Kinetic studies of transition metal ion catalyzed oxidation of some fragrance alcohols

Article abstract of DOI:10.14233/ajchem.2014.17437

The controlled oxidation of the aliphatic alcohols 2-propanol, 2-butanol and 3-methyl-1-butanol to the corresponding carbonyl compounds has been carried out using Ce (IV) in acidic medium in the absence and presence of transition metal ions of the first series. The aliphatic alcohols are widely used as diluents in the perfumery industry. The oxidation reaction was monitored under pseudo unimolecular conditions with respect to [Ce (IV)] in the temperature range 303-318 K. Aliquots of the reaction were withdrawn at regular time intervals, quenched using ice and the unreacted oxidant was estimated titrimetrically using standard ferrous ammonium sulphate with ferroin as indicator. The pseudo first order rate constants were determined from the linear plots of log (a-x) versus time. It was observed that the rate increases with alcohol concentration but decreases with Ce(IV) concentration. This has been attributed to the formation of unreactive dimeric [Ce(IV)]₂at higher concentration of Ce(IV). Potassium sulfate was used to study the effect of ionic strength on the oxidation rate. The thermodynamic activation parameters were determined from the effect of temperature on the oxidation rate. The Ru(VIII), Os(VIII) and Cr(VI) ions have been exhaustively used to catalyse a variety of organic reactions. In the present study, relatively low-cost metal ions of the first transition series have been used as effective catalysts for the oxidation of the fragrance alcohols under study. The reaction mechanism suggested for the oxidation process involves intermediates with hypervalent ions i.e., M(III). The catalytic efficiency of the metal ions is based on the stability of the complexes formed as reaction intermediates which in turn depends on the charge density of the metal ions involved. We have observed some discrepancies as the experimentally determined sequence of catalytic efficiency of metal ions does not follow the theoretically expected sequence. Suitable reaction mechanisms have been suggested for the oxidation of the alcohols in the absence and presence of transition metal ions. In the absence of metal ions, the oxidation rates of aliphatic alcohols the sequence: 2-propanol > 2-butanol > 3-methyl-1-butanol. The relative rates of oxidation of alcohols have been discussed and explained on the basis of structures, steric factors and isomeric characteristics of the perfumery alcohols under study.

Full text of DOI:10.14233/ajchem.2014.17437

Asian Journal of Chemistry; Vol. 26, No. 19 (2014), 6669-6673
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.17437
Kinetic Studies of Transition Metal Ion Catalyzed Oxidation of Some Fragrance Alcohols
*
D.V. PRABHU , H.A. PARBAT and M.A. TANDEL
Department of Chemistry, Wilson College (University of Mumbai), Mumbai-400 007, India
*Corresponding author: E-mail: dvprabhu48@gmail.com
Received: 21 February 2014;
Accepted: 7 May 2014;
Published online: 16 September 2014;
AJC-15984
The controlled oxidation of the aliphatic alcohols 2-propanol, 2-butanol and 3-methyl-1-butanol to the corresponding carbonyl compounds
has been carried out using Ce (IV) in acidic medium in the absence and presence of transition metal ions of the first series. The aliphatic
alcohols are widely used as diluents in the perfumery industry. The oxidation reaction was monitored under pseudo unimolecular conditions
with respect to [Ce (IV)] in the temperature range 303-318 K. Aliquots of the reaction were withdrawn at regular time intervals, quenched
using ice and the unreacted oxidant was estimated titrimetrically using standard ferrous ammonium sulphate with ferroin as indicator. The
pseudo first order rate constants were determined from the linear plots of log (a-x) versus time. It was observed that the rate increases with
alcohol concentration but decreases with Ce(IV) concentration. This has been attributed to the formation of unreactive dimeric [Ce(IV)]2
at higher concentration of Ce(IV). Potassium sulfate was used to study the effect of ionic strength on the oxidation rate. The thermodynamic
activation parameters were determined from the effect of temperature on the oxidation rate. The Ru(VIII), Os(VIII) and Cr(VI) ions have
been exhaustively used to catalyse a variety of organic reactions. In the present study, relatively low-cost metal ions of the first transition
series have been used as effective catalysts for the oxidation of the fragrance alcohols under study. The reaction mechanism suggested for
the oxidation process involves intermediates with hypervalent ions i.e., M(III). The catalytic efficiency of the metal ions is based on the
stability of the complexes formed as reaction intermediates which in turn depends on the charge density of the metal ions involved. We
have observed some discrepancies as the experimentally determined sequence of catalytic efficiency of metal ions does not follow the
theoretically expected sequence. Suitable reaction mechanisms have been suggested for the oxidation of the alcohols in the absence and
presence of transition metal ions. In the absence of metal ions, the oxidation rates of aliphatic alcohols the sequence: 2-propanol >
2-butanol > 3-methyl-1-butanol. The relative rates of oxidation of alcohols have been discussed and explained on the basis of structures,
steric factors and isomeric characteristics of the perfumery alcohols under study.
