Conductivity and dissociation constants of quaternary ammonium perchlorates and picrates in 4-methyl-pentan-2-one

Article abstract of DOI:10.1021/je9008969

The dissociation of 14 ionophores, namely, seven symmetrical (C₁ to C₇) and five asymmetrical quaternary ammonium perchlorates and two tetraalkylammonium picrates (all with linear hydrocarbon chains), in 4-methyl-pentan-2-one was studied at 25 °C (ε_r = 12.92) using the conductance method. The values of the association constants of the quaternary ammonium cation, Ct⁺, with ClO₄^- vary from (7.4 ± 0.3) ·10³ L·mol^-1 for tetramethylammonium to (2.4 ± 0.1) ·10³ L·mol^-1 for tetrahexyl- and tetraheptylammonium; a distinct dependence on the size of the Ct⁺, especially for symmetrical cations, is evident. The values of the limiting molar conductivities Λ₀/S·mol^-1·cm² vary from 122.8 to 90.0 (± 0.7). The plot of Λ₀ versus the reciprocal cube root of the total van der Waals volume of the cations, V _Ct^-1/3, is close to linear up to tetrapentylammonium and hexadecyltrimethylammonium, while for larger cations (with 21 to 28 carbon atoms) the Λ₀ values stay practically constant. At the same time, symmetrical and asymmetrical cations with the same V_Ct values possess equal mobility.

Full text of DOI:10.1021/je9008969

J. Chem. Eng. Data 2010, 55, 1887–1892
1887
Conductivity and Dissociation Constants of Quaternary Ammonium Perchlorates
and Picrates in 4-Methyl-pentan-2-one†
Sergey T. Goga, Alexander V. Lebed, and Nikolay O. Mchedlov-Petrossyan*
Department of Physical Chemistry, Kharkov V. Karazin National University, Kharkov, 61077, Ukraine
The dissociation of 14 ionophores, namely, seven symmetrical (C1 to C7) and five asymmetrical quaternary
ammonium perchlorates and two tetraalkylammonium picrates (all with linear hydrocarbon chains), in
4-methyl-pentan-2-one was studied at 25 °C (εr ) 12.92) using the conductance method. The values of the
association constants of the quaternary ammonium cation, Ct+, with ClO4- vary from (7.4 ( 0.3) ·103 L·mol-1
for tetramethylammonium to (2.4 ( 0.1) · 103 L · mol-1 for tetrahexyl- and tetraheptylammonium; a distinct
dependence on the size of the Ct+, especially for symmetrical cations, is evident. The values of the limiting
molar conductivities Λ0/S · mol-1 · cm2 vary from 122.8 to 90.0 (( 0.7). The plot of Λ0 versus the reciprocal
cube root of the total van der Waals volume of the cations, VCt-1/3, is close to linear up to tetrapentylammonium
and hexadecyltrimethylammonium, while for larger cations (with 21 to 28 carbon atoms) the Λ0 values stay
practically constant. At the same time, symmetrical and asymmetrical cations with the same VCt values
possess equal mobility.
The values of molar conductivities of a set of TAA+ ions
Introduction
with n from 1 (or 2) to 7 (or 8) are available in several solvent
The data on equilibrium constants and conductivities of
systems,24,29,31,32 but in the case that the viscosity is high, the
ionophores are of principal importance both for solution
Λ0 values are rather small and relatively close to each other.
chemistry and chemical engineering.1–7
The same concerns the data in nitrobenzene,9 1,2-dichloroben-
zene,14 sulfolane,25 ethylene glycol,26 and propylene carbonate.30
The study and interpretation of ionic equilibria and conduc-
tivity of electrolytic solutions containing tetraalkylammonium
In these solvents, except for 1,2-dichlorobenzene, the dissocia-
tion degree of salts is high, and thus the comparison of the KA
ions (TAA+) is of special significance for solution chemistry,
solvent extraction, phase-transfer catalysis, polarography, colloid
values is problematic. In some works, the tetraalkylammonium
chemistry, and so forth. Therefore, the number of papers devoted
salts studied contained different anions, X-,19,22,23,31 and even
to the behavior of tetraalkylammonium salts (TAAX) in
if the Λ+ values were estimated, their exact comparison should
solutions of various natures is huge.
be hindered by some ambiguities of the dividing procedure.
