M. DELLA MONICA,U. LAMANNA, AND L. SENATORE
2124
1p
Q
The main feature of the structure is thus the overcrowding of bromine atoms in cis relationship which leads to distortion of the cyclobutane ring and is also reflected in the irregular shape of the quinoid ring. The complete molecular conformation is shown in Figure 7. It is interesting to note that this arrangement has been reached only by a distortion of the butane ring and does not involve a lengthening of the C-Br bonds. Within experimental error these correspond in length with the mean C-Br distance of 1.937 f 0.003 d in polyhalogenated methanes. l4 The lengthening of the central C-JC bonds predicted by Kitaigorodskii'o and by Glocker" is also not observed, and, apart from its nonplanarity, the cyclobutane ring can be described as a normal single-bonded four-membered ring.
Figure 7. Perspective view of the molecule to illustrate its conformation.
crowding, the cyclobutane ring is tetrahedrally distorted. The parameters J. and 4, which have the values 54.5" and 45" in the regular centrosymmetric structure, have the values +2 = 36", 42 = 28" and $3 = 59", 43 = 36" at C(2) and C(3), respectively. The equilibrium separation of the two bromine atoms in cis relationship is increased by this distortion to 3.370 -f 0.004 d. Although significantIy Iess than 3.,8 A, this distance is comparable to the 3.377 f 0.004 A between bromine atoms in l,2,4,5-tetrabromobenzene.la
Acknowledgment. The authors wish to thank Dr. J. Dekker of the Department of Chemistry, Potchefstroomse Universiteit vir Christelike Hoer Onderwys, Potchefstroom, South Africa, who synthesized the compound and supplied us with the crystals. (16) G. Gafner and F. H. Herbstein, Acta Crystallogr., 13, 706 (1960). (17) G. Glocker, J . Phys. Chem., 61, 31 (1957).
Transport Numbers and Ionic Conductances in Sulfolane at 30" by M. Della Monica, U. Lamanna, and L. Senatore Istituto d i Chimica fisica, U n i m s i t h d i Bari, Bari, Italy Accepted and Transmitted by The Faraday Society
(November 16, 1967)
The transport number of C104- ion for four different concentrations of AgC104 in anhydrous sulfolane at 30" was determined using the Hittorf method. From measured values of the equivalent conductance, values of A- for C104- ion were determined at each concentration. With a suitable equation, Xo- for C104- ion was calculated. From the Iimiting equivalent conductances of severaI salts in sulfolane, ionic conductances A0 for some ions were derived.
Introduction I n a previous paper1 we reported the equivalent conductances at infinite dilution of lithium, sodium, potassium, rubidium, cesium, and ammonium perchlorates in sulfolane (tetramethylenesulfone) at 30". Subsequent measurements2 of the equivalent conductances of sodium, potassium, rubidium, and cesium thiocyanates have shown the applicability of Kohlrausch's law of the independent ion migration in this solvent. The present work was undertaken to measure the transport numbers of perchlorate ion in sulfolane The Journal of Physical Chemistry
solutions of silver perchlorate and, consequently, to obtain the equivalent conductances of the ions.
Experimental Section The silver perchlorate used was recrystallized from conductivity water and dried at 110" under reduced pressure. Sulfolane, kindly supplied by Shell Italiana, was distilled from solid sodium hydroxide under reduced (1) M. Della Monica, U. Lamanna, and L. Jannelli, Gazz. C h h . Ttal., 97, 367 (1967). (2) M. Della Monica and U.Lamanna, (bid., in press.