Keywords: Oxidation, Aliphatic alcohols, Entropy of activation, Metal ion catalysis, Hypervalent ions.
INTRODUCTION
EXPERIMENTAL
The quantitative conversion of alcohols to carbonyl
compounds has been studied by several workers1-7. However,
there are few reports available in literature on the kinetic study
of oxidation of fragrance and cosmetic alcohols8.
All the chemicals and reagents used were of AR Grade:
aliphatic alcohols 2-propanol, 2-butanol and 3-methyl-1-
butanol (SH Kelkar and Co., Mumbai and Ultra International),
cerric ammonium sulphate (West Coast Laboratories).
A.R.K2SO4 was used to study the effect of ionic strength on
reaction rate. All the metal salts used for the catalytic study
were of AnalaR grade (B.D.H.).
This paper deals with (i) the kinetics of oxidation of the
aliphatic alcohols 2-propanol, 2-butanol and 3-methyl-1-
butanol by Ce(IV) in H2SO4 in the temperature range 303-318
K (ii) the effect of ionic strength on the oxidation rate of the
above alcohols using K2SO4 (iii) the kinetics of the metal ion
catalysed oxidation of the above aliphatic alcohols using Ni(II),
Cu(II), Zn(II), Mn(II), Co(II) as well as Cd(II) ions in order to
study their relative catalytic efficiency.
Methods: The oxidation of the aliphatic alcohols was
studied under pseudo unimolecular conditions with respect to
the oxidizing agent and the progress of the reaction was
monitored titrimetrically. The solutions of alcohol and oxidi-
zing agent in requisite amounts were allowed to equilibrate in
a previously adjusted thermostat (accuracy 0.1 °C).After the
temperature equilibrium was reached, the solutions were mixed
to start the reaction. Aliquots of the reaction mixture were
All the data collected has been collated and suitable reaction
mechanisms have been suggested for the oxidation of the
aliphatic alcohols in the presence and absence of metal ions.

6670 Prabhu et al.
Asian J. Chem.
withdrawn at regular intervals and the reaction was arrested
using ice. The unreacted Ce(IV) was estimated by titration
against standard ferrous ammonium sulphate in H2SO4 using
ferroin as an indicator.
The product of the oxidation i.e., ketone was identified
by 2,4-dinitrophenyl hydrozone test and confirmed by TLC.
In aqueous H2SO4 medium, Ce(IV) has been found to oxidize
alcohols through complexation followed by free radical gene-
ration9-11. The rate constant decreases with increase in Ce(IV)
concentration (Table-1). This decrease in oxidation rate is due
to the formation of an unreactive dimeric [Ce(IV)]2 species12-14
which increases with [Ce(IV)]
The reaction was studied in the temperature range 303-
318 K. The plots of log (a-x) vs. time were found to be straight
lines and the pseudo first order rate constants were evaluated
from the slopes of the linear plots. From the Arrhenius plots
of log k vs. T-1, the energy of activation and other thermody-
namic activation parameters were calculated.
2Ce(IV)
The oxidation rates of the alcohols understudy followed
the sequence:
[Ce(IV)]2
An identical procedure was used to study the oxidation
rate in presence of metal ions in the concentration range
2-propanol > 2-butanol > 3-methyl-1-butanol
-4
[M (II)] = 2.5 to 5 × 10 mol dm-3 in the range 303-318 K.
TABLE-1
RATE CONSTANT DATA FOR THE OXIDATION OF ALIPHATIC
ALCOHOLS BY Ce(IV) IN 0.1M H2SO4, TEMPERATURE = 303 K
The pseudo first order rate constants for the metal ion catalysed
reaction were determined from the linear plots of log (a-x) vs.
time.
k × 103 (s-1)
The effect of ionic strength (µ) on oxidation rate was
studied in dilute solution in the range, µ = 5 to 25 × 10-2 mol
dm-3 at 313 K using K2SO4.
