originates from pink of permanganate and blue from hypomanganate during the course of the reaction. The colour change of KMnO4 solution from violet Mn(VII) ion to dark green Mn(VI) ion through blue Mn(V) ion has been observed. The reaction between methocarbamol and permanganate in alkaline medium has a stoichiometry of 1:4 with an order of less than unity for both alkali and methocarbamol. First order dependence on permanganate concentration has observed during the reaction. No effect of the products was observed. The following mechanism has been proposed in the form of Scheme 1.
114
Fig. IV (x) Effect of temperature on the oxidation of methocarbamol by permanganate in aqueous alkaline medium at 25 oC
1/T x 10 3 3.20
3.25
3.30
3.35
-2.20 -2.22
logk ( y* cal )
-2.24 -2.26 -2.28 -2.30 -2.32 -2.34 -2.36
115
3.40
3.45
3.50
Table IV (iv) Effect of temperature on the oxidation of methocarbamol by permanganate in aqueous alkaline medium with respect to slow step of Scheme 1
Temperature
1/T x 103
k x 102
log k
log k
(K)
(x)
(dm3 mol-1 s-1)
(y)
( y* cal)
288
3.472
0.45
-2.346
-2.345
298
3.355
0.53
-2.275
-2.277
308
3.246
0.61
-2.214
-2.213
Activation Parameters Parameters
Values
Ea (kJ mol-1)
12.0±0.3
ΔH# (kJ mol-1)
9.0±0.3
ΔS# (JK-1 mol-1)
-213±5
ΔG# (kJ mol-1)
73±3
log A
2.0±0.02
116
K1
MnO4 - + OH -
O [MnO4 . OH]
2-
[MnO4 . OH] 2-
CH3 O O C NH2
O
+
K2
Complex( C)
OH O k slow
Complex( C)
+ O NH2 H2 C C O
O
CH3 O
+
OH -
+ + H2C O C NH2 . H O OH
fast
CH3
H O NH2 HO C C H O (II)
O + [MnO4 . OH] 2-
O
+ MnO4 2- + OH -
CH3
fast
2+ H2 O + MnO4
O H
. H O
OH
O
CH3 O
+
H
2[MnO4(OH)] 2-
fast
O
CH3 + 2MnO4 2- + H2O
O OH
O
O
(I)
Scheme 1 The results indicate that the OH- combines first with permanganate to give an alkaline permanganate species [MnO4.OH]2- in a prior equilibrium step
117
14, 15
,
which is also supported by the observed less than unit order in OH- concentration and the Michaelis–Menton plot, which is linear with positive intercept. The permanganate species then reacts with methocarbamol to give a complex (C), which decomposes in a slow step to give a free radical of 2-methoxy phenoxy acetic acid (I) and hydroxyl methyl carbamate (II) . Such type of free radicals have been reported in the literature
16
. This free radical of 2-methoxy phenoxy acetic
acid then reacts with three more molecules of permanganate in further fast steps to yield the product 2-methoxy phenoxy acetic acid as given in Scheme 1. Spectroscopic evidence for the complex formation between oxidant and substrate was obtained from UV–vis spectra of [methocarbamol] = 5.0 X 10-3, [permanganate] =1.0 X 10-4, [OH-] = 0.15 mol dm-3 and mixture of both. A hypsochromic shift of about 4 nm from 310 nm to 306 nm in the spectra of potassium permanganate compared with the reaction mixture containing potassium permanganate and methocarbamol was observed . Such type of complex between a substrate and an oxidant has been observed in other studies 17. The rate law for the Scheme 1could be derived as Rate =
-d [ MnO4- ]
= k( C )
dt
=
k K1 K2 [MnO4 -][MET] [OH-]
( 2)
2[MnO4-]T = [MnO4 ]f + [MnO4.OH] + Complex ( C )
=
[MnO4-]f + K1 [MnO4 ] [OH ] + K2 [MET] [HMnO4]
118
= [MnO4-]f 1 + K1 [OH ] + K1K2 [MET] [OH ]
[MnO4-]f =
[MnO4 -]T 1 + K1 [OH -] + K1K2 [MET][OH-]
(3)
where T and f stands for total and free concentration of [MnO-4] Similarly, [MET]T = [MET]f + [Complex(C)]
= [MET]f + K1K2[MET][OH-][MnO4-]
(4)
[MET]T= [MET]f [ 1+ K1K2[OH-][MnO4-]]
[MET]f =
[MET]T 1 + K1K2[OH-][MnO4-]
(5)
In view of the low concentration of MnO4- used in the experiment, the term K1K2[OH-][MnO4-] can be neglected. Hence, [MET]f = [MET]T
(6)
[OH-]f =
(7)
Similarly,
[OH -]T
Substituting equations (3), (6) and (7) in equation ( 2 ) and omitting subscripts we get
