Kinetics of malachite green fading in alcohol-water binary mixtures

Article abstract of DOI:10.1002/kin.20500

The rate constant of alkaline fading of malachite green (MG⁺) was studied in alcohol-water binary mixtures. This reaction was studied under pseudo-first-order conditions at 283-303 K. It was observed that the reaction rate constants were increased in the presence of different weight percentages of methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1,2-propanediol, and glycerol (up to 19.3%). In aqueous glycerol solutions higher than 19.3%, the rate constant of reaction slightly decreases, which is due to high viscosity values of solvent mixtures. The fundamental rate constants of MG⁺ fading in these solutions were obtained by using the SESMORTAC model. Owing to the charged character of activated complex, with an increase in the weight percentage of the used cosolvents or temperature, κ₂ values change according to the trend of hydroxide ion nucleophilic parameter values. Also, using MG⁺ solvatochromism, a simple test, called MAGUS, is introduced for measuring the glycerol concentration in its aqueous solutions.

Full text of DOI:10.1002/kin.20500

Kinetics of Malachite Green
Fading in Alcohol–Water
Binary Mixtures
BABAK SAMIEY, ALI RAOOF TOOSI
Department of Chemistry, Faculty of Science, University of Lorestan, 68137-17133, Khoramabad, Islamic Republic of Iran
Received 6 May 2009; revised 9 August 2009, 9 December 2009, 9 February 2010; accepted 22 February 2010
DOI 10.1002/kin.20500
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The rate constant of alkaline fading of malachite green (MG+) was studied in
alcohol–water binary mixtures. This reaction was studied under pseudo-first-order conditions
at 283–303 K. It was observed that the reaction rate constants were increased in the pres-
ence of different weight percentages of methanol, ethanol, 1-propanol, 2-propanol, ethylene
glycol, 1,2-propanediol, and glycerol (up to 19.3%). In aqueous glycerol solutions higher than
19.3%, the rate constant of reaction slightly decreases, which is due to high viscosity values of
solvent mixtures. The fundamental rate constants of MG+ fading in these solutions were ob-
tained by using the SESMORTAC model. Owing to the charged character of activated complex,
with an increase in the weight percentage of the used cosolvents or temperature, k2 values
change according to the trend of hydroxide ion nucleophilic parameter values. Also, using
MG+ solvatochromism, a simple test, callꢀed MAGUS, is introduced for measuring the glycerol
C
concentration in its aqueous solutions.
508–518, 2010
2010 Wiley Periodicals, Inc. Int J Chem Kinet 42:
this work, we have studied the MG+ alkaline fading
in binary mixtures of water with different weight per-
centages of methanol, ethanol, 1-propanol, 2-propanol,
ethylene glycol, 1,2-propanediol, and glycerol at 283–
303 K. The MG+ fading is a one-step reaction [14,15],
and as reported kinetics of these kinds of reactions in
binary mixtures can be studied using the SESMORTAC
model [16].
INTRODUCTION
Solvent effects on reactivity may be very large.
Alcohols, as cosolvents, can change the rate of or-
ganic, inorganic, and enzymatic reactions [1–9]. Mala-
chite green (MG+) is a triphenylmethane dye. These
dyes represent a class of dyes of commercial and ana-
lytical importance [10,11]. Malachite green is used to
dye materials such as silk, leather, cotton, and paper
and can be used as a saturable absorber in dye lasers,
as a pH indicator or as a bacteriological stain [12]. It
is also used as a topical antiseptic or to treat parasites
and bacterial infections in Þsh and Þsh eggs [13]. In
EXPERIMENTAL
Materials
Malachite green oxalate, methanol (>99.5%), ethanol
(≥99.9%), 1-propanol (≥99%), 2-propanol (≥99.5%),
ethylene glycol (≥99%), 1,2-propanediol (≥99.5%),
glycerol (≥99.5%), and NaOH were all purchased from
Merck.
Correspondence to: B. Samiey; e-mail: babsamiey@yahoo.com.
Figures S1 and S2 and Tables S1–S3 are available as Supporting
Information in the online issue at www.interscience.wiley.com.
c
ꢀ
2010 Wiley Periodicals, Inc.

KINETICS OF MALACHITE GREEN FADING IN ALCOHOL–WATER MIXTURES
509
628
626
624
622
620
618
616
N(CH3)2
(CH3)2N+
OH–
OH
+
(CH3)2N
N(CH3)2
MG+
Carbinol base
0
20
40
60
80
100
Walcohol
%
Scheme 1
Figure 1 λmax values of MG+ vs. weight percentages of
ꢀ
ꢀ, methanol; , ethanol; , 1-propanol; , 2-propanol; ×,
ꢁ
ꢂ
Kinetic Procedure
ethylene glycol; ♦, 1,2-propanediol; and +, glycerol in water
The fading of MG+ was followed at its maximum
wavelength (λmax) values in a thermostated cell com-
partment of a Shimadzu UV-1650PC spectrophotome-
ter. The experiments were conducted at 283, 293, and
303 K within 0.1 K in a stoppered cell. All the ki-
netic runs were carried out at least in triplicate. To
perform each kinetic run, a 100-μL aliquot of 1.38 ×
10−4 M MG+ solution was added by a microsyringe
under alkaline conditions at room temperature.
for the same cation with water in water, and N is
+
a parameter that is characteristic of the nucleophilic
system and is independent of cation. This equation is
applied to the reactions between nucleophiles and cer-
tain large and relatively stable organic cations in vari-
ous solvents. k0 values for MG+ are 1.46 × 10−8 and
9.93 × 10−8 M−1 min−1 at 283 and 303 K, respectively
into 2.9 mL of a solution containing 5.44 × 10−4
M
sodium hydroxide and a certain concentration of alco-
hol. The reaction between MG+ and hydroxide ion has
been found to be bimolecular, Þrst order with respect to
each reactant, but pseudo-Þrst-order conditions (excess
alkali) were used in all cases (Scheme 1).
[15]. N values obtained for hydroxide ion in the MG+
+
fading reaction increase with an increase in the alco-
hol weight percentage (except for zone 3 of glycerol–
water mixtures) and decrease with an increase in the
temperature, as shown in footnotes of Tables I–VII. As
shown in Tables I–VII, with an increase in the content
of cosolvents the rate constant of reaction increases.