[Alc.] × 101 Ce(IV) × 103
3-Methyl-1-
2-Propanol 2-Butanol
butanol
mol dm-3
1.00
mol dm-3
2.50
10.17
9.12
5.76
5.14
4.93
2.74
3.68
4.93
5.76
7.14
8.68
9.12
9.67
5.76
2.76
2.53
2.07
1.52
3.22
3.69
4.15
4.84
7.37
5.76
5.14
3.68
2.49
0.37
0.30
0.29
1.22
1.36
1.68
2.63
3.45
3.68
1.00
5.00
RESULTS AND DISCUSSION
1.00
10.00
15.00
20.00
25.00
5.00
1.00
Kinetics of oxidation of alcohols: The aliphatic alcohols
2-propanol (A), 2-butanol (B) and 3-methyl-1-butanol (C) were
oxidized using Ce(IV) in H2SO4. The values of the rate constant
of oxidation are listed in Table-1. The rate constant increases
with alcohol concentration as expected but decreases with
increase in Ce(IV) concentration.
1.00
1.00
0.25
0.50
5.00
0.625
0.75
5.00
5.00
0.875
1.00
5.00
Reaction mechanism of oxidation:
5.00
IV
R
R
K
10
9
8
7
6
5
4
3
2
1
+
Ce (IV)
CHOH
CH - O
H
Ce
2-Propanol
2-Butanol
R'
R'
(1)
(2)
Complex
IV
R
R
k
.
3-Methyl-1-butanol
+
CH - O
H
Ce
COH
+
+
H
Ce (III)
slow
R'
R'
Complex
R
.
where
COH is a free radical generated during the course of
R'
0
0
0.2
0.4
0.6
0.8
1.0
1.2
the reaction.
[Alc.] × 101 mol–3
Fig. 1. Variation of rate constant of oxidation of aliphatic alcohols with
[Alc]
R
.
R
+
Ce (IV)
+
(3)
(4)
COH
+
Ce (III)
+
COH
R'
R'
Effect of ionic strength: K2SO4 was used to study the
effect of ionic strength (µ) on oxidation rate in dilute solution
in the range µ = 5 to 25 × 10-2 mol dm-3 at 313 K (Table-2,
R
R
+
fast
H
+
C=O
R'
ketone
COH
R'
Fig. 2). The graphs of log k vs.
were found to be straight
µ
lines parallel to the axis indicating that the oxidation rate
µ
R
was independent of ionic strength.
Net reaction :
CHOH
+ 2Ce (IV)
Effect of temperature: The oxidation was studied in the
temperature range 303-318 K. From the effect of temperature
on reaction rate, the energy of activation and other thermo-
dynamic parameters were evaluated (Table-3).
R'
R
(5)
2H+
+
C=O
+2Ce (III)
R'

Vol. 26, No. 19 (2014)
Kinetic Studies of Transition Metal Ion Catalyzed Oxidation of Some Fragrance Alcohols 6671
Cd(II) in the concentration range, M(II) = 2.5 to 5 × 10-4 mol
Table-2
dm-3 at 303-318 K. The values of the rate constants of the metal
ion-catalyzed oxidation are given in Table-4a-c. For each of
the metal ion catalysts, the oxidation rate increases linearly
with [M(II)]. The thermodynamic activation parameters for
the metal ion catalyzed oxidation of alcohols are given in
Table-5a-c.
EFFECT OF IONIC STRENGTH ON THE OXIDATION
RATES OF ALCOHOLS BY Ce(IV) IN 0.1M H2SO4 [ALC.]
= 0.1 M, [Ce(IV)] = 2.5 × 10-3 M, Temperature = 313 K
k × 103 (s-1)
2-Butanol 3-Methyl-1-butanol
µ × 102 (mol dm-3)
2-Propanol
9.02
0.00
5.51
5.76
5.70
5.51
5.88
5.14
5.25
5.30
5.30
5.07
5.30
5.75
05.00
10.00
15.00
20.00
25.00
9.12
9.26
TABLE-4
CATALYTIC EFFECT OF METAL IONS ON OXIDATION
OF SOME FRAGRANCE ALCOHOLS
9.02
9.24
9.24
[ALC.] = 0.1M; [Ce(IV)] = 2.5 × 10-3 M; TEMPERATURE = 303 K
[M(II)] × 104
k × 104 (s-1)
(mol dm-3)
TABLE-3
THERMODYNAMIC ACTIVATION PARAMETERS FOR
OXIDATION OF ALCOHOLS BY Ce(IV) IN H2SO4 [Alc.]
