The Reactions of Free Radicals

A summary of the major chemical reactions of free radicals is given in Table 4.3. Broadly speaking these can be classified as unimolecular reactions of dissociations and isomerizations, and bimolecular reactions of additions, disproportionations, substitutions, etc. The complexity of many photochemical reactions stems in fact from these free radical reactions, for a single species formed in a simple primary process can lead to a variety of final products. 

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The reactions of free radicals in ethylene are well known (5, 24), and the applicability of this information to radiation chemistry has been demonstrated (32). Kinetic analysis of radical reactions revealed that the formation of methyl radicals and methane cannot be ascribed to excited precursors alone (32, 37). 

Chemical interactions also occur in the condensed phases. Some of these are expected to be quite complex, e.g., the reactions of free radicals on the surfaces of or within aerosol particles. Simpler sorts of interactions also exist. Perhaps the best understood is the acid-base relationship of NH3 with strong acids in aerosol particles and in liquid water (see Chapter 16). Often, the main strong acid in the atmosphere is H2SO4, and one may consider the nature of the system consisting of H2O (liquid), NH3, H2SO4, and CO2 under realistic atmospheric conditions. Carbon dioxide is not usually important to the acidity of atmospheric liquid water (Charlson and Rodhe, 1982) the dominant effects are due to NH3 and H2SO4. The sensitivity the pH of cloud (or rainwater produced from it) to NH3 and... 

Although NMR spectrometers of operating frequencies > 400 MHz are cosdy and require specialist technical support staff, the technique provides a broad picture of the chemical modifications arising from the reactions of free radicals or related oxidants in complex, multicomponent systems such as intact biofluids, tissue sample... 

Class II second-order rate expressions are one of the most common forms one encounters in the laboratory. They include the gas phase reaction of molecular hydrogen and iodine (H2 + I2 -> 2HI), the reactions of free radicals with molecules (e.g., H -f Br2 -> HBr -f Br), and the hydrolysis of organic esters in nonaqueous media. 

Hydrogen bromide was found to initiate the autoxidation of decane [197]. The reactions of free radicals generation are the following ... 

We can see that the rate of initiation increases during autoxidation from 10 7 to 10 4 mol L 1 s-1 (about 1000 times). Due to increasing concentrations of 2-methylbutyl alcohol and acetic acid, the latter becomes a very important reactant in the reactions of free radical generation. 

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,... 

The reaction of the peroxyl radical with the sulfonyl radical was studied by pulse photolysis technique [38]. Both radicals were generated photochemically by a light pulse (A = 270 -380 nm) in the system DBP-cyc/o-CgHnSCkCI ryc/o-CgH lRH) air (T 293 K). The reactions of free radical formation were the following ... 

The reactions of free radicals with furan and its derivatives can give both addition and substitution products depending on the specific system (11-13). With 2-substituted furans, the attack takes place predominantly at C5 and leads, by additon, to the corresponding furyl radicals which must be viewed as relatively stabilized interemediates because of the dienic-aromatic character of the furan heterocycle. These premises are essential to the understanding of the varied responses of furan monomers to free-radical activation. 

Moad G, Rizzardo E, Solomon DH (1982) Selectivity of the reaction of free radicals with styrene. Macromolecules 15 909-914... 

With the reaction of free radicals or atoms much higher magnitudes of specific impulse may be obtained. 

Photolysis of phenyl disulfide in various nonhydroxylic solvents under nitrogen atmosphere gives 0- and p-HSCoHiSCoHj and thiophenol. The reaction of free radicals (2C6H6S-) to give C6HsSC6H4SH is completely prevented by blocking all of the ortho- and para positions of phenyl disulfide. 177-231... 

Kinetics of the Reaction of Free Radicals with Oxygen... 

In cells, DNA is always surrounded by proteins (cf. Fig. 12.2). The attachment of proteins modifies the DNA damage by various effects hampering an easy access of free-radicals, protection by compaction and repair of some of the damage by electron/hydrogen-donation. On the other hand, it may even induce some DNA damage via reactive intermediates formed upon the reaction of free radicals with the proteins. For this reason, the structure of DNA in solution and in the cellular environment will also have to be addressed. 

Maillard B. Rate constants for the reactions of free radicals with oxygen in solution. KU Ingold and JC Scaiano. J Am Chem Soc 1983 105 5095-5099. 

The process of obtaining alkyl sulphonate in an autoclave with a mixer has been studied. Basic reagents were water solution of sodium hydrosulfite 36-38% and industrial olefin fractions at 240-320 °C. NaN03 and oxygen from air were used as initiators of the reaction of free radicals. System factors are x, reaction time, h x2 temperature of reaction, °C x3 mole ratio of sodium hydrosulfite and olefin x3 mole ratio of NaN03 and olefin x5 volume ratio of N-propanol and olefin. System response is a yield of alkyl sulfonate as a per cent of theoretical yield. FRFE design... 

Russell, G. A. Solvent effects in the reactions of free radicals and atoms. II. Effects of solvents on the position of attack of chlorine atoms upon 2,3-dimethylbutane, isobutane and 2-deuterio-2-methyl-propane. J. Amer. chem. Soc. 80, 4987 (1958). 

The autoxidation of S02 solutions is known to involve free radicals. Recent work on the reaction of free radicals with sulfite and bisulfite and on the reaction of the sulfite and peroxysulfite radicals is beginning to allow this complex system to be understood better. This is particularly true of the effect of added chemicals on S02 autoxidation and chemical transformations induced by this system. 

On the other hand, the indirect type of ozonation is due to the reactions of free radical species, especially the hydroxyl radical, with the organic matter present in water. These free radicals come from reaction mechanisms of ozone decomposition in water that can be initiated by the hydroxyl ion or, to be more precise, by the hydroperoxide ion as shown in reactions (4) and (5). Ozone reacts very selectively through direct reactions with compounds with specific functional groups in their molecules. Examples are unsaturated and aromatic hydrocarbons with substituents such as hydroxyl, methyl, amine groups, etc. [45,46],... 

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