CONDUCTANCES OF SOMEUNI-UNIVALENT ELECTROLYTES
range of 0-2 and 2.5 m for the amino acid and the urea, respectively. Since this is roughly the range over which the binary models fit, the model chosen to represent the ternary system seems justified.
905
Acknowledgments. The author is indebted to the University of Adelaide for postdoctoral support and to Dr. P. J. Dunlop for discussion during the course of this work.
Conductances of Some Uni-univalent Electrolytes in Adiponitrile at 25"
by Paul G. Sears, Joseph A. Carum, and Alexander I. Popov Department of Chemistry, Michigan State University, East Lansing, Michigan 48823 (Received August $3,1966)
Conductances of five sodium and potassium salts and twelve quaternary ammonium salts in adiponitrile have been measured at 25". The data have been analyzed by the FuossOnsager conductance equation using the latest FORTRAN computer program of Kay for both nonassociated and associated electrolytes. The dissociating power of adiponitrile is reflected by fourteen of the salts showing no association and the other three having association constants of 28 or less. Limiting ionic equivalent conductances have been evaluated by the metbod of Coplan and Fuoss using triisoamylbutylammonium tetraphenylborate as a reference electrolyte. The dielectric constant of adiponitrile was determined to be 32.45 at 25".
Introduction This paper reports a part of a systematic investigation of nonaqueous solvents as reaction media especially, but not exclusively, as media for complexation reactions. I n this respect adiponitrile presents an especially interesting case since it is a relatively polar solvent with high dielectric constant and an appreciable dipole moment and, at the same time, it has respectable donor properties towards Lewis acids such as transition metal ions. However, before one can undertake the study of complexation reactions in adiponitrile, it is essential to determine the behavior of simple electrolytes in this solvent. Several previous papers have described the conductances of electrolytes in mononitriles such as acetonitrile,l-10 benzonitrileJ9-l2 propionitrile,la isobutyronitrile,8 and a-naphthonitrile.9 The study described in this article supplements the preceding investigations and, more importantly, involves the initial use of a dinitrile as an electrolytic solvent. Litera-
ture reports indicate that adiponitrile (1,4-dicyanobutane) has a viscosity of 0.0621 poise,13 density of (1) D. F. Evans, C. Zawoyski, and R. L. Kay, J . Phys. Chem., 69, 3878 (1965). (2) A. C. Harkness and H. M. Daggett, Jr., Can. J . Chem., 43, 1215 (1965). (3) J. F. Coetzee and G. P. Cunningham, J. Am. Chem. Soc., 87, 2529 (1965). (4) M. A. Coplan and R. M.Fuoss, J . Phys. Chem., 68, 1181 (1964). (5) A. I. Popov and R. E. Humphrey, J . Am. Chem. SOC.,81, 2043 (1959). (6) C. M. French and D. F. Muggleton, J . Chem. SOC.,2131 (1957). (7) P. Walden and E. J. Birr, 2. Phgsik. Chem., A144, 269 (1929). (8) A. M. Brown and R. M. Fuoss. J. Phys. Chem., 64, 1341 (1960). (9) C. M. French and I. G . Roe, Trans. Faraday SOC.,49, 314 (1953). (10) G. J. Janz. A. E. Marcinkowsky, and I. Ahmad, J. Electrochem. SOC.,112, 104 (1965). (11)A. R.Martin, J. Chem. SOC.,3270 (1928);530 (1930). (12) P. Walden, 2. Physik. Chem., 54, 129 (1906); 55, 683 (1906). (13) A. L.Woodman, W. J. Murbaoh, and M. H. Kaufman, J. Phys. Chem., 64, 658 (1960).
