Except for a study of the behavior of inorganic ions in sulfolane (tetrahydrothiophene-l,l-dioxide) 1, all of the polarographic investigations conducted to date in organic sulfoxo solvents have been in dimethyl sulfoxide. In this study, we have examined the electrochemical behavior of copper(II) and copper(I) ions in dimethyl O sulfoxide ((CHa)2SO), diethyl sulfite (C2HsOSOC2Hs), sulfolane /~ ~)o2/ , 2,4-dimethylsulfolane /~so, ) 3-methylsulfolane (~) , , methyl methanesulfonate O O (CH3SOCH3), and diethyl sulfate (C2HsOSOCzHs). The information on the rela-O O tive order of solvation of copper ions in these solvents provided by the electrochemical study is consistent with nuclear magnetic resonance and infrared spectral data on the coordinating ability of these solvent molecules and the dielectric constant of the solvents--in governing ion-association.
EXPERIMENTAL
Dimethyl sulfoxide (Crown Zellerbach) was purified by two distillations under reduced pressure over calcium hydride, the first and last 10% of the distillates being discarded. Sulfolane (courtesy of Shell Chemical Co.), 2,4-dimethylsulfolane (Aldrich Chemical Co.), and 3-methylsulfolane (Aldrich Chemical Co.) were purified by the following adaptation of the method of Jones z : distillation below 100 Β° under reduced pressure (a) over crushed sodium hydroxide, (b) after treatment with hydrogen peroxide and sulfuric acid and removal of remaining hydrogen peroxide and water (500 ml of sulfolane with 25 ml of 30 ~ H 2 O2 and 25 ml of 96~o H~S O4), (c) from solid sodium hydroxide, and (d) twice from calcium hydride. Methyl nlethanesulfonate and diethyl sulfite, both from Aldrich Chemical Co., and diethyl sulfate, from Matheson Coleman and Bell, were distilled twice in vacuo, with the sulfate distilled over anhydrous sodium sulfate. Preparation of methyl methanesulfinate was attempted by the method described by Douglass 3. Methanesulfinyl chloride was prepared first, then converted to the sulfinate. Despite several attempts, only a small amount of product was obtained. Spectroquality carbon tetrachloride (Matheson Coleman and Bell) was used without further purification.
Copper(II) perchlorate 6-hydrate (G. F. Smith Chemical Co.) was dried at 85 Β°