Electrolytic Production of Lead Carbonate

Electrolytic production of white lead is based on this principle during this process the lead anode is immersed in a solution of alkali chlorate or acetate with a small quantity of alkali carbonate. In the course of electrolysis the lead is dissolved and forms at first a soluble chlorate or acetate the ions Pb++ diffuse and migrate into the bulk of the solution where the necessary amount of OH- and CO3 ions is found with which they react and precipitate as insoluble, basic lead carbonate. The solution is thus deprived of the carbonate ions which are then supplemented by a continuous absorption of carbon dioxide in the electrolyte. By using chromate, instead of carbonate chromium yellow is formed. Analogously also zinc white could be produced. 

In the case of nitrobenzoates, for example, it has been claimed that an acceleration of the cathodic partial process by reduction of the nitro group may lead, in addition to the effect of oxygen in the thin electrolyte layer, to a complete passivation of iron or ordinary steels. Contributions from the two parts of the dissociated molecule to the inhibitive effect is very likely and explains a synergistic effect of the inhibitor at the cathodic and anodic sites, as was suggested long ago. For example, it was shown by autoradiographic studies that the dissociation products of cyclohexylamine carbonate act separately on anodic and cathodic sites, with the former effect predominating. 

In 1898, Cowper-Coles 2 claimed to have successfully effected the electrolytic reduction of an acid solution of vanadium pentoxide to metallic vanadium, but the product was subsequently shown by Fischer 3 to have been a deposit of platinum hydride. Fischer, in a series of over three hundred experiments, varied the temperature, current density, cathode material, concentration, electrolyte, addition agent, and construction of cell, but in not one instance was the formation of any metallic vanadium observed. In most cases reduction ceased at the tetravalent state (blue). At temperatures above 90° C. reduction appeared to proceed to the divalent state (lavender). The use of carbon electrodes led to the trivalent state (green), but only lead electrodes produced the trivalent state at temperatures below 90° C. Platinum electrodes reduced the electrolyte to the blue vanadyl salt below 90° C. using a divided cell and temperatures above 90° C. the lavender salt was obtained. 

An alternative approach to synthesis of this ring system involves insertion of CO into the brominated secondary base (43), by treatment with carbon monoxide, lead tetra-acetate, and triphenylphosphine in tributylamine, the product being the amide (44), reduction of which affords the amine.81 Govadine (42 R1 = R4 = OMe, R2 = R5 = OH, R3 = H) has been synthesized by the conventional ring-closure, with formaldehyde, of the diphenolic base (45), or of its dibenzyl ether, in acid solution.82 Tetrahydroberberines, together with N-benzyltetrahydroisoquinolines, have also been obtained by the electrolytic reduction of 3,4-dihydroisoquinolines of structure (46).83... 

It will be seen from this equation that the dissolving component of the electrolyte, i. e. sodium acetate or chlorate, is continually regenerated in the course of the process. The sodium carbonate and hydroxide consumed in the reaction are supplemented by the migration of C(K and OH- ions from the catholyte. At the cathode made of lead or of iron hydrogen is liberated whereby the concentration of hydroxyl ions in the catholyte increases. In order to maintain their concentration within suitable limits and to replace the carbonate ions consumed in the production of white lead the eleotrolyte is continuously saturated by carbon dioxide thus converting the hydroxide to carbonate. 

While these experiments, which were carried out without giving a theoretical insight into the nature of the electrochemical reaction, yielded almost all the possible oxidation products in the oxidation of methyl alcohol, Elbs and Brunner 2 have discovered a method which gives 80% of the current yield in formaldehyde. This is exactly the substance which could not be proven present up to that time among the electrolytic oxidation products of methyl alcohol. Elbs and Brunner electrolyzed an aqueous solution of 160 g. methyl alcohol and 49 to 98 g. sulphuric acid in a litre. They employed a bright platinum anode in an earthenware cylinder, using a current density of 3.75 amp.1 and a temperature of 30°. Only traces of formic acid and carbonic acid and a little carbon monoxide, aside from the 80 per cent, of formaldehyde, were formed. Plating the platinum anode with platinum decreased the yield of formaldehyde at the expense of the carbon dioxide. With an anode of lead peroxide the carbon dioxide exceeded the aldehyde. 

One way of producing carbon nanomaterial in the condensed phase is the electrolytic conversion of graphite electrodes in a melt of alkali halogenides. Depending on the reaction conditions, various carbon nanostructures are formed especially in molten hthium chloride and bromide. In the apparatus shown in Figure 4.22, the depth of immersion and the amperage are the leading parameters to control whether MWNT, carbon onions, or amorphous material are the main product. Apart from that, the temperature is another important factor as carbon nanostructures wiU only be formed above 500 °C. The carbon onions observed in... 

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