Alcohols have a lower dielectric constant than wa-
ter and according to Hughes–Ingold rules for solvent
effects in nucleophilic substitution reactions [20–22],
formation of the neutral carbinol base from two op-
positely charged reactants is more favorable in higher
weight percentages of alcohols. ConÞrming this result,
it has been found the rate constant of crystal violet
(CV+) fading decreases in urea–water mixtures where
the dielectric constant increases [23] and increases in
the presence of cosolvents such as ethylene glycol,
1,2-propanediol, ethanol [5], 2-methoxy ethanol [24],
and tetrahydrofuran [25]. On the other hand, the reac-
tion rate of bromophenol blue (BPB=) fading, which
forms charged product, decreases with an increase in
the weight percentage of alcohol in a series of alcohol–
water mixtures [16,26]. Thus, it seems that in this work,
the formation of neutral product from charged reac-
tants has a central role in increasing the reaction rate
of MG+ fading with an increase in the concentration
of alcohols.
RESULTS AND DISCUSSION
The reaction of MG+ with hydroxide ion brings about
fading the color of MG+ and results in the formation
of colorless carbinol base (Scheme 1). In this work,
we studied the inßuence of various concentrations of
a series of mono- and polyhydroxylic alcohols on the
kinetics of MG+ fading. These hydroxylic cosolvents
were chosen to compare the effect of number of OH
groups and chain length on the reaction rate. As seen
in Fig. 1, with an increase in weight percentage of the
cosolvents, the λmax value of MG+ shifts to red. The
redshift has been previously reported for other com-
pounds upon going from polar to apolar solvents, as
a result of hydrophobic interaction [17]. A reaction of
MG+ fading is an electrophile–nucleophile combina-
tion reaction. The rate constants for these reactions are
correlated by using the Ritchie equation [18,19]
log k = log k0 + N
where k is the rate constant for the reaction of a given
cation with a given nucleophilic system (i.e., given nu-
cleophile in a given solvent). k0 is the rate constant
(1)
+
As seen in Tables I–VII and Fig. S1 in the Support-
ing Information, at the same molar ratios of alcohols
International Journal of Chemical Kinetics DOI 10.1002/kin

510
SAMIEY AND RAOOF TOOSI
Table I kobs and Ea Values of MG+ Fading in Ethanol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
WEtOH
%
[EtOH] (M) [H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
9.7
0.000
2.050
2.540
3.053
3.989
6.097
7.598
9.295
10.884
12.388
55.556
48.609
46.919
45.470
43.037
37.673
31.835
26.448
21.131
16.605
18.89 1.03
31.80 5.70
38.98 2.60
51.89 6.80
59.01 3.54
74.18 3.3
128.01 2.80
198.62 38.54
399.16 14.91
716.60 48.53
46.98 2.10
73.40 15.53
86.97 2.54
105.19 2.22
128.02 4.00
170.81 6.23
269.22 8.71
533.47 8.78
846.72 6.20
118.60 4.97
169.70 8.07
190.46 3.74
222.48 4.77
269.31 5.80
342.86 13.38
598.34 8.85
1055.69 97.23
1879.90 140.05
2730.45 617.14
65.5 2.0
59.7 1.7
56.5 1.1
51.9 2.1
54.1 1.2
54.6 2.0
54.9 2.5
59.6 5.2
55.2 2.3
47.8 3.5
12.1
14.5
19.3
29.0
38.7
48.3
58.0
67.7
1554.94 182.64
kmc values are given in the box.
Zones 1 and 2 are in the range of 0–14.5% and 14.5–67.7%, respectively.
values are in the range of 9.11–11.09 and 9.08–10.44 at 283 and 303 K, respectively.
N
+
Table II kobs and Ea Values of MG+ Fading in 1-Propanol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
W1−PrOH
%
[1-PrOH] (M) [H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
4.8
9.7
0.000
0.794
1.581
3.066
3.786
4.493
5.857
7.157
8.398
55.556
51.700
48.724
42.781
39.598
37.042
31.353
25.803
20.440
18.89 1.03
25.09 1.70
35.08 2.69
49.60 1.80
68.29 1.82
101.81 1.97
172.07 2.47
365.05 5.78
539.46 53.16
46.98 2.10
55.97 3.08
80.89 1.90
93.15 2.52
124.95 2.04
198.14 2.28
320.28 1.47
710.60 4.43
1058.04 27.93
118.60 4.97
138.00 3.31
170.47 7.02
196.85 2.00
209.31 4.00
382.18 13.60
654.69 11.85
1389.66 34.15
1705.83 335.12
65.5 2.0
60.7 3.5
56.4 1.5
49.1 3.5
39.9 1.3
47.1 1.1
47.6 3.0
47.6 1.4
41.1 3.3
19.3
24.2
29.0
38.7
48.3
58.0
kmc values are given in the box.
Zones 1 and 2 are in the range of 0–19.3% and 19.3–58.0%, respectively.
values are in the range of 9.11–10.57 and 9.08–10.23 at 283 and 303 K, respectively.
N
+
Table III kobs and Ea values of MG+ fading in 2-propanol–water solutions at 283–303 K
kobs (M−1 min−1
)
W2-PrOH
%
[2-PrOH] (M) [H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
9.7
0.000
1.518
2.951
3.638
4.308
5.599
6.862
7.418
8.035
9.106
55.556
48.437
43.013
39.831
37.078
31.438
25.893
23.462
20.451
15.804
18.89 1.03
24.16 1.01
24.00 9.06
25.97 1.16
50.00 3.08
56.85 5.65
69.67 11.31
114.61 2.15
266.45 31.02
658.32 69.83
46.98 2.10
54.30 1.30
54.00 1.08
64.05 1.10
96.60 3.28
117.58 8.79
166.93 14.40
257.94 7.25
580.99 63.45
118.60 4.97
131.50 7.50
145.00 4.19
154.46 7.72
207.70 8.72
275.48 10.56
400.86 27.70
600.63 61.14
1221.66 56.59
1893.18 452.12
65.5 2.0
60.3 2.8
64.0 5.1
63.5 1.5
50.7 3.3
56.2 3.8
62.4 1.7
59.0 2.2
54.3 1.1
37.6 1.3
19.3
24.2
29.0
38.7
48.3
53.2
58.0
67.7
1106.17 149.34
kmc values are given in the box.
Zones 1 and 2 are in the range of 0–24.2% and 24.2–67.7%, respectively.
values are in the range of 9.11–10.66 and 9.08–10.28 at 283 and 303 K, respectively.
