Alkoxylation, diffusion

The active alkoxyl radicals formed by this reaction start new chains. Apparently, the hydroperoxide group penetrates in the polar layer of the micelle and reacts with the bromide anion. The formed hydroxyl ion remains in the aqueous phase, and the MePhCHO radical diffuses into the hydrocarbon phase and reacts with ethylbenzene. The inverse emulsion of CTAB accelerates the decay of hydroperoxide MePhCHOOH. The decomposition of hydroperoxide occurs with the rate constant k = 7.2 x 1011 exp(-91.0/R7) L mol-1 s-1 (T = 323-353 K, CTAB, ethylbenzene [28]). The decay of hydroperoxide occurs more rapidly in an 02 atmosphere, than in an N2 atmosphere. 

That lipid alkoxyl radicals recombine (Reaction 71) at diffusion controlled rates (k= 10 M s ) (198, 305) probably accounts for the presence of low levels of peroxides even under mild conditions and low levels of oxidation. In one study, oxidation of linoleic acid at 30°C gave —C—O—O—C— dimers. Reactions 71-73 were found in linolenic acid oxidized under mild conditions to PV 585 this increased to > 50% at PV 4000 and to > 75% after heating to 40°C (276). Alkoxyl radicals from hydroperoxyepidioxides heated at 40°C generated > 90% dimers (276). 

The antioxidant role of NO comes Ifom its reaction with oxygen, carbon and nitrogen centred radicals and can be seen to have a scavenger role under a range of conditions [112]. This is because of the unpaired electrons of NO which react rapidly with alkoxyl and alkyl hydroperoxyl radicals at near diffusion reaction rates (2x10 M s [113]). It is these reactions that have been suggested to have a modulatory role in enzyme- or metal-catalysed... 

The solubility of alkylene oxides in the reaction mass is another important parameter, because the reaction takes place in the liquid phase and the gaseous monomer is transferred from the gas phase to the liquid phase. Because all the propoxylation and ethoxylation reactions are strongly diffusion dependent, the surface of the gas-liquid interface is a very important parameter for the mass transfer from the gas to liquid, and the real consumption of alkylene oxides depends strongly on this parameter. Between the alkoxylation of fatty alcohols and the alkoxylation of glycerol, there are many similarities if we use the Santacesaria kinetic model. Thus if RXH are considered to be the hydroxyl groups of the starter, the reaction rate of alkylene oxides addition is ... 

Peroxyl radicals (ROO ) are also formed in cells via lipid peroxidation. These radicals are quite stable and can diffuse to remote cellular locations. It is estimated that the half-lives of peroxyl radicals are upto a few seconds [41], Among several ROO, HOO is the simplest peroxyl radical formed due to the protonation of 02 in living cells. It can modify fatly acids, proteins and DNA. HOO mediated damage to DNA mainly occurs through its reactions with the bases and sugar moieties. Similarly, metal induced catalysis of organic peroxyl radicals can generate alkoxyl radicals (RO ), which are even more reactive than ROO. However, the half-life of an alkoxyl radical is much shorter than that of a typical ROO. ... 

Chien and Kiang [44] carried out oxidative pyrolysis of PP at temperatures between 240 °C and 289 °C. The products were separated by GC and identified online by an interface GC peak-identification system. The major products were CO, H O, acetaldehyde, acetone, butanal, formaldehyde, methanol and other ketones and aldehydes. These identifications were confirmed by MS. Most of the products can be accounted for by well-known reactions of alkoxyl and peroxyl radicals the major products are derived from the secondary alkoxy and peroxy species. Oxygen starvation is manifested in diffusion-limited products of olefins and dienes, and the increase in the formation of CO and H O in an atmosphere of pure oxygen. The first-order rate constant at 240 °C is 2.4 x 10 Vs, with an overall activation energy of approximately 16 kcal/mol (67 kj/mol). If one assumes that the oxidative pyrolysis shares the same reaction pathways as autoxidation at lower temperatures, then the observed rate constants and activation energy may be calculated from kinetic... 

Many alkoxyl radicals recombine with the diffusion rate constant... 

Atoms or unlikely charged metal ions meet in the cage and immediately enter into the reaction, whose rate is limited by translatory diffusion. Many radicals, in particular, hydroxyl, alkoxyl, alkyl, and phenoxyl radicals, react in the same way. For such reactions T) and... 

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