Tertiary butyl Nitrite mediated Nitration of Phenols –Solvent and
Structure dependent Kinetic Study
M. Satish Kumar, K. C. Rajanna*, M. Venkateswarlu, K. Mahesh, P. K. Saiprakash
Department of Chemistry, Osmania University, Hyderabad-500 007, T.S. India
E mail: kcrajannaou@yahoo.com
Supplementay Data
3.2. Experimental Details
3.2.4. Kinetic Method of Following the Reaction
The TBN content could be estimated from the previously constructed calibration curve
showing absorbance (A) versus [TBN] at 430 nm. Absorbance values were in agreement with
each other with an accuracy of ±3percentage error.
Determination of the Order of Reaction: If At = absorbance of nitrate species produced
during the course of reaction at a given time, A∞ is the absorbance at infinite time(at the end
of the reaction) and A0, the absorbance (if any) before the on-take of reaction, then (A∞- At)
is proportional to (a –x) and (A∞- A0) = (a). To determine “Order of the reaction”, we have
used graphical method of approach based on the integrated rate expressions of second order
and first order kinetics, according to standard procedures.
(i) Kinetic plots of [1 / (a - x)] or (1/ (A∞- At)) Vs time of this reaction with equal
concentrations of [TBN)]0 = [S]0 (under second order conditions), have been found to be
linear with a positive gradient and definite intercept on ordinate (vertical axis) indicating over
all second order kinetics (Figure 3.1, 3.2), according to the following expression:
1
=
(a  x)
1
 kt
(a)
(1)
(ii) Under the conditions, viz., [Phenol] >> [TBN)], the plots of ln [(A∞-A0)/ (A∞- At)] or [ln
(a/(a-x)] Vs time were linear with positive slope passing through origin according to the
following equation.
ln
a
=
(a  x)
kt
(2)
This observation indicated first order kinetics in [TBN)] in all the systems studied. First order
rate constant (k’) could be obtained from the slopes of these linear plots. S Since the order
with respect to [TBN] is already verified as one under pseudo conditions, and overall order is
second order, it is clear that order in [S] is also one. Similar observations were noticed when
the reactions were studied in all the solvents used in this study (Figs 3.3 to 3.16).
Accordingly, in the present study, the rate law of TBN mediated nitration reaction could be
represented by considering the following general scheme:
OH
OH
Tertiary Butyl Nitrite / MeCN
NO2
Conventional method
R = EWD or ED group
R
R
Scheme 1: Nitration of Phenols under conventional conditions
Rate law for the above scheme comes out as,
V = k1[TBN] [S]
3.2.5. Computation of Activation parameters
The free energy of activation (∆G#) at various temperatures is calculated using Eyring’s
theory of reaction rates,
∆G#
= RT 1n (RT/Nhk)
Gibbs – Helmholtz equation (9) for the evaluation of enthalpy and entropies of activation
(∆H# and ∆S#):
∆G# = ∆H# - T∆S#
3.3. Results and Discussion
3.3.1. Synthesis and characterization of products
In order to optimize suitable and a more practical nitration procedure, we have screened a
variety of solvents such as dichloromethane (DCM), dichloroethane (DCE), and acetonitrile
(MeCN). Even though the reaction times did not differ much, the yield of product was
substantially high in acetonitrile (MeCN). Based on these results we have finally employed
MeCN as solvent for conventional reactions to optimize nitration procedure for all the
reactions.
Reactions of Phenols with tertiary butyl nitrite (TBN) afforded the corresponding nitro
phenol derivatives (Scheme – 1) in about 1-3 hours under conventional stirred conditions at
room temperature. All the products were characterized by physical data (m.p / b.p), 1H NMR
and mass spectra, with authentic samples are found to be satisfactory (Table -S.1).