N
+
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF MALACHITE GREEN FADING IN ALCOHOL–WATER MIXTURES
511
Table IV kobs and Ea Values of MG+ Fading in Methanol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
WMeOH
%
[MeOH] (M) [H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
1.0
1.5
0.000
0.309
0.454
0.758
1.503
2.943
4.365
5.747
7.394
8.388
9.672
10.914
13.326
55.556
54.153
53.946
53.857
52.196
48.385
45.795
42.661
39.710
37.044
33.930
31.541
26.332
18.89 1.03
44.28 2.36
65.56 4.03
46.98 2.10
89.12 7.63
122.10 1.75
210.65 6.18
229.66 4.80
528.09 6.33
118.60 4.97
179.44 17.47
242.50 9.74
65.5 2.0
49.9 1.4
46.6 2.4
40.7 0.8
44.0 0.9
43.0 1.3
34.9 3.4
44.9 0.9
46.0 1.1
44.4 1.8
44.3 1.8
47.8 4.9
49.3 3.0
2.4
4.8
9.7
117.46 7.63
122.14 1.72
289.88 7.38
526.92 9.94
583.43 50.25
691.66 22.40
788.91 8.18
1022.64 23.00
1213.87 21.62
1419.35 93.33
367.47 16.70
420.22 19.51
968.03 33.78
1398.90 46.65
2054.88 14.77
2514.45 40.15
2738.51 144.54
3536.95 174.43
4656.86 204.45
5654.61 313.53
14.5
19.3
24.2
29.0
33.8
38.7
48.3
947.32 17.86
1126.11 63.65
1367.75 18.41
1560.28 27.67
2015.58 52.07
2164.47 473.48
3104.81 68.99
kmc values are given in the boxes.
Zones 1, 2, and 3 are in the range of 0–2.4%, 2.4–14.5%, and 14.5–48.3%, respectively.
values are in the range of 9.11–10.99 and 9.08–10.76 at 283 and 303 K, respectively.
N
+
Table V kobs and Ea Values of MG+ Fading in Ethylene Glycol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
Weg%
[eg] (M)
[H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
1.0
1.9
2.4
0.000
0.179
0.292
0.395
0.788
1.577
2.372
3.181
4.817
6.491
8.202
9.952
11.717
13.536
15.392
55.556
55.255
54.062
53.407
52.445
50.139
47.742
45.027
40.230
35.093
29.702
24.349
18.988
13.439
7.844
18.89 1.03
33.47 1.22
39.47 1.25
56.98 1.16
82.53 3.41
108.04 3.10
123.35 4.99
134.45 4.30
139.59 1.33
143.00 5.74
147.14 5.5
158.54 2.41
212.81 11.09
266.62 6.57
374.25 14.04
46.98 2.10
54.98 3.37
65.89 2.98
118.60 4.97
144.47 12.20
156.37 4.89
180.26 1.45
279.00 7.15
369.89 9.56
400.00 68.2
419.11 16.41
487.54 7.38
573.77 18.39
610.00 20.31
698.94 11.17
898.57 13.31
1110.25 27.34
1493.86 56.52
65.5 2.0
51.9 10.7
48.9 8.1
40.9 8.8
43.5 2.4
43.9 1.0
42.0 4.0
40.6 3.7
44.6 3.1
49.5 1.6
50.7 1.3
52.9 1.3
51.3 2.4
52.5 1.4
49.4 0.7
83.60 3.19
4.8
9.7
163.78 6.72
202.23 11.73
249.43 1.08
264.00 13.10
286.72 6.94
302.17 3.97
312.56 3.55
347.70 12.62
425.05 13.82
544.95 12.10
780.12 8.83
14.5
19.3
29.0
38.7
48.3
58.0
67.7
77.3
87.0
[eg] = Ethylene glycol.
kmc values are given in the boxes.
Zones 1, 2, and 3 are in the range of 0–4.8%, 4.8–19.3%, and 19.3–87.0%, respectively.
values are in the range of 9.11–10.41 and 9.08–10.18 at 283 and 303 K, respectively.
N
+
and temperatures, the rate constants of the MG+ fading
reaction in the low mole ratios of alcohols change as
follows:
where kMeOH, keg, kGl, kprd, k1−Pr OH, kEtOH, k2−PrOH, and
kw are the rate constants of the MG+ fading reaction in
aqueous mixtures of methanol, ethylene glycol, glyc-
erol, 1,2-propanediol, 1-propanol, ethanol, 2-propanol,
and in water, respectively. In relation (2), it seems that
afÞnity of hydroxide ions and thus, the rate constants
of the MG+ fading increase approximately according
kw < k2−PrOH ≈ kEtOH < k1−PrOH ≈ kprd
< kGl < keg ≤ kMeOH
(2)
International Journal of Chemical Kinetics DOI 10.1002/kin

512
SAMIEY AND RAOOF TOOSI
Table VI kobs and Ea Values of MG+ Fading in 1,2-Propanediol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
Wprd
%
[prd] (M)
[H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
0.3
1.0
0.000
0.048
0.155
0.396
1.170
1.556
3.135
4.715
6.306
7.902
9.514
11.131
12.759
55.556
54.516
54.342
53.569
51.065
49.683
44.546
39.593
34.431
29.125
23.844
18.332
12.699
18.89 1.03
28.00 1.21
29.99 1.70
35.09 5.70
37.43 6.89
40.64 0.94
60.89 2.32
64.73 2.55
73.42 2.67
87.70 2.95
111.48 5.28
175.37 1.77
296.78 1.16
46.98 2.10
66.44 2.95
70.87 2.20
77.77 4.22
84.60 4.46
92.53 2.12
122.50 1.97
142.53 3.24
156.79 9.59
199.27 5.01
259.44 3.43
395.26 8.17
640.73 7.93
118.60 4.97
148.45 3.73
158.99 6.81
177.13 14.32
192.49 2.97
196.69 7.56
239.28 5.51
287.10 5.68
312.10 6.75
422.58 8.29
555.14 24.85
798.20 12.57
1212.13 18.03
65.5 2.0
59.5 1.2
59.5 1.2
57.7 2.0
58.3 1.7
56.2 1.2
48.8 1.1
53.1 1.3
51.6 1.2
56.1 1.2
57.2 1.3
54.0 1.6
50.2 2.0
2.4
7.3
9.7
19.3
29.0
38.7
48.3
58.0
67.7
77.3
[prd] = 1,2-Propanediol.
kmc values are given in the boxes.
Zones 1, 2, and 3 are in the range of 0–2.4%, 2.4–19.3%, and 19.3–77.3%, respectively.
values are in the range of 9.11–10.31 and 9.08–10.09 at 283 and 303 K, respectively.
