Redox reactions radical addition

Heck reaction (Redox-neutral radical addition) 1 Ti(II) 3.2... 

Siefert et al. [136] simulated the chemical conditions of cloudwater using ambient aerosol samples suspended in an aqueous solution. Electron donors that are known to exist in atmospheric cloudwater (oxalate, formate, and acetate) were then added to the simulated cloudwater, and the solution irradiated with UV fight at A, > 300 nm. In all cases, H2O2 and Fe(II)aq were produced as a function of irradiation time. In addition, H2O2 was also produced without added electron donors simply using ambient aerosols collected from four different sites around the US. In addition, the production of Fe(II)aq showed that Fe from the ambient aerosol was available for photochemical redox reactions. In addition, the simultaneous release of Fe(II) and hydrogen peroxide will result in the indirect photochemical production of hydroxyl radical as follows ... 

Emulsion polymerization occurs almost entirely following the radical mechanism. The function of the initiator is to generate free radicals, which in turn lead to the propagation of the polymer molecules. The free radicals can be commonly produced by two main ways (i) thermal decomposition, or (ii) redox reactions. In addition, the free-radical initiators can be either water or oil-soluble. 

Another redox reaction leading to arenediazonium salts was described by Morkov-nik et al. (1988). They showed that the perchlorates of the cation-radicals of 4-A,A-dimethylamino- and 4-morpholinoaniline (2.63) react with gaseous nitric oxide in acetone in a closed vessel. The characteristic red coloration of these cation-radical salts (Michaelis and Granick, 1943) disappears within 20 min., and after addition of ether the diazonium perchlorate is obtained in 84% and 92% yields, respectively. This reaction (Scheme 2-39) is important in the context of the mechanism of diazotization by the classical method (see Sec. 3.1). 

There is an additional problem that arises in continuous radiolysis studies. If the solutions contain, Cl-, S0 , NO3 or CO ions the products of H2O radiolysis can react to produce the corresponding radicals. These radicals, CI2, SOiJ, or CO3 can then undergo redox reactions with the Pu ions such as... 

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

Initiation. Initiation in radical polymerisation consists of two steps the dissociation of the initiator to form two radical species, followed by addition of a single molecule to the initiating radical (Figure 18). Initiators include any organic compound with a labile group, such as an azo (-N = N-), disulfide (—S—S—) or peroxide (-0-0-) compound. The labile bond can be broken by various ways like heat, UV light, /-irradiation or by a redox reaction. 

Other methods of producing the initiating radicals include photochemical and redox reactions.) Initiation is followed by propagation of the radical by the successive additions of very large numbers (usually thousands) of monomer molecules... 

Steenken, S. One Electron Redox Reactions between Radicals and Organic Molecules. An Addition/Elimination (Inner-Sphere) Path. 177, 125-146 (1996). 

Two additional systems were exploited in order to confirm the involvement of free-radical processes during vindoline oxidations. These were the enzyme peroxidase and photochemistry. Horseradish peroxidase (HRP) oxidized both vindoline and 16-O-acetylvindoline in the presence of hydrogen peroxide. Vindoline was converted to the enamine dimer 59 (78). During the reaction, the following sequence of redox reactions occurs ... 

Case 1 appears to accurately predict the observed dependence on persulfate concentration. Furthermore, as [Q]+otal approaches [KX], the polymerization rate tends to become independent of quat salt concentration, thus qualitatively explaining the relative insensitivity to [Aliquat 336]. The major problem lies in explaining the observed dependency on [MMA]. There are a number of circumstances in free radical polymerizations under which the order in monomer concentration becomes >1 (18). This may occur, for example, if the rate of initiation is dependent upon monomer concentration. A particular case of this type occurs when the initiator efficiency varies directly with [M], leading to Rp a [M]. Such a situation may exist under our polymerization conditions. In earlier studies on the decomposition of aqueous solutions of potassium persulfate in the presence of 18-crown-6 we showed (19) that the crown entered into redox reactions with persulfate (Scheme 3). Crematy (16) has postulated similar reactions with quat salts. Competition between MMA and the quat salt thus could influence the initiation rate. In addition, increases in solution polarity with increasing [MMA] are expected to exert some, although perhaps minor, effect on Rp. Further studies are obviously necessary to fully understand these polymerization systems. 

A water-soluble Cj-symmetrical trisadduct of Cjq showed excellent radical scavenging properties in vitro and in vivo and exhibits remarkable neuro-pro tective properties [7,8]. It is a drug candidate for the prevention of ALS and Parldnsoris disease. Concerning the reaction mechanism, nucleophilic additions and radical additions are closely related and in some cases it is difficult to decide which mechanism actually operates [92]. For example, the first step in the reaction of f-eo with amines is a single electron transfer (SET) from the amine to the fullerene. The resulting amines are finally formed via a complex sequence of radical recombinations, deprotonations and redox reactions [36]. 

The effects of heteroatoms on autoxidation reactions are reviewed and discussed in terms of six phenomena (1) the effect on reactivity of a-hydrogens in the hydroperoxide chain mechanism in terms of electron supply and withdrawal (2) the effect on a-hydrogen acidity in base-catalyzed oxidation (3) the effect on radical ion stability in base-catalyzed redox chains (4) the possibility of heteroatom hydrogen bond attack and subsequent reactions of the resulting heteroradical (5) the possibility of radical attack on higher row elements via valence expansion (6) the possibility of radical addition to electron-deficient II and III group... 

Reversible redox reactions can initiate radical chemistry without a follow-up reduction or oxidation reaction. In successful reactions of this type, the redox step that produces the radical is thermodynamically disfavored. For example, Cu(I) complexes react reversibly with alkyl hahdes to give Cu(II) hahde complexes and an alkyl radical. The alkyl radical can react in, for example, an addition reaction, and the product radical will react with the Cu(II) hahde to give a new alkyl halide. This type of reaction sequence, which has been apphed in living radical polymerizations, is in the general family of nonchain radical reactions discussed earlier. ... 

Other examples of the EC mechanism include nucleophilic addition of Z (such as H20 or CN") to electrogenerated organic radical cations, ligand exchange reactions in the case of coordination compounds, and redox reactions between R and Z (or O and Z in the case of a reduction). 

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