TRANSPORT NUMBERS AND IONIC CONDUCTANCES IN SULFOLANE pressure (10-4 torr) until its conductivity decreased to 2.0 X lo-* ohm-' cm-l. The Hittorf method was applied using the apparatus described by W a ~ h b u r n with , ~ a modified form of the two electrodes. The cathode and the anode were made from two spirals (I = 12 cm, h = 1 cm) of silver wire gauze sealed to a silver wire passing through the glass stopper. The gauze was covered with a spongy coating of silver by decomposition of silver oxide a t 400". The electrodes were cleaned by having them stand overnight in conductivity water and were subsequently dried for 1 hr a t 150". Stock solutions of four concentrations of AgC104 were prepared by weighing both the solute and the solvent; all weights were corrected to their values under vacuum. I n order to obtain the concentrations in equivalents per liter, the density of each solution was determined at 30" by pycnometric weighings (see Table 11). The preparation of solutions and filling of the apparatus were carried out in a dry nitrogen box. The apparatus was then placed in a water bath a t 30 & 0.01". A modified form of coulometer was used (see Figure 1). The anodic compartment was separated from the cathodic compartment, and a glass tubing ( i d . 2 mm) filled with solution was used as the electrical connection. Silver perchlorate was cliosen as the most suitable electrolyte, because the use of the silver covered with silver halide electrodes in halide solutions was unf e a ~ i b l e . ~The cathode was placed at the upper end of the apparatus since the solution around it became more dilute during the electrolysis. The range of current and time of electrolysis were strictly dependent upon the conductivity of the solution. Since the conductivity of silver perchlorate in sulfolane is small (Ao g 11.5)) 84 V was applied to the apparatus. I n order to detect a suitable change of concentration at the electrodes with the most dilute solution of AgC104, an electrolysis time of 36 hr (current = 0.8 mA) was required. I n the other extreme case, the time was 21 hr and the current was 3 mA. We made certain that, in each case, the concentrations of the cathode and anode middle portions did not change during the time of electrolysis. I n fact, for the most dilute solution, a change in the middle portions was detected only after 48 hr. Analyses of the solutions were made with a standard solution of potassium iodide in sulfolane6 according to the differential potentiometric method described by Mac Innes and Dole.6
Results and Discussion The relevant data for four concentrations of AgC104 are summarized in Table I. Transport numbers were obtained by averaging the anodic gain and the cathodic loss; the measurements were repeated for each concentration, and the average deviation from the mean transport number for two runs was &0.0005.
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+
7
Figure 1. Silver coulometer.
The equivalent conductance A of AgC104 measured on a Jones and Josephs bridge (Leeds and Northrup) at the frequency of 2500 Hz, together with the calculated conductance of C104-, is reported in Table I1 for each concentration. The experimental change of equivalent conductance of C104'' with concentration was analyzed using the equation proposed by Shedlovsky7 for uni-univalent electrolytes, in a modified forms applicable to the equivalent conductance of a single ion
where A-, Xo- are the equivalent conductances of the Clod- ion, a and /3 are the coefficients of Onsager's equation (0.546 and 7.30, respectively, in sulfolane at 30"), c is the concentration in equivalents per liter and b is an empirical parameter to be determined. Plotting the value of Xo' = (Al/&di)/(l a&) = Xobc vs. c, the equivalent conductance at infinite dilution can be obtained by linear extrapolation (see Figure 2). The straight line follows the equation
+
+
io' = 6.685
+ 5.445~