Meanwhile, despite the numerous data on the equilibrium
Some popular solvents such as acetonitrile and acetone are
constants of cation-anionic (Ct+ + X-) association, KA, and
appropriate for the comparison of Λ0 values, owing to their low
limiting molar conductivities, Λ0, of TAAX salts, less attention
viscosity (around 0.3 mPa ·s),11,19,23 but the association (TAA+
was paid to the comparison of these parameters for symmetrical
+ X-) is less expressed, and thus the corresponding KA values
are low. French and Muggleton18 report that the disymmetry in
the cation markedly reduces the dissociation constant of
corresponding picrates in acetonitrile, but actually it deals with
a cation with a NH group, able to hydrogen bond.
and asymmetrical TAA+ ions.
Indeed, it is natural to expect (and is repeatedly proved
experimentally8–32) that the Λ0 values of N(n-CnH2n+1)4X salts
with fixed X- ion or of the individual cationic mobilities, Λ+,
decrease along with the increase in n. However, the data for n
> 5 are few in number.21,22,24,29,31,32 On the other hand, the
asymmetrical cations, for example, N(n-C18H37)(CH3)3+ or N(n-
The set of data for TAAPic in 1,2-dichloroethane reported
by Sawada and Chigira29 is rather complete, but it must be noted
that their KA values are 1.6 times lower than those reported
earlier by Tucker and Kraus,8 while the Λ0 values agree better.
C18H37)(n-C4H9)3+, exhibit a smaller mobility as compared
respectively with N(CH3)4+ and N(n-C4H9)4
.
12,14–16 However,
+
there is a lack of data for making firm conclusions about such
properties of symmetrical and asymmetrical cations of equal
total van der Waals size. Probably, the sole exception is the
report of Hughes and Price24 on the mobilities both of
symmetrical TAA+ ions (C1 to C8) and asymmetrical ones, such
as N(n-C4H9)3(CH3)+ and N(n-C7H15)3(CH3)+ in methyl ethyl
ketone. Interestingly, some authors state that in media of low
relative permittivity the conductivity of tetraalkylammonium
salts is not greatly affected by the length of the hydrocarbon
chain of the cation.33
Therefore, we decided to systematically study the conductance
and ion association of a set of 12 ionophores of quaternary
ammonium perchlorate type, symmetrical and asymmetrical
(including two N-alkylpyridinium salts), and two picrates, in
4-methyl-pentan-2-one (methyl isobutyl ketone, MIBK), a
solvent with εr ) 12.92 and η ) 0.542 mPa ·s at 25 °C. Here,
both KAand Λ0 values are high enough. The work was aimed
to determine and analyze these quantities from the viewpoint
of the influence of the size and structure of the cations, Ct+ (all
with linear hydrocarbon chains), also keeping in mind the limited
number of data for MIBK as compared with most popular
solvents.
† Part of the “Josef M. G. Barthel Festschrift”.
* Corresponding author. E-mail: mchedlov@univer.kharkov.ua.
10.1021/je9008969  2010 American Chemical Society
Published on Web 03/23/2010

1888 Journal of Chemical & Engineering Data, Vol. 55, No. 5, 2010
were used. The density was calculated using the additive
scheme; for the pure solvent, it was taken as 0.7961 g ·cm-3
Experimental Section
,
MIBK (Merck, for synthesis or for extraction analysis) was
twice-distilled, and the fraction with t ) (114.2 to 114.8) °C
(99.7/kPa) was used for further work.
and for the salts, they were determined experimentally. The
correction for pure solvent conductance was used in the
calculations of molar conductance values, Λ; the last-named
were obtained with an uncertainty of (0.05 to 0.1) %. The
conductivity of the pure solvent did not exceed (0.2 to 0.3) %
of that of the most diluted salt solution. The experimental data
are presented in Table 1. Some typical phoreograms are
exemplified in Figure 1.