N
+
Table VII kobs and Ea Values of MG+ Fading in Glycerol–Water Solutions at 283–303 K
kobs (M−1 min−1
)
WGl
%
[Gl] (M)
[H2O] (M)
283 K
293 K
303 K
Ea (kJ mol−1
)
0.0
0.7
1.3
2.4
0.000
0.142
0.279
0.529
1.059
2.141
3.253
4.379
6.771
11.704
17.200
55.556
54.433
54.342
53.858
51.237
50.757
48.576
46.267
41.398
31.701
20.298
18.89 1.03
33.67 1.56
38.83 2.66
47.67 4.23
61.10 1.35
65.40 3.48
70.07 4.09
74.16 4.56
71.08 1.67
62.79 1.49
60.12 2.26
46.98 2.10
68.00 6.27
73.11 2.73
99.67 8.03
125.37 1.76
131.35 2.77
141.73 2.42
159.69 6.76
150.58 5.16
135.17 5.60
130.97 1.35
118.60 4.97
149.67 9.86
167.46 1.75
206.67 10.07
222.38 7.80
236.88 11.46
252.70 5.90
308.84 8.02
291.90 1.90
280.60 1.20
264.33 3.10
65.5 2.0
53.1 3.0
52.0 5.2
52.3 1.3
46.1 2.3
45.9 1.6
45.8 1.9
50.9 1.6
50.4 1.3
53.4 1.1
52.8 1.2
4.8
9.7
14.5
19.3
29.0
48.3
67.7
[GI] = Glycerol.
mc1and kmc3values are given in the boxes.
Zones 1, 2, and 3 are in the range of 0–4.8%, 4.8–19.3%, and 19.3–67.7%, respectively.
values are in the range of 9.11–9.62 and 9.08–9.43 at 283 and 303 K, respectively.
k
N
+
to a decrease in hydrophobicity of the used alcohols
[27–29].
In high mole ratios of alcohols, reaction rates change
as follows:
phenyl groups attached to the positively charged tert-
carbon atom at the center and has quinoid resonating
forms and its solvation in aqueous mixtures of dif-
ferent cosolvents is likely to be an involved process.
Because of the large size of MG+ and the low sur-
face charge density around this large-sized ion, elec-
trostatic interactions seem negligibly small and disper-
sion interaction is likely most effective factor in MG+
solvation. However, the extent of hydrogen-bonding
interactions in aquo-organic mixtures is likely to de-
termine the accessibility of the hydrophobic portion
kw < kGl < kprd ≤ keg < k2−PrOH ≤ kEtOH
< k1−PrOH ꢁ kMeOH
(3)
To interpret these facts, it can be said MG+ is a tri-
phenyl methyl dye with two (CH3)2N-substituted
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF MALACHITE GREEN FADING IN ALCOHOL–WATER MIXTURES
513
630
H
OH
H
H
H
H
628
626
624
622
620
618
616
λmax = 0.125WGl% + 617.01
HO
H
H
H
HO
HO
CH3
R2 = 0.999
H
H
HO
HO
H
1b
1a
2a
OH
H
OH
H
H
H
H
H
H
H
CH2OH
HO
H
CH3
CH2OH
HO
HO
HO
0
20
40
60
80
100
WGl
%
3a
3b
2b
Figure 2 λmax values of MG+ vs. weight percentages
of glycerol in water under neutral conditions at room
temperature.
Scheme 2
of the organic cosolvent molecule for dispersion in-
teraction. Thus, the presence of the increased number
of hydrogen-bonding centers is likely to decrease the
hydrophobicity of an organic cosolvent molecule in
aqueous mixtures and thus reduce the magnitude of
dispersion interaction with an organic solute. It seems
that the approach of the large MG+ molecule toward
the hydrophobic methylene chain of polyhydroxylic
alcohols is sterically hindered owing to OH groups
of alcohol molecules, as it is expected from confor-
mational structures of ethylene glycol (1a) and (1b),
1,2-propanediol (2a) and (2b), and glycerol (3a) and
(3b), as shown in Scheme 2. Steric hindrance due to
the position of the OH group reduces the hydrophobic
interaction between MG+ and a methylene chain of
2-propanol compared to that of 1-propanol and results
in a decrease in the rate constant of the fading reaction
compared to 1-propanol.
in the observed decrease in the reaction rate in glyc-
erol weight percentages above 19.3%. As shown in
Fig. 1, over a wide concentration range of ethylene
glycol, 1,2-propandiol, and glycerol, which have high
viscosity values, there is a linear relation between the
redshift of λmax values of MG+ and their concentra-
tions in their aqueous solutions. On the other hand, it
was observed that in the absence of NaOH, this relation
holds over most of the concentration range of glycerol
(Fig. 2). This test shows that in spite of hydrophobic
interactions that occurred between MG+ and glycerol
molecules, the reaction rate decreases, which is due to
high viscosity values of glycerol solutions. This test,
called MAGUS, is explained in the Appendix and can
be used for measuring the glycerol concentration in its
aqueous solutions.
On the other hand, in relation (3), the rate constants
of MG+ fading decrease approximately according to
the increase in viscosity of the alcohols used [30]. It
seems that with an increase in viscosity of solvents,
mobility of reactants decreases and as observed in re-
lation (3), the rate constants of MG+ fading in polyhy-
droxylic alcohols (with high viscosity values) are less
than those of monohydroxylic alcohols.
As shown in Table VII, the rate constants of the
MG+ fading reaction in aqueous glycerol mixtures up
to 19.3% increase and then slightly decrease. Similar
situation has been found for crystal violet fading in
glycerol–water mixtures [19,31]. As reported, reaction
rates decrease with an increase in viscosity of solvent
[32,33]. Thus, it seems that an increase in the glyc-
erol concentration results in a decrease in dielectric
constant of a mixed solvent and a dramatic increase
in the solvent viscosity, which in the former case in-
creases the reaction rate and the latter decreases it.
