Quinone-containing polymers

Takada K, Gopalan P, Ober CK, Abruna HD (2001) Synthesis, characterization, and redox reactivity of novel quinone-containing polymer. Chem Mater 13 2928-2932... 

These tellurium-containing polymers were checked for their catalytic activity in the ep-oxidation of olefins1 and as oxidizing agents2. The polymeric 4-methoxyphenyl tellurium oxide did not react with amines, amides, alcohols, or phenols, but oxidized hydroquin-ones to quinones, thiols to disulfides, thioketones to ketones, thioesters to esters, and thiobenzamides in organic solvents to cyanobenzenes and in acetic acid to 2,5-diaryl-4,l,3-thiadiazoles2. 

It should be mentioned that few, if any, examples are known of carbon-containing species chemisorbed at electrodes that are directly electroactive like H or OH/O species. Only in the case of adsorbed quinones or polymer-bound redox functions at chemically modified electrodes is direct surface electroactivity known. Some organic sulfide/disulfide pairs such as cystine/cys-teine are also electroactive when adsorbed. 

Piro B, Haccoun J, Pham MC, Tran LD, Rubin A, Perrot H, Gabiielli C (2005) Study of the DNA hybridization transduction behavior of a quinone-containing electroactive polymer by cyclic voltammetry and electrochemical impedance spectroscopy. J Electroanal Chem 557 155-165... 

Humic acid and the corresponding fulvic acid are complex polymers whose structures are incompletely resolved. It is accepted that the structure of humic acid contains oxygenated structures, including quinones that can function as electron acceptors, while reduced humic acid may carry out reductions. These have been observed both in the presence of bacteria that provide the electron mediator and in the absence of bacteria in abiotic reactions, for example, reductive dehalogenation of hexachloroethane and tetrachloromethane by anthrahydroquininone-2,6-disulfonate (Curtis and Reinhard 1994). Reductions using sulfide as electron donor have been noted in Chapter 1. Some experimental aspects are worth noting ... 

In addition to this reaction, quinones and other alkyl radical acceptors retard polymer oxidation by the reaction with alkyl radicals (see earlier). As a result, effectiveness of these inhibitors increases with the formation of hydroperoxide groups in PP. In addition, the inhibiting capacity of these antioxidants grows with hydroperoxide accumulation. The results illustrating the efficiency of the antioxidants with cyclic chain termination mechanisms in PP containing hydroperoxide groups is presented in Table 19.12. The polyatomic phenols producing quinones also possess the ability to terminate several chains. 

With respect to the polymeric backbone, two approaches exist for the preparation of functional polymers, the polymerization or copolymerization of monomers which carry the desired functionality, and secondly the chemical modification of preformed polymers. The former concept, the polymerization of prefunctionalized monomers, was often tested in the early days of polymer-assisted syntheses, e. g. in the preparation of polymers containing pyridine [12] or quinone [13] residues, and benzaldehyde [14] or phosphine [15] functionalities. Although the latter approach demands that the synthetic organic chemist acquires profound knowledge of polymers and polymerization, this strategy can have advantages because... 

Electrooxidation of the pyrrole unit results in the formation of a pyrrole polymer that coats the electrode surface as it is formed. The amount of polymer deposited can be controlled by the number of CV cycles into the pyrrole oxidation wave. With 30, thick polymer layers give broad CV waves in the quinone voltage region, but thinner layers produce a well-resolved wave for the quinone 0/—1 reduction, which is reasonably stable when the electrodes are placed into fresh electrolyte solution with no 30. As in solution, addition of different urea derivatives causes this wave to shift positive. The relative magnitude of the shifts mirror that seen in solution. Furthermore, the 2 moves back to the original potential when the derivatized electrode is put back into a blank solution containing no urea. 

There are no reports in the literature of the formation of pyrrole derivatives by the oxidative degradation of the o-quinone rings of the simple aminochromes. However, several pyrrolecarboxylic acids have been obtained on oxidation of the melanins, which are considered by some authors to contain aminochrome units in the polymer (cf. ref. 168), (see Section V, A), and pyrrole-2,3,5-tricarboxylic acid has been... 

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