Sodium carboxylates, electrolytic

Foreign cations can increasingly lower the yield in the order Fe, Co " < Ca " < Mn < Pb " [22]. This is possibly due to the formation of oxide layers at the anode [42], Alkali and alkaline earth metal ions, alkylammonium ions and also zinc or nickel cations do not effect the Kolbe reaction [40] and are therefore the counterions of choice in preparative applications. Methanol is the best suited solvent for Kolbe electrolysis [7, 43]. Its oxidation is extensively inhibited by the formation of the carboxylate layer. The following electrolytes with methanol as solvent have been used MeOH-sodium carboxylate [44], MeOH—MeONa [45, 46], MeOH—NaOH [47], MeOH—EtsN-pyridine [48]. The yield of the Kolbe dimer decreases in media that contain more than 4% water. 

Many acrylic acid copolymers are water-soluble but unlike poly(vinyl alcohol) they are not degraded by alkali. In fact they need alkali for effective desizing as they are more soluble at alkaline pH than in neutral solutions. They are sensitive to acidic media, which should not be used. Solubilisation occurs by the formation of sodium carboxylate groups from the anionic polyacid. The polyelectrolyte formed in this way is readily soluble and shows a rapid rate of dissolution. However, the presence of electrolytes such as magnesium or calcium salts from hard water can inhibit removal [191]. 

A pH gradient is produced by incorporating a mixture of Ampholines with appropriate p/ values in either a polyacrylamide slab or column. An acid is used at the anode and an alkali at the cathode, the pH of these being approximately the same as the pi values of the two extremes of the Ampholine range. Phosphoric acid and sodium hydroxide are suitable for wide range separations while various amino or carboxylic electrolytes are used for intermediate pH ranges. 

Methanol is the solvent of choice for the Kolbe electrolysis. The following electrolytes with methanol as solvent have been used methanol/sodium carboxylate, methanol/sodium methoxide/carboxylic acid, methanol/water/sodium hydroxide/carboxylic acid, methanol/triethylamine/pyridine/carbox-ylic acid. An increasing amount of water often decreases the yield of dimer. 

The CMC samples were analyzed for actual DS by potentlometrlc titration of the sodium carboxylate group. Samples were prepared for injection by dissolving 10 or 50 mg of CMC In 10 ml of distilled water. No slgnlflc2mt advantage In the appeeurance of zone shapes was observed when samples were dissolved In leading electrolyte as is sometimes recommended. 

Latex Types. Latexes are differentiated both by the nature of the coUoidal system and by the type of polymer present. Nearly aU of the coUoidal systems are similar to those used in the manufacture of dry types. That is, they are anionic and contain either a sodium or potassium salt of a rosin acid or derivative. In addition, they may also contain a strong acid soap to provide additional stabUity. Those having polymer soUds around 60% contain a very finely tuned soap system to avoid excessive emulsion viscosity during polymeri2ation (162—164). Du Pont also offers a carboxylated nonionic latex stabili2ed with poly(vinyl alcohol). This latex type is especiaUy resistant to flocculation by electrolytes, heat, and mechanical shear, surviving conditions which would easUy flocculate ionic latexes. The differences between anionic and nonionic latexes are outlined in Table 11. 

The nickel oxide electrode is generally useful for the oxidation of alkanols in a basic electrolyte (Tables 8.3 and 8.4). Reactions are generally carrried out in an undivided cell at constant current and with a stainless steel cathode. Water-soluble primary alcohols give the carboxylic acid in good yields. Water insoluble alcohols are oxidised to the carboxylic acid as an emulsion. Short chain primary alcohols are effectively oxidised at room temperature whereas around 70 is required for the oxidation of long chain or branched chain primary alcohols. The oxidation of secondary alcohols to ketones is carried out in 50 % tert-butanol as solvent [59], y-Lactones, such as 10, can be oxidised to the ketoacid in aqueous sodium hydroxide [59]. 

Reduction of the carboxylic acid group passes through the intermediate aldehyde. For a number of examples in the heterocyclic series, the aldehyde becomes a major product because it is trapped as the hydrated vfc.-diol form. Examples include imidazole-2-caiboxylic acid [139], thiazole-2-carboxylic acid [140] and pyridine-4-carboxylic acid [141] reduced in dilute aqueous acid solution. Reduction of imidazole-4-carboxylic acid proceeds to the primary alcohol stage, the aldehyde intermediate is not isolated. Addition of boric acid and sodium sulphite to the electrolyte may allow the aldehyde intermediate to be trapped as a non-reducible complex, Salicylaldehyde had been obtained on a pilot plant scale in this way by... 