= 0.1 M [Ce(IV)] = 2.5 × 10-3 M temperature = 303 K
2-Propanol
Ni(II) Cu(II)
Zn(II)
3.68
4.38
4.84
4.84
5.99
9.67
10.13
Mn(II) Co(II) Cd(II)
∆S*
(kJ K-1
0.0
2.5
3.0
3.5
4.0
4.5
5.0
3.68
4.15
5.57
3.68
5.53
9.21
9.67
3.68
4.61
2.76
6.45
8.52
8.98
11.28
3.68
4.15
6.45
2.07
8.29
9.44
9.99
3.68
4.26
5.32
5.55
3.68
7.21
8.97
9.66
Temp.
(K)
Ea
(kJ mol-1)
∆H*
∆G*
k × 103 s-1
K* × 1015
( kJ mol-1) (kJ mol-1)
mol-1)
2-Propanol
1.44
303
308
313
318
9.12
10.70
26.81
57.57
13.24
13.24
13.24
13.24
10.72
10.67
10.64
10.60
86.09
87.15
86.22
85.61
-0.2487
-0.2482
-0.2414
-0.2359
6.67 10.27
7.59 11.87
8.29 13.03
1.67
4.11
8.69
2-Butanol
2-Butanol
0.91
0.0
2.5
3.0
3.5
4.0
4.5
5.0
2.97
2.30
3.68
6.22
7.83
9.21
12.66
2.97
5.29
5.99
6.91
7.60
8.52
11.97
2.97
4.96
2.97
2.76
4.15
5.99
7.37
7.60
8.52
2.97
3.68
4.61
6.22
2.97
3.92
4.38
6.68
303
308
313
318
5.75
6.91
11.05
11.05
11.05
11.05
8.53
8.49
8.45
8.40
87.25
88.27
86.60
86.48
-0.2598
-0.2590
-0.2497
-0.2455
1.08
6.22
23.05
41.45
3.54
8.52
6.26
10.36
11.74
13.81
6.91 11.05
8.75 12.66
2.30 14.27
3-Methyl-1-butanol
303
308
313
318
3.68
4.73
14.41
0.59
0.23
0.29
0.30
11.89
88.38
92.23
93.09
88.44
-0.2524
-0.2609
-0.2597
-0.2411
14.41
14.41
14.41
11.85
11.81
11.77
3-Methyl-1-butanol
9.11
0
2.69
3.60
4.21
4.53
5.53
8.29
8.98
2.69
3.50
3.86
4.26
5.21
7.14
8.29
2.69
2.30
2.69
2.69
2.99
3.02
3.30
3.47
3.60
2.69
3.27
3.56
3.68
3.86
2.69
4.15
4.38
4.38
7.14
13.78
2.5
3.0
3.5
4.0
4.5
5.0
4.65
µ
–2.00
–2.05
–2.10
–2.15
–2.20
–2.25
–2.30
–2.35
6.45
8.13
0
0.1
0.2
0.3
0.4
0.5
0.6
10.82
12.66
4.26 10.59
4.53 12.20
2-Propanol
Reaction mechanism of metal ion-catalysed oxidation
of alcohols: Mn, Co, Ni and Cu form the hypervalent ions
Mn(III), Co(III), Ni(III) and Cu(III), respectively as their third
ionization enthalpies (third ionization potentials) are compa-
ratively small unlike Zn and Cd. In Zn and Cd, the energies of
solvation or lattice solvation cannot suffice to make the 3+
chemical state chemically stable.
2-Butanol
3-Methyl-1-butanol
In presence of Mn (II), Co (II), Ni (II) and Cu (II) ions:
The reaction mechanism has been explained on the basis of
the formation of an intermediate complex involving hyper-
valent M(III) ions and alcohol.