Competition between these two effects Þnally results
Proposed Reaction Mechanism
Data of Tables I–VII were analyzed by using the SES-
MORTAC model. In the SESMORTAC model [16], a
range of solvent composition in which the equation of
logarithm of reaction rate constant, log k, versus recip-
rocal of the dielectric constant of the solution, D−1, is
linear [34–41], is called a “zone” and a solvent compo-
sition in which a zone Þnishes and another zone starts,
which is called “mechanism change point” (abbrevi-
ated as mc point). Consideration of a mechanism on the
basis of point charge on a dielectric continuum suggests
that the plots of log k against D−1 should be linear. The
failure of the simple electrostatic interpretation shows
theimportanceof hydrogen bondingand other nonelec-
trostatic medium effects in controlling the reactivity of
the substrates [40,42]. In such cases, the differential
solvation of the initial and transition states is the con-
trolling factor for changes in the rate constant with
the solvent composition. In the SESMORTAC model,
International Journal of Chemical Kinetics DOI 10.1002/kin

514
SAMIEY AND RAOOF TOOSI
variation in mechanism is followed through the study
of changes in microenvironment (or solvent cage) of
the activated complex. Dielectric constants of the used
alcohol–water solutions are obtained from the works
seen that in each region of alcohol–water systems, there
is a linear relation between ꢀS= and ꢀH= values of
the fading reaction (Figs. S2(a)–(g) and Table S3 in
the Supporting Information) and therefore a compen-
sation effect between them that results in the weak
dependence of ꢀG= upon composition of the used
alcohols. As seen in Table S2 in the Supporting In-
formation, ꢀS= value of the fading reaction in water
is positive. As found in [34], for reactions between
oppositely charged ions, there is an increase in the
ꢀS= value going from reactants to activated complex.
Thus, the activated complex has less charge than the
reactants and will be partially desolvated [34]. It seems
that negative ꢀS= values in alcohol–water binary mix-
tures (Table S2 in the Supporting Information) are due
to solvation of activated complex by alcohol molecules
added to ACSM in each zone, which support the for-
mation of more ordered transition states compared to
it in water.
A large body of experimental data and theoretical
calculations (e.g., of the Kirkwood–Buff integral func-
tions) has shown that many aqueous binary mixtures
are microheterogeneous, there exist microdomains
composed of organic solvent surrounded by water, and
of water solvated by organic solvent. The onset and
composition of these microdomains depend on the pair
of solvents. There exist the possibilities of solvation of
the solute by one of the two solvent microdomains
[52–56]. Thus, the composition of the solvation shell
differs from that of bulk mixture [57], and there is a
solvent exchange equilibrium between molecules of
binary mixture components in the solvation shell of
solute [58,59].
û
of Verbeek et al. [43] and Akerlof [44].
It is found that in the used concentration range of
alcohols, mixtures of water with ethanol, 1-propanol,
and 2-propanol were two-zone and aqueous mixtures of
methanol, 1,2-propanediol, ethylene glycol, and glyc-
erol were three-zone. As seen from Tables I–VII, Eact
values decrease sharply at the boundary of zones. On
the other hand, difference between activation free en-
ergies of the reaction in solvent systems and water,
ꢀG=t , can be obtained by applying the Eyring equa-
tion as follows:
ꢀG=t = ꢀGS= − ꢀGW= = RT ln(kw/ks)
(4)
where ꢀG=S and ꢀG=W are the free energies of activa-
tion in solvent systems and water, respectively. kw and
ks are the reaction rate constants in water and solvent
systems, respectively. As seen in Fig. 3, in all cases
ꢀG=t values of the MG+ fading reaction are negative
and change sharply about boundary of zones. It sug-
gests that the system is more stabilized when water is
replaced by the alcohol–water mixture.
As shown in Tables S1 and S2 in the Supporting
Information, ꢀS= (except for the zone 3 of glycerol–
water mixtures) and ꢀH= values reach their mini-
mum values about the boundaries of zones. These
may be due to the dissolution of alcohol molecules
in the solvent cage [45–50] and nonelectrostatic, es-
pecially hydrophobic interactions [51], between MG+
and alcohol molecules when ACSM forms. ACSM is
an abbreviation for “activated complex formed in the
second mechanism” and will be explained later. It is
In aqueous organic mixtures, formation of 1:1
hydrogen-bonded species between organic and wa-
ter molecules leads to the solvent exchange equilib-
ria, which results in the preferential solvation of so-
lute molecules [60]. The number of solvent molecules
whose exchange in the solvatochromic indicator (or
probe) solvation shell affects its solvent polarity scale
is usually ≤ 2, and concentration of the solvent species
are effective [60].
0
0
20
40
60
80
100
–2
–4
The solvent cage is the microenvironment of the
MGδ+–OHδ− contact pair and, inspite of the Þrst solva-
tion shell, includes many water and alcohol molecules,
and its dielectric constant value is an intensive prop-
erty. Thus, in each region, n molecules of water can
be replaced by n molecules of alcohol. Here, two
processes occur simultaneously, a chemical reaction
between MG+ and OH− (Þrst order in contact ion)
and replacement of n water molecules of the ACSM
microenvironment by n alcohol molecules of its sur-
rounding (n order in solvent molecules); the progress of
the Þrst process is the driving force of the second one.
–6
t
G
–8
–10
–12
Walcohol
%
Figure 3 ꢀG=t values of MG+ fading reaction vs. weight
percentages of ꢀ, methanol; , ethanol; , 1-propanol;
ꢀ
,
ꢁ
ꢂ
2-propanol; ×, ethylene glycol; ♦, 1,2-propanediol; and +,
glycerol in water under alkaline conditions at 293 K.
