Carboxylic acids anodic processes

Early electrochemical processes for the oxidation of alcohols to ketones or carboxylic acids used platinum or lead dioxide anodes, usually with dilute sulphuric acid as electrolyte. A divided cell is only necessary in the oxidation of primary alcohols to carboxylic acids if (he substrate possesses an unsaturated function, which could be reduced at the cathode [1,2]. Lead dioxide is the better anode material and satisfactory yields of the carboxylic acid have been obtained from oxidation of primary alcohols up to hexanol [3]. Aldehydes are intermediates in these reactions. Volatile aldehydes can be removed from the electrochemical cell in a... 

Oxidative ring cleavage of cyclohexanones is achieved in ethanol at a platinum anode. Cleavage of the carbon-carbonyl bond occurs and the carbonyl centee is trapped as the carboxylic acid. The radical centre formed after bond cleavage is oxidised to the carbocation. This rearranges to the most stable centre and is then trapped by the carboxyl group to form a lactone [4, 5], An identical process is... 

Substituents stabilising a carbonium ion influence the course of the anodic oxidation of carboxylic acids by promoting fast oxidation of the radical intermediate to the carbonium ion. Subsequent chemical steps are those expected of this ionic intermediate and the overall process is termed the non-Kolbe reaction. Reaction at... 

Finally, we note that the photocorrosion process is strongly pH-dependent, occurring most readily in strongly acid solutions, and that the presence of a carboxylic acid is required for the occurrence of severe photocorrosion. In Table II we present analytical results, based on inductively coupled argon plasma (ICP) emission spectroscopy, for representative electrolyte solutions after 6-8 hr. of photo-Kolbe electrolysis with n-SrTiC anodes. It can be seen that the formation of soluble strontium and titanium species is... 

In addition to the electrolytic preparation of fluorine, the electrochemical fluorination of carboxylic acid and sulfonic acid derivatives have also become important industrially. The Simons process (Ni anodes, HF as solvent) has been realized industrially by 3 M 69). The most important products are perfluorooctanecarboxylic and perfluorooctanesulfonic acids, which are used as surfactants and for surface treatments. 

On the other hand, acetylenic alcohols can be electrochemically converted to the corresponding acetylene carboxylic acids in acidic electrolytes using Pb02 anodes. Processes for the synthesis of propynoic acid and acetylene dicarboxylic acid have been developed at BASF 303 - 30. ... 

In an undivided electrolytic cell, the electro-Fenton process leads to the destruction of organics contained in wastewaters by simultaneous oxidation with OH formed at the anode surface from reaction (19.9) and in the medium from Fenton s reaction (19.12). Parallel slower reaction of pollutants with weaker oxidants such as H202, H02, S20g2-, and O3 formed from reactions (19.1), (19.4), (19.10), and (19.11), respectively, is also possible. In addition, final carboxylic acids can form complexes with iron ions that are difficult to be oxidized by OH. We will see the notable influence of the anode material (Pt or BDD) on the degradation of these compounds in further sections. 

Kolbe synthesis — The definition and use of the terms - Kolbe synthesis, K. reaction, K. electrolysis, and K. process are not very clearly distinguished and often bear different nuances of meaning. Kolbe electrolysis or synthesis mainly accounts for the anodic oxidation of carboxylic acids or carboxylates, followed by a decarboxylation step, when concentrated aqueous solutions of the respective carboxylates are electrolyzed. Kolbe picked up earlier results from -> Faraday on the electrolysis of acetic acid or acetate solutions to CO2 and ethane [i] and continued these experiments during 1843-1845 with further homologs as, e.g., valerianic acid [ii]. The carboxy-late R-COO- is anodically oxidized to form an unstable radical R-COO, which is stabilizing via a decarboxylation reaction, leaving radical rest R ... 

Simons process — Electrochemical polyfluorination reactions of organic compounds are the only efficient way to industrial production of perfluorinated compounds. The reaction proceeds in the solution of KF in liquid HF (b.p. 19.5 °C), where the starting substances as alcohols, amines, ethers, esters, aliphatic hydrocarbons and halo-hydrocarbons, aromatic and heterocyclic compounds, sulfo- or carboxylic acids are dissolved. During anodic oxidation, splitting of the C-H bonds and saturation of the C=C bonds occur and fluorine atoms are introduced. 

The electrochemistry of amino acids has been studied in strong acid solutions. In general, the compounds are decomposed to carboxylic acids, aldehydes, ammonia, and carbon dioxide. The results are reviewed by Weinberg [35]. The anodic oxidation mechanism has been studied in pH 10 buffer solution. Decarboxylation accompanied by C-N bond cleavage is the main reaction process [182]. The synthetically interesting Hofer-Moest decarboxylations of A/ -protected amino acids and a-amino malonic half esters under the formation of A/ -acyliminium ions is treated in the following section. 

For alkenes more difficult to reduce than CO2, such as butadiene (63a), electron transfer from C02 to the alkene may be involved. Cross-coupling of CO2 and 63a in MeCN has been carried out in an undivided flow cell at constant current. Using Et4N salts of formate or oxalate as supporting electrolyte, the anode process is formation of CO2 and H" ", which are both consumed in the cathode process [167]. The outcome (up to 63% total yield) was a mixture of isomers of C5, Cg, and Cjo unsaturated carboxylic acids and diacids. The detailed mechanism is not known, but the products may arise from initial addition of C02 to the unreduced butadiene [167], although electron transfer from C02 to 63a or direct reduction of 63a (present in large excess) cannot be ruled out. Based on the observed influence of experimental parameters on the distribution of the C5, Cg, and C]o acid products, the authors suggest that the reactions take place between adsorbed intermediates [167]. 

With a multilayer membrane containing both carboxylic and sulfonic acid groups, however, it is possible to neutralize proton from the anolyte with hydroxyl anion at the surface of or in the membrane before the proton reaches the carboxylic acid layer facing the catholyte, and thus achieve high chlorine purity and longer anode life, as indicated in Table I. This is one of the essential features of the Asahi Chemical process patented in various countries (39). Another advantage of the... 

Commercial electropainting only dates from the early 1960s and the first processes to be introduced used anodic deposition. Some typical paint formulations would contain (i) polycarboxylic acids based on acrylic acid as monomer solubilized by an organic amine, (ii) alkyds, i.e. branched polyesters based on naturally occurring long-chain carboxylic acids and polyalcohols, e.g. glycerol, and (iii) epoxy resins based on phenols, e.g. 

---