Volume 71, Number 4
March 1067
906
0.9579 g/l.,I3 and a dipole moment of 3.76 D.I4 It has a very broad liquid range (2--~300") and may be purified by fractional freezing or fractional distillation. &lost quaternary ammonium salts readily dissolve in adiponitrile whereas alkali metal salts generally are much less soluble even though some such as sodium perchlorate and sodium iodide form solvates. Experimental Section
Purijication and Properties of Solvent. Adiponitrile (Eastman grade) was subjected initially to successive fractional freezings until a constant freezing temperature of 2.15" was obtained. The solvent then was fractionally distilled over barium oxide through a 24-in. Vigreux column at 1 mm and 123". The retained middle fractions had the following properties at 25" : specific conductance, 1-2 X ohm-' cm-'; dielectric constant at 1Mc, 32.45; viscosity, 0.0599 poise; density, 0.9585 g/ml. The procedures for the measurements of the dielectric constant, viscosity, and density have been described in detail previously.ls Comparison data for the specific conductance and dielectric constant are unavailable. However, our values for the viscosity and density of adiponitrile differ somewhat from the corresponding data of 0.0621 poise and 0.9579 g/ml in the 1iterat~re.l~The solvent was recovered from the salt solutions for reuse by distillation. Salts. Triisoamylbutylammonium iodide and triisoamylbutylammonium tetraphenylborate were synthesized and purified using the method of Coplan and Fuoss.16 Good agreement was found with the reported melting point of the former salt, but the melting point of the tetraphenylborate (using a Fisher-Johns apparatus with a calibrated thermometer) was found to be 264-265' instead of 274-275" reported in the literature.16 The melting point remained constant on several recrystallizations. Eastman grade tetrabutylammonium iodide, tetrahexylammonium iodide and tetrahexylammonium bromide, along with reagent grade potassium and sodium salts, were used without further purification. The other seven quaternary ammonium salts were recrystallized a t least twice from appropriate systems. All salts were dried in vacuo at 50" to constant weight prior to their use in the preparation of stock solutions. The subsequent confirmation of additivity of ionic conductances reflected that the salts were generally pure. Apparatus and Procedures. Resistances were measured normally at 2000 cps with a bridge assembly designed arid described by Thompson and Rogers.'' An oscilloscope was used as a null-point detector. Periodic measurements were made also at 400 and 4000 The Journal of Physical Chemistry
P. G. SEARS,J. A. CARUSO, AND A. I. POPOV
cps, but no significant frequency dependency on resistance was observed. When the cell resistances were greater than 30,000 ohms, the cell was shunted in parallel with 30,000 ohms and the conductance cell resistance was computed from the measured parallel resistance. Two flask cells, similar to those designed by Daggett, Bair, and Kraus,18 were employed. Following the recommendation and procedure of Jones and Bollinger,lSthe electrodes were lightly platinized (6 coulombs/ cm2). The cell constants of 0.2409 f 0.0001 and 0.2320 f 0.0001 cm-I were determined using dilute aqueous potassium chloride solutions and data of Lind, Zwolenik, and F u o s ~ . The ~ ~ cell constants were checked periodically during the study; no changes were observed. Resistance measurements were made at 25.00 f 0.03" by maintaining the cells in a Sargent 5-84805 thermostatic bath assembly filled with light mineral oil. The temperature of the bath was established with a thermometer calibrated by the National Bureau of Standards. The weight dilution method was used for the preparation of the solutions in the flask cells. The preparation of the stock solutions, the filling of the cells and the Friedman-LaMer weighing pipets, and the addition of stock solutions to the conductance cells were made under normal laboratory conditions since brief exposures of the nonhygroscopic solvent and solutions to the atmosphere caused no observable changes in resistances. In calculating concentrations on a volume basis, it was assumed that the densities of the very dilute solutions were equal to that of the solvent. All weights were corrected to vacuum. The conductivity of a salt was calculated by subtracting the conductivity of the solvent from that of the solution. Two independent series of measurements of the conductance of each salt were made. Results and Discussion The measured equivalent conductances and the corresponding concentrations in moles per liter are summarized in Table I. These data were analyzed by (14) H. B. Thompson and S. L. Hanson, J. Phys. Chem., 6 5 , 1005 (1961). (15) J. W.Vaughn and P. G. Sears, ibid., 6 2 , 183 (1958). (16) M.A. Coplan and R. M. Fuoss, i b X , 6 8 , 1177 (1964). (17)H. B. Thompson and M. T. Rogers. Rev. Sci. Ine.fr., 27, 1079 (1956). (18) H. M.Daggett, E. J. Bair, and C. A. Kraiis, J. Am. Chem. Soc., 73, 799 (1951). (19) G.Jones and D. M. Bollinger, ibid., 57, 280 (1935). (20) J. E.Lind, Jr., J. J. Zwolenik, and R. M. Fuoss,ibid.,81, 1557 (1959).