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KINETICS OF MALACHITE GREEN FADING IN ALCOHOL–WATER MIXTURES
515
Table VIII n, k1, k−1, k2, and Ea (k1) Values of Different Zones for the MG+ Fading Reaction in Various Alcohol–Water
Binary Mixtures Obtained from the SESMORTAC Model at Different Temperatures
n
k1 (M−(n+1) min−1
)
k
(M−n min−1
2nd
)
k2(min−1
)
Ea(k1) (kJ mol−1
)
−1
T (K) 1st 2nd 3rd
1st
2nd
3rd
1st
3rd
1st
2nd
3rd
1st 2nd 3rd
Ethanol + water
4.90E–5 3.28E–8
2.63E–5 1.17E–7
1.24E–4 7.33
283 2.45 3.56
293 2.00 3.22
303 1.83 3.01
–
–
–
2.12
6.26
13.42
0.23
1.07
3.77
–
–
–
–
–
–
9.37E5 1.81E6
6.43E5 1.10E6
4.88E5 7.58E5
–
–
–
65.9 99.8
53.3 41.5
–
–
–
1-Propanol + water
9781.57 1.50E–5
1769.44 1.11E–5
5647.15 5.01E–6
283 1.75 2.13
293 3.90 2.22
303 2.36 2.24
–
–
–
11.05
33.85
48.89
15.58
26.65
50.01
–
–
–
–
–
–
9781.57 4.64E5
1769.44 3.81E5
5647.15 2.98E5
–
–
–
2-Propanol + water
283 RC 7.74
293 RC 7.31
303 1.20 7.19
–
–
–
–
–
7.49
0.011
0.053
0.162
–
–
–
RC
RC
5.01E–3
3.31E–2
–
–
–
–
–
3.91E7
4.24E7
–
–
–
–
96.0
1.50E–4 0.101
6.07E5 5.42E7
Methanol + water
283 1.49 4.19 2.97 147.98
293 1.53 3.17 1.50 264.59
16.26
49.29
303 1.47 3.93 1.26 375.69 205.34 277.32 8.26E–4 2437.75 84.58 1.58E5 2.99E5 1.57E5
6.39 4.82E–4 1.34E3 797.41 2.71E5 1.11E6 1.42E6 33.1 90.2 134.9
79.97 5.01E3 1.61E3 1.38E–5 1.92E5 4.14E5 2.53E5
Ethylene glycol + water
283 0.97 0.84 3.41 81.29
293 1.77 2.17 3.16 184.33
303 1.37 0.56 2.07 221.84 134.71
36.43
89.41
0.05 1.85E–3 2.85E4 6.59E–9 3.96E5 3.35E5 3.53E6 36.0 46.8 168.8
0.13 1.03E3 1.39E4 1.37E–7 2.39E5 2.18E5 1.77E6
5.90 5.35E–4 3.62E4 4.27E–6 2.01E5 1.96E5 6.46E5
1,2-Propanediol + water
283 0.29 2.28 3.63 20.73
293 0.22 2.30 3.10 37.42
303 0.33 1.23 2.60 78.63
4.35
13.67
17.97
0.06 7.40E–3 4.47E3 5.70E–8 4.73E5 9.95E5 3.10E6
0.46 0.004 8.09E3 1.33E–7 4.45E5 6.06E5 8.18E5 47.4 50.9 135.0
2.64 2.42E–3 6.42E–4 5.61E–7 3.00E5 4.89E5 7.84E5
Glycerol + water
283 0.54 1.18 3.47 40.78
293 0.82 1.68 3.03 86.79
303 0.84 2.19 1.36 148.81
3.98 6.60E–4 1.64E–4 2.98E4 2.50E3 3.53E5 7.62E5 6.24E6
4.55 2.81E–3 0.005 1.68E–4 4.79E2 3.19E5 7.27E5 1.22E6 46.2 17.0 235.4
6.43
0.51 1.16E–3 2.52E–4 1.55E–4 2.36E5 6.52E5 1.67E5
RC, Rate constant is approximately constant.
Ea (k1) values are activation energy of k1 values.
As described in the theory of the SESMORTAC
model (and as seen in Table VIII), the values of n
are different from one region to the next one and this
causes a break in the plot of log k vs. D−1 at each mc
point. In computational chemistry, a computed con-
tinuum solvent may be considered between each two
successive mc points and mc points may be assumed
as nodal points.
The Þrst mechanism occurs in pure solvent. Starting
in the Þrst zone, this mechanism can be written as
follows:
k1 ꢀꢁ
ꢂꢃ=
δ+
[(MG+ + OH−)]cage
MG − OHδ−
−→
←−
AC
cage
k−1
k2
−→ Product
(5)
In this reaction, the solvent is not a reactant. Thus,
because of the SESMORTAC model, this reaction is of
type I. In the MG+ fading reaction, in the presence of
the used alcohols (except for the zone 3 of glycerol–
water mixtures) the reaction rate increases and the pro-
posed mechanism for the MG+ fading reaction in these
solutions involves two kinds of mechanisms.
where AC is activated complex; k1, k−1, and k2 are the
fundamental rate constants of the MG+ fading reac-
tion, and we cannot determine them. The related rate
equation, v1, is written as follows:
v1 = k[MG+][OH−]
(6)
where k is the observed rate constant in water.
International Journal of Chemical Kinetics DOI 10.1002/kin

516
SAMIEY AND RAOOF TOOSI
Adding alcohol to a reaction medium results in for-
mation of ACSM and increases the reaction rate. The
second mechanism is written as follows:
is replaced by
ꢁ
ꢂ
n
k12k22 [S] − [S]mc
1
kobs = kmc
+
ꢁ
ꢂ
(12)
(13)
n
1
k−2 1 [H2O]mc − [H2O] + k22
1
[MG+ + OH−) · nH2O]cage + nS
where
k1 ꢀꢁ
ꢂ
ꢃ=
MGδACSM − OHδ− · nS
+ nH2O
−→
←−
cage
k11k21[S]nmc
k−1 1[H2O]n + k21
k
−1
1
kmc = k +
1
k2
mc1
−→ Product
(7)
[S]mc and [H2O]mc are the concentrations of alco-
1
1
where alcohol molecules are shown by S and k1,
hol and water in mc1 point, respectively, and k12, k−2 1
,
k
−1, and k2 are the fundamental rate constants of
and k22 are the fundamental rate constants of the MG+
fading reaction in the second zone. The second term
in Eq. (12) shows the effect of alcohol molecules on
the rate equation in the second zone. kobs values of
the third zones of methanol, ethylene glycol, and 1,2-
propanediol aqueous mixtures are obtained as follows:
the MG+ fading reaction in alcohol–water binary
mixtures. In each binary mixture, structure of ACSM
depends on the structure of solvent cage. Dielectric
constant values of alcohols are less than that of water
and when ACSM forms in each zone, n molecules of
water existing in the solvent cage are replaced by n
molecules of alcohol from its surrounding. This de-
creases the dielectric constant value of the microenvi-
ronment of (MGδ+ − OHδ−) in ACSM, and formation
of neutral product, MGOH, is more favorable. This re-
sults in an increase in the rate of the fading reaction. In
the Þrst zone, assuming that a steady-state concentra-
tion of ACSM is reached in the used binary mixtures,
we have
ꢁ
ꢂ
n
k3k3 [S] − [S]mc
2
1
2
kobs = kmc
+
ꢁ
ꢂ
(14)
n
2
k−3 1 [H2O]mc − [H2O] + k23
2
where
k11k21[S]nmc
1
kmc = k +
2
k−1 1[H2O]n + k21
mc1
ꢁ
ꢂ
n
k12k22 [S] − [S]
k11[MG+][OH−][S]n
k−1 1[H2O]n + k21
mc2
mc1
+
ꢁ
ꢂ
(15)
[ACSM] =
(8)
n
k−2 1 [H2O]mc − [H2O]mc + k22
1
2
[S]mc and [H2O]mc are the concentrations of alco-
The effect of alcohol molecules to the reaction rate
equation in the Þrst zone, v2, is as follows:
2
2
hol and water in mc2 point, respectively, and k13, k−3 1
,
and k23 are the fundamental rate constants of the MG+
fading reaction in the third zone. The second term in
Eq. (14) shows the effect of alcohol molecules on the
rate equation in the third zone.
