Oxidative coupling dimer

The preparation of a fully ordered polymer containing both PDA and polyacetylene moieties from the oxidatively coupled dimer of 1,11-dodecadiyne (3) has been reported (46). While the polymerization of the acetylene to an ordered polymer is revealed by the reported crystal structure ( ), the intrinsic properties of this novel polymer are imcertain at present. 

Other phenolic compounds underwent similar reactions. GAC after application of either free or combined chlorine became capable of promoting reactions such as hydroxylation of the aromatic ring, oxidation to phenols, chlorine substitution, carboxylation, and oxidative coupling (dimer and trimer formation). The formation of chlorohydroxybiphenyls ( hydroxylated PCBs 113) by dimerization of chloro-... 

Semicommercial production of 3,3/4,4 -biphenyltetracarboxyhc dianhydride [2420-87-3] in the United States has been announced by Occidental Chemical Corp. (74). This polyimide resin intermediate is prepared by dehalogenative dimerization of 4-chlorophthalate salts (75) or by oxidative coupling of phthalate esters (76). 

In a very recent study, it has been demonstrated116 that zinc 5,15-bis(3,5-di-tert-butylphenyl)-porphyrin (13) without any activating halogen atoms at the chromophore can be directly linked in a very simple oxidative coupling reaction with silver(I) hexafluorophosphate to a mixture of porphyrin dimers, trimers and tetramers. The separation of the product mixture was achieved by gel-permeation chromatography based on the molecular weights of the oligomers. The dimer when re-exposed to the same reaction conditions yielded 25% of the tetramer.116... 

A range of products was obtained from aniline including those from oxidative coupling (azozybenzene, azobenzene, and benzidine), and phenazine by dimerization (Chan and Larson 1991). Oxidation of m-phenylenediamine was initiated by the oxidation of two molecules to produce an A-phenyl-2-aminoquinone-imine that reacted with m-phenylenediamine to produce 2-amino-5-phenylaminoquinone-imine after further oxidation (Kami et al. 2000). 

Reaction of compound 134, either with sodium carbonate or potassium /tz -butoxide, leads in moderate yields to the enolized bicyclic compound 135 along with a dimer resulting from the oxidative coupling of the initial enolate of substrate 134 (Scheme 24) <2005T1693>. 

Although permanganate ions are not generally used to effect oxidative coupling of phenols, it has been shown that, in the presence of a catalyst in an organic solvent, 2-methoxyphenols are coupled oxidatively under very mild conditions to produce the dimeric products (>50%) [48], Unsaturated substituents are not oxidized under the mild conditions. 

Poly(phenylene oxide) PPO, or poly(phenylene ether) PPE, is an engineering polymer developed by General Electric. It concerns the oxidative coupling of phenols discovered in 1956 by Allan S. Hay [21], Oxidative coupling leads to the formation of carbon-oxygen bonds between carbon atoms 2,4, and 6 and the phenolic oxygen atom. To avoid coupling with carbon atoms 2 and 6, alkyl substituents at these two positions were introduced. In addition to the polymer a 4,4 dimer is formed, named diphenoquinone (DPQ). The... 

Figure 15.18. Oxidative coupling of dimethylphenol dimers to tetramers...

In phenolic oxidative coupling reactions, these phenol-derived radicals do not propagate a radical chain reaction instead, they are quenched by coupling with other radicals. Thus, coupling of two of these resonance structures in various combinations gives a range of dimeric systems, as shown. The... 

In addition to the aforementioned total syntheses. Shannon et al. observed the formation of an N-C3-linked dimer during the transformation of a 3-bromocarbazole to a 3-cyanocarbazole by reaction with copper(I) cyanide in DMF under reflux (668). Harrity et al. reported the synthesis of non-natural (+ )-N,N -dimethylbismurrayafoline A via a chromium-mediated benzannulation, followed by a palladium-catalyzed oxidative coupling reaction (669). 

Table I. Dimeric Products of the Oxidative Coupling of Protein-Bound Tyrosine Residues under Various Conditions...

Soluble heptapnicanortricyclane anions [Pny] (Fig. 3a) and trishomocubane-shaped (ufosane-like) anions [Pnn] (Fig. 3d) are very common and known as in the binary solids for Pn = P, As, Sb (Table 2). Oxidative coupling of these monomers leads to the dimers [Pny-Pny]" and [Pnn-Pnn]" for Pn = P and As (Fig. 3b, e), which - as observed for the tetrel element clusters - have an external homoatomic bond, but in this case the structures of the monomeric units are fully retained upon dimerization. A trimeric oxidative coupling product of [Py] is the... 

The formation of bicarbazoles can also be achieved electrolytically in acetonitrile solution once again, at the anode, the carbazole cation radical is produced and dimerizes. The further oxidation of 3,3 -bicar-bazole under these conditions with loss of two electrons and formation of a dication-diradical was demonstrated. Anodic oxidative coupling occurs at nitrogen best in the presence of collidine, presumably via deprotonation. 

Guyot, S., Vercauteren, J., and Cheynier, V., Colourless and yellow dimers resulting from (+)-catechin oxidative coupling catalysed by grape polyphenoloxidase. Phytochemistry 42, 1279, 1996. 

During the oxidative couplings a considerable amount of heat is evolved which makes the reaction easy to follow the point of complete conversion can often be determined with an "accuracy" of about 10 min. An additional indication for the end point in many of the oxidations is the marked change in colour when all RCsCH has been consumed, copper remains present as Cu, which has another colour than Cu. Careful observation of the reaction thus, can prevent attack of sensitive "dimers" RC=CCsCR by oxygen. 

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