Ferrous ions-peroxide system

The presence of two hydroxyl groups per molecule in poly-(methyl methacrylate) and in polystyrene, each polymerized in aqueous media using the hydrogen peroxide-ferrous ion initiation system, has been established " by chemical analysis and determination of the average molecular weight. Poly-(methyl methacrylate) polymerized by azo-bis-isobutyronitrile labeled with radioactive has been shown to... 

The most common water-soluble initiators are ammonium persulfate, potassium persulfate, and hydrogen peroxide. These can be made to decompose by high temperature or through redox reactions. The latter method offers versatility in choosing the temperature of polymerization with —50 to 70°C possible. A typical redox system combines a persulfate with ferrous ion ... 

Lipid peroxidation is probably the most studied oxidative process in biological systems. At present, Medline cites about 30,000 publications on lipid peroxidation, but the total number of studies must be much more because Medline does not include publications before 1970. Most of the earlier studies are in vitro studies, in which lipid peroxidation is carried out in lipid suspensions, cellular organelles (mitochondria and microsomes), or cells and initiated by simple chemical free radical-produced systems (the Fenton reaction, ferrous ions + ascorbate, carbon tetrachloride, etc). In these in vitro experiments reaction products (mainly, malon-dialdehyde (MDA), lipid hydroperoxides, and diene conjugates) were analyzed by physicochemical methods (optical spectroscopy and later on, HPLC and EPR spectroscopies). These studies gave the important information concerning the mechanism of lipid peroxidation, the structures of reaction products, etc. 

In contrast to numerous literature data, which indicate that protein oxidation, as a rule, precedes lipid peroxidation, Parinandi et al. [66] found that the modification of proteins in rat myocardial membranes exposed to prooxidants (ferrous ion/ascorbate, cupric ion/tert-butyl-hydroperoxide, linoleic acid hydroperoxide, and soybean lipoxygenase) accompanied lipid peroxidation initiated by these prooxidant systems. 

The initiators used in emulsion polymerization are water-soluble initiators such as potassium or ammonium persulfate, hydrogen peroxide, and 2,2 -azobis(2-amidinopropane) dihydrochloride. Partially water-soluble peroxides such a succinic acid peroxide and f-butyl hydroperoxide and azo compounds such as 4,4 -azobis(4-cyanopentanoic acid) have also been used. Redox systems such as persulfate with ferrous ion (Eq. 3-38a) are commonly used. Redox systems are advantageous in yielding desirable initiation rates at temperatures below 50°C. Other useful redox systems include cumyl hydroperoxide or hydrogen peroxide with ferrous, sulfite, or bisulfite ion. 

The most common initiators are acyl peroxides, hydroperoxides, or azo compounds. Hydrogen peroxide, potassium persulfate, and sodium perborate are popular in aqueous systems. Ferrous ion in some cases enhances the catalytic effectiveness. 

The free-radicals are generated by discharge of proton, peroxides and easily reducible compounds at the cathode according to Eq. (1—4). The radial-anion of monomer is obtained by both direct and indirect electron transfer process [Eq. (5—6)]. The indirect process means that the active oxidizing species is formed from the electrolytes by electrode reaction, followed by interaction with the monomer. An unstable monomer like a,a -2-trichloro-p-xylene is formed and polymerizes instantaneously [Eq. (7)]. The regeneration of ferrous ion from the pool of used up ferric ion in a redox system is electrolytically successful [Eq. (8)] and an... 

The reactions of tert-alkyl hydroperoxides with ferrous ion generate alkoxy radicals. These free-radical initiator systems are used industrially for the emulsion polymerization and copolymerization of vinyl monomers, c.g., butadiene-styrene. Alkyl hydroperoxides are among tile most drermally stable organic peroxides. However, hydroperoxides are sensitive to chain decomposition reactions initiated by radicals and/or transition-metal ions. Such decompositions, if not controlled, can be autoaccelerating and sometimes can lead to violent decompositions when neat hydroperoxides or concentrated solutions of hydroperoxides are involved,... 

