Russell mechanism reactions

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. 

Site Density and Entropy Criteria in Identifying Rate-Determining Steps in Solid-Catalyzed Reactions Russell W. Maatman Organic Substituent Effects as Probes for the Mechanism of Surface Catalysis M. Kraus... 

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) ... 

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... 

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. 

Thus, the calculations [13] have produced evidence in favor of the Kornblum-Russell mechanism elucidating certain details of the nature and structural conditions for realization of its individual steps. Of course, so far only the simplest models have been considered, and the effect of the simplifying assumptions may in some cases be quite substantial. For example, experimental studies of radical-anions of various halogennitrobenzyl compounds IV using the impulse radiolysis technique [28] show that, unlike the chloronitromethyl radical considered earlier, the compounds IV do exist in solution for some finite time. Even so, their decomposition is, in accordance with the theoretical prediction, speeded up upon weakening of the C—X bond. The reaction proceeds by the scheme of intramolecular, inner-sphere electron transfer whose relatively low rate constant (10 -10 s) can be accounted for by the small overlap of the Ti-orbital, which carries the unpaired electron in the initial form IV and is localized predominantly at the nitro group, and the (j -orbital C—X ... 

PP correlates well with the oxygen uptake and the CL intensity is assumed to be directly proportional to the rate of oxidation [578]. The intensity of emitted light is proportional to the rate of termination for the reactions involved in the Russell mechanism. Chemiluminescence reveals a difficulty in the definition of the induction period and the steady state of oxidation as the sensitivity of the CL analysis is increased, the apparent induction time and the limiting rate decrease. 

The Russell mechanism requires one of the terminating radicals to be either primary or secondary so that a six-membered transition state can be formed. Such a mechanism may be prevalent in PE and PA, but not in PP, where the chaincarrying radical is tertiary. For this polymer, more complex alternative routes for chemiluminescence-produdng reactions have been proposed [Ref. 10, p. 175]. 

The reaction of these radicals takes place according to the Russell mechanism resulting in ketones [146a],... 

Two mechanisms have been considered for the self-reaction of primary and secondary alkylperoxy radicals, the Russell mechanism (lO) reactions (26), (27), and (28) and a mechanism involving the intermediacy of alkoxy radicals ( 3, kk) reactions (29), (30), (31), and (32). The reactions involved in these two mechanisms are presented in Scheme II. 

The work of Lindsay et at provides good evidence that not all S-RO2 undergo bimolecular self-reaction at ambient temperatures entirely by the Russell mechanism. It would, however, appear from their work that the yield of alkoxy radicals is very dependent on the structure of the peroxy radical. This lead these workers ( 6) to propose that the tetroxide may decompose by multiple bond scission by a concerted but non-eyelie mechanism. 

The difference in termination rate constants between secondary (and primary) alkylperoxys and tertiary alkylperoxys is, therefore, almost entirely due to differences in the rate constants for irreversible tetroxide decay. Thus at 303K 2k- for t-Bu0a = 1.2 X 10 M s and 2k+ for s-BuOa = 10 M" s . That is kt/k-j = 8.3 X 10. Now Ingold (bl) has suggested that AS° for (27) fn-lk.k cal deg mol because of the entropy loss from four hindered internal rotors (i+x3.6 cal deg mol ). Thus A /A and E-b-E-t should be 10 and 9.6 kcal mol , respectively, for t-BuOa and s-BuOa, i.e., E should be ca 1 kcal mol negative. Neither of these predictions are observed experimentally and we are forced to conclude that kinetic data for self-reaction of S-RO2 provides further evidence against the complete acceptance of the Russell mechanism. 

The termination step occurs by the Russell mechanism [1] via the unstable tetraoxide (5). The products are a ketone, oxygen and an alcohol as shown. The conservation of spin in this assumed concerted reaction, as previously discussed, leads, to formation of the ketone in the triplet excited state. Although singlet oxygen may be found in low yield, the carbonyl excited state certainly predominates. 

However, it is very improbable that a radical chain reaction can proceed in relatively immobile polymers. Thus the chemiluminescence observed as well as the previously mentioned carbonyl groups may not be caused by the Russell mechanism (perhaps via trioxides [54]). 

The first example of a tetrakisimido analogue of the orthophosphate ion, PO, the solvent-separated ion pair [(THF)4Li][(THF)4Li2P(Nnaph)4] (16), was reported by Russell et al. [21]. This complex was isolated in low yield from the reaction of P2I4 with a-naphthylamine in THF/NEt3, followed by the addition of "BuLi. The mechanism of this remarkable redox process is not understood. 

Ito et a/.18 supported the above reaction pathways for various cathode materials, such as In, Sn, Cd, and Pb, from the similarity in Tafel slopes. Hori and Suzuki46 verified the above mechanism in various aqueous solutions on Hg. Russell et al.19 also agreed with the above mechanism. Adsorbed CO J anion radical was found as an intermediate at a Pb electrode using modulated specular reflectance spectroscopy.47 This intermediate underwent rapid chemical reaction in an aqueous solution the rate constant for protonation was found to be 5.5 M-1 s-1, and the coverage of the intermediate was estimated to be very low (0.02). 

This reaction is very exothermic (e.g., AH 405 kJ mol-1 for cyclohexyltetroxide) and supposed to occur rapidly. The values of rate constants for primary and secondary R02 cover the range at 300 K, 2kt = 106 to 108 L mol-1 s-1 (see Table 2.15). According to Russell s mechanism, tetroxide decomposition proceeds via the cyclic transition state and includes the abstraction of the C—H bond ... 

The chain mechanism is complicated when two hydrocarbons are oxidized simultaneously. Russell and Williamson [1,2] performed the first experiments on the co-oxidation of hydrocarbons with ethers. The theory of these reactions is close to that for the reaction of free radical copolymerization [3] and was developed by several researchers [4-9], When one hydrocarbon R H is oxidized in the liquid phase at a sufficiently high dioxygen pressure chain propagation is limited only by one reaction, namely, R OO + R H. For the co-oxidation of two hydrocarbons R1 and R2H, four propagation reactions are important, viz,... 

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