The electrostatic model for the micellar effect on the hydrolysis of phosphate monoesters is also consistent with the results of inhibition studies (Bunton et al., 1968, 1970). The CTAB catalyzed hydrolysis of the dinitrophenyl phosphate dianions was found to be inhibited by low concentrations of a number of salts (Fig. 9). Simple electrolytes such as sodium chloride, sodium phosphate, and disodium tetraborate had little effect on the micellar catalysis, but salts with bulky organic anions such as sodium p-toluenesulfonate and sodium salts of aryl carboxylic and phosphoric acids dramatically inhibited the micelle catalysis by CTAB. From equation 14 and Fig. 10, the inhibitor constants, K, were calculated (Bunton et al., 1968) and are given in Table 9. The linearity of the plots in Fig. 10 justifies the assumption that the inhibition is competitive and that incorporation of an inhibitor molecule in a micelle prevents incorporation of the substrate (see Section III). Comparison of the value of for phenyl phosphate and the values of K for 2,4-and 2,6-dinitrophenyl phosphates suggests that nitro groups assist the... 

In this work, the efTect of anodic oxidation treatments on activated carbon fibets (ACFs) was studied in the context of Cr(Vl), Cu( II), and Ni( II) ion adsorption behaviors. Ten wt% phosphoric acid and sodium hydroxide were used for acidic and basic electrolytes, respectively. Surf properties of the ACFs were determined by XPS. The specific surface area and the pore stnicture were evaluated from nitrogen adsorption data at 77 K. The heavy metal adsorption rates of ACFs were measured by using a UV spectrometer and 1C P. As a result, the anodic treatments led to an increase in the amount of total acidity by an increase of acidic functional groups such as carboxyl, lactone, and phenol, in spite of a decrease in specific surface area, due to the pore blocking by increased acidic functional groups. 

There has been considerable research into the electrolytic reduction of aromatic carboxylic acids to the corresponding aldehydes. A general procedure has been described in which key elements are the use of the ammonium salt of the acid, careful control of the pH and the presence of an organic phase (benzene) to extract the aldehyde and thus minimize overreduction. The method appears to work best for relatively acidic substrates for example, salicylaldehyde was obtained in 80% yield. Danish workers have shown that, under acidic conditions, controlled electrolytic reductions are possible for certain pyridine-, imidazole- and thiazole-carboxylic acids. In these cases, it is thought that the product aldehydes are protected by geminal diol formation. A chemical method which is closely related to electrolysis is the use of sodium amalgam as reductant. Although not widely used, it was successfully employed in the synthesis of a fluorinated salicylaldehyde. ... 

Electrolytic decarboxylative coupling of sodium salts of carboxylic acids takes place during their electrolysis. Carbon dioxide is eliminated, and the free radicals thus generated couple to form hydrocarbons or their derivatives. The reaction is referred to as the Kolbe electrosynthesis and is exemplified by the synthesis of 1,8-difluorooctane from 5-fluorovaleric acid (equation 469) [574]. Yields of homologous halogenated acids range from 31% to 82% [574]. 

Aliphatic carboxylic acids are reducible to the alcohol in low yield in strongly acidic electrolytes. Thus, phenylacetic acid is reduced to 2-phenylethanol in 25-50% yield at a lead cathode in 50% sulfuric acid-ethanol [39] and butyric acid to butanol in 80% sulfuric acid in 6.5% yield [40]. The latter conversion can also be performed in 17% yield in 7% aqueous sodium hydroxide, despite the fact that the carboxylate form of the acid, which is reducible only with difficulty, predominates in bulk solution, suggesting an electrocatalytic reduction involving specific interaction of the substrate and electrode surface. 

By anodic decarboxylation carboxylic acids can be converted simply and in large variety into radicals. The combination of these radicals to form symmetrical dimers or unsymmetrical coupling products is termed Kolbe electrolysis (Scheme 1, path a). The radicals can also be added to double bonds to afford additive monomers or dimers, and in an intramolecular version can lead to five-membered heterocycles and carbocycles (Scheme 1, path b). The intermediate radical can be further oxidized to a carbenium ion (Scheme 1, path c). This oxidation is favored by electron-donating substituents at the a-carbon of the carboxylic acid, a basic electrolyte, graphite as anode material and salt additives, e.g. sodium perchlorate. The carbocations lead to products that are formed by solvolysis, elimination, fragmentation or rearrangement. This pathway of anodic decarboxylation is frequently called nonKolbe electrolysis. 

Ionic additives to the electrolyte can influence the Kolbe electrolysis in a negative way. Anions other than the carboxylate should be excluded, because they hinder the formation of a carboxylate layer at the anode, that seems to be a prerequisite for the decarboxylation. In the electrolysis of phenyl acetate the coupling to dibenzyl is totally suppressed when sodium perchlorate is present in concentrations of 5 x 10" mol 1" benzyl methyl ether, the nonKolbe product, is formed instead. This shift from the radical... 

Other electrolytes that have been applied, are dimethyl sulfoxide/sodium hydride, glycol methyl ether/water/potassium carbonate or acetic acid/potassium carboxylate. ... 

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