The first report of the polymerization of tetrafluoroethylene was by Plunkett in 1941, who had a cylinder of tetrafluoroethylene cut open to see why the expected amount of gas was not released when the valve was opened. His perspicacity led to the discovery of an inert, white, opaque solid with a waxy feel. Various methods of polymerization were tried after the adventitious discovery and the preferred methods for polymerization now involve aqueous media and super-atmospheric pressures. Suitable initiators (Hanford and Joyce) include ammonium, sodium, or potassium persulfate, hydrogen peroxide, oxygen, and some organic peroxy compounds. Oxidation-reduction initiation systems involving the use of persulfate with either ferrous ion or bisulfite or the use of bisulfite with ferric ion are also useful and have been discussed by Berry and Peterson. 

Merz and Waters (1949) showed that oxidation of organic compounds by Fenton s reagent could proceed by chain as well as non-chain mechanisms, which was later confirmed by Ingles (1972). Kremer (1962) studied the effect of ferric ions on hydrogen peroxide decomposition for Fenton s reagent. It was confirmed that once ferric ions are produced the ferric-ferric system is catalytic in nature, which accounts for relatively constant concentration of ferrous ion in solutions. 

NADPH-cytochrome P-450 reductase catalyzes the reduction of ferric ion to ferrous ion in the presence of chelators (384, 588). This reaction is similar to the peroxidation of microsomal lipids which has been shown to be dependent on the NADPH oxidase system of microsomes (389, 390). Lipid peroxidation is thought to be involved in prostaglandin biosynthesis (390-392). The microsomal system can be mimicked in the peroxidation of extracted microsomal lipid by a combination of NADPH, NADPH-cytochrome P-450 reductase, and ferric ion chelated with EDTA (374,... 

Minisci, Galli and co-workers have studied a variety of radical reactions which result in the formation of organic azides. These processes commonly involve the interaction of an organic peroxide, an alkene, and azide ion in the presence of a ferrous-ferric redox system. The initial step is the reduction of the peroxide by Fe " " to form a free alkoxy radical (Fenton reaction, equation 104). 

The one-electron reduction of hydrogen peroxide by low-valence transition-metal ions has been studied by e.s.r. using flow-system techniques. There is evidence that, when ferrous ion is the reducing agent, the reaction may be represented by the following modification (Uri, 1952) of the original proposal by Haber and Weiss (1934) ... 

Polymerization of a monomer in an emulsion system is similar to suspension polymerization in that the bulk medium in both cases is water. But there the similarity ends [8-10]. Monomer and initiator are still present, but this time the initiator must be a water-soluble, monomer-insoluble type. Suitable for this purpose is the persulfate-ferrous ion or peroxide-ferrous ion systems (Eqs. 22.7 and 22.8). 

Photoreactions that involve transition metal ions, complexes or compounds can usually be classified as (photo)redox (simultaneous oxidation and reduction) processes. A representative non-photoassisted catalytic system is Fenton s reagent that produces HO radicals on reaction of ferrous ions (Fe2 +) and hydrogen peroxide (Scheme 6.287a). Its photochemical counterpart is the photo-Fenton process,1527 in which ferric (Fe3 + ) complexes in aqueous solutions (absorbing over 300 nm) are reduced to ferrous ions (Scheme 6.287b). 

The application of these reagents to synthetic problems has not yet been attempted. Possibly the effect of hydrogen atoms on aqueous systems can be studied by using a static ozonizer discharge containing aqueous solutions. It has been demonstrated that ceric ions may be reduced to cerous ions and that ferrous ions are oxidized to ferric ions (with formation of hydrogen peroxide) by simple exposure of the appropriate solutions to a silent electric discharge (63, 64). These reactions are believed to involve the formation of H atoms and OH radicals. 

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