k11k21[MG+][OH−][S]n
v2 = k21[ACSM] =
(9)
k−1 1[H2O]n + k21
In zone 3 of the glycerol–water solvent system, the
reaction rate decreases with an increase in the glycerol
and the equation of reaction rate in binary mixtures, v,
is
concentration and kmc is the lowest observed rate con-
3
stant in the third zone. In this zone, it is assumed that n
molecules of glycerol existing in the solvent cage are
replaced by n molecules of water from its surround-
ing and the following equation is used for the second
mechanism:
v = v1 + v2 = kobs[MG+][OH−]
ꢄ
ꢅ
k11k21[S]n
=
k +
[MG+][OH−] (10)
k−1 1[H2O]n + k21
where
n
k13k23 ([H2O] − [H2O]mc3
)
kobs = kmc3
+
(16)
k11k21[S]n
k−1 1[H2O]n + k21
k−3 1 ([S]mc3 − [S])n + k23
kobs = k +
(11)
where the second term in Eq. (16) shows the contribu-
tion of water molecules on the reaction rate in this zone.
Also, it has been shown that k1 values in each zone obey
the Arrhenius equation [16] and the related activation
energy, Ea(k1), values are given in Table VIII. Data
kobs and k are the second-order rate constant in a binary
mixture and water, respectively, and k11, k−1 1, and k21
are the fundamental rate constants of the MG+ fading
reaction in the Þrst zone. In the second zone, Eq. (11)
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS OF MALACHITE GREEN FADING IN ALCOHOL–WATER MIXTURES
517
Table A.1 Measuring Glycerol Concentration in a
Series of Samples by the MAGUS Test
of the Þrst zone Þtted properly in Eq. (11), those of
the second and third zones Þtted suitably in Eqs. (12),
(14), and (16), and the results are given in Table VIII.
As seen in Table VIII, at each certain temperature, k1
values decrease with an increase in the alcohol concen-
tration from zone 1 to higher zones. To interpret this
fact, we may say an increase in alcohol concentration
decreases both dissociation of reactants into their con-
stituent ions and mobility of ions which in most cases
results in an increase in Ea(k1) values from zone 1 to
higher zones (Table VIII). It is found that k2 values
increase with an increase in the alcohol concentration
from zone 1 to higher zones because the formation of
neutral carbinol base from partially charged activated
complex [61] is more favorable with an increase in the
alcohol concentration. Also, k2 values decrease with
an increase in the temperature in each certain zone. As
seen in Tables I–VIII, with an increase in the weight
percentage of the used cosolvents or temperature, k2
values change according to the trend of hydroxide ion
WGl% in samples
Prepared
Calculated
λmax (nm)
1.1
2.5
7.7
17.1
23.6
44.8
64.9
84.9
95.0
1.5
3.1
8.1
16.4
23.0
44.5
64.4
85.9
94.2
617.2
617.4
618.0
619.0
619.8
622.4
624.8
627.4
628.4
ing aqueous glycerol concentration. It is good to say
that MAGUS is an ancient Persian word meaning wise
man and holy man. Tests show that the λmax − WGl%
relation does not hold over the concentration range of
0–1%, where the λmax value of MG+ remains constant
at 617 nm. To carry out the MAGUS test, a 100-μL
aliquot of 1.38 × 10−4 M MG+ solution is added by
a microsyringe into 2.9 mL of an unknown concen-
tration aqueous glycerol solution and the λmax value
of MG+ is measured. Then, using the λmax − WGl%
relation and considering the dilution effect in measur-
ing cell, the glycerol concentration is calculated. The
concentration of glycerol in a series of samples was
measured, and the results are presented in Table A1.
The experimental and calculated data were compared
by statistical paired t-test and regression line methods,
and no signiÞcant difference was observed.
nucleophilic parameter, N , values.
+
CONCLUSIONS
The rate constant of the MG+ fading reaction increases
in the presence of methanol, ethanol, 1-propanol,
2-propanol, ethylene glycol, 1,2-propanediol, and
glycerol (up to 19.3%). But it is found that in aqueous
glycerol solutions higher than 19.3%, the rate constant
of reaction slightly decreases, which is due to their
high viscosity values. The fundamental rate constants
of the MG+ fading reaction in the used solvent sys-
tems are obtained by the SESMORTAC model. It is
observed that k2 values change according to the trend
of hydroxide ion nucleophilic parameter values and
at each certain temperature, k1 values decrease from
zone 1 to higher zones. On the other hand, using MG+
solvatochromism, a simple test, called MAGUS, was
introduced for measuring the glycerol concentration in
its aqueous solutions.
SUPPORTING INFORMATION
The following data are presented as Support-
ing Information in the online issue at www
.interscience.wiley.com:
Figure S1 shows kobs values of the MG+ fading
reaction in terms of different mole ratios of the
used alcohols in water at 293 K. Figures S2a–S2g
show the compensation plots of ꢀS= versus ꢀH=
values of the MG+ fading reaction in different
weight percentages of the used alcohols in water.
In Table S1, ꢀH= values, in Table S2 ꢀS= values,
and in Table S3 equations of the compensation
effect between ꢀS= and ꢀH= values of the MG+
fading reaction in different weight percentages of
the used alcohols in water are presented.
•
APPENDIX
Measuring Aqueous Glycerol Concentration
Using Dye Solvatochromism (MAGUS) Test
•
As seen in Figs. 1 and 2, there is a linear relation be-
tween λmax values of MG+ and weight percentages
of glycerol (abbreviated as λmax − WGl% relation) in
both alkaline and neutral aqueous glycerol solutions
at room temperature, which can be used for measur-
International Journal of Chemical Kinetics DOI 10.1002/kin

518
SAMIEY AND RAOOF TOOSI
31. Basu-Mullick, I. N.; Kundu, K. K. Can J Chem 1980,
58, 79.
BIBLIOGRAPHY
32. Jez, J. M.; Noel J. P. J Biol Chem 2002, 277, 1369.
33. Uribe, S.; Sampedro, J. G. Biol Proced Online 2003, 5,
108.
1. Iwanaga, R. Bull Chem Soc Japan 1962, 35, 869.
2. Wada, G.; Kobayashi, Y. Bull Chem Soc Japan 1975,
48, 2451.
