Platinum cathode

Hydrazine is prepared, anhydrous and in good yield, by glow discharge electrolysis of liquid ammonia a platinum cathode is immersed in liquid and a platinum wire anode is mounted just... 

A mercury cathode finds widespread application for separations by constant current electrolysis. The most important use is the separation of the alkali and alkaline-earth metals, Al, Be, Mg, Ta, V, Zr, W, U, and the lanthanides from such elements as Fe, Cr, Ni, Co, Zn, Mo, Cd, Cu, Sn, Bi, Ag, Ge, Pd, Pt, Au, Rh, Ir, and Tl, which can, under suitable conditions, be deposited on a mercury cathode. The method is therefore of particular value for the determination of Al, etc., in steels and alloys it is also applied in the separation of iron from such elements as titanium, vanadium, and uranium. In an uncontrolled constant-current electrolysis in an acid medium the cathode potential is limited by the potential at which hydrogen ion is reduced the overpotential of hydrogen on mercury is high (about 0.8 volt), and consequently more metals are deposited from an acid solution at a mercury cathode than with a platinum cathode.10... 

Constant current procedure. With the exception of lead, which from nitric acid solutions is deposited on the anode as Pb02, the ions listed in Table 12.1 are deposited as metal on the cathode. With the ions indicated by an asterisk in Table 12.1, it is advisable to use a platinum cathode which has been plated with copper before the initial weighing this is because, in these cases, the deposited metals cannot be readily distinguished on a platinum surface and it is difficult to be certain when deposition is complete. 

Advisable to use a platinum cathode plated with copper before initial weighing see text. 

Supporting electrolyte. Prepare a supporting electrolyte composed of l.OOM pyridine and 0.50M chloride ion, adjusted to a pH of 7.0 0.2 for use with a silver anode, or LOOM pyridine, 0.30M chloride ion and 0.20M hydrazinium sulphate, adjusted to a pH of 7.0 0.2, for use with a platinum cathode. A small background current is obtained with the latter. 

Note. The above techniques are generally applicable to many other acids, both strong and weak. The only limitation is that the anion must not be reducible at the platinum cathode and must not react in any way with the silver anode or with silver bromide (e.g. by complexation). 

A selection of coulometric titrations of different types is collected in Table 14.2. It may be noted that the Karl Fischer method for determining water was first developed as an amperometric titration procedure (Section 16.35), but modern instrumentation treats it as a coulometric procedure with electrolytic generation of I2. The reagents referred to in the table are generated at a platinum cathode unless otherwise indicated in the Notes. 

The nature of the cathode material is not critical in the Kolbe reaction. The reduction of protons from the carboxylic acid is the main process, so that the electrolysis can normally be conducted in an undivided cell. For substrates with double or triple bonds, however, a platinum cathode should be avoided, as cathodic hydrogenation can occur there. A steel cathode should be used, instead. 

Let the electrolysis of dilute sulfuric acid (so-called electrolysis of water) with a platinum cathode and a platinum anode be considered next. Pure water is a very weak electrolyte and consequently a very poor conductor of electricity. It dissociates very slightly into H+ ions (it may be recalled that in fact, H+ ions does not remain as such but forms hydronium in H30+ by combining with a molecule of water, H+ + H20 H30+) and OFT ions. In the presence of little sulfuric acid (or for that matter any other strong electrolyte) the conductivity, i.e., ionization is greatly increased. The acidified water now contains H+ ions, OFT and SC3 ions. During electrolysis with platinum electrodes, H+ ions are attracted to the cathode, where each ion gains an electron and becomes a hydrogen atom ... 

To investigate heparin release in response to an electric current, the swollen heparin-polymer matrix was attached to a woven platinum cathode in a continuously stirred PBS solution (pH 7.4), and an electric current of 20 mA was applied. When the electric current was on, the polymer surface facing the cathode dissolved, thereby releasing heparin. The amount of heparin released was assayed by the Azure II method at pH 11 to prevent complexation of the two dissolved polymers. The release pattern of heparin showed a complete on-off profile in response to the applied electric field, as shown in Figure 23 [50],... 

