Electrochemistry in the Dry Box

Steven N. Frank Texas Instruments, Dallas, Texas 

Su-Moon Park The University of New Mexico, Albuquerque, New Mexico 

Controlled atmospheres are employed in electrochemistry whenever oxygen, water, or other constituents of the air may interfere with the reaction under study. The problem is basically twofold to supply and contain an atmosphere of suitable composition, and to exclude air. For our present purposes it is sufficient to confine the discussion to inert atmospheres that is, gases devoid of oxygen and water (and sometimes nitrogen). The use of high-purity argon, helium, or nitrogen is most common. 

The advantages of using a dry box over vacuum techniques may be summarized as follows  

Dry-box procedures are often simpler than vacuum-line techniques. 

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As we have pointed out previously, oxygen and water concentrations can be kept at extremely low levels with a properly maintained purification train. In fact, contamination by water is much more easily controlled in a dry box than on a vacuum line. This may result in part from the number of operations and manipulations necessary to use a vacuum line. The oxidation of the cation radical of thianthrene to the dication illustrates this point. The dication is very electrophilic and is rapidly attacked by any nucleophiles (e.g., water). The electrochemistry of the dication in solutions prepared in the dry box (with acetonitrile as the solvent purified as described earlier) is reversible if a little care is taken in preparing the solvent and in drying the glassware. It is more difficult to obtain such reversible behavior when solutions are prepared on a vacuum line. 

Although there are several classes of dry boxes as described earlier, we limit our discussion to the considerations involved in using a fairly sophisticated dry box equipped for gas recirculation through a purification train and including an evacuation transfer chamber. The dry box will also provide for automatic control of the gas pressure within the box. These features make a dry box especially well suited for carrying out high-quality nonaqueous electrochemistry with a minimum of effort. 

Figure 19.2 Typical dry box suitable for high-quality electrochemistry. The purification train, recirculation unit, and automatic pressure control system are housed in the unit beneath the dry box. [Courtesy of Vacuum/Atmospheres Corporation, Hawthorne, CA.]...

Dry boxes also offer significant advantages over vacuum line techniques in the study of mixed-solvent systems. It is difficult to mix two different solvents accurately on a vacuum line. In a dry box, the procedure is rendered almost trivial. Definite advantages of a dry box can also be envisioned for electrochemistry in low-temperature molten salts, which are often very hygroscopic. 

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