CONDUCTANCES OF SOMEUNI-UNIVALENT ELECTROLYTES
907
Table I : Conductances of Salts in Adiponitrile a t 25'"'' 104c
A
104c
-NaI-. 2.461 10.23 16.50 24.88 37.10 2.245 4.418 8.944 14.95 23.38 35.56
12.07" 11.69 11.47 11.25 11.00 12.1Ib 11.96 11.74 11.53 11.31 11.05
-NaClO44.562 11.04 18.29 28.05 42.03 6.606 12.96 21.29 33.58 50.58
12.53" 12.21 11.94 11.67 11.34 12.43' 12.14 11.86 11.55 11.19
-MesPhNBr--. 2.778 12.38" 5.716 12.15 11.37 11.78 19.35 11.40 30.56 10.99 45.55 10.59 2.401 12.43b 5.202 12.19 11.65 11.76 19.29 11.40 30.79 10.98 46.66 10.56
104c
A
-KI1.337 9.093 15.74 24.69 37.72 4.441 9.874 17.15 27.72 41.78
12.92" 12.43 12.19 11.93 11.64 12.68' 12.40 12.14 11.85 11.57
-NaBPh44.535 9.013 14.68 22.95 34.52 5.116 9.306 15.30 23.81 35.44 -MeaPhNI2.382 9.796 17.16 27.08 41.17 1.993 4.846 9.693 17.19 26.40 40.54
-KSCN2.538 5.978 12.85 23.41 38.43 57.24 2.362 5.675 12.05 22.95 36.96 55.56
-EtrNBr8.68" 4.853 8.52 10.38 8.38 18.00 8.21 28.17 42.52 8.04 8.64' 3.893 8.50 9.272 16.43 8.35 25.61 8.18 39.18 8.02 12.83" 12.39 12.08 11.77 11.44 12.88' 12.65 12.37 12.08 11.78 11.46
-PrdNBr1.921 4.817 10.63 17.53 27.51 41.37 1.932 5.301 10.26 17.67 26.94 41.24
104c
A
15.36" 15.04 14.51 13.96 13.40 12.86 15.38* 15.03 14.56 14.01 13.48 12.94
-PraNI--2.181 5.026 9.937 16.86 26.16 39.55 2.180 4.980 9.756 16.43 25.62 38.80 -HexdNB3.434 6.978 12.44 19.69 29.21 43.57 2.262 4.764 9.011 16.31 24.50 37.04
12.44" 12.17 11.90 11.61 11.32 12.51* 12.22 11.95 11.68 11.38 11.33" 11.14 10.87 10.67 10.42 10.18 11.34' 11.11 10.90 10.67 10.44 10.19
Superscripts a and b designate series of determinations. Bu = n-butyl; Hex = n-hexyl; i-Am = isoamyl.