Table -S.1: Nitration of certain Phenols using Tertiary butyl nitrite
S.N
Substrate
Product
M.P (oC)
1
Phenol
2
o-Cresol
3
p-Cresol
4
m-Cresol
5
o-Cl phenol
6
7
8
p- Cl phenol
p-Br phenol
p-OH phenol
9
α-Naphthol
10
β-Naphthol
4-NO2Phenol (M)
2-NO2Phenol (m)
2-Me- 4-NO2 Phenol (M),
2-Me- 6-NO2 Phenol (m)
2-NO2 4-Me Phenol(M),
3-NO2 4-Me Phenol(m)
3-Me- 4-NO2 Phenol (M),
3-Me-6-NO2 Phenol (m)
4-NO2 2-Cl Phenol (M),
6-NO2 2-Cl Phenol (m)
2-NO2 4-Cl Phenol
2-NO2 4-Br Phenol
2- NO2 Benzene-1,4-diol
2- NO2-1-Naphthol (M)
2, 4 Di NO2 1-Naphthol (m)
1-NO2-2-Naphthol
(%Yield)
85
86
111-113 (114)
43-46(43-47)
95-98 (93-98)
71-74 (70)
32-35 (30-34)
77-80 (78-81)
127-129 (128)
56-58 (53-56)
106-108 (105)
69-72 (67-71)
88-90 (85-87)
82
90
92-96 (90-94)
306-308b (305)
72
126-129 (125-127)
133-136 (130-133)
98-100 (100-103)
84
85
80
88
70
Reaction times: 1-3 hrs (Conventional method); 30-45 min (Sonication); 2-4 min (MWAR)
b = Boiling point of liquids; M = Major product; m = Minor product
Fig-3.1: Plot of [1/(A∞-At)] vs Time (Second Order plot)
[p- Cresol] = 0.01 mol/dm3; [TBN] = 0.01 mol/dm3 Solvent = MeCN; Temp = 303 K
Time
(min)
O.D
(Absorbance)
1/(A∞-At)
0
0.11
7.14286
5
0.11
7.14286
10
0.12
7.69231
15
0.12
7.69231
20
0.13
8.33333
25
0.13
8.33333
30
0.14
9.09091
35
0.14
9.09091
40
0.15
10
45
0.15
10
50
0.16
11.1111
55
0.16
11.1111
60
0.17
12.5
Fig-3.2: Plot of [1/(A∞-At)] vs Time (Second Order plot)
[m- Chloro phenol] = 0.01 mol/dm3; [TBN] = 0.01 mol/dm3; Solvent = DCE; Temp = 303 K
Time
(min)
O.D
(Absorbance)
1/(A∞-At)
0
0.04
7.69231
5
0.07
10
10
0.1
14.2857
15
0.12
20
20
0.13
25
25
0.14
33.3333
30
0.15
50
60
0.16
100
Fig-3.3: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order plot)
[Phenol] = 0.10 mol/dm3; [TBN] = 0.01 mol/dm3 ; Solvent = MeCN; Temp = 303 K
Time
O.D
ln [(A∞- A0)/
(min)
(Absorbance)
(A∞-At)]
0
0.21
0
5
0.26
0.13005
10
0.31
0.27958
15
0.35
0.41774
20
0.39
0.57808
25
0.41
0.66905
30
0.43
0.76913
35
0.45
0.88036
40
0.46
0.94098
45
0.47
1.00552
50
0.49
1.14862
55
0.5
1.22867
60
0.51
1.31568
Fig-3.4: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order plot)
[p-Br Phenol] = 0.10 mol/dm3; [TBN] = 0.01 mol/dm3 ; Solvent = MeCN; Temp = 303 K
ln [(A∞-A0)/
Time
O.D
(A∞-At)]
0
0.1
0
5
0.11
0.105361
10
0.12
0.223144
15
0.13
0.356675
20
0.13
0.356675
25
0.14
0.510826
30
0.14
0.510826
35
0.14
0.510826
40
0.15
0.693147
45
0.15
0.693147
50
0.16
0.916291
55
0.16
0.916291
60
0.16
0.916291
Fig-3.5: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order plot)
[Resorcinol] = 0.10 mol/dm3; [TBN] = 0.01 mol/dm3 ; Solvent = MeCN; Temp = 303 K
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.46
0
5
0.5
0.05799
10
0.54
0.11955
15
0.57
0.16834
20
0.6
0.21963
25
0.62
0.25535
30
0.63
0.2737
35
0.65
0.31144
40
0.66
0.33085
45
0.67
0.35066
50
0.68
0.37086
55
0.69
0.39148
60
0.7
0.41253
Fig-3.6: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order plot)
[Catechol] = 0.10 mol/dm3; [TBN] = 0.01 mol/dm3 ; Solvent = MeCN; Temp = 303 K
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.5
0
5
0.54
0.0656
10
0.57
0.11778
15
0.6
0.17284
20
0.62
0.21131
25
0.63
0.23111
30
0.64
0.25131
35
0.65
0.27193
40
0.67
0.31449
45
0.68
0.33647
50
0.7
0.38193
55
0.71
0.40547
60
0.72
0.42956
Fig-3.7: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[p-Nitro Phenol] = 0.10 mol/dm3 ; [TBN] = 0.010 mol/dm3 ;Temp=303K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.06
0
5
0.08
0.08701
10
0.11
0.23361
15
0.14
0.40547
20
0.16
0.539
25
0.19
0.78016
30
0.2
0.87547
35
0.21
0.98083
40
0.22
1.09861
45
0.23
1.23214
50
0.24
1.38629
Fig-3.8: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[p-Nitro Phenol] = 0.10 mol/dm3 ; [TBN] = 0.010 mol/dm3 ;Temp=308K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.06
0
5
0.11
0.17589
10
0.15
0.34294
15
0.2
0.60077
20
