A Conductance Study of 1-1
Electrolytes in Propylene Carbonate
A Conductance Study of 1-1 Electrolytes in Propylene Carbonate Murray L. Jansen and Howard L. Yeager" Department of Chemistry, The University of Calgary, Calgary, Alberta, Canada (Received July 26, 7973) Publication costs assisted by the National Research Council of Canada
Precise conductance measurements are reported for alkali metal and tetraalkylammonium halides and perchlorates in propylene carbonate. Analysis of the data by an extended form of the Fuoss-Onsager conductance theory indicates negligible ion pairing. Single ion conductivities were derived using the reference electrolyte (i-Am)rN(i-Am)4B. Ion mobilities are discussed in terms of the Boyd-Zwanzig equation and the solvent properties of propylene carbonate.
Introduction Propylene carbonate (PC) is an interesting dipolar aprotic solvent in several respects. It has a wide liquid range (mp -49.2"; bp 241.7"), high dielectric constant (64.92 a t 25"),l and is inert toward reducing materials such as lithium metal. PC appears to be a relatively unstructured liquid1q2 as evidenced by a Trouton constant of 23 and a Kirkwood correlation factor of unity (g = 1.01 at 25").' Several studies of ionic solvation thermodynamics in this solvent have been r e p ~ r t e d . ~The - ~ results indicate that PC has moderate Lewis base and weak Lewis acid properties, and it has served as a useful reference for comparison of ionic solvation parameters among solvent^.^ Electrolytic conductance measurements are also important in order to characterize ionic solvation processes, but few studies have been reported in PC.3a,8-11 Of these, only Mukherjee and coworkerslo-ll have studied a relatively wide variety of salts with high precision methods. However, lack of internal consistency among several salts suggests large systematic errors. For example, the Kohlrausch difference between the perchlorate and the chloride salts of lithium is +1.42, but the corresponding difference for the tetraethylammonium salts is -0.42. This represents possible errors of over 5% in reported limiting equivalent conductances. We have, therefore, repeated some of this work and have measured the conductances of several additional alkali metal and tetraalkylammonium salts in PC. Single ion conductivities have been derived using the reference electrolyte tetraisoamylammonium tetraisoamylboride. The results are interpreted in terms of the cation and anion solvating ability of PC and comparison is made with results obtained in other dipolar aprotic solvents. q 4 q 7
Experimental Section Reagents. Propylene carbonate (Jefferson Chemical Co.) was stirred over molecular sieves (J. T. Baker Type 5A) for 48 hr and then distilled using a 1.5-m vacuum-jacketed column packed with nichrome helices (Podbielniak, Inc.). The column was operated a t a reflux ratio of lO:l, with a stillhead temperature of 80" at 1-mm pressure. Only the middle 60% of the distillate was used. Water content of the purified product by Karl Fischer titration was