A
11.67" 11.49 11.27 11.05 10.82 10.57 11.68' 11.50 11.28 11.07 10.83 10.58 9.60" 9.44 9.26 9.08 8.90 8.69 9.65' 9.54 9.37 9.18 9.02 8.82
(GAm)8BuNBPha 7.149" 4.061 7.542 7.025 10.81 6.929 16.88 6.789 25.91 6.634 37.77 6.480 3.410 7.185* 7.262 7.041 10.622 6.940 16.84 6.797 25.56 6.644 6.490 37.38
' Ph
=
104c
A
---BuaNBr--2.545 4.851 9.616 16.01 24.71 37.59 2.560 4.869 9.745 16.53 25.54 38.50
10.53" 10.38 10.20 9.99 9.79 9.56 10.53' 10.39 10.19 9.98 9.77 9.55
-Hex4NI5.467 9.872 15.86 25.00 36.95 5.019 9.237 15.95 25.07 37.73
9.85" 9.66 9.49 9.29 9.09 9.86' 9.68 9.50 9.30 9.09
10'C
-Bu4NI--2.688 5.208 9.979 16.91 25.99 39.15 2.693 5.053 10.03 16.69 25.32 38.67
A
10.87" 10.72 10.52 10.31 10.09 9.86 10.87' 10.73 10.52 10.32 10.13 9.88
-(i-Am)3BuNI2.492 10.49" 6.160 10.30 10.14 10.15 16.84 9.95 25 84 9.75 38.91 9.52 2.978 10.47' 5.324 10.34 9.683 10.15 17.60 9.92 27.01 9.71 40.07 9.49
MeaPhNOaSPh 11.44" 1.816 5.125 11.12 10.00 10.84 17.20 10.51 27.10 10.17 40.88 9.79 1.535 11.49' 5.259 11.13 9.481 10.88 16.85 10.54 26.62 10.20 9.82 40.48
phenyl; Me = methyl; E t = ethyl; P r = n-propyl;
- K~Cynfz (2)
tions of salts in adiponitrile, the normally small viscosity corrections associated with J were omitted. The viscosity correction in each case has no effect on A. or on the association constant and, if applied, leads only t o slightly higher values for J and uo. For each salt the upper concentration limit was below the concentration a t which KU = 0.2. Calculations were made not only with unweighted values of A but also with
for associated electrolytes. I n these equations all symbols have their usual meanings.22 Owing to the lack of information concerning the viscosities of solu-
(21)R. M. Fuoss and L. Onsager, J. Phys. Chen., 61, 668 (1957). (22) R. M. Fuoss and 1.Accascina, "Electrolytic Conductance," Interscience Publishers, Inc., New York, N. Y., 1959.
the Fuoss-Onsager conductance equation21J2 which can be expressed as A =
A0
- SC"'
+ EC log C + J C
(1)
for unassociated electrolytes and as A =
A0
- S(CT:)''~+ E C y log C y + JCY
Volume 71,Number 4
March 1967
P. G. SEARS,J. A. CARUSO, AND A. I. POPOV
908
Table 11: Calculated Parameters of the Fuoss-Onsager Equation for Salts in Adiponitrile ao
KA
S
E
12.52f0.01 12.52f0.01
3 . 8 f0 . 1 4.0 f 0 . 1
0 0
24.81 24.81
75.9 75.9
181.6 188.8
0.004 0.001
13.26 f 0.01 13.26 f 0.004
3 . 5 i0 . 1 3.6 rt 0.03
0 0
25.45 25.45
81.4 81.4
181.1 182.2
b
0.004 0.002
15.93f0.03 15.89 f 0.01
3 . 4 =k 0 . 5 2.9 i 0 . 2
24 & 4 18 f 2
27.75 27.71
101.4 101.0
211.4 182.4
NaClOa
a b
0.005 0.005
13.15f0.01 13.16=kO0.O1
2.9 f 0 . 1 2.9 f 0 . 1
0 0
25.35 25.36
80.5 80.7
153.5 152.4
NaBPb
a b
0.004 0.003
9.17 f 0.01 9.15 f 0.01