(2) obtained by applying the least-squares method. The values of A- (calculated from eq 2) are reported in the last column of Table 11. The agreement between experimental and calculated values is very good. The equivalent limiting conductances ha for a series of ions, calculated by means of the value of Xo- of c104ion, are collected in Table 111. (3) E.W. Washburn, J. Am. Chem. Soc., 31, 322 (1909). (4) M. Della Monica, U. Lamanna, and L. Senatore, submitted for publication. (6) The titrations of silver ion in sulfolane will be fully described elsewhere. (6) D. A. Mac Innes and M. Dole, J . Am. Chem. Soc., 51, 1119 (1929). (7) T. Shedlovsky, ibid., 54, 1405 (1932). (8) D. A. Mac Innes, T. Shedlovsky, and L. G. Longsworth, ibid., 54, 2758 (1932). Volume 72, Number 6 June 1068
M. DELLAMONICA, U. LAMANNA, AND L. SENATORE
2126
Table I: Data Concerning Determinations of Transference Numbers of Silver Perchlorate in Sulfolane a t 30" Concentration, N Amperes Time of electrolysis, hr Transference no.] lolor-( anode) Transference no., tclo,-( cathode) Mean value, tclo4Mean value, tclo, for two runs
0.02
0.02 0.0008 36 36 0.5935 0.5947 0.5944 0.5940 0.5940 0.5944 0.5942
0.0008
0.05 0.05 0.0015 0 0015 26 24 0.6080 0.6074 0.6078 0.6O70 0.6078 0.6072 0.6075 I
0.07 0.07 0.0025 0.0025 23 23 0.6164 0.6155 0,6156 0.6161 0.6160 0.6158 0.6159
0.1 0.1 0.0030 0.0030 23 21 0.6199 0.6210 0.6207 0.6204 0.6203 0.6207 0.6205
Table I1: Summary of Transference and Conductance Measurements on Silver Perchlorate in Sulfolane a t 30"
cx
x-1
A -,
102
Density
A
t-
obsd
oalcd
9.4829 7.4317 4.9442 2.0065
1.2775 1.2743 1.2703 1.2655
7.843 8.181 8.724 9.679
0.6205 0.6159 0.6075 0.5942
4.867 5.039 5.300 5.751
4.868 5.041 5.299 5.752
=el
Table I11: Limiting Ionic Equivalent Conductances in Sulfolane a t 30' Cation
Li + Na
+
K+ Rb + Cs + 4"
+
EtrN + Reference 1.
b
XO +
Anion
4.33" 3.61" 4.05" 4.16" 4. 27a 4.97" 3.98"
c104SCNClBr-
Reference 2.
IPFs-
651 A0
-
6.685 9 . 64a 9 . 3OC 8.9ZC 7.22O 5.950
Reference 9.
From a survey of Table I11 one can see the regular trend of the limiting ionic conductances from sodium to cesium, whereas the lithium ion has an anomalously high conductance greater than that of the cesium ion. This result is in agreement with the limiting equivalent conductance for the series of alkaline metal perchlorates in sulfolane recently reported,* but it contrasts with the normal behavior of the conductance in other solvents such as water,lO methanol," formamide,12 dimethylformamide,13 dimethyl sulfoxide,'* and pyridine. 1s*16 The conductance of lithium ion is slightly greater than that of sodium ion only in liquid hydrogen cyanide" ( X o , t i + = 135.5; X ~ , N * + = 132.4). Furthermore, in Table I11 it may be observed that the conductivity sepsibly increases in the series from
The Journal
of
Physical Chemistry
R02
0.04
0.06
0.08
I
0,l
c, equtv/l,
Figure 2. Plot of A'a us. normality of AgClOd.
I- to C1- ions, whereas in the previously mentioned solvents these anions have practically the same conductivity. At the present time we do not have a satisfactory explanation of these facts. We think that more work is needed to explain fully the behavior of these ions in sulfolane. (9) R.Fernandez-Prini and J. E. Prue, Trans. Faraday Soc., 62, 1257 (1966). (10) R. A. Robinson and R. H. Stokes, "Electrolyte Solutions," Butterworth and Co. Ltd., London, 1959,p 463. (11) R. E. Jervis, D. R. Muir, J. P. Butler, and A. R. Gordon, J. Am. Chem. SOC.,75, 2855 (1953). (12) J. M. Notley and M. Spiro, J . Phya. Chem., 70, 1502 (1966). (13) J. E. Prue and P. J. Sherrington, Trans. Faraday Soc., 57, 1795 (1961). (14) J. N.Butler, J. Electroanal. Chem., 14, 89 (1967). (15) D. 6 . Burgess and C. A. Kraus, J . Am. Chem. Soc., 70, 706 (1948). (16)The values of the ionic conductances in dimethyl sulfoxide, pyridine, and hydrogen cyanide are not accurately known for the lack of data of transport numbers. In these cases the ionic conductances were obtained by applying the Walden rule to the limiting conductances of salts of large organic ions. (17) J. E. Coates and E. G . Taylor, J. Chem. SOC.,1245 (1936).