0.23
0.79493
25
0.27
1.1314
30
0.28
1.23676
35
0.29
1.35455
40
0.3
1.48808
Fig-3.9: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[p-Nitro Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp=313K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.06
0
5
0.11
0.18924
10
0.18
0.53408
15
0.23
0.88239
20
0.26
1.17007
25
0.28
1.42139
30
0.29
1.57554
35
0.3
1.75786
40
0.31
1.981
Fig-3.10: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[p-Nitro Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp=318K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.06
0
5
0.13
0.23052
10
0.22
0.63599
15
0.29
1.12847
20
0.32
1.44692
25
0.33
1.58045
30
0.35
1.91692
35
0.36
2.14007
40
0.36
2.14007
Fig-3.11: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[p-Nitro Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp=323K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.06
0
5
0.2
0.47542
10
0.29
0.97186
15
0.32
1.21302
20
0.35
1.53148
25
0.37
1.81916
30
0.38
2.00148
35
0.39
2.22462
40
0.41
2.91777
Fig-3.12: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[m-Cl Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp= 303K; Solvent = MeCN
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.03
0
5
0.06
0.17185
10
0.07
0.23639
15
0.08
0.30538
20
0.09
0.37949
30
0.1
0.45953
40
0.11
0.54654
50
0.12
0.64185
60
0.13
0.74721
Fig-3.13: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[m-Cl Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp= 303K; Solvent = DMF
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.03
0
10
0.04
0.03077
15
0.04
0.03077
20
0.05
0.06252
25
0.05
0.06252
30
0.06
0.09531
35
0.06
0.09531
40
0.07
0.12921
45
0.07
0.12921
50
0.08
0.1643
55
0.08
0.1643
60
0.09
0.20067
Fig-3.14: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[m-Cl Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp= 303K; Solvent = DCE
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.05
0
5
0.09
0.28768
10
0.1
0.37469
15
0.12
0.57536
20
0.13
0.69315
25
0.13
0.69315
30
0.14
0.82668
40
0.16
1.16315
60
0.17
1.38629
Fig-3.15: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[m-Cl Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp= 303K; Solvent = CCl4
Time
(min)
0
5
10
15
20
25
30
35
40
O.D
(Absorbance)
0.04
0.08
0.11
0.12
0.14
0.15
0.16
0.17
0.18
ln [(A∞-A0)/
(A∞-At)]
0
0.10008
0.18232
0.21131
0.27193
0.30368
0.33647
0.37037
0.40547
Fig-3.16: Plot of ln [(A∞-A0)/(A∞-At)] vs Time (First Order Plot)
[m-Cl Phenol] = 0.10 mol/dm3; [TBN] = 0.010 mol/dm3; Temp= 303K; Solvent = Toluene
Time
(min)
O.D
(Absorbance)
ln [(A∞-A0)/
(A∞-At)]
0
0.11
0
5
0.15
0.10536
10
0.18
0.19237
15
0.2
0.25489
20
0.22
0.32158
25
0.23
0.35667
30
0.24
0.39304
35
0.25
0.43078
40
0.26
0.47
Table- 3.2. Second order rate constants and Activation parameters in MeCN medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
(J/K/mol)
17.5
200
18.48
196
24.36
179
28.17
167
18.59
193
303
0.215
78.12
308
0.229
79.29
313
0.253
80.36
y = 200.44x + 17501
318
0.294
81.29
R² = 0.9955
323
0.351
82.13
303
0.235
77.9
308
0.265
78.9
313
0.309
79.84
y = 196.13x + 18480
318
0.346
80.86
R² = 0.9998
323
0.393
81.83
303
0.165
78.79
308
0.205
79.57
p-Cl
313
0.23
80.61
y = 179.55x + 24357
Phenol
318
0.27
81.51
R² = 0.998
323
0.329
82.31
303
0.154
78.96
308
0.209
79.52
p-Br
313
0.242
80.47
y = 167.26x + 28165
Phenol
318
0.278
81.44
R² = 0.9934
323
0.344
82.19
303
0.308
77.21
308
0.346
78.23
313
0.408
79.12
y = 193.5x + 18586
318
0.468
80.06
R² = 0.9989
323
0.508
81.14
Phenol
p- Cresol
Quinol
Table- 3.3. Second order rate constants and Activation parameters in MeCN medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
( J/K/mol)
18.87
194
53.29
92.0
37.81
138
303
0.256
77.68
308
0.328
78.37
p-OMe
313
0.387
79.25
y = 193.5x + 18868
Phenol
318
0.403
80.45
R² = 0.9906
323
0.448
81.49
303
0.062
81.25