5.2 i0.2 5.2 =k 0 . 1
0 0
21.92 21.90
50.8 50.6
172.3 173.5
EtdNBr
a b
0.003 0.002
13.05 f 0.007 13.06 f 0.004
3 . 3 f0 . 1 3.3 f 0 . 1
0 0
25.27 25.27
79.8 79.9
168.6 167.3
Me3PhNBr
a b
0.003 0.002
12.93 f 0.02 12.93f0.01
4 . 0 10 . 6 4 . 2 f0 . 5
27 f 4 28 f 3
25.16 25.16
78.9 78.9
197.0 202.7
Me3PhNI
a b
0.003 0.004
13.27 f 0.01 13.26f0.01
2 . 7 f0 . 1 2 . 8 f0 . 1
0 0
25.46 25.44
81.5 81.3
145.5 149.8
Pr4NBr
a b
0.003 0.003
11.70 f 0.01 11.71 f 0.01
3.9 f 0 . 1 3 . 9 10.1
0 0
24.10 24.11
69.7 69.7
173.8 174.3
PnNI
a b
0.003 0.004
12.08f0.01 12.08 f 0.01
4.0 f 0 . 1 3.910.1
0 0
24.42 24.43
72.5 72.6
182.4 180.0
BurNBr
a b
0.004 0.002
10.94f0.01 10.94 f 0.01
4.2 f0.1 4 . 2 10 . 1
0 0
23.44 23.44
64.0 64.0
171.9 172.3
BuaNI
a b
0.003 0.005
11.30f0.01 11.3O=kO0.01
4.1 f 0 . 1 4 . 2 10.1
0 0
23.75 23.76
66.7 66.7
173.7 177.2
HeaNBr
a b
0.004 0.006
10.06f0.01 10.05 f 0.02
4.4 f0.1 5 . 0 f 0.2
0 0
22.69 22.67
57.4 57.4
165.8 181.8
HeaNI
a b
0.002 0.005
10.40f0.01 10.40f0.01
4.4 f 0.1 4 . 5 10.1
0 0
22.98 22.98
60.0 60.0
169.8 173.4
(i-Am),Bu NI
a b
0.005 0.003
10.91f0.01 10.91f0.01
4 . 2 f0 . 1 4 . 1 f0 . 1
0 0
23.42 23.42
63.8 63.8
172.6 170.2
(i-Am)tBuNBPhr
a b
0.002 0.002
7.585 & 0.006 7.578 =k 0.005
4 . 9 i 0.1 4.9 10 . 1
0 0
20.55 20.55
38.9 38.9
138.4 138.4
MeSPhNOaSPh
a b
0.003 0.002
11.79 f 0.02 11.81f0.01
2.6 f 0 . 5 2.9 f 0.4
13 f 4 15 f 3
24.18 24.20
70.4 70.5
125.7 137.7
Salt
Series
uA
NaI
a b
0.004 0.004
KI
a b
KSCN
a
AQ
J"
' No viscosity correction applied.
values of A weighted by C. Since weighted data yielded a considerably better fit to the theoretical equations, as evidenced by much smaIIer values of uA, the final results are reported on that basis. The conductance parameters obtained from leastsquares analy988s8 of the data in Table I with respect to eq 1 and 2 using a CDC-3600 computer are summarized in Table 11. Included also in Table I1 are data for uA, the standard deviation associated with the
individual A values. The detailed results given in Table I1 are summarized in Table I11 where the result of the two series of measurements on each salt have been averaged by weighting each parameter inversely by its standard d e ~ a t i o n . (23),Dr. R. L. Kay of the MelIon Institute, Pittsburgh, Pa., kindly provided the FORTRAN program which was used in the treatment of our data.
CONDUCTANCES OF SOME UNI-UNIVALENT ELECTROLYTES
-
calculated; the results are summarized in Table IV. These data will reproduce the BOvalue for each of the salts within 0.01 unit. The potassium and sodium ions have limiting conductances between those of the trimethylphenylammonium and tetra-n-propylammonium ions; all other ionic conductances occur in the expected sequences.