All of the below salts were prepared from analytical grade
reagents, if not otherwise specified. Tetramethylammonium
perchlorate was prepared from tetramethylammonium hydroxide
and perchloric acid, four times recrystallized from water, and
dried under vacuum to a constant mass at (60 to 70) °C.
Tetraethylammonium perchlorate was prepared from tetraethy-
lammonium iodide and sodium perchlorate, three times recrys-
tallized from acetone, and dried under vacuum to a constant
mass at (60 to 70) °C. Tetrapropylammonium perchlorate was
prepared from tetrapropylammonium bromide and sodium
perchlorate, three times recrystallized from acetone, and dried
under vacuum to a constant mass at (60 to 70) °C. Tetrabuty-
lammonium perchlorate was prepared from tetrabutylammonium
iodide and sodium perchlorate, three times recrystallized from
acetone, and dried under vacuum to a constant mass at (60 to
70) °C. Tetrapentylammonium perchlorate was prepared from
tetrapentylammonium bromide (Aldrich, g 99 %) and sodium
perchlorate, three times recrystallized from aqueous ethanol with
mass fraction ω ) 0.956, and dried under vacuum to a constant
mass at (60 to 70) °C. Tetrahexylammonium perchlorate was
prepared from tetrahexylammonium bromide (Aldrich, 99 %)
and sodium perchlorate, three times recrystallized from acetone,
and dried under vacuum to a constant mass at (60 to 70) °C.
Tetraheptylammonium perchlorate was prepared from tetrahep-
tylammonium bromide (Aldrich, g 99 %) and sodium perchlo-
rate, three times recrystallized from acetonitrile, and dried under
vacuum to a constant mass at (60 to 70) °C. Hexadecyltrim-
ethylammonium perchlorate was prepared from hexadecyltri-
methylammonium bromide (Merck, pharm.) and perchloric acid,
three times recrystallized from acetone, and dried under vacuum
to a constant mass at a temperature not higher than 60 °C.
N-Hexadecylpyridinium perchlorate was prepared from N-
hexadecylpyridinium chloride or bromide and perchloric acid,
four times recrystallized from acetone, and dried under vacuum
to a constant mass at a temperature not higher than 60 °C.
Hexyltriethylammonium perchlorate was prepared from hexy-
ltriethylammonium hydrosulfate and sodium perchlorate, three
times recrystallized from water, and dried under vacuum to a
constant mass at (60 to 70) °C. Octadecyltrimethylammonium
perchlorate was prepared from octadecyltrimethylammonium
bromide and sodium perchlorate, three times recrystallized from
water, and dried under vacuum to a constant mass at (60 to
70) °C. N-Butylpyridinium perchlorate was prepared from
N-butylpyridinium bromide and silver perchlorate, three times
recrystallized from acetone, and dried under vacuum to a
constant mass at 30 °C. The preparation and characterization
of tetraethylammonium and tetrabutylammonium picrates was
described in the previous paper,34 and the same samples were
used in the present study.
Results
Data Processing. General Principles. Conductance data were
processed using the nonlinear least-squares method to obtain
the limiting molar conductance Λ0 and association constant KA
values. The algorithm and main details of the calculation
procedure are described previously.34,35 The Lee-Wheaton
equation4,36–39 for molar conductivity (see also the Supporting
Information) and second approach of the Debye-Hu¨ckel theory
for activity coefficients were used.
