Acid addition, electrochemical oxidation

Highly pure perchloric acid can also be produced by a patented electrochemical process ia which 22% by weight hypochlorous acid is oxidized to chloric acid ia a membrane-separated electrolyzer, and then additionally oxidized to perchloric acid (8,84). The desired electrochemical oxidation takes place ia two stages ... 

As mentioned above, the electrochemical oxidation of a diene yields 1,2- and 1,4-addition products when the reaction is carried out in the presence of a nucleophile such as methanol or acetic acid. When the oxidation is carried out in the absence of the nucleophile it usually yields a polymeric compound as the major product. The formation of a small amount of the Diels-Alder adduct is, however, observed when the reaction is carried out in CH2CI2 with graphite anode. One of the proposed reaction pathways is shown in equation 68, though it is not clear whether the cyclohexadienyl radical serves as a diene (as shown in equation 6) or a dienophile in the Diels-Alder reaction. 

Electrochemical oxidation of aliphatic tertiary amines in acetonitrile together with compounds having weakly acidic hydrogens, such as dimethyl malonate, leads to addition of the malonate anion to the immonium cation intermediate. 2,4,6-Collidine is added to combine with protons, which are released during reaction [90],... 

The voltammetric response of curcumin and carthamin must, in principle, be dominated by the oxidation of the phenol and/or methoxyphenol groups (see Scheme 2.2). The electrochemistry of methoxyphenols has claimed considerable attention because of their applications in organic synthesis [159-163]. As studied by Quideau et al., in aprotic media, 2-methoxyphenols are oxidized in two successive steps into cyclohexadienone derivatives [163], whereas a-(2)- and a-(4-methoxyphenoxy) alkanoic acids undergo electrochemically induced spirolac-tonization to develop synthetically useful orthoquinone bis- and monoketals. In the presence of methanol, the electrochemical pathway involves an initial one-electron loss, followed by proton loss, to form a monoketal radical. This undergoes a subsequent electron and proton loss coupled with the addition of alcohol to form an orthoquinone monoketal. The formal electrode potential for the second electron transfer... 

In addition to the synthesis of saccharin, also a number of other side-chain oxidations have been studied leading to aromatic carboxylic acids by indirect electrochemical oxidation using chromic acid as oxidizing agent. They include the oxidation of p-nitrotoluene 2,4-dinitrotoluene toluene, p-xylene, and p-tolualdehyde... 

The electrochemical oxidation of aromatic aldehydes (1) must be studied in strongly alkaline media. Acidity functions for strongly alkaline aqueous solutions of alkali metal and quaternary ammonium hydroxides, corresponding to dissociation of proton (H ), are well established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators for establishment of such scales, but whether an acidity scale based on one type of indicator can be rigorously applied to acid-base equilibria involving structurally different acidic groups for reactions in strongly alkaline media remains questionable. For substituted anilines, behavior both parallel (7) and nonparallel (8) to the H scale based on indole derivatives has been reported. The limited solubility of anilines in aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative with more than one hydroxide ion, irreversible substitution reactions (9), and the possibility of hydroxide ion addition rather than... 

Nicotinic acid and nicotinamide, members of the vitamin B group and used as additives for flour and bread enrichment, and as animal feed additive among other applications, are made to the extent of 24 million pounds (nearly 11 million kilograms) per year throughout the world. Nicotinic acid (pyridine-3-caiboxylic acid), also called niacin, has many uses. See also Niacin. Nicotinic acid is made by the oxidation of 3-picolme or 2-mcthyl-5-cthylpyridine (the isocinchomcnc acid produced is partially deearboxylated). Alternatively, quinoline (the intermediate quinolinic acid) is partially deearboxylated with sulfuric add in the presence of selenium dioxide at about 300° C or with nitric acid, or by electrochemical oxidation. Nicotinic acid also can be made from 3-picoline by catalytic ammoxidation to 3-cyanopyridine, followed by hydrolysis. 

In the case of A-acylated amino acid derivatives, the oxidation has to take place via an indirect electrochemical process using chloride ions as redox catalysts. In methanol as solvent, methylhypochlorite is formed as oxidant, which yields, via -chlorination, HC1 elimination, and methanol addition, the a-methoxylated amino acids as amidoalkylation reagents [27] ... 

Fused ring 7-lactones may also be formed by cyclizations of l-cycloalkeneacetic acids under equilibrating conditions. Nicolaou obtained evidence for the presence of an unstable -lactone in the phenyl-selenolactonization of 1-cyclohexeneacetic acid, but rearrangement occured readily at room temperature to the more stable 7-lactone (equation 12).32 An example of a one-step conversion of a 2-methyl-1-cyclohexeneacetic acid to a fused butenolide by use of diphenyldiselenide and electrochemical oxidation has been reported.47 Recent studies by Rutledge showed that simultaneous addition of bromine and thallium carbonate to 1-cyclohexeneacetic acid gave the 7-lactone as the exclusive product (compare to Table 2) however, the mechanism of this reaction may differ from other cyclofunctionalizations.21... 

In a subsequent study Devynck and co-workers81,82 studied the electrochemical oxidation of alkanes and alkenes in triflic acid monohydrate. The acidity of CF3SO3H H20 was found to be intermediate between that of aqueous acid media and superacidity. Alkanes undergo two-electron oxidation, whereas alkenes are protonated to yield carbenium ions in this medium. In addition to various transformations characteristic of carbenium ions [Eqs. (5.36)—(5.38)], they undergo a reversible disproportionation to give an alkane and an aldehyde [Eqs. (5.40)]. 

Ulsch2 has made some observations on the complete electrochemical oxidation of cane sugar to carbonic acid and water. In a sulphuric acid of 1.15 sp. gr., with the addition of manganese sulphate as an oxygen-carrier, about 98% of the theoretically calculated amount of carbonic acid is obtained. The oxidation at 40°-80° in barium-hydrate solution is also fairly complete, but not directly to carbonic acid oxalate appears also to be formed. 

Pyrogallol (pyrogallic acid).—According to A. G. Perkin and F. M. Perkin,3 purpurogallin CuEgOs, can readily be obtained by electrochemical oxidation of pyrogallol in dilute sulphuric acid with addition of sodium sulphate at a platinum-iridium anode. 

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