308
0.098
81.46
p-NO2
313
0.142
81.86
y = 91.78x + 53285
Phenol
318
0.191
82.43
R² = 0.9653
323
0.248
83.06
303
0.112
79.76
y = 138.1x + 37810
m-Cl
313
0.205
80.91
R² = 0.9902
Phenol
323
m-Cresol
Resorcinol
0.303
82.53
303
0.233
77.92
y = 190.8x + 20160
313
0.287
80.03
R² = 0.9962
323
0.407
81.73
303
0.066
81.1
y = 134.25x + 40276
313
0.134
82.01
R² = 0.9677
323
0.19
83.78
20.16
40.28
190
134
Table- 3.4. Second order rate constants and Activation parameters in DMF medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
(J/K/mol)
17.68
198
13.8
207
44.22
121
43.64
122
20.26
0.178
303
0.238
77.86
308
0.292
78.67
313
0.322
79.73
y = 198.3x + 17682
318
0.366
80.71
R² = 0.9976
323
0.397
81.80
303
0.395
76.59
308
0.452
77.55
313
0.507
78.55
y = 207.1x + 13795
318
0.562
79.57
R² = 0.9985
323
0.587
80.75
303
0.064
81.17
308
0.096
81.52
p-Cl
313
0.132
82.05
y = 121.3x + 44220
Phenol
318
0.176
82.64
R² = 0.9631
323
0.2
83.64
303
0.066
81.1
308
0.101
81.39
p-Br
313
0.136
81.97
y = 122.9x + 43644
Phenol
318
0.181
82.57
R² = 0.9604
323
0.205
83.58
303
0.947
74.38
308
1.211
75.02
313
1.312
76.08
y = 178.2x + 20264
318
1.566
76.87
R² = 0.9943
323
1.684
77.92
Phenol
p- Cresol
Quinol
Table- 3.5. Second order rate constants and Activation parameters in DMF medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
( J /K/mol)
11.44
0.206
49.88
0.108
33.66
0.149
10.59
0.207
303
1.086
74.04
308
1.125
75.21
p-OMe
313
1.245
76.21
y = 206.83x + 11438
Phenol
318
1.389
77.18
R² = 0.9989
323
1.503
78.23
303
0.033
82.84
y = 108.64x + 49847
m-Cl
313
0.07
83.70
R² = 0.9859
Phenol
323
0.12
85.01
303
0.16
78.86
y = 149.23x + 33659
313
0.25
80.39
R² = 0.9998
323
0.39
81.85
303
1.341
73.51
y = 207.55x + 10587
313
1.651
75.48
R² = 0.9991
323
1.856
77.66
m-Cresol
Resorcinol
Table- 3.6. Second order rate constants and Activation parameters in CCl4 medium
Substrate Temp
Temp
Substrate
kk
(K)
(K)
p-OMe
Phenol
Phenol
p-NO2
Phenol
p- Cresol
≠
∆G
∆G≠
Equation
Equation
≠
∆H
∆H≠
(k (k
J/mol)
J/mol)
&&RR22
(k
(k J/mol)
J/mol)
(( J/K/mol)
J/K/mol)
36.06
139
49.99
103
37.41
136
44.68
117
303
303
0.176
0.116
78.62
79.67
308
308
0.255
0.179
79.01
79.92
313
313
318
0.343
0.24
0.405
79.57
80.5
80.44
318
323
0.306
81.18
323
303
0.36
0.058
82.06
81.42
308
303
0.094
0.143
81.57
79.15
313
308
0.131
0.221
82.07
79.38
318
313
323
0.46
0.173
0.296
0.216
81.41
82.69
79.95
0.344
80.87
m-Cl
323
313
0.394
0.175
81.82
81.32
Phenol
303
323
0.104
0.263
79.95
82.91
303
308
0.124
0.152
79.51
80.34
m-Cresol
p-Cl
313
313
0.27
0.215
80.19
80.78
Phenol
318
323
303
0.082
0.409
0.263
0.161
R² = 0.9632
y = 103x ++49997
y = 136.81x
37414
R² = 0.9538
R² = 0.9515
80.55
81.72
81.58
78.85
y = 117.93x + 44678
R² = 0.9614
y = 110.74x + 45812
R² = 0.9534
y = 126.55x
+ 41420
303
323
0.102
0.531
79.99
81.02
308
0.161
80.19
p-Br
313
0.216
80.77
y = 130.52x + 40175
Phenol
318
0.257
81.64
R² = 0.9512
323
0.302
82.54
303
0.196
78.35
308
0.307
78.54
313
0.374
79.34
y = 139.55x + 35800
318
0.457
80.12
R² = 0.9635
323
0.525
81.05
Quinol
79.53
110
126
R² = 0.9654
82.49
0.348
45.81
41.42
y = 108.58x + 45815
0.307
313
120
R² = 0.9689
323
Resorcinol
42.85
≠
83.44
318
303
y = 139.79x + 36056
y = 120.81x + 42854
-∆S≠
-∆S
R² = 0.9557
45.82
108
40.18
0.13
35.8
139
Table- 3.7. Second order rate constants and Activation parameters in CCl4 medium
Table- 3.8. Second order rate constants and Activation parameters in Toluene medium
Substrate Temp
Substrate Temp
(K)
(K)
303
303
308
308
Phenol
313
p-OMe
313
318
Phenol
318
323
323
303
303
308
308
p- Cresol
313
p-NO2
313
318
Phenol
318
323
323
303
303
308
m-Cl
313
p-Cl
313
Phenol
323
Phenol
318
303
323
m-Cresol
313
303
323
308
303
p-Br
313
Resorcinol
313
Phenol
318
323
323
Quinol
k
k
0.213
0.281
0.293
0.395
0.345
0.498
0.405
0.552
0.47
0.575
∆G≠ ≠
Equation
∆H≠ ≠
-∆S≠ ≠
∆G
Equation
∆H
-∆S
(k J/mol)