Fig. 2. Variation of rate constant of oxidation of aliphatic alcohols with
ionic strength
The negative values of ∆S* (-0.2570 kJ K-1 mol-1 for A,
-0.2601 kJ K-1 mol-1 for B and -0.2603 kJ K-1 mol-1 for C)
indicate a decrease in the degrees of freedom due to the for-
mation of a rigid activation complex resulting in an extensive
reorientation of solvent molecules. The negative values of ∆S*
can be explained by a model in which the water molecules are
tightly held to the -OH bond which is the site of oxidation15.
Kinetics of metal ion catalysed oxidation of aliphatic
alcohols: The aliphatic alcohols 2-propanol (A), 2-butanol (B),
3-methyl-1-butanol (C) were oxidized using Ce(IV) in H2SO4
in the presence of Ni(II), Cu(II), Zn(II), Mn(II), Co(II) and
K
(R)2CHOH + M(II)
M(II)·(R)2CHOH
(i)
Complex C1
k
Slow
M(II)·(R)2CHOH + Ce(IV) → M(III)·(R)2CHOH + Ce(III) (ii)
Complex C2
The electron transfer reaction is slow16.
•
+
(R) OH + H + M(II)
fast
C
Complex C2
(iii)
→
2
•
C
where (R)2 OH is a free radical generated during the course
of the reaction.

6672 Prabhu et al.
Asian J. Chem.
•
(R) +COH + Ce(III) (iv)
2
3-methyl-1-butanol
Ni(II)
fast
C
(R)2 OH + Ce(IV)
(R)2+COH
→
(R) C=O + H+
(v)
fast
→
2
303
308
313
318
1.599
1.612
2.763
3.915
20.64
9.72
9.67
2.51
94.24 -0.2790
97.89 -0.2864
98.12 -0.2827
98.81 -0.2806
20.64
20.64
20.64
4.24
5.70
5.91
ketone
9.63
9.59
Net Reaction: (R)2CHOH + 2Ce(IV) →
(R)2C= O + 2H+ + 2Ce(III)
Cu(II)
20.05
20.00
19.97
19.93
Zn(II)
32.79
32.75
32.71
32.67
303
308
313
318
1.612
2.763
3.499
3.915
19.26
19.26
19.26
19.26
3.21
4.24
5.55
5.91
94.31 -0.2451
97.89 -0.2529
98.12 -0.2497
98.81 -0.2481
TABLE-5
THERMODYNAMIC ACTIVATION PARAMETERS OF
METAL ION CATALYSED OXIDATION OF SOME
FRAGRANCE ALCOHOLS AT DIFFERENT TEMPERATURES
∆S*
(kJ K-1
mol-1)
Temp.
(K)
k × 104
(s-1)
Ea
∆H*
∆G*
K* × 1017
303
308
313
318
2.303
2.992
3.915
4.372
19.16
19.16
19.16
19.16
3.65
4.67
6.00
6.60
95.37 -0.2065
96.31 -0.2064
97.22 -0.2061
98.52 -0.2071
(kJ mol-1)
(kJ mol-1) (kJ mol-1)
2-Propanol
Ni(II)
18.67
18.63
18.59
18.55
303
308
313
318
4.140
4.560
5.750
6.750
21.19
21.19
21.19
21.19
6.56
7.11
8.82
10.20
93.89
95.23
96.22
97.37
-0.2482
-0.2487
-0.2480
-0.2478
Mn(II)
47.05
47.00
47.97
46.93
Co(II)
20.94
20.89
20.85
20.81
Cd(II)
20.96
20.91
20.86
20.83
303
308
313
318
0.921
1.151
1.612
2.303
13.24
13.24
13.24
13.24
1.46
1.79
2.47
3.48
97.67 -0.1670
98.76 -0.1680
99.53 -0.1679
100.21 -0.1676
Cu(II)
16.62
16.58
16.54
16.50
Zn(II)
17.32
17.28
17.24
17.20
4.609
5.290
5.291
6.491
19.14
19.14
19.14
19.14
7.30
8.115
8.25
93.62
94.85
96.43
97.47
-0.2541
-0.2541
-0.2553
-0.2547
303
308
313
318
303
308
313
318
3.684
3.965
5.066
5.551
11.04
11.04
11.04
11.04
5.84
6.18
7.77
8.38
94.18 -0.2417
95.60 -0.2425
96.55 -0.2418
97.88 -0.2424
9.80
303
308
313
318
1.010
1.380
4.139
8.750
19.84
19.84
19.84
19.84
1.60
2.50
6.35
97.44
98.29
97.07
96.68
-0.2644
-0.2630
-0.2551
-0.2499
303
308
313
318
1.145
1.381
1.612
1.842
18.80
18.80
18.80
18.80
2.15
2.47
2.78
6.57
93.88 -0.2407
98.29 -0.2512
99.53 -0.2513
100.80 -0.2515
13.20
Mn(II)
16.58
16.54
16.50
16.46
303
308
313
318
4.141
4.370
5.750
7.598
19.14
19.14
19.14
19.14
6.56
6.81
93.89
95.34
96.22
97.06
-0.2551
-0.2559
-0.2547
-0.2435
8.82
11.50
At any given time, the steady state concentrations of the
intermediate complexes C1 and C2 are very small.
