Redox aromatic amines

The cure reaction of structural acrylic adhesives can be started by any of a great number of redox reactions. One commonly used redox couple is the reaction of benzoyl peroxide (BPO) with tertiary aromatic amines. Pure BPO is hazardous when dry [39]. It is susceptible to explosion from shock, friction or heat, and has an autoignition temperature of 79°C. Water is a very effective stabilizer for BPO, and so the initiator is often available as a paste or a moist solid [40], The... 

A redox mechanism. An oxidized form of a more efficient component of a synergic mixture is reduced by the presence of a less reactive component. Example aromatic amines + phenols. 

The low specificity of electron-donating substrates is remarkable for laccases. These enzymes have high redox potential, making them able to oxidize a broad range of aromatic compounds (e.g. phenols, polyphenols, methoxy-substituted phenols, aromatic amines, benzenethiols) through the use of oxygen as electron acceptor. Other enzymatic reactions they catalyze include decarboxylations and demethylations [66]. 

The yeast-mediated enzymatic biodegradation of azo dyes can be accomplished either by reductive reactions or by oxidative reactions. In general, reductive reactions led to cleavage of azo dyes into aromatic amines, which are further mineralized by yeasts. Enzymes putatively involved in this process are NADH-dependent reductases [24] and an azoreductase [16], which is dependent on the extracellular activity of a component of the plasma membrane redox system, identified as a ferric reductase [19]. Recently, significant increase in the activities of NADH-dependent reductase and azoreductase was observed in the cells of Trichosporon beigelii obtained at the end of the decolorization process [25]. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

On the other hand, there is at least one case of an aromatic amine without a hydroxy group in the 2-position, namely 1-aminophenazine (25) which, after the initial diazotiza-tion, is oxidized within minutes by air or additional nitrous acid to the quinone diazide 26 (equation 9)46. In the corresponding diazotization of 2-aminophenazine the proportion of the quinone diazide (isomer of 26) amounted to only 16%, but 30% unsubstituted phenazine was also found. The phenazine may have resulted from the overall redox reaction. 

Alkali, alkaline-earth, and rare-earth metal cations also catalyze electron transfer reactions. Thus, in the pair of Co -tetraphenylporphyrin complex with BQ, no redox reaction takes place, or it takes place too slowly to be determined. The metal cations promote this reaction. For example, in the presence of 80(0104)3, the corresponding rate constant of 2.7 X 10 M s was observed. BQ transforms into benzosemiquinone under these conditions (Fukuzumi and Ohkubo 2000). Zinc perchlorate accelerates the reaction between aromatic amines and quinones (Strizhakova et al. 1985). This reaction results in the formation of charge-transfer complexes [ArNHj Q ]. The complexes dissociate in polar solvents, giving ion-radicals ... 

Aromatic amines Redox Clays (review) In presence of metal ions that are good redox agents... 

Up to the present time, use has been made almost entirely of dimethacrylates which are polymerized by free radical mechanisms to yield crosslinked products (81. Polymerization is initiated by redox systems, such as benzoyl peroxlde/aromatic amine, and by... 

Since autoxidations of phenols and aromatic amines are non-chain radical processes, they require some rapid radical-generating step. In a few systems—e.g., hydroquinone autoxidation, this is supplied by a direct redox reaction with oxygen (11). 

Huttermann J, Ward JF, Myers LS Jr (1971) Electron spin resonance studies of free radicals in irradiated single crystals of 5-methylcytosine. Int J Radiat PhysChem 3 117-129 Huttermann J, Ohlmann J, Schaefer A, Gatzweiler W (1991) The polymorphism of a cytosine anion studied by electron paramagnetic resonance spectroscopy. Int J Radiat Biol 59 1297-1311 Hwang CT, Stumpf CL, Yu Y-Q, Kentamaa HI (1999) Intrinsic acidity and redox properties of the adenine radical cation. Int J Mass Spectrom 182/183 253-259 Ide H, Otsuki N, Nishimoto S, Kagiya T (1985) Photoreduction of thymine glycol sensitized by aromatic amines in aqueous solution. J Chem Soc Perkin Trans 2 1387-1392 Idris Ali KM, Scholes G (1980) Analysis of radiolysis products of aqueous uracil + N20 solutions. J Chem Soc Faraday Trans 176 449-456... 

Figure 6.31 Molecular structure of a typical electroactive aromatic amine, with a redox potential well into the band-gap region...

For independent confirmation of peroxide accumulation in polymers it was necessary to detect the peroxides analytically after the radicals had disappeared. For this purpose we used the folloving technique. The semistable radicals formed in redox reactions of peroxides and aromatic amines have been studied formerly by paramagnetic resonance [34). 

In this section an illustrative discussion on kinetics of photopolymerization initiated via an intermolecular photoinduced electron transfer for a dye-tertiary aromatic amine initiating photo-redox couple [193] and for 4-carboxybenzophenone-sulfur-containing carboxylic acids initiating systems will be presented. 

Further examples of related multi redox-active macrocycles 89 — 91 have also been synthesised and their electrochemistry examined [108 — 110], Calix-4-arenes have also been derived from ferrocene to form monomeric macrocycles of type 92 or 93 together with dimeric compounds of type 94 [102] and crystal structures of the latter two compounds were reported. Solution HNMR and electrochemical studies in CH3CN, CHCI3, or CH2CI2 showed, however, that there was no complex formation between these calixarenes and either aliphatic or aromatic amines. 

The magnitudes of the standard redox potentials (e.g., —1.56 and -I-1.53 V vs. SCE in acetonitrile) and the relatively low energy of excited Mo6Clfj (1.9eV) have also made possible observation of ECL from the annihilation of Mo6Cl] 4 and MofiClf with a variety of electroactive donors D (aromatic amines forming stable... 

Tris(4-bromophenyl)ammoniumyl hexachloro antimonate is commercially available (e.g., Fluka product, 5g cost 70). It is commonly used as an oxidizing reagent by means of electron transfer and is elegantly applied to induce cycloadditions and cyclodimerization ([2 -I- 2] reactions) by Bauld [115]. However, aromatic amine radical cations as the oxidizing reagent can be easily obtained anodically [116] and their redox potentials (between -1-1 V and -1-2 V vs. NHE) modulated as a function of different substituents for utilization if indirect oxidation reactions are to be conducted. Therefore, such a redox catalysis process appears to be a cheap and elegant method to selectively achieved in situ oxidation, provided that polar solvents, electrolytes, and room temperatures are acceptable experimental conditions to perform a given reaction. 

Oxidative carbonylation of aliphatic and aromatic amines in the presence of supported platinum metals or platinum metal salts as catalysts and iodide ions gives carbamates [118, 119]. Iodide is presumed to promote the partial redox reactions... 

Clays and oxides have the ability to promote certain redox reactions such as the oxidation of phenols and aromatic amines. These are surface reactions, involving an adsorption step and electron transfer step, unlike many of the chemical reactions... 

A major drawback of redox-based assays is that any oxidizable compound in the sample solution will react, too. Ascorbic acid, sulphur dioxide (in wines), aromatic amines and carbohydrates (production of endiol reductones in alkaline solution) are the most frequently encountered reductants [47,106]. 

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