& R2 2
(k J/mol) (J/K/mol)
(k J/mol)
&R
(k J/mol) ( J/K/mol)
78.14
77.45
78.66
77.89
28.35
163
79.55
y = 163.82x + 28353
25.98
169
78.6
y = 169x + 25975
80.44
R² = 0.9913
79.62
R² = 0.9686
81.35
80.81
0.247
0.068
77.77
81.02
0.366
0.093
78.09
81.6
0.487
0.137
164.88x + 27560 27.56
79.07 y =
30.02
82.53
y = 167.86x + 30021
R² = 0.9769
79.95
83.31
R² = 0.9917
0.543
0.153
0.139
0.112
0.191
0.203
0.242
0.299
0.285
0.189
0.339
0.286
0.134
0.412
0.196
0.056
0.25
0.064
0.309
0.094
0.338
80.96
84.36
79.22
79.76
y = 139.98x + 37272
79.75
37.27
80.93
R² = 0.991
32.85
80.47
y = 152.57x + 32853
82.56
81.37
R² = 0.991
78.44
y = 162.84x + 29093
82.23
29.09
80.04
R² = 0.9999
79.31
81.70
79.69
81.51
y = 208.04x + 18587
34.78
80.39
y = 146.25x + 34780
18.59
83.94
R² = 0.9908
81.16
R² = 0.9715
85.67
82.23
303
0.355
76.86
308
0.425
77.71
313
0.498
78.6
y = 191.85x + 18649
318
0.549
79.64
R² = 0.9975
323
0.601
80.69
0.416
0.11
18.65
164
167
140
152
162
146
208
191
Table- 3.9. Second order rate constants and Activation parameters in Toluene medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
(J/K/mol)
29.02
163
33.04
152
303
0.163
78.82
308
0.211
79.5
313
0.288
80.02
y = 163.86x + 29018
318
0.32
81.06
R² = 0.9793
323
0.351
82.13
303
0.135
79.29
308
0.185
79.84
313
0.238
80.52
y = 152.16x + 33042
318
0.287
81.35
R² = 0.9869
323
0.325
82.34
order rate
303
0.183
78.53
constants
308
0.279
78.78
p-Cl
313
0.338
79.61
y = 151.87x + 32246
Phenol
318
0.389
80.55
R² = 0.9702
323
0.454
81.44
303
0.198
78.33
in DCE
308
0.26
78.96
medium
p-Br
313
0.326
79.7
y = 165x + 28206
Phenol
318
0.373
80.66
R² = 0.9921
323
0.427
81.61
303
0.109
79.83
308
0.168
80.08
313
0.205
80.91
y = 149.11x + 34390
318
0.244
81.78
R² = 0.97
323
0.283
82.71
Phenol
p- Cresol
Quinol
Table- 3.10.
Second
and
32.25
151
Activation
parameters
28.21
165
34.39
149
Table- 3.11. Second order rate constants and Activation parameters in DCE medium
Substrate
Temp
k
(K)
∆G≠
Equation
∆H≠
-∆S≠
(k J/mol)
& R2
(k J/mol)
( J/K/mol)
43.67
118
30.58
154
25.51
172
33.2
151
47.70
106
303
0.113
79.74
308
0.152
80.34
p-OMe
313
0.218
80.75
y = 118.88x + 43668
Phenol
318
0.286
81.36
R² = 0.9851
323
0.342
82.20
303
0.284
77.42
308
0.394
77.9
p-NO2
313
0.508
78.55
y = 153.94x + 30584
Phenol
318
0.577
79.51
R² = 0.9799
323
0.653
80.46
303
0.224
78.02
y = 172.69x + 25513
m-Cl
313
0.393
79.21
R² = 0.9695
Phenol
323
0.449
81.47
303
0.142
79.16
y = 151.05x + 33198
313
0.282
80.08
R² = 0.9502
323
0.344
82.19
303
0.1
80.05
y = 106.88x + 47701
313
0.181
81.23
R² = 0.9963
323
0.344
82.19
m-Cresol
Resorcinol
3.3.3. Effect of Varying Solvent & Solvochromic Studies
All the TBN mediated nitration of different phenols reactions have been studied in different
solvent media at four to five temperatures in twenty centigrade degree range (30 - 50oC).
Rate of nitration increased with an increase in temperature in different the solvent media
(acetonitrile (MeCN), dichloroethane (DCE), CCl4, dimethylformamide (DMF) and toluene).
Free energy of activation (∆G#) obtained from Eyring’s equation [27]; and enthalpy and
entropies of activation (∆H# and ∆S#) obtained from the slopes and intercepts of GibbsHelmholtz plots (Figs 3.17 to 3.20). Tables 3.11 to 3.14 show the results pertaining to
solvent effect studies.
Literature reports revealed that physical constants such as melting
and boiling point, vapour pressure, heat of vaporization, refractive index, density, viscosity,
surface tension, dipole moment, relative permittivity, polarizability, specific conductivity,
etc. can be generally used to characterize the properties of a solvent. A change in the nature
of solvent may influence the reaction rate alone with or without influencing the mechanism
[28-32]. Solvents can affect rates through equilibrium-solvent or frictional-solvent effects
[28 a].