Coleman, Kobylecki, and Utley studied the electrochemical reduction of the conformationally fixed ketones 4-tert-butylcyclohexanone and 3,3,5-tri-methylcyclohexanone 82>. Stereochemically, the cleanest reductions took place at a platinum cathode in a mixture of hexamethylphosphoramide and ethanol containing lithium chloride. Under these conditions the equatorial alcohol predominated heavily (95% from 4-fer/-butylcyclohexane and 91% from 3,3,5-trimethylcyclohexanone).In acidic media roughly equal quantities of axial and equatorial alcohol were produced. It was suggested that organo-lead intermediates are involved in the reductions in aqueous media. This is reasonable, based upon the probable mechanism of reduction in acid 83F Reductions in acid at mercury cathodes in fact do result in the formation of... 

Benkeser and Tincher 128>, on the other hand, reduced acetylenes preferentially to trans olefins using solvated electrons generated at a platinum cathode by electrolytic reduction of lithium chloride in methylamine [lithium metal is formed from lithium ion at the cathode in this electrolysis its dissolution in methylamine generates the solvated electron and regenerates lithium... 

Some experiments indicate that the cathode reaction may be due to eh at least, it is an open question (Walker, 1966, 1967 Hills and Kinnibrugh, 1966). Walker (1966), using platinum cathode, found that N20 reduces the H20 by about 65% but further addition of 0.1 M methanol did not change the N2 /H2 ratio. The result may be explained by the cathodic reaction... 

The miniature PHSS design was based on the original design of the macro PHSS [41], The 2 mm diameter PHSS utilized a cylindrical polished-tip platinum anode that was electrically insulated along the side from a platinum cathode that was coiled around the core (Fig. 8.3). The core was housed in a 2mm outside diameter stainless steel cylindrical sleeve that served as an electrical shield and to which a 25 om thick H2S-permeable membrane was fixed to cover the tip. The reservoir between the sleeve and core... 

An interesting example is the electrolysis of alkyl halides on tin anodes and platinum cathodes which yields dialkyltin dihalides. The current yield is extremely high, Ca 5 g... 

The electrolysis of alkyl halides on platinum cathode and tin anode has been mentioned above. A completely different mechanism is associated with alkylation on tin cathodes. Electroreduction of allyl bromide on tin electrodes yields tetraallylstannane (Ca 90%). This is done in acetonitrile solutions with LiClC>4, Et4NBr or BujNBr as electrolyte and followed by CV with Ag/AgBr reference. Yields decrease to 78% in DMF. The proposed mechanism67 in this case is ... 

Allred et al. studied the electrochemical reduction of Me3SiCl in acetonitrile using a platinum cathode [82], They reported that the choice of the supporting electrolyte is important for the formation of the disilane. When Bu4NC104 was... 

Kunai and Ishikawa et al. have reported that electrolysis of monochloro-silanes in 1,2-dimethoxyethane using a platinum cathode and a mercury anode gives disilanes in high yield (Scheme 40) [84]. Silver can also be used as an excellent anode material in place of mercury. The electrolysis of a mixture of two different monochlorosilanes produces unsymmetrical disilanes. Trisilanes can also be synthesized by the electrolysis of a mixture of monochlorosilanes and dichlorosilanes. They also reported that the use of copper electrodes is effective for the synthesis of disilanes, trisilanes, tetrasilanes, and pentasilanes [85]. 

Fig. 10-26. Energy diagram for a cell of photoelectrolytic decomposition of water consisting of a platinum cathode and an n-type semiconductor anode of strontium titanate of which the Fermi level at the flat band potential is higher than the Fermi level of hydrogen redox reaction (snao > epM+zHj) ) he = electron energy level referred to the normal hydrogen electrode ri = anodic overvoltage (positive) of hole transfer across an n-type anode interface t = cathodic overvoltage (negative) of electron transfer across a metallic cathode interface.

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