Choice of Distance Parameter R. The parameter R of closest
approach distance can be either calculated together with Λ0 and
KA as a fitted parameter or assigned to a constant value, which
should be defined using some external approach. According to
the most popular approaches,2,40 the value of the parameter R
can be equated to the following: (i) the Bjerrum distance R )
q ) e2/(8πε0εrkT), (ii) the sum of ionic radii R ) r+ + r-, and
(iii) the sum of ionic radii and solvent molecule diameter R )
r+ + r- + dsolv. We have performed various testing calculations
for N(n-C4H9)4ClO4 in MIBK using the above-mentioned
approaches for R. It should be noted that the estimation of ionic
radii of quaternary ammonium ions is a separate problem.
Taking into account that in Lee-Wheaton model, the parameter
R has the meaning of Gurney cosphere,36 we estimated these
values by the quantum-chemical semiempirical AM1 method
as a recommended radius for SCRF solvation model calculations
in Gaussian 03 package.41 The results of calculations are
summarized in Table 2.
The comparison of data in Table 2 shows that varying the R
parameter does not influence the fitted Λ0 and KA values within
the confidence limit. The fitted value of R is close to that
calculated by the (R ) r+ + r-) relationship, but in this case
the estimation error is rather large. Thus all conductance data
were processed with fixed R ) r+ + r- values of the distance
parameter.
Chemical Equilibrium Scheme. The simple equilibrium of
ion association into ionic pairs, Ct+ + X- a Ct+X-, was
always taken into account, whereas ionic triplet formation
is questionable. Usually it is accepted that ionic triplet
formation becomes noticeable in solvents with very low
relative permittivity, εr < (9 to 10). For MIBK εr ) 12.92,
and according to Fuoss,42 the critical concentration of triplet
formation is Cctr ) 1.19 · 10-14(εrT)3 ) 6.8 · 10-4 mol · L-1
.
Conductance measurements were carried out using platinized
platin electrodes in molybdenum-glass cells with the Precison
LCR Meter GW Instek LCR-817 apparatus operating at a
frequency of 1 kHz. The cells were calibrated using 12 standard
aqueous solutions of potassium chloride, within concentration
range (1·10-4 to 0.01) mol·L-1. All of the measurements were
done at (25.00 ( 0.05) °C. The solutions were prepared by
precise weighing of the solid sample, dissolving in the proper
amount of the solvent with further dilutions. The analytical
balances VLA-200 and GR-202, A&D (Japan) with the uncer-
tainty of weighting respectively (( 0.0002 and ( 0.00001) g
We have performed two testing calculations for the system
N(n-C4H9)4ClO4 + MIBK taking into account the possibility
of ionic triplet formation. We assumed that equilibrium
constants of formation of cationic and anionic triplets are
+
-
equal to KT ) KT ) KT, and thus four parameters, Λ0, Λ0T,
+
-
KA, and KT, were to be calculated (Λ0T ) Λ0T + Λ0T ). In
the second calculation we reduced the number of fitted
parameters to three by an additional relation Λ0T ) 0.693Λ0.43
The results are also placed in Table 2. As follows from these
results, the Λ0 and KA values almost do not depend on
