Oxidation autoxidation

Other nonpolymeric radical-initiated processes include oxidation, autoxidation of hydrocarbons, chlorination, bromination, and other additions to double bonds. The same types of initiators are generally used for initiating polymerization and nonpolymerization reactions. Radical reactions are extensively discussed in the chemical Hterature (3—15). 

Terpenoids are susceptible to a number of alterations mediated by oxidation and reduction reactions. For example, the most abundant molecule in aged Pinus samples is dehydroabietic acid [Structure 7.10], a monoaromatic diterpenoid based on the abietane skeleton which occurs in fresh (bleed) resins only as a minor component. This molecule forms during the oxidative dehydrogenation of abietic acid, which predominates in rosins. Further atmospheric oxidation (autoxidation) leads to 7-oxodehydroabietic acid [Structure 7.11]. This molecule has been identified in many aged coniferous resins such as those used to line transport vessels in the Roman period (Heron and Pollard, 1988 Beck et al., 1989), in thinly spread resins used in paint media (Mills and White, 1994 172-174) and as a component of resin recovered from Egyptian mummy wrappings (Proefke and Rinehart, 1992). 

Kharitonov, V., Sundquist, AR, and Sharma, VS (1994). Kinetics of nitric oxide autoxidation in aqueous solution. J Biol Chem 269(8) 5881-5883. 

Kinetics and mechanism—homolytic processes, oxidation, autoxidation, organo-metallic peroxides... 

Lactams are formed by bromination (bromine, iV-bromosuccinimide) of cyclic tertiary amines, resulting in an intermediate iminium salt that can be isolated. Oxidation by met oxides, autoxidation, photochemical oxidation and electrooxidation are alternatives with limited scope. 

The radical chain mechanism outlined here avoids the ineffective direct reaction of molecular oxygen with the substrate hydrocarbon. The fast propagation reactions produce ROOH that in turn can initiate new radical chains. As the primary product of the reaction initiates new reactions, one ends up with an autocatalytic acceleration. The propagating peroxyl radicals can also mutually terminate and yield one molecule of alcohol and ketone in a one-to-one stoichiometry. The ratio between the rate of propagation and the rate of termination is referred to as the chain length and is of the order of 50-1000. As the desired chain products are more susceptible to oxidation, autoxidations are normally carried out at low conversions in order to keep the selectivity to an economically acceptable level. 

Figure 2. Thermal oxidation, autoxidation, and light-induced oxidation without...

As a part of their research prograirune on the chemistry of melanins. Swan and his group in Newcastle have recently studied the tyrosine catalysed and auto-oxidation of dopamine (19) and DOPA (3) and a number of related compounds [57-60]. This group has also investigated the oxidation of 2,4,5-trihydroxyphenylethylamine (20) and synthesised a number of dimeric catecholamines 5,5, 6,6 -tetrahydroxy biphenyl-3,3 -ylenedi(ethyla-mine) (21) 5,5, 6,6 -tetrahydroxybiphenyl-2,2 -ylenedi(ethylamine) (22) 5,5, 6,6 -tetrahydroxybiphenyl-2,3 -ylenedi(ethylamine) (23) 2,3-bis(3,4-dihydroxyphenyl)butane-l,4-diamine (24) and 5,5, 6,6 -tetrahydroxybi-phenyl-3,3 -ylenedialanine (25) [58] and studied their tyrosinase catalysed oxidation, autoxidation, and oxidation with silver oxide, to melanins [59]. 

Furan fatty acids (3-32) are present in plants, fishes, amphibians, reptiles and mammals, including man. In some fish, F-acids can typically represent 1-6% of the fatty acids in the liver lipids. In some freshwater fish, however, furan fatty acids may represent up to 25% of the total fatty acids. They also occur in butter, meat, vegetable oils, shrimps and mushrooms in small amounts. For example, virgin oHve oils contain non-olefinic 10,13-epoxy-ll,12-dimethyloctadeca-10,12-dienoic acid co = 8, n = 4, R=CH3) and 12,15-epoxy-13,14-dimethyleicosa-12,14-dienoic acid ( = 10, n = 4, R = CHj) and two olefinic derivatives 12,15-epoxy-13,14-dimethyleicosa-12,14,16-eicosatrienoic acid (ct)= 10, n = 2, R=CH3) and 12,15-epoxy-13,14-dimethyleicosa-10,12,14-eicosatrienoic acid a> = 8, = 4, R = CHj). Furan fatty acids also arise as products of Hpid oxidation. Autoxidation or photoxidation of fiiran fatty acids yields a,p-unsaturated y-lactones known as bovoHdes (see Figure 8.54). 

Phenols can also be oxidised to the corresponding o-diphenols and o-quinones by hydrogen peroxide, which arises, for example, as a product of ascorbic acid oxidation, autoxidation of o-diphenols or autoxidation of cuprous ions in an acidic solution ... 

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