In the presence of Zn (II) and Cd (II) ions:
Co(II)
16.62
15.77
15.74
15.70
303
308
313
318
5.560
6.669
7.830
8.980
18.34
18.34
18.34
18.34
8.81
10.40
12.00
13.60
93.14
94.26
95.41
96.61
-0.2526
-0.2548
-0.2546
-0.2545
K
(R)2CHOH + M(II)
M(II)·(R)2CHOH
(i)
Complex
Cd(II)
16.76
16.72
•
303
308
313
318
3.450
3.680
6.450
6.900
19.28
19.28
19.28
19.28
5.47
5.74
94.35
95.78
95.92
97.31
-0.2561
-0.2567
-0.2532
-0.2537
k
Slow
+
Complex + Ce(IV) → (R)2 OH + H + M(II) + Ce(III) (ii)
C
16.68
16.64
9.89
10.40
•
C
where (R)2 OH is a free radical generated during the reaction.
•
2-Butanol
( R) C+OH + Ce(III) (iii)
2
fast
Ni(II)
18.12
18.08
18.04
18.00
C
(R)2 HOH + Ce(IV)
→
303
308
313
318
2.994
3.380
4.375
5.296
20.64
20.64
20.64
20.64
3.65
5.27
6.71
8.00
95.37
96.00
96.93
98.08
-0.2549
-0.2530
-0.2520
-0.2516
+
fast
(R) OH
2 C
(R) C=O + H+
(iv)
→
2
ketone
Net reaction: (R)2CHOH + 2Ce (IV) →
Cu(II)
16.74
16.70
16.66
16.62
Zn(II)
16.65
16.61
16.56
16.52
2.993
2.993
5.527
9.669
19.26
19.26
19.26
19.26
4.24
4.67
94.71
96.31
96.32
96.42
-0.2573
-0.2585
-0.2545
-0.2510
303
308
313
318
(R)2C=O + 2H+ + 2Ce(III)
8.48
14.60
Comparative study of the catalytic efficiency of metal
ions: The catalytic efficiency of metal ions is inversely propor-
tional to the stability of their complexes which may be formed
as short lived intermediates during the course of reaction. The
stability of the complexes generally depends on the charge
density of the metal ions involved in addition to several other
factors. Thus, the stability order for the complexes of the metal
ions under study is expected to be
Cu(II) > Zn(II) > Ni(II) > Co(II) > Mn(II) > Cd(II)17,18
and their catalytic efficiency is expected to follow the sequence,
Cd(II) > Mn(II) > Co(II) > Ni(II) > Zn(II) > Cu(II). However
such generalizations are only approximate guides19 to metal
ion behavior and discrepancies are often observed and reported
in literature.
303
308
313
318
4.957
5.066
5.527
6.219
19.17
19.17
19.17
19.17
7.85
7.90
8.48
9.39
93.43
94.96
96.32
97.59
-0.2534
-0.2544
-0.2548
-0.2550
Mn(II)
10.72
10.68
10.64
10.60
303
308
313
318
2.763
2.992
3.684
5.527
13.24
13.24
13.24
13.24
4.38
4.67
5.65
8.34
94.91
96.31
97.37
97.90
-0.2778
-0.2786
-0.2771
-0.2745
Co(II)
8.52
303
308
313
318
2.303
2.565
2.763
3.455
11.04
11.04
11.04
11.04
3.65
4.00
4.24
5.21
95.36
96.70
98.12
99.14
-0.2866
-0.2865
-0.2865
-0.2854
8.48
8.44
8.40
Cd(II)
16.28
16.24
16.20
16.16
303
308
313
318
3.915
4.146
7.140
9.213
11.04
11.04
11.04
11.04
6.20
6.46
94.02
95.47
95.65
96.54
-0.2566
-0.2573
-0.2538
-0.2528
In the present study, the sequence, of the catalytic
efficiency is as follows:
10.90
13.90

Vol. 26, No. 19 (2014)
2-Propanol (Fig. 3a):
Kinetic Studies of Transition Metal Ion Catalyzed Oxidation of Some Fragrance Alcohols 6673
Conclusion
Cd (II) > Cu (II) > Zn (II) > Ni (II) > Mn (II) > Co (II)
2-Butanol (Fig. 3b):
The oxidation rates of the aliphatic alcohols using Ce(IV)
in H2SO4 follow the sequence, 2-propanol > 2-butanol > 3-
methyl-1-butanol. The oxidation rates are found to be indepen-
dent of ionic strength.