chemical equilibrium scheme and can be reliably calculated

Journal of Chemical & Engineering Data, Vol. 55, No. 5, 2010 1889
Table 1. Molar Conductances of Quaternary Ammonium Perchlorates and Picrates in MIBK at 25 °C
c·103
Λ
c·103
Λ
c·103
Λ
mol·L-1
S·mol-1 ·cm2
mol·L-1
S·mol-1 ·cm2
mol·L-1
S·mol-1 ·cm2
Tetramethylammonium Perchlorate
Tetraethylammonium Perchlorate
Tetrapropylammonium Perchlorate
0.0093380
0.0111958
0.015300
0.019798
0.025819
0.032755
0.042922
0.055284
0.070081
0.092310
112.96
112.31
110.65
107.69
104.77
101.39
97.55
93.36
89.42
84.68
0.016220
91.71
89.78
88.84
87.37
85.25
82.97
81.18
0.063291
0.088925
0.12145
0.15196
0.20897
0.27510
0.36995
0.49125
0.65910
0.88385
1.1831
85.50
81.65
77.78
74.41
69.85
65.70
61.20
56.94
52.59
48.38
44.40
40.64
37.08
33.79
30.81
0.027054
0.034990
0.045257
0.058234
0.074686
0.097608
1.5815
2.1242
2.8434
3.7943
Tetrabutylammonium Perchlorate
Tetrapentylammonium Perchlorate
Tetrahexylammonium Perchlorate
0.097470
0.13412
0.19022
0.23665
0.31860
0.43250
0.57811
0.76833
1.0163
1.3800
1.8394
2.4567
3.3088
77.25
73.72
69.30
66.17
62.16
57.65
53.48
49.50
45.74
41.80
38.33
35.08
31.98
29.20
26.71
0.096604
74.26
71.86
67.98
64.69
60.57
56.23
52.45
48.74
46.84
41.33
37.99
34.72
31.77
29.01
26.50
0.098760
0.12950
0.17623
0.22072
0.27977
0.36868
0.47880
0.62088
0.80882
1.0555
72.68
70.52
67.22
64.46
61.33
57.77
54.33
50.90
47.50
44.10
40.90
37.95
35.08
32.44
29.95
0.12071
0.16851
0.21462
0.29218
0.40035
0.52957
0.70167
0.90208
1.2617
1.6738
2.2572
3.0137
4.0356
1.3803
1.7818
2.3212
3.0061
4.4184
5.8932
5.4004
3.9170
Tetraheptylammonium Perchlorate
Hexadecyltrimethylammonium Perchlorate
N-Hexadecylpyridinium Perchlorate
0.071785
0.10356
0.13175
0.15937
0.22438
0.29737
0.40503
0.54379
0.72664
0.97751
1.3065
76.50
72.94
70.40
68.29
63.90
60.32
56.32
52.50
48.68
44.98
41.43
38.05
34.83
31.89
29.17
0.11718
0.15128
0.20964
0.26363
0.35837
0.50710
0.65885
0.87057
1.1681
1.5473
2.1055
2.7972
3.7599
5.0115
6.6834
63.69
59.97
55.29
51.86
47.59
42.73
39.36
35.92
32.56
29.53
26.51
23.96
21.56
19.44
17.50
0.092384
0.13292
0.16909
0.22611
0.29544
0.41379
0.53882
0.72135
0.96707
1.3033
68.75
64.02
60.77
56.48
52.66
48.00
44.44
40.59
36.98
33.55
30.58
27.65
24.98
22.59
20.46
1.7191
2.3176
3.1196
4.1698
1.7510
2.3546
3.1488
4.2077
5.5689
Hexyltriethylammonium Perchlorate
Octadecyltrimethylammonium Perchlorate
N-Butylpyridinium Perchlorate
0.094374
0.13619
0.17394
0.21948
0.28624
0.37458
0.48564
0.63452
0.81696
1.0563
80.83
76.63
73.21
69.49
65.53
61.36
57.43
53.44
49.79
46.19
42.60
39.23
36.24
33.31
30.66
0.10489
0.13712
0.17413
0.22633
0.28917
0.38093
0.48923
0.63110
0.81478
1.0619
63.44
60.11
56.75
53.11
49.70
45.85
42.50
39.24
36.14
33.03
30.21
27.55
25.14
22.90
0.10141
75.31
70.94
66.90
62.72
57.95
53.27
48.97
44.64
40.76
36.91
33.53
30.30
27.41
24.77
22.48
0.13841
0.17908
0.23318
0.31264
0.42240
0.55852
0.75438
1.0035
1.3455
1.7981
2.4194
3.2404
4.3482
5.7868
1.3854
1.8099
2.3340
3.0488
1.3863
1.8022
2.3372
3.0321
3.9749
without assuming triplet formation. Therefore, all data were
processed using the simple scheme of ion-pair formation.
The resulting Λ0 and KA values are summarized in Table 3.
