Cathode additives

Cathodic additions (such as copper and chromium) to low-alloy steels influence the rate of rusting by raising the potential of the surface to more noble values so encouraging passivation Electrochemical measurements certainly seem to bear this out and they have been used in attempts to develop improved compositions . ... 

This method K4 yields a reduction or cathodic additional current owing to the pulse increase with a current maximum around E analogously, K3 yields an oxidation or anodic additional current owing to the pulse decrease with a current minimum around E. Both additional currents are depicted in Fig. 3.52 for a completely reversible redox system the cathodic maximum and the anodic... 

Scheme 65 Heterocycles by Nickel catalyzed intramolecular cathodic addition of halides to double bonds.

Fig. 16 Regioselective cathodic addition of allyl substituted allyl halides to carbonyl compounds [93].

Fig. 17 Regioselective cathodic addition of prenyl chloride to a, yS-unsaturated esters [94].

Cathodic addition involves either the reduction of a 7T-system in an ECEC process (electrochemical, chemical, electrochemical, chemical) and the chemical reaction (C) of the intermediates with a carbon or heteroatom electrophile or the cathodic conversion of a C—X bond in an ECE process into an anion that adds to an electrophilic jr-system. The electrochemical Birch reduction of arenes... 

Fig, 18 Regioselective cathodic addition of propargyl bromides to aldehydes [106]. 

Halides The nickel-catalyzed cathodic addition of (Z)- or ( )-alkenylhahdes to electron-deficient olefins in the presence of a sacrificial iron rod anode proceeds with complete retention of... 

Scheme 90 Cathodic addition of ethyl bromide to 2-methyl-l -penten-3-one.

Scheme 157 Palladium-zinc-mediated cathodic addition of allyl acetate to carbonyl compounds.

Dibromobutane affords 29 % cyclobutane along with butane and butene at a vitreous carbon cathode. Addition of l,l,l,3,3,3-hexafiuoropropan-2-ol as a proton... 

Cathodic addition reactions are of great preparative value, since the general scheme (9) of course accommodates the synthetically important reduction of unsaturated compounds ... 

In cathodic addition reactions solvated electrons, radical anions or anions are generated at the cathode and added to activated or unactivated double or triple bonds. This broad spectrum of reactions is partially treated a) in section 8.2 when group conversion generates a reactive intermediate which undergoes addition reactions 1 S5a,b and b) in section 12.2 when olefins are coupled via addition of a cathodically generated radical anion to an activated double bond. 

In a cathodic addition reaction two electrophile molecules add across a double bond or system of double bonds with addition of two electrons [eqn (16)]. The most important reaction here is... 

No doubt the reader by now suspects that one can create the worst possible set of complications by mixing eqns (32) and (33) as done previously for cathodic addition [eqn (23)]. It is, however, highly improbable that such a reaction would proceed with anything near selectivity toward the formal product, and hence we refrain from considering it. As far as we are aware, no such case is known. 

Iron always contains a small amount of carbon and other impurities unless it is specially prepared, say for spectroscopic purposes. The impurities are dissolved during production, phosphorus and sulphur from the ore, silicon and carbon from the limestone and coke. Silicon and carbon do not greatly reduce the corrosion resistance of iron when present in small quantities. Sulphur, however, may increase corrosion rates if allowed to precipitate as FeS. Crystals of FeS have a fairly high conductivity and can act as local cathodes. Additions of small amounts of manganese to the melt will cause the formation of MnS rather than FeS, the former being a poor conductor. 

Cathodic addition of trichloromethylbenzene to ketones gives or.yS-unsaturated ketones [139]. Methyl esters of trifluoromethylbenzoic acid can be defluorinated by reduction at lead cathodes in MeOH [140,141]. Fry and Touster [142] have reduced a benzal halide at stainless steel in DMF containing trimethylchlorosilane to synthesize both the (cy-halo-benzyl)silane and the benzal disilane. 

Aryl radicals that are generated by cathodic reduction of aryl halides have been added to phenols [167]. With aromatic radical anions as mediators, the follow-up reduction of aryl radicals can be suppressed, which enables the cathodic addition of... 

The cathode formulations further employ metallic catalysts to promote the recombination of hydrogen gas generated within the zinc anode at very low (0.025 %) or zero mercury content [41,42,43]. The hydrogen scavenger can form a discrete auxiliary electrode in electronic contact with the cathode or can be introduced simply as a cathode additive in a ratio of 30/70 in the cathode preparation process. A very reliable catalytic material even at elevated temperatures (65°C) is Ag20. The auxiliary electrode may be an annulus or a disk of similar... 

As seen from this table, the result of electrochemical aging for all the studied electrodes was a decrease in the specific surface area and the micropore volume herewith, these changes in the anode are much greater than in the cathode. Additional studies showed that a decrease in the volume of micropores and mesopores is the consequence of their degradation and also the result of their clogging up by the products of decomposition of electrolyte. AC made of a synthetic precursor (sample C) shows the high structural stability as compared to ACs made of natural precursors (samples A and B). 

The LUMO/HOMO relationship of solvents for 3-V hthium metal battery and 4-V LIB for anode and cathode additives is shown in Fig. 19.7. Solvents for a lithium metal battery - which are mostly ethers - should be stable against lithium metal anode and therefore their LUMO values should be high. The solvents - mainly cyclic and chain carbonates - for 4-V LIB have lower HOMO values, which means they are strong against oxidation. A modified version of the software was used for MO calculation, so the data for additives may differ from values from the usual commercial software. The relation between HOMO and LUMO values for first-generation additives (candidate for anode additives) and second-generation additives for candidate of cathode were calculated using the modified MO theory and are shown in Fig. 19.7. These calculations were used to SCTeen the candidates to identify additives. 

Fig. 19.7 Classification of solvents for lithium-metal battery, for 4-V LIB, for anode and cathode additives by the MO theory...

---