Table 3. 12: Amis and Kirkwood’s plots for Phenol -TBN system (Solvent effects)
Solvent
k
logk
D
1/D
(D-1)
2D+1
(D-1)/(2D+1)
MeCN
0.215
-0.6676
37.5
0.02667
36.5
76
0.48026
DMF
0.238
-0.6234
37
0.02703
36
75
0.48
DCE
0.163
-0.7878
17.95
0.05571
16.95
36.9
0.45935
CCl4
0.116
-0.9355
10.96
0.09124
9.96
22.92
0.43455
Toulene
0.213
-0.6716
11.18
0.08945
10.18
23.36
0.43579
Table 3. 13: Amis and Kirkwood’s plots for p-Cresol -TBN system (Solvent effects)
Solvent
k
logk
D
1/D
(D-1)
2D+1
(D-1)/(2D+1)
MeCN
0.235
-0.6289
37.5
0.02667
36.5
76
0.48026
DMF
0.395
-0.4034
37
0.02703
36
75
0.48
DCE
0.135
-0.8697
17.95
0.05571
16.95
36.9
0.45935
CCl4
0.143
-0.8447
10.96
0.09124
9.96
22.92
0.43455
Toulene
0.247
-0.6073
11.18
0.08945
10.18
23.36
0.43579
Linear Solvation Energy Relationship in TBN mediated nitration:
Based on the foregoing discussion on solvent energy relationships, we have used a basic form
of Koppel and Palm’s Multivariate Linear Solvent Energy Relationship (MLSER), to
explain the multiple interacting effects of the solvent on the reactivity of substrates in the
nitration of phenols:
logk = p1 π* + p2 α + p3β +p4δ + Constant
(14)
Where π* = solvent dipolarity/polarizability; α = hydrogen bond donor (HBD); β = hydrogen
bond acceptor (HBA) basicity parameter; δ = Hildebrand Solubility Parameter and p 1, p2, p3 &
p4 are corresponding coefficients. Multiple linear regression analysis (MLRA) of the
kinetic data pertains to the nitration of phenols in various solvents furnished the parameters
p1, p2, p3 & p4. These values are compiled in tables 3.14 to 3.20.
Table 3.14: Applicabity of MLSER for para substituted phenols 303K
Substrate
Phenol
p-Cresol
p-Cl Phenol
p-Br Phenol
Quinol
p-OMe Phenol
p1
0.829
0.229
0.269
0.300
0.257
0.524
-0.099
0.038
0.097
0.736
0.438
0.887
0.255
0.420
0.779
0.522
1.0422
0.343
0.532
0.264
-0.548
-1.088
-0.303
-0.581
0.084
-0.404
-1.052
-0.112
-0.415
p2
2.124
0.201
0.063
1.954
-0.042
1.931
0.977
2.488
1.749
0.927
2.716
2.279
-0.324
-2.669
0.790
-0.773
-3.394
-
p3
1.061
0.189
0.263
1.564
0.830
-0.286
-0.719
-1.012
-0.498
-0.870
-1.155
2.561
1.381
1.705
2.153
1.444
1.856
-
p4
-0.263
0.021
-0.021
0.024
-0.273
-0.50
0.090
-.130
-0.207
0.090
-0.082
-0.112
-0.245
0.087
-0.109
-0.356
0.329
-0.096
0.193
-0.214
0.362
-0.124
0.192
constant
1.106
-0.936
-1.128
-0.778
-1.150
1.369
-0.751
-0.364
-1.539
-0.062
-1.074
0.541
-1.774
-0.341
-0.238
-1.110
0.810
-1.788
-0.153
2.296
-0.468
-3.097
0.275
-2.140
1.070
-0.590
-1.3463
0.370
-2.259
R2
1
0.684
0.586
0.679
0.585
1
0.852
0.882
0.473
1
0.963
0.986
0.874
0.211
1
0.980
0.968
0.923
0.280
1
0.923
0.679
0.951
0.424
1
0.975
0.799
0.995
0.442
Remarks
Considering all parameters
Parameter δ excluded
Parameter β excluded
Parameter α excluded
Parameters α and β excluded
Considering all parameters
Parameters δ and β excluded
Parameter α and β excluded
Parameter α excluded
Considering all parameters
Parameter δ excluded
Parameter β excluded
Parameter α excluded
Parameters α and β excluded
Considering all parameters
Parameter δ excluded
Parameter β excluded
Parameter α excluded
Parameters α and β excluded
Considering all parameters
Parameter δ excluded
Parameter β excluded
Parameter α excluded
Parameters α and β excluded
Considering all parameters
Parameter δ excluded
Parameter β excluded
Parameter α excluded
Parameters α and β excluded
It is of interest to note that similar results are obtained for other phenols, which can be readily
seen from tables 3.14 to 3.20. (However, for convenience only table 3.14 is shown here,
while rest of the tables 3.15 to 3.20 is given at the end of this)
Kamlet and Taft’s Multivariate Linear Solvent Energy Relationship:
Kamlet and Taft’s group and others [41-43] modified original form of Koppel and Palm’s
“Multivariate Linear Solvent Energy Relationship” as shown in the following equation:
log k = A0 + sπ* + aα+ bβ
(20)
Where π*, β and α represent their usual scale of the solvent. The coefficients s, a, and b
measure the relative susceptibilities of the solvent-dependent solute property (log k or as
ΔG#) to the corresponding solvent parameters. However, to have further insight into the
solvation, we have designed another “Multivariate Linear Solvent Energy Relationship”
using equilibrium and frictional solvent effects, as shown in equation-2.