Table I11 : Averaged Conductance Parameters for Adiponitrile Solutions Salt
NaI KI KSCN NaClOd NaBPh4 Et4NBr MesPhNBr MeaPhNI PrrNBr PsNI BuaNBr Bu~NI Hex4NBr Hex4NI (i-Am)3BuNI (i-Am)3BuNBPh4 MelPhNOaSPb
a0
An
12.52 13.26 15.91 13.16 9.16 13.06 12.93 13.27 11.71 12.08 10.94 11.30 10.06 10.40 10.91 7.58 11.80
3.9 3.6 3.1 2.9 5.2 3.3 4.2 2.7 3.9 4.0 4.2 4.2 4.6 4.4 4.1 4.9 2.8
KA
0 0 20 0 0 0 28 0 0 0 0
Table IV : Single-Ion Limiting Equivalent Conductances in Adiponitrile Based on Triisoamylbutylammonium Tetraphenylborate as Reference Electrolyte Ion
0 0
EtaN+ MeaPhN+ K+ Naf Pr4N + Bu~N + (i-Am)sBuN+ HexrN +
0 0 0 14
The constants a,p, El, and Ezfor adiponitrile at 25" have values of 0.8620, 14.014, 7.479, and 17.806, respectively, where S and E in eq 1 and 2 are defined by
S = aiio
+ /3;
E
=
Elno - E2
The A0 values listed in Table I1 consistently are 0.010.02 unit larger than those calculated using unweighted data and about 0.05 unit larger than the corresponding values obtained from preliminary Shedlovsky plots24 of A', vs. C. Calculation of the conductance differences at infinite dilution between corresponding bromides and iodides and between corresponding sodium and triisoamylbutylammonium salts indicates an uncertainty in A, values of 0.03 unit or about 0.3%. This apparent level of accuracy is nevertheless quite satisfactory in comparison to the results for most other nonaqueous systems and reflects the general consistency of the over-all results. Single-ion limiting equivalent conductances were obtained on the basis of the assumption that the limiting conductance of the triisoamylbutylammonium ion, shown by Coplari and Fuoss16to be equal to that of the tetraphenylborate ion in methanol, is the same m that of the latter in all solvents. That is b(i-AmsBuN+i = hO(BPh,-)
=
l/ZAO(i-AmsBuNBPhd
909
(3)
Using data for salts with common ions, limiting equivalent conductances of 14 ions in adiponitrile have been
A0 +
6.29 6.15 6.12 5.38 4.94 4.17 3.79 3.28
Ion
SCNc101IBrPhSOsBPh4-
XO
-
9.79 7.77 7.13 6.77 5.65 3.79
It is seen from the above results that adiponitrile is a good dissociating or smenocolyticz6 solvent, since only three of the seventeen salts studied show any ionpair association in the concentration range of to 5 X low3M . The relatively high viscosity is reflected in the low values obtained for the limiting conductance (e.g., A, value for Bu4NI is 11.30 as compared with 164.6 for the same salt in acetonitrile' and 101.72 in methanolz6). It is interesting to note that the dielectric constants of acetonitrile and methanol are very close t o that of adiponitrile (36.02 and 32.63 vs. 32.45 at 25'). The latter seems to have comparable and perhaps greater dissociating power, since it has been shown that tetraalkylammonium salts generally are very slightly associated both in acetonitrile' and in methanol.% Despite its high viscosity, therefore, adiponitrile should be a very useful solvent for the study of inorganic reactions. Acknowledgment. The authors are very grateful to Dr. Robert L. Kay for the use of his FORTRAN program in this investigation. (24) T. Shedlovsky, J. Am. Chem. Soc., 54, 1405 (1932). (25) R. M. Fuoss, J . Chem. Educ., 32, 527 (1955). (26) R. L. Kay, C. Zawoyski, and D. F. Evans, J . Phys. Chem., 69, 4209 (1965).
Volume 71, Number 4
March 1967