119
k K1 K2 [MnO4-] [OH-] [MET]
Rate =
Rate [MnO4-]
1+ K1[OH-] + K1K2[MET][OH-]
(8)
k K1 K2 [OH-] [MET]
= kobs =
1+ K1[OH-] + K1K2[MET][OH-]
The rate law (8) can be rearranged to equation (9) which is suitable for verification 1 k obs
=
1
1 -
k K1K2[MET][OH ]
+
kK2[MET]
+
1
(9)
k
According to equation (9), the plots of 1/kobs versus 1/[OH-] and 1/kobs versus 1/[MET] were linear (Fig. IV(xi)(p.121)); from the intercepts and slopes of such plots, the reaction constants K1, K2 and k were calculated as(0.67 x 10-1)dm3 mol-1, (44.2 x 103) dm3 mol-1 and (0.53x10-2) s-1, respectively. The value of K1 is in neighborhood of literature value (K1 = 5.6 × 10-1) 18. The thermodynamic quantities for the different equilibrium steps in Scheme 1 can be evaluated as follows. The methocarbamol and hydroxide ion concentrations (Table IV(ii)(p.109)) were varied at different temperatures. The plots of 1/kobs versus 1/[MET] and 1/ kobs versus 1/[OH-] should be linear (Fig. IV(xi)(p.121). From the slopes and intercepts, the values of K1 are calculated at different temperatures. A van’t Hoff plot was made for the variation of K1 with temperature [i.e., log K1 versus 1/T] and the values of the enthalpy of reaction ΔH, entropy of reaction ΔS and free energy of reaction ΔG, were calculated. These values are also given in Table IV(v)(p.122). 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
120
Fig. IV (xi) Verification of rate law (8) in the form of (9) for the oxidation of methocarbamol by permanganate in aqueous alkaline medium at different
temperatures
(a) 1/kobs versus 1/[MET] (b)1/kobs versus 1/[OH-]
1.4 1.2
1/kobs x 10-3
1.0
288 K
0.8 0.6
298 K
0.4
308 K
0.2 0.0 0.0
0.5
1.0 -3
1.5 3
1/kobs x 10-3 s
1/[MET] X 10 dm mol
1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0
2.0
-1
288 K 298 K 308 K
0
0.1
0.2
0.3
0.4
1/[OH-] x 10-2 dm3 mol-1
121
0.5
0.6
Table IV (v) Effect of temperature on first and second equilibrium step of Scheme 1
Temp. (K)
K1 x 102 dm3 mol-1
K2 x10-3 dm3 mol-1
288
4.4
60.4
298
6.7
44.2
308
7.4
32.7
Thermodynamic quantities with respect to K1 and K2 Quantities
Using K1values
Using K2 values
H (kJ mol-1)
19.56
-22.58
S (J K-1mol-1)
42.41
13.13
G (kJ mol-1)
6.92
-26.63
122
limiting step, supporting the fact that the reaction before the rate determining step is fairly slow and involves a high activation energy
19
. In the same manner, K2
values were calculated at different temperatures and the corresponding values of thermodynamic quantities are given in Table IV(v)(p.122).The negative value of ΔS# (-244 ± 11) suggests that the intermediate complex is more ordered than the reactants 20. The observed modest enthalpy of activation and a higher rate constant for the slow step indicates that the oxidation presumably occurs via an innersphere mechanism.This conclusion is supported by earlier observations
21
. The
moderate value of ΔH# (9.12 kJ/mol) was due to energy of solution changes in the transition state. CONCLUSION It is interesting that the oxidant species MnO4- requires a pH = 12, below which the system becomes disturbed and the reaction proceeds further to give a reduced product of the oxidant as Mn(IV). Hence, it becomes apparent that the role of pH in the reaction medium is crucial. It is also noteworthy that under the conditions studied, the reaction occurs in successive one electron reduction in a single step. The description of the mechanism is consistent with all the experimental evidence. Rate constant of slow step and other equilibrium constants involved in the mechanism are evaluated and activation parameters with respect to slow step of reaction were computed. The overall mechanistic sequence described here is consistent with product, mechanistic and kinetic studies.