logk = m1 φ1+ m2φ2 + m3φ3+ m4φ4 + Constant (21)
Where φ1 = dielectric constant function = (D-1)/(2D+1); φ2 = viscosity function = 1/viscosity;
φ3 = refractive index function= (η2-1)/(η2+2); φ4 = Density, while m1, m2, m3 and m4 are
corresponding coefficients. Further, φ1, and φ3 indicate equilibrium solvent parameters while
φ2 (reciprocal of viscosity) and φ4 (density) indicate frictional solvent properties. Statistical
analysis using “multiple linear regression technique” afforded parameters under different
conditions. The coefficients m1, m2, m3 and m4 corresponding to φ1, φ2 , φ3 and φ4 and
correlation coefficients (R2 values) are presented in table 3.21 as a typical example. A
perusal of the computed results (using equation 17) which are given in table – 3.21
clearly show that when all solvent parameters (φ1, φ2 , φ3 and φ4) are used in the
regression analysis excellent linearity is obtained with correlation coefficient of unity
(R2 = 1.00). However, except for phenol and m-cresol, in all other cases regression
analysis afforded poor correlation coefficients (R2 < 0.900 or even lesser than this value)
when any one of the solvent parameters is excluded from the analysis. This observation
probably strengthens our view once again cumulative contributions of basic solvent
parameters might be responsible for solvation. In addition, to this the observed results may
also indicate the importance of equilibrium as well as frictional solvent effects and solventsolute interactions for solvation of transition state during nitration of phenols.
Table 3.21: Kamlet and Taft’s Multivariate Linear Solvent Energy Relationship (MLSER) at 303K
Substrate
Phenol
p-Cl Phenol
m-Cresol
Catechol
Quinol
o-Cresol
Resorcinol
p-Cresol
m1
0.711
8.883
0.892
2.941
35.6
-4.024
-2.479
8.180
-2.216
3.071
-0.255
-2.873
-72.372
-0.169
-5.131
9.388
-64.450
16.504
2.838
10.202
47.712
3.190
2.722
6.681
-50.010
19.538
17.138
37.986
-23.531
11.333
1.719
5.843
m2
-0.075
0.191
-0.069
1.464
0.076
0.243
0.022
0.194
0.085
-2.734
-0.386
-0.578
-2.496
0.136
-0.339
1.372
-0.075
-0.071
-2.943
-0.681
-0.789
-1.049
0.149
-0.175
-
m3
-0.166
7.198
1.891
35.108
-0.599
-5.289
-1.809
2.956
-2.415
-61.995
3.071
13.447
-62.038
10.914
6.845
41.480
1.360
3.620
-61.909
0.764
19.287
-25.124
8.096
3.826
m4
-0.433
-0.424
-0.318
2.099
0.209
-0.157
-0.280
-0.183
-0.314
-3.825
-0.487
0.388
-4.228
-0.948
-0.441
2.358
0.125
0.244
-3.684
-0.351
0.850
-1.953
-0.600
-0.336
Constant
-0.432
-6.978
-0.577
-2.230
30.924
0.815
-0.381
4.384
0.976
-3.259
-0.598
1.505
57.112
-0.722
3.179
-8.826
53.700
-11.144
-0.271
-6.506
-.7.996
-2.335
-1.910
-4.906
46.801
-8.906
-7.058
-24.167
21.325
-8.202
-0.532
-3.977
R2
1
0.951
1
0.996
1
0.455
0.517
0.334
1
0.971
0.996
1
1
0.656
0.714
0.559
1
0.364
0.579
0.459
1
0.178
0.196
0.302
1
0.819
0.838
0.710
1
0.568
0.774
0.687
Remarks
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
Using all parameters
Parameter φ4 excluded
Parameter φ3 excluded
Parameter φ2 excluded
3.3.4. Quantitative Structure Reactivity Study:
Hammett’s Plots: A closer look into the kinetic data pertaining to the TBN nitration of
phenols revealed that the reaction is sensitive to the structural variation of phenol. Reaction
rates accelerated with the introduction of electron donating groups and retarded with electron
withdrawing groups. Accordingly the reactivity of structurally different phenols was found
to follow the sequence: p- OH > p-MeO > P-Me > H > m-Me > p-Cl > p – Br > m- Cl > p –
NO 2 > m – OH. Hammett’s theory of linear free energy relationships furnishes an efficient
tool to analyze the kinetic data quantitatively that is useful to understand the mechanism of a
reaction [46]. According to Hammett’s relationship, the rate or equilibrium constant for a
reaction of a compound varies as a function of Sigma (), the Substituent constant.
log (k/k-0) =  
(18)
The value of Sigma () of a substituted compound differs from that of the parent compound.
