Coupling anodic

Seb cic Acid. Sebacic acid [111-20-6] C QH gO, is an important intermediate in the manufacture of polyamide resins (see Polyamides). It has an estimated demand worldwide of approximately 20,000 t/yr. The alkaline hydrolysis of castor oil (qv), which historically has shown some wide fluctuations in price, is the conventional method of preparation. Because of these price fluctuations, there have been years of considerable interest in an electrochemical route to sebacic acid based on adipic acid [124-04-9] (qv) as the starting material. The electrochemical step involves the Kolbn-type or Brown-Walker reaction where anodic coupling of the monomethyl ester of adipic acid forms dimethyl sebacate [106-79-6]. The three steps in the reaction sequence from adipic acid to sebacic acid are as follows ... 

Fig. 1.64 Polarisation curves for zinc anodes coupled to aluminium and copper cathodes in I.On NaCI at 25°C (potentials vs. S.H.E.) (after Pryor and Kier - )...

Y = Ph, OR, OSiMej, NHCOR Scheme 2 Anodic coupling of alkenes. 

The earlier literature on oxidative coupling of phenols is reviewed in Ref. [168] and that on anodic coupling in Ref. [169, 170] some examples of the coupling reactions are summarized in Table 11, see also Chapter 6. 

The anodic coupling of aryl ethers is reviewed in Ref. [180]. Aryl ethers are more selectively coupled than phenols for the following reasons The carbon-oxygen coupling is made impossible and the ortho-coupling and the oxidation to quinones become more difficult. A mixture of triflu-oroacetic acid (TFA) and dichloromethane proved to be the most suitable electrolyte [181]. TFA enhances the radical cation stability and suppresses the nucle-ophilicity of water. Of further advantage is the addition of alumina or trifluo-roacetic anhydride [182]. Table 12 compiles representative examples of the aryl ether coupling. 

I 5 Anodic Reactions of Alkanes, Alkenes, and Aromatic Compounds Tab. 12 Anodic coupling of arylethers... 

Scheme 10 Anodic coupling of /3-naphthol mediated by TEMPO.

Scheme 1 Anodic coupling of iodobenzene to the 4-iododiphenyliodonium cation [5].

R = H, CH3, C2H5 Scheme 59 Dihydrofurans by anodic coupling of phenols. 

Scheme 127 Unsymmetrical dimer by anodic coupling of a tetrahydrocarbazole.

In all of the cyclization reactions, Moeller has found only a small difference between the use of alkyl and silyl enol ethers. Since both styrenes and enol ethers have similar oxidation potentials, even the styrene moiety could function as the initiator for oxidative cyclization reactions. The anodic oxidation of simple styrene type precursors leads to low yields of cyclized products so that enol ether moiety seems to be the more efficient initiator for intramolecular anodic coupling reactions [93]. 

While XAS techniques focus on direct characterizations of the host electrode structure, nuclear magnetic resonance (NMR) spectroscopy is used to probe local chemical environments via the interactions of insertion cations that are NMR-active nuclei, for example lithium-6 or -7, within the insertion electrode. As with XAS, NMR techniques are element specific (and nuclear specific) and do not require any long-range structural order in the host material for analysis. Solid-state NMR methods are now routinely employed to characterize the various chemical components of Li ion batteries metal oxide cathodes, Li ion-conducting electrolytes, and carbonaceous anodes.Coupled to controlled electrochemical in-sertion/deinsertion of the NMR-active cations, the... 

Contrary to the noncatalytic Kolbe synthesis or other anodically initiated radical reactions at Pt anodes, the anodic functionalization and anodic coupling of vinyl compounds by direct anodic oxidation of olefins in alcohols as... 

A comparable positive influence as experienced with anodic dimerization of olefins, styrene in particular, exerts carbon anodes on the anodic formation of trisarene sulfonium cations by anodic coupling of diarylsulfide radical cations to arenes (226-228). 

Hydroxyphenyl)semicarbazide undergoes an intramolecular anodic coupling reaction to 2-benzoxazolinone.119 A by-product is the dimer l-(2-hydroxyphenyl)carbamoyl-4-(2-hydroxyphenyl)semicarbazide. 

Another anodic coupling reaction was achieved by anodic oxidation of N-methylbenzthiazolone-2-hydrazone (274) in aqueous sulfuric acid containing dimethylaniline. The final product (275) was isolated in 30% yield426 [Eq. (142)]. 

Anodic coupling of carboxylates, carbanions, or CH-acidic methylene compounds. 

Intramolecular anodic coupling of enol ethers to vinylsilanes generates carbon-carbon bonds while breaking the vinyl-silicon bond this may be used either to form new rings or to place a vinyl group where it is needed (Scheme 70)167. 

---