The solubilities of the first two perchlorates in MIBK were
limited. Moreover, in the case of tetraethylammonium
perchlorate, the measurements in extremely diluted solutions
were uncertain, probably due to adsorption on the platinum
interface. Therefore, in this case the Λ0 value was estimated
using Kohlrausch’s law and the Λ0 values for N(n-
C4H9)4ClO4, N(C2H5)4Pic, and N(n-C4H9)4Pic determined in
the present study. Our results for tetrabutylammonium picrate
(Table 3) somewhat differ from those reported by Juillard

1890 Journal of Chemical & Engineering Data, Vol. 55, No. 5, 2010
Table 1. Continued
c·103
Λ
c·103
Λ
mol·L-1
S·mol-1 ·cm2
mol·L-1
S·mol-1 ·cm2
Tetraethylammonium Picrate
Tetrabutylammonium Picrate
0.090841
0.13139
0.16800
0.21378
0.28982
0.39559
0.51759
0.69569
0.93050
1.2491
85.00
82.41
79.93
77.42
74.05
70.44
67.01
63.20
59.59
55.80
52.19
48.72
45.36
42.26
39.39
0.10090
0.13104
0.17830
0.22803
0.30782
0.41501
0.56430
0.75778
0.99625
1.3485
74.47
72.71
70.12
67.86
64.86
61.72
58.36
55.03
51.99
48.57
45.37
42.28
39.37
36.60
34.10
1.6735
2.2461
3.0046
4.0207
1.8195
2.4358
3.2487
4.3553
5.3688
5.8089
nary ammonium picrates in 1,2-dichlorobenzene,14 the log KA
values decrease from 4.94 to 4.74 on going from tetraethyl- to
tetrapentylammonium, while for octadecyltrimethylammonium
the value of 5.72 was reported.14 In nitrobenzene,9 the log KA
value for teteraethylammonium equals 0.85, while those for
tetramethyl-, ethyltrimethyl-, and phenyltrimethylammonium
picrates are around 1.4.9 In pyridine,12 the corresponding values
from tetraethyl- to tetrapentylammonium coincide (log KA from
2.98 to 2.95), while for picrates in acetonitrile18 KA even increase
from tetraethyl- to tetrapentylammonium.
In acetone, the difference in log KA values of tetraethyl- and
tetrabutylammonium picrates is 0.11,11 but processing these
experimental data by Lee-Wheaton equation, we obtained for
tetrabutylammonium picrate the value log KA ) 1.94 ( 0.1734
instead of 1.65 reported by the authors,11 though the Λ0 value
was the same (152.4 S ·mol-1 ·cm2).
Hughes and Price24 observed the decrease in KA values of
symmetrical tetraalkylammonium iodides and bromides in
methyl ethyl ketone along with the lengthening of the hydro-
carbon chains (C1 to C8), but for methyltripropyl-, methyltribu-
tyl-, and methyltriheptylammonium iodides the KA values exceed
those of teteraethyl- and tetrapropylammonium iodides and
approach that of tetramethylammonium iodide.
Figure 1. Phoreograms in MIBK: tetraethylammonium picrate (1), tetrabu-
tylammonium picrate (2), tetrabutylammonium perchlorate (3), N-butylpy-
ridinium perchlorate (4), N-hexadecylpyridinium perchlorate (5), and
hexadecyltrimethylammonium perchlorate (6).
and Kolthoff44 but better agree with the data of Naganawa
and Sekine.45
We processed the experimental data of Hughes and Price24
for tetraheptylammonium and tetraoctylammonium iodides by
using our algorithm, equating R to 1.2 nm. The Λ0 values of
(130.8 ( 0.1 and 128.4 ( 0.1) S·mol-1 ·cm2 coincide with those
reported by Hughes and Price (respectively, (130.5 and 128.2)
S·mol-1 ·cm2), while the log KA values of 2.601 ( 0.002 and
2.594 ( 0.001, obtained by us, are somewhat higher as
compared with the earlier data (respectively, 2.490 and 2.488).24
Though the conductance data processing shows that the
formation of ionic triplets cannot be excluded, this equilibrium
is expressed to a very low extent (Table 2). In any case, such
complication of the model does not practically influence the
KA and Λ0 values.
