Russel mechanism

An alternative chain-terminating decomposition of the tetroxide, known as the Russell mechanism (29), can occur when there is at least one hydrogen atom in an alpha position the products are a ketone, an alcohol and oxygen (eq. 15). This mechanism is troubling on theoretical grounds (1). Questions about its vaUdity remain (30), but it has received some recent support (31). 

Methyl ethyl ketone, a significant coproduct, seems likely to arise in large part from the termination reactions of j -butylperoxy radicals by the Russell mechanism (eq. 15, where R = CH and R = CH2CH2). Since alcohols oxidize rapidly vs paraffins, the j -butyl alcohol produced (eq. 15) is rapidly oxidized to methyl ethyl ketone. Some of the j -butyl alcohol probably arises from hydrogen abstraction by j -butoxy radicals, but the high efficiency to ethanol indicates this is a minor source. 

Asymmetric 0-0 bond homolysis of the tetroxide as a first step to product formation has been invoked (Khursan et al. 1990), and the idea of the Russell mechanism replaced by a three-step mechanism [reactions (52)—(54)]. 

In this reaction, a 5 -phosphate end group is formed and the base is released. The products that result from the C(l )-C(3 ) fragment are not yet fully established. Malonaldehyde is a potential one. For this product to be formed, the C(3 ) per-oxyl radical has to be reduced, e.g., via the Russell mechanism (Chap. 8.8). 

Termination reactions. A very common termination reaction, known as the Russel mechanism from its discoverer, is the recombination of two peroxy radicals to form an unstable tetroxide that decomposes through a concerted mechanism to yield a hydroxy moiety and a carbonyl moiety (13) ... 

Several mechanisms have been suggested to produce the energy required to populate an excited carbonyl, which is at least 290-340 kj mol-1 [8]. Direct homolysis of hydroperoxides [9, 10], disproportion of alkoxy radicals [11] and /2-scission of alkoxy radicals [12] are all exothermic enough. However, the most widely accepted mechanism has been the highly exothermic (460 kj mol-1) bimolecular termination of primary or secondary alkyl per-oxyl radicals, i.e. the Russell mechanism (Scheme 2). It proceeds via an intermediate tetroxide to give an excited carbonyl, an alcohol, and oxygen [13, 14]. 

Polypropylene, in which tertiary radicals predominate, nevertheless gives CL. This has been an argument against the validity of the Russell mechanism, which requires at least one of the peroxy radicals to be primary or secondary. However, Mayo and co-workers [15, 16] showed that termination reactions are accompanied by production of alkoxy radicals that will cleave to... 

Results by Achimsky et al. [18] showed a linear relationship between the maximum chemiluminescence intensity and the oxygen concentration. The conclusion was drawn that the light emission comes from decomposition of hydroperoxides rather than from the Russell mechanism shown in Scheme 2. Matisova-Rychla and Rychly have recently published several papers in favour for decomposition of hydroperoxides as being responsible for the light emission during oxidation of PP [19, 20, 21]. 

Russell mechanism proposed by Hiatt and coworkers, the linear representation for the transition state appears to be more accurate. 

In the bimolecular decay of peroxyl radicals, a short-lived tetroxide is an intermediate. When a hydrogen is present in /3-position to the peroxyl function, a carbonyl compound plus an alcohol and O2 [Russell mechanism, e.g. reaction (42)] or two carbonyl compound plus H2O2 (Bennett mechanism, not shown) may be formed in competition to a decay into two oxyl radicals plus O2 [e.g. reaction (43) for details of peroxyl radical chemistry in aqueous solution, see Refs. 2 and 39]. 

There is considerable controversy over whether and how the Russell Mechanism involving tetroxide intermediates (107) actually occurs in lipids, and whether the oxygen is released as O2. In early work, Ingold proposed that the Russell mechanism (Reaction 69) was the most important termination process for sec... 

There are two bimolecular reactions of peroxy radicals that are of special significance. The first is a chain termination reaction, widely proposed as the principal chain termination reaction (eq. (6)) and known as the Russell Mechanism [8, 10, 12, 16] ... 

The predominant reaction for the formation of cyclohexanol and cyclohexanone is the Russell mechanism of decomposition of secondary cyclohexylperoxy radicals, vhich first yields the product of coupling and then reacts by a non-radical, six-center 1,5-H-atom shift (termination of the radical-chain sequence) ... 

Peroxy radicals can react by yet other competing routes. For example, evidence for lipid peroxy radical combination through a tetraoxide has been reported recently (8). Such tetraoxides could generate singlet oxygen and nonradical products by the Russell mechanism (9) as shown in Reaction D. 

AD Russell. Mechanisms of bacterial resistance to antibiotics and biocides. Prog Med Chem 35 134-197, 1998. 

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