Mercury cathodes, replacement

The Kolbe reaction is earned out in an undivided cell with closely spaced platinum electrodes. Early examples used a concentrated, up to 50 %, aqueous solution of an alkali metal salt of the carboxylic acid and the solution became strongly alkaline due to hydrogen evolution at the cathode. Ingenious cells were devised with a renewing mercury cathode, which allowed removal of alkali metal amalgam. These experimental conditions have been replaced by the use of a solution of the carboxylic acid in methanol partially neutralised by sodium methoxide or trieth-... 

Several methods are employed for the reductive defluorination of 2-fluoro-l-phenyl-ethanones. Electrolytic reduction at a mercury cathode selectively replaces fluorine in 2-fluoro-l -phenylethanone by hydrogen.94 The hydrodefluorination of fluoroacetophenones, e.g. 7, to dithioacetals of the corresponding defluorinated ketones with aluminum chloride and ethanethiol take place readily by stirring the mixture in dichloromethane at 0°C under nitro-... 

Replacing the Mercury Cathode. Professor Martin and his colleagues undertook an entrepreneurial evaluation of alternative cathode materials and process conditions using the new sulfoxide substrate. They identified tin as the closest to mercury. Dr. David Genders proposed that a greatly increased surface area of the cathode would help to increase the yield of the desired exomethylene sulfoxide and speed the reaction. This indeed proved to be the case. 

The electrode assembly shown (Figure 1) is fairly versatile and has been used by the submitter in flasks with electrolyte volumes of ca. 40 mL to 4 L. Additionally, the platinum electrodes may be replaced by other electrodes that fit directly into the thermometer adaptor, e.g., commercially available A in. graphite or stainless-steel rods. In the present example the electrodes are positioned vertically and are of opposite polarity. In other cases they may be positioned horizontally (parallel to a mercury cathode) and are both anodic. 

Calcium was first isolated by Sir Humphry Davy in 1808. Davy produced calcium amalgam by electrolyzing an aqueous solution of the chloride, CaCl, using a liquid-mercury cathode such as in the chlor-alkali process employing a mercury cathode. After distilling mercury from the amalgam formed, he obtained the pure calcium metal. His discovery showed lime to be an oxide of calcium. Later, Moissan reduced the calcium diiodide with sodium. The first industrial production of calcium metal was reported in 1904 and attributed to Brochers and Stockem, who prepared it by electrolysis of the molten chloride. This process was discontinued in 1940 and replaced by aluminothermic reduction of the oxide. 

Castner-Kellner process A process once used to produce chlorine and sodium hy-droxidebythe electrolysis of sodium chloride solution. The electrolysis took place in a cell with a mercury cathode and graphite anode. The cell consisted of three compartments with a common bed of mercury and solution of sodium chloride above. The cathode was in the central com partment and anodes in the other two. It was invented independently by American industrial chemist Hamilton Young Castner (1858-99), who was working in the UK at the time, and Austrian chemical engineer Karl Kellner (1851-1905). The process was abandoned due to concerns over mercury pollution and replaced by various diaphragm-based electrolytic processes. 

A serious drawback of the experimental techniques, like the one proposed in Reference 105, lies in that neither the cathode nor the solution can be replaced in the course of the experiment, and hence it is impossible to verify the reproducibility of the results. In view of this, we decided to use a technique similar to the one described in Reference 102, where the final purification of the solution was carried out electrolytically with the help of an auxiliary mercury cathode. 

Indium chemicals and electroplated metal deposits ate replacing mercury (qv) in the manufacture of alkaline batteries (qv). Indium, like mercury, functions to reduce outgassing within the battery and promotes the uniform corrosion of the anode and cathode while the battery is under electrical load. Indium inorganic chemicals also find use as catalysts in various chemical processes. 

Recently, using very small currents, Bowden has found capacities of the order 20 / f. per sq. cm. for mercury.8 The balance of evidence therefore is that a cathodically polarized surface, whose real area is equal to the apparent area, has a capacity of about 20 /Ltf. per sq. cm. and this is lowered by organic substances. We may perhaps regard the lowering of capacity by adsorbed organic substances as the replacement of a surface... 

Since the synthetic membrane of membrane cells replaces the older asbestos fiber diaphragm cells, no control precautions are necessary. Graphite (or later, titanium) cathodes avoid the use of mercury eliminating the need for mercury control. However, if membrane cells are operated on the same site as mercury cells, they do require a separate brine circuit from the mercury cells to maintain their mercury-free status. 

---