Mechanism of free radical

The mechanism of free radical polymerization of ethylene is outlined m Figure 6 17 Dissociation of a peroxide initiates the process m step 1 The resulting per oxy radical adds to the carbon-carbon double bond m step 2 giving a new radical which then adds to a second molecule of ethylene m step 3 The carbon-carbon bond forming process m step 3 can be repeated thousands of times to give long carbon chains... 

Bamford and coworkers [24] also investigated the kinetics and mechanism of free radical polymerization of bulk MMA photoinitiated by Mn2(CO)io or Re2(CO)io in the presence of a series of fluoro-olefms such as ... 

A question which inevitably arises on surveying the enormous sucess of the Amoco catalyst is why the combination Co/Mn/Br in acetic acid In order to answer this question we must first examine the mechanism of free radical chain autoxidations of alkylaromatics (ref. 4). 

The mechanism of free-radical addition follows the pattern discussed in Chapter 14 (pp. 894-895). The method of principal component analysis has been used to analyze polar and enthalpic effect in radical addition reactions. A radical is generated by... 

Still another, and chains, long or short, may be built up. This is the mechanism of free-radical polymerization. Short polymeric molecules (called telomers), formed in this manner, are often troublesome side products in free-radical addition reactions. 

Mechanisms of Free-radical Damage in Activity in Diabetic Vascular Disease 193... 

Hepatic reperfusion injury is not a phenomenon connected solely to liver transplantation but also to situations of prolonged hypoperfusion of the host s own liver. Examples of this occurrence are hypovolemic shock and acute cardiovascular injur) (heart attack). As a result of such cessation and then reintroduction of blood flow, the liver is damaged such that centrilobular necrosis occurs and elevated levels of liver enzymes in the serum can be detected. Particularly because of the involvement of other organs, the interpretation of the role of free radicals in ischaemic hepatitis from this clinical data is very difficult. The involvement of free radicals in the overall phenomenon of hypovolemic shock has been discussed recently by Redl et al. (1993). More specifically. Poll (1993) has reported preliminary data on markers of free-radical production during ischaemic hepatitis. These markers mostly concerned indices of lipid peroxidation in the serum and also in the erythrocytes of affected subjects, and a correlation was seen with the extent of liver injury. The mechanisms of free-radical damage in this model will be difficult to determine in the clinical setting, but the similarity to the situation with transplanted liver surest that the above discussion of the role of XO activation, Kupffer cell activation and induction of an acute inflammatory response would be also relevant here. It will be important to establish whether oxidative stress is important in the pathogenesis of ischaemic hepatitis and in the problems of liver transplantation discussed above, since it would surest that antioxidant therapy could be of real benefit. 

In this volume centred around different disease processes, various basic mechanisms of free radical processes and injury are dissected. In each case there is an emphasis given to potential therapeutic strategies that develop from this new knowledge. We would like to thank all our contributors for their efforts and beg their forgiveness for our mild eccentricities. 

The fundamental mechanisms of free radical reactions were considered in Chapter 11 of Part A. Several mechanistic issues are crucial in development of free radical reactions for synthetic applications.285 Free radical reactions are usually chain processes, and the lifetimes of the intermediate radicals are very short. To meet the synthetic requirements of high selectivity and efficiency, all steps in a desired sequence must be fast in comparison with competing reactions. Owing to the requirement that all the steps be fast, only steps that are exothermic or very slightly endothermic can participate in chain processes. Comparison between addition of a radical to a carbon-carbon double bond and addition to a carbonyl group can illustrate this point. 

According to this scheme the fundamental difference in the mechanism of free-radical copolymerization of MA with TASM and of MA with alkyl acrylates is due to the fact that in the former copolymerization intermolecular coordination is involved. This coordination is similar to the effect of various complexing agents (ZnCl2, SnCft and A1C13) on free-radical homo- and copolymerization of vinyl monomers. This effect seems to favor the appearance of isotactic configurations along the main chain. 