This depends on the nature of Substituent. In the present study Hammett’s plots of log (k/k0)
Vs  ehibited very good linear relationship as evidenced from the correlation coefficient
values (R2) which were greater than 0.960. The negative value of  indicates that electron
donating substituent accelerates the reaction rate. A negative ρ value also indicates the
electron flow away from aromatic ring takes place in the rate determining step and thus
produces electron deficiency (often a positive charge) in the activated complex.
Table-3.22: Hammett’s Plot at 303K (Fig.3.25)
Substrate
k
kx/ko
log (kx/ko)
σ
Phenol
0.213
1
0
0
p- Cresol
0.247
1.15962
0.06432
-0.17
p-Cl
0.139
0.65258
-0.1854
0.23
p- Br
0.134
0.62911
-0.2013
0.23
Quinol
0.355
1.66667
0.22185
-0.37
p-OMe
0.281
1.31925
0.12033
-0.268
p-NO2
0.068
0.31925
-0.4959
0.77
Resorcinol
0.056
0.26291
m-Cl
0.112
0.52582
-0.2792
0.373
m-Cresol
0.189
0.88732
-0.0519
-0.069
0.121
Table-3.23: Hammett’s Plot at 313K in CCl4 (Fig.3.26)
Substrate
k
kx/ko
log
(kx/ko)
σ
Phenol
0.24
1
0
0
p- Cresol
0.296
1.233333
0.09108
-0.17
p-Cl
0.215
0.895833
-0.04777
0.23
p- Br
0.216
0.9
-0.04576
0.23
Quinol
0.374
1.558333
0.19266
-0.37
p-Ome
0.343
1.429167
0.155083
-0.268
p-NO2
0.131
0.545833
-0.26294
0.77
Resorcinol
0.348
1.45
m-Cl
0.175
0.729167
-0.13717
0.373
m-Cresol
0.27
1.125
0.051153
-0.069
0.121
Table-3.24: Hammett’s Plot at 308K in MeCN (Fig.3.27)
Table-3.29: Hammett’s Plot at 318K in MeCN (Fig.3.28)
Substrate
k
kx/ko
log (kx/ko)
σ
Phenol
0.366
1
0
0
p- Cresol
0.562
1.535519
0.186255
-0.17
p-Cl
0.176
0.480874
-0.31797
0.23
p- Br
0.181
0.494536
-0.3058
0.23
Quinol
1.566
4.278689
0.631311
-0.37
p-OMe
1.389
3.795082
0.579221
-0.268
Rho (ρ) Values for Various Electrophilic Substitutions. The rate-determining step for most
electrophilic substitutions is the attack step in which the electrophile reacts with the aromatic
to form the arenium ion. The degree to which the TS for this reaction resembles the arenium
ion is a major determinant of the size of the rho value for a particular type of electrophilic
substitution. For bromination, the rho value is quite large (-12.1), indicating a TS which
strongly resembles the arenium ion. This is consistent with the accepted mechanism, in which
neutral bromine is the (relatively mild) electrophile, so that the attack step is strongly
endothermic. In Friedel-Crafts acylation, where the active electrophile is the acylium cation,
the rho value decreases to-9.1. The rho value for nitration in acetonitrile is –6.2. The reaction
constant (Hammett’s ρ) is a measure of the sensitivity eof the reaction towards the electronic
effects of the substituent. Data presented in table 3.30 revealed that the rho (ρ) values
obtained from the present experiments are fairly large negative values (ρ < 0), indicating
attack of an electrophile in the aromatic ring. Increase in temperature decreases the reaction
constant (ρ) values. According to Exner (ρ) values [47], for a given reaction, are influenced
by the temperature according to the following relation:
(ρ) = A [1 – β/T]
(19)
Where A is a constant and β is the isokinetic temperature. When β = T, (ρ) = 0, thus
isokinetic temperature is the temperature at which the effect of substituent on rate of reaction
vanishes and all the substituted compounds in a given series have the same reactivity.
Obtained “Isokinetic temperature (β)” values are in the range of 225 to 290, as can be seen
from table 3.30. These values are far below the experimental temperature range (303 to
323K) indicating that the entropy factors are probably more important in controlling the
reaction. Even though, the concept of isokinetic temperature (β) from has been criticized by
Peterson, Cornish-Bowden and others [48], multivariate linear solvatochromic effects
coupled with isokinetic temperature values certainly support our contention that entropy
factors are important in controlling nitration of phenols by TBN in the present study.
Table - 3.25: Effect of temperature / solvent on Hammett’s reaction constant (ρ)
Solvent
MeCN
Temp (K)
303
308
313
318
323
DMF
303
308
313
318
323
CCl4
303
308
313
318
323
Toluene 303
308
313
318
323
Hammett’s ρ Equation
-1.584
-2.099
-2.49
y = 10202x - 35.19
-2.97
R² = 0.978
-3.76
-0.461
-0.520
-0.556
y = 798.4x - 3.104
-0.601
R² = 0.984
-0.624
-2.165
-2.280
-2.473
y = 3723.x - 14.41
-2.745
R² = 0.980
-2.885
-1.591
-1.644
-1.673
y = 1421.x - 6.260
-1.793
R² = 0.945
-1.881
β(Value in K)
290
257
258
227