Discussion
Though the KA values of quaternary ammonium perchlorates
vary within a relatively narrow range, from (7.4 ( 0.3)·103
L·mol-1 for tetramethylammonium to (2.4 ( 0.1)·103 L·mol-1
for tetrahexyl- and tetraheptylammonium, a distinct dependence
on the size of the Ct+, especially for symmetrical cations, is
evident. Indeed, the log KA values gradually decrease from
tetramethyl- to tetrapentylammonium; for tetrahexyl- and tet-
raheptylammonium, they are equal within the confidence limits
(3.38 and 3.40). But in the case of long-tailed cations with three
ethyl or methyl groups the KA values increase: the log KA values
for hexadecyltrimethylammonium and octadecyltrimethylam-
monium are equal (3.76 and 3.75) and approach that of
teteramethylammonium (3.87). The same is the case with
N-butyl- and N-hexadecylpyridinium: log KA ) 3.69 and 3.68;
the difference of the latter and that for hexadecyltrimethylam-
monium is too small to warrant a discussion.
The last-named quantities decrease along with the increase
in molar volume. However, inspection of Table 3 reveals two
significant points. First, the plot of Λ0 versus the reciprocal cube
-1/3
root of the total van der Waals volume of the cations, VCt
(or reciprocal ionic radius, r+-1), is close to linearity up to
tetrapentylammonium and hexadecyltrimethylammonium, while
for larger cations (with 21 to 28 carbon atoms) the Λ0 values
stay practically constant (Figure 2).
Interestingly, the KA values of the two picrates in MIBK
coincide (Table 3), while the regularities observed for TAAPic
in 1,2-dichloroethane8,29 resemble those for TAAClO4 in MIBK
described above. For tetraethylammonium the log KA value is
0.15 units higher than for tetrabutylammonium.8,29 For quater-
Secondly, symmetrical and asymmetrical cations with one
and the same VCt values possess equal mobility, in contrast to

Journal of Chemical & Engineering Data, Vol. 55, No. 5, 2010 1891
Table 2. Comparative Results of Conductance Data Processing for N(n-C4H9)4ClO4 in MIBK at 25 °C
R
Λ0
Λ0T
optimized parameters
additional relations
nm
S ·cm2 ·mol-1
log KA
S·cm2 ·mol-1
log KT
Simple Equilibrium Scheme
Λ0, KA, R
Λ0, KA
0.95 ( 0.10
96.1 ( 2.1
94.9 ( 1.3
96.1 ( 0.7
96.0 ( 0.8
3.44 ( 0.02
3.43 ( 0.02
3.44 ( 0.01
3.45 ( 0.02
R ) q
2.169
a
Λ0, KA
R ) r+ + r-
0.89
1.31
b
Λ0, KA
R ) r+ + r- + dsolv
Equilibrium Scheme with Ionic Triplets
Λ0, KA, Λ0T, KT
Λ0, KA, KT
R ) r+ + r-
R ) r+ + r-
Λ0T ) 0.693Λ0
0.89
0.89
95.9 ( 0.8
95.4 ( 1.8
3.43 ( 0.02
3.41 ( 0.07
63.7 ( 2.5
66.13
1.5 ( 0.5
1.8 ( 0.8
a The used ionic radii (see the text) are 0.56 nm (N(n-C4H9)4+) and 0.33 nm (ClO4-). b The used radius for the MIBK molecule equals 0.42 nm.