Everett, S.A., Kundu, S.C., Maddix, S., and Willson, R.L. 1995. Mechanisms of free-radical scavenging by the nutritional antioxidant (3-carotene. Biochem. Soc. Trans. 23 230S. 

N.A. Porter, S.E. Caldwell, K.A. Mills, Mechanisms of free radical oxidation of unsaturated lipids, Lipids, 30, 277 290 (1995). 

Mechanisms of Free Radical Reactions in Tumor Cells... 

Mechanisms of Free Radical-Mediated Inflammatory Processes... 

The cyclic mechanism of free radicals generation in oxidation of aldehydes catalyzed by transition metal ions was demonstrated C. Bawn and J. Williamson [65]... 

Different mechanisms of free radical formation as a result of the decomposition of initiators are known. 

The study of the detailed mechanism of free radical initiation (rate constant k ) and ozone decay (rate constant d) by the reaction with cyclohexane, cumene, and aldehydes gave the following results (7 = 298 K) ... 

The chain generation by the reaction with dioxygen was studied for esters of different structures. Four mechanisms of free radical formation were evidenced. 

The decay of 1,1-dimethylethyl hydroperoxide into free radicals under action of mineral acids was also established [229]. The similar kinetic equation was observed in this system and the rate of initiation was found to be propotional to the electroconductivity of the solution. The following mechanism of free radical generation was proposed [229]. 

Formation of hydroxyl radicals has been suggested in many studies, which are considered in subsequent chapters in connection with the mechanisms of lipid peroxidation and protein and DNA destruction as well as the mechanisms of free radical pathologies. Furthermore, hydroxyl radical generation occurs under the conditions of iron overload and is considered below. 

The formation of hydroxyl or hydroxyl-like radicals in the reaction of ferrous ions with hydrogen peroxide (the Fenton reaction) is usually considered as a main mechanism of free radical damage. However, Qian and Buettner [172] have recently proposed that at high [02]/ [H202] ratios the formation of reactive oxygen species such as perferryl ion at the oxidation of ferrous ions by dioxygen (Reaction 46) may compete with the Fenton reaction (2) ... 

The mechanism of free radical formation in the reactions catalyzed by MPO and other heme peroxidase may be presented as follows [180] ... 

At present, numerous free radical studies related to many pathologies have been carried out. The amount of these studies is really enormous and many of them are too far from the scope of this book. The main topics of this chapter will be confined to the mechanism of free radical formation and oxidative processes under pathophysiological conditions. We will consider the possible role of free radicals in cardiovascular disorders, cancer, anemias, inflammation, diabetes mellitus, rheumatoid arthritis, and some other diseases. Furthermore, the possibilities of antioxidant and chelating therapies will be discussed. 

Bromine-atom atomic resonance absorption spectrometry (ARAS) has been applied to measure the thermal decomposition rate constants of CF3Br in Kr over the temperature range 1222-1624 K. The results were found to be consistent with recently published theory. The formation of cyclopent[a]indene and acenaphthylene from alkyl esters of biphenyl-mono- and -di-carboxylic acids has been observed in flash vacuum pyrolyses at 1000-1100 °C. The kinetics and mechanisms of free-radical generation in the ternary system containing styrene epoxide, / -TsOH, and i-PrOH have been examined in both the presence and absence of O2. ... 

Knowledge of bond dissociation enthalpies (DH) has always been considered fundamental for understanding kinetics and mechanisms of free radicals. DHs offer an interesting window through which to view stability of radicals. Indeed, based on Reaction (2.1) the bond dissociation enthalpy of silanes D/f(R3Si—H) is related to enthalpy of formation of silyl radicals, A//f (RsSi ), by Equation (2.2). 

Many of the synthetic elastomers now made are still polymerized by a free radical mechanism. Polychloroprene, polybutadiene, polyisoprene, and styrene-butadiene copolymer are made this way. Initiation by peroxides is common. Many propagation steps create high molecular weight products. Review the mechanism of free radical polymerization of dienes given in Chapter 14, Section 2.2. 

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