123
REFERENCES 1.
A. Shaabani, F. Tavasoli-Rad and D. G. Lee, Synthetic Commun., 35, 571 (2005)
2.
S. Caron, R. W. Dugger, S. G. Ruggeri, J. A. Ragan and D. H. Brown Ripin, Chem. Rev., 106, 2943 (2006)
3.
D. G. Lee, “Oxidation in Organic Chemistry”, Part D, Trahanovsky, W. S. Ed., academic Press, New York, (1982)
4.
L. I. Simandi, “The Chemistry of Functional Groups”, Suppl. C, S. Patai, Z. Rappoport, Ed. Wiley, Chichester (1983)
5.
D. G. Lee, E. J. Lee and K. C. Brown, “Phase Transefer Catalysis, New
Chemistry, Catalysis and Applications”,
ACS Symposium series No.326, American Chemical Society, Washington DC, (1987) 6.
A. J. Fatiadi, Synthesis, 106, 85 (1987)
7.
J. F. Perez-Benito and D. G. Lee, J. Org. Chem., 52, 3239 (1987)
8.
R. Stewart, K. A. Gardner, L. L. Kuehnert and J. M. Mayer, Inorg. Chem., 36, 2069 (1997)
124
9.
L. I. Simandi, M. Jaky, C. R. Savage and Z. A. Schelly, J. Am. Chem. Soc.,107, 4220 (1985)
10. P. L. Timmanagoudar, G. A. Hiremath and S. T. Nandibewoor, Transition Met. Chem., 22, 193 (1997) 11. R. B. Bruce, L. B. Turnbull, J. H. Newman, J. Pharm Sci.,60 (1), 104–106(1971 ) 12. G. H. Jeffery, J. Bassett, J. Mendham and R. C. Denny, “Vogel’s Textbook of Quantitative Chemical Analysis”, 5th edn., ELBS, Longman, Essex U.K.,(1996) 13. A. Carrington and M. C. R. Symons, J. Chem. Soc., 3373 (1956), 14. R. G. Panari, R. B. Chougale and S. T. Nandibewoor , J. Phy. Org. Chem., 11, 448(1998) 15. C. F. Baes and R. E. Mesmer, “The Hydrolysis of Cations”, Wiley, New York, (1976). 16. V. C. Seregar, C. V. Hiremath and S. T. Nandibewoor, Transit. Met. Chem., 31,541 (2006) 17. S. A. Farokhi, A. K. Kini and S. T. Nandibewoor, Inorg. React. Mech., 4, 67 (2002) 18. P. N. Naik , S. A. Chimatadar , S. T. Nandibewoor , Ind. Eng. Chem. Res., 48 (5), 2548 (2009)
125
19. K. S. Rangappa, M. P.
Raghavendra, D. S. Mahadevappa and D.
Channegouda , J Org Chem., 63, 531(1998) 20. A. Weissberger , “Investigation of Rates and Mechanism of Reactions in Techniques of Chemistry”, In: Lewis ES (ed), vol 4. ,Wiley, New York, (1974) 21. S. A. Farokhi and S. T. Nandibewoor , Tetrahedron , 59, 7595(2003)
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