Table 3. Logarithms of (Cation + Anion) Association Constants and Limiting Molar Conductances of the Salts in MIBK at 25 °C and Total
van der Waals Volumes of the Cationsa
Λ0
R ) r+ + r-
103 ·VCt
ionophoreb
N(CH3)4ClO4
N(C2H5)4ClO4
N(C3H7)4ClO4
S·mol-1 ·cm2
log KA
nm
nm3
122.8 ( 0.9
3.87 ( 0.02
3.75 ( 0.11d
3.52 ( 0.01
3.45 ( 0.01
3.43 ( 0.02
3.38 ( 0.01
3.40 ( 0.01
3.50 ( 0.01
3.76 ( 0.02
3.75 ( 0.01
3.69 ( 0.01
3.68 ( 0.02
3.05 ( 0.02
3.03 ( 0.02f
0.72
0.78
0.85
0.89
0.93
0.97
1.00
0.85
0.91
0.93
0.78
0.91
0.91
1.01
176.38
312.46
448.55
584.63
720.72
856.80
992.89
448.55
686.70
754.74
294.18
702.43
312.46
584.63
107.4c
102.2 ( 0.7
96.1 ( 0.8
92.0 ( 1.0
89.6 ( 0.6
90.3 ( 0.6
101.9 ( 0.8
92.0 ( 1.0
90.0 ( 0.5
102.7 ( 0.9
91.8 ( 0.9
96.3 ( 0.8
85.0 ( 0.7e
N(C4H9)4ClO4
N(C5H11)4ClO4
N(C6H13)4ClO4
N(C7H15)4ClO4
N(C6H13)(C2H5)3ClO4
N(C16H33)(CH3)3ClO4
N(C18H37)(CH3)3ClO4
C4H9NC5H5ClO4
C16H33NC5H5ClO4
N(C2H5)4Pic
N(C4H9)4Pic
a The VCt values were calculated as a sum of van der Waals atomic volumes; the latter were calculated using the van der Waals radii: 0.171 nm (C),
0.116 nm (H), and 0.150 nm (N).46 b All of the hydrocarbon chains are linear. c This value was estimated using Kohlrausch’s law and the Λ0 values for
N(C4H9)4ClO4, N(C2H5)4Pic, and N(C4H9)4Pic determined in this work. d Calculated using the Λ0 value estimated using Kohlrausch’s law. e In ref 44,
the value 93 was reported. f In ref 44, the value 3.27 was reported (KA ) 5.4·10-4) as determined by the conductance method, while in ref 45 the
-1
value of 2.98 ( 0.12 was obtained by solvent extraction method.
sions. The following sets of values were used: (i) r+ ) (3VCt/
4π)1/3, where VCt is a sum of van der Waals atomic volumes,
(ii) r+ as the recommended radius for the SCRF solvation model
calculations in the Gaussian 03 package (see above), (iii) r+
estimated by Lepori and Gianni from group contribution, as
reported by Katsuta et al.,47 (iv) r+ values recommended by
Kuznetsova,48 and (v) van der Waals r+ values utilized by
Sawada and Chigira.29 In any case, our first conclusion on the
Λ0 regularities stays valid.
Interestingly, in 1,2-dichloroethane29 and methyl ethyl ke-
tone24 the mobilities of symmetric tetraalkylammonium ions
continue to decrease up to n ) 8 (e.g., see Figure 2). However,
these data are in line with our observation concerning the
mobilities of symmetrical and asymmetrical TAA+ ions of
approximately equal size.
Supporting Information Available:
The Lee-Wheaton equation for molar conductivity and related
Figure 2. Dependence of the limiting molar conductivities of the quaternary
expressions are presented. This material is available free of charge
via the Internet at http://pubs.acs.org.
ammonium salts on the reciprocal cube root of the total van der Waals
volume of the cations: ], tetraalkylammonium iodides in methyl ethyl
ketone,24 O, TAA+ perchlorates in MIBK; b, pyridinium perchlorates in
MIBK; 4, TAA+ picrates in 1,2-dichloroethane (Λ0 values from ref 29).
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Received for review October 27, 2009. Accepted March 9, 2010.
Support via Grant 0107U000661 from the Ukrainian Ministry of
Education and Science is acknowledged.
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