Cd (II) >Zn (II) > Cu (II) > Ni (II) > Co (II) > Mn (II)
3-Methy-l-butanol (Fig. 3c):
Zn (II) > Cd (II) > Ni (II) > Cu (II) Co (II) > Mn (II)
Metal ions Ni(II), Zn(II), Cu(II), Mn(II), Co(II) and Cd(II)
serve as effective catalysts for the oxidation of the alcohols
though, certain discrepancies are observed in their relative
catalytic efficiencies and hence in the oxidation rates of alcohols.
The reaction mechanism of the metal ion catalysed oxidation
reaction has been explained on the basis of the formation of
an intermediate complex involving hypervalent Mn(III),
Co(III), Ni(III) and Cu(III) ions. Cd (II) appears to be the most
effective catalyst for the oxidation of the aliphatic alcohols
under study.
Ni(II)
(a)
12.5
10.5
8.5
Cu(II)
Zn(II)
Cd(II)
Mn(II)
Co(II)
Expon.
(Ni(II))
Expon.
(Cu(II))
Expon.
(Zn(II))
Expon.
(Cd(II))
Expon.
(Mn(II))
Expon.
(Co(II))
6.5
REFERENCES
4.5
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2.5
0
1
2
3
4
5
6
[Metal] × 104 mol dm–3
Cd(II) > Cu(II) > Mn(II) > Zn(II) > Ni(II) > Co(II)
Ni(II)
(b)
14
12
10
8
Cu(II)
Zn(II)
Cd(II)
Mn(II)
Co(II)
8. D.V. Prabhu, M.A. Tandel and H.A. Parbat, Proceedings of the Fourth
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9. H. Richardson, in ed.: K.B. Wiberg, Oxidation in Organic Chemistry,
Academic Press, New York, Part-I, p. 244 (1965).
Expon.
(Ni(II))
Expon.
(Cu(II))
Expon.
(Zn(II))
Expon.
(Cd(II))
Expon.
(Mn(II))
6
10. G. Mino, S. Kaizerman and E. Rasmussen, J. Am. Chem. Soc., 81,
1494 (1959).
4
Expon.
(Co(II))
11. F.R. Duke and A.A. Forist, J. Am. Chem. Soc., 71, 2790 (1949).
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1301 (1973).
2
0
1
2
3
4
5
6
[Metal] × 104 mol dm–3
Zn(II) > Cd(II) > Cu(II) > Ni(II) > Co(II) > Mn(II)
Ni(II)
(c)
12
10
8
Cu(II)
15. J.V. Bell, J. Heisler, H. Tannenbaum and J. Goldenson, J. Am. Chem.
Soc., 76, 5185 (1954).
Zn(II)
Cd(II)
16. K. Das Asim, J. Indian Chem. Soc., 77, 225 (2000).
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19. R.J.P. Williams, J. Chem. Soc., 8 (1956).
Mn(II)
Co(II)
Expon.
(Ni(II))
Expon.
(Cu(II))
Expon.
(Zn(II))
Expon.
(Cd(II))
Expon.
(Mn(II))
Expon.
(Co(II))
6
4
2
0
1
2
3
4
5
6
[Metal] × 104 mol dm–3
Zn(II) > Cd(II) > Ni(II) > Cu(II) > Co(II) > Mn(II)
Fig. 3. (a)Variation of rate constant of oxidation of 2-propanol with [M(II)]
(b) Variation of rate constant of oxidation of 2-butanol with [M(II)]
(c) Variation of rate constant of oxidation of 3-methyl-1-butanol
with [M(II)]