34. Reichardt, C. Solvents and Solvent Effects in Organic
Chemistry, 2nd ed.; VCH: Weinheim, Germany, 1998;
pp. 189–207.
35. Meretoja, A. Acta Chem Scand 1948, 2, 352.
36. Amis, E. A.; La Mer, V. K. J Am Chem Soc 1939, 61,
905.
3. Raff, R. A.V.; Silverman, B. H. Can J Chem 1951, 29,
857.
4. Brinchi, L.; Di ProÞo, P.; Germani, R.; Salvelli, G.;
Spreti, N. J Colloid Interface Sci 2002, 247, 429.
5. Yesin, T. R.; Sinem, G.; Melda, T. Colloids Surf A 2005,
270–271, 72.
37. Amis, E. A.; Cook, S. E. J Am Chem Soc 1941, 63,
2621.
6. Monuz, M.; Graciani, M.; Rodriguez, A.; Moya, M. L.
Int J Chem Kinet 2004, 36, 634.
38. Zaghloul, A. A. Int J Chem Kinet 1997, 29, 431.
39. Ismail, A. M.; Zaghloul, A. A. Int J Chem Kinet 1998,
30, 463.
7. Xu, B. Q.; Aamundstad, T. A.; Lillekjendlie, B.;
Bjørneboe, A.; Christophersen, A. S. Pharmacol Tox-
icol 1997, 80, 171.
40. El-Subruiti, G. M. Int J Chem Kinet 2002, 34, 495.
41. El-Subruiti, G. M.; Chehata, A. K.; Massoud, S. S. Int J
Chem Kinet 2002, 34, 1.
42. Laidler, K. J.; Landskroener, P. A. Trans Faraday Soc
1956, 52, 200.
43. Verbeek, R. M. H.; Thun, H. P.; Verbeek, F. Bull Soc
Chim Belg 1977, 86, 125.
û
44. Akerlof, G. J Am Chem Soc 1932, 54, 4125.
45. Hribar-Lee, B.; Dill, K. A. Acta Chim Slov 2006, 53,
257.
8. Waugh, E. J.; Purchase, B. S. Biotechnol Lett 1987, 9,
151.
9. Gao, Z. H., Gu, J. Y.; Bai, X. D. Pigment Resin Technol
2007, 36, 90.
10. Gregory, P. In Encyclopedia of Chemical Technology;
Kroschwitz, J. I. (Ed.); Wiley: New York, 1993; Vol. 8,
p. 544.
11. Duxbury, D. F. Chem Rev 1993, 93, 381.
12. Wikipedia. Available at http://en.wikipedia.org/wiki/
malachite green. Accessed 2010.
46. Bertrand, G. L.; Millero, F. J.; Wu, C. H.; Hepler, L. G.
J Phys Chem 1966, 70, 699.
47. Davis, M. I.; Ham, E. S. Thermochim Acta 1991, 190,
251.
13. Culp, S. J.; Beland, F. A. Int J Toxicol 1996, 15, 219.
14. Ritchie, C. D. J Am Chem Soc 1975, 97, 1170.
15. Ritchie, C. D.; Wright, D. J.; Huang, D. S.; Kamego, A.
A. J Am Chem Soc 1975, 97, 1163.
48. Parsons, M. T.; Lau, F. W.; Yee, E. G. M.; Koga, Y. J
Solution Chem 2003, 32, 137.
16. Samiey, B.; Alizadeh, K.; Mousavi, M. F.; Alizadeh, N.
Bull Korean Chem Soc 2005, 26, 384.
49. To, E. C. H.; Davis, J. V.; Tucker, M.; Westh, P.;
Trandum, C.; Suh, K. S. H.; Koga, Y. J Solution Chem
1999, 28, 1137.
50. Dohnal, V.; Roux, A.H.; Hynek, V. J Solution Chem
1994, 23, 889.
17. Caetano, W.; Tabak, M. J Colloid Interface Sci 2000,
225, 69.
18. Ritchie, C. D. Can J Chem 1986, 64, 2239.
19. Mandal, U.; Sen, S.; Das, K.; Kundu, K. K. Can J Chem
1986, 64, 300.
51. Matulis, D. Biophys Chem 2001, 93, 67.
52. Suppan, P.; Ghoneim, N.; Solvatochromism, N. The
Royal Society of Chemistry: Cambridge, UK, 1997;
p. 21.
53. Shulgin, I.; Ruckenstein, E. J Phys Chem B 1999, 103,
872.
20. Hughes, E. D. Trans Faraday Soc 1941, 37, 603.
21. Ingold, C. K. Structure and Mechanism in Organic
Chemistry; Bell: London, 1993.
22. Burton, C. A. Nucleophilic Substitution at a Saturated
Carbon Atom; Elsevier: London, 1963.
23. Wyman, J. J Am Chem Soc 1933, 55, 4116.
24. Bhattacharya, A.; Das, A. K.; Kundu, K. K. Can J Chem
1981, 59, 1153.
54. Shulgin, I.; Ruckenstein, E. J Phys Chem B 1999, 103,
2496.
55. Marcus, Y. Chem Soc Rev 1993, 22, 409.
56. Marcus, Y. Monatsh Chem 2001, 132, 1387.
57. El Seoud, O. A. Pure Appl Chem 2007, 79, 1135.
58. Bosch, E.; Roses, M. J Chem Soc, Faraday Trans 1992,
88, 3541.
59. Roses, M.; Rafols, C.; Ortega, J.; Bosch, E. J Chem Soc,
Perkin Trans 2 1995, 1607.
60. Tada, E. B.; Silva, P. L.; El Seoud, O. A. J Phys Org
Chem 2003, 16, 691.
25. Datta, J.; Kundu, K. K. Can J Chem 1981, 59, 3141.
26. Amis, E. S.; La Mer, V. K. J Am Chem Soc 1939, 61,
905.
27. Gupta, A. R. J Phys Chem 1979, 83, 2986.
28. Richardson, E. A.; Stern, K. H. J Am Chem Soc 1960,
82, 1296.
29. Wikipedia. Available at http://en.wikipedia.org/wiki/
Ion-association. Accessed 2010.
30. Lide, D. L., (Ed.). CRC Handbook of Chemistry and
Physics, 87th ed.; CRC Press/Taylor and Francis: Boca
Raton, FL, 2006; Section 6, pp. 175–176.
61. Pham, T. V.; McClelland, R. A. Can J Chem 2001, 79,
1887.
International Journal of Chemical Kinetics DOI 10.1002/kin