Ceric ion redox

To sum up, the optimum conditions for methylmethacrylate grafting onto pulp by the ceric ion redox system can be summarized as follows the grafting is done at 30°C for a 1-h reaction time, using liquor ratio 40 1, acid concentration 1%, initiator concentration 0.1%, and monomer 1 mL/g pulp. 

Graft Copolymerization of Vinyl Monomers Onto Macromolecules Having Active Pendant Group via Ceric Ion Redox or Photo-Induced Charge-Transfer Initiation... 

Mino, G., and S. Kaizerman A new method for the preparation of graft copolymers. Polymerization initiated by ceric ion redox systems. J. Polymer Sci. 31, 242 (1958). 

Polymerization Initiator. Some unsaturated monomers can be polymerized through the aid of free radicals generated, as transient intermediates, in the course of a redox reaction. The electron-transfer step during the redox process causes the scission of an intermediate to produce an active free radical. The ceric ion, Ce" ", is a strong one-electron oxidizing agent that can readily initiate the redox polymerization of, for example, vinyl monomers in aqueous media at near ambient temperatures (40). The reaction scheme is... 

Following the findings of Mino and Kaizerman [51] that ceric ion can form a redox system with cellulose, grafting onto various natural polymers has been carried out by the ceric ion method. In the case of cellulose, the reaction between ceric ion and cellulose occurs to produce active sites on cellulose in the following manner ... 

Misra et al. have utilized the ceric-amine redox system for grafting MM A onto wool [60] and gelatin [61], The graft yield was explained in terms of basicity, nu-cleophilicity, and steric requirements of amines. A complex of ceric ion and amine (AH) decomposes to generate free radical species, which produce additional active sites onto the polymeric backbone where grafting can occur. 

Mino and Kaizerman [12] established that certain. ceric salts such as the nitrate and sulphate form very effective redox systems in the presence of organic reducing agents such as alcohols, thiols, glycols, aldehyde, and amines. Duke and coworkers [14,15] suggested the formation of an intermediate complex between the substrate and ceric ion, which subsequently is disproportionate to a free radical species. Evidence of complex formation between Ce(IV) and cellulose has been studied by several investigators [16-19]. Using alcohol the reaction can be written as follows ... 

A final class of multifunctional initiators is based on the use a (muUi)functional polymer and a low molecular weight redox agent. Radicals on the polymer chain arc generated from the polymer bound functionality by a redox reaction. Ideally, no free initiating species are formed. The best known of this class are the polyol-redox and related systems. Polymers containing hydroxy or glycol and related functionality are subject to one electron oxidation by species such as ceric ions or periodate (Scheme 7.23).266,267 Substrates such as cellulose,... 

The redox reaction occurring on addition of ceric ion to the solution of ferrous ion is as follows ... 

There is no redox couple in solution at the start of the ferrous-ceric titration because the solution contains only Fe ". The oxidation of ferrous to ferric occurs as soon as an aliquot of ceric ions enter the solution to effect the redox reaction shown in equation (4.1). The bulk of the initially present ferrous ions remain, with the ferric products of the redox reaction residing in the same solution, i.e. a Fe " ", Fe + redox couple is formed. This couple has the electrode potential Epf + pg2+. 

Note that all of the ceric ions in the aliquot are converted (in this case, reduced) to form cerous ions, i.e. there is only one redox form of the cerium in solution. 

As we have just seen, there are no redox couples - either Ce , Ce or Fe - in solution before the titration is started. As soon as ceric ions are added to the solution, the Fe, couple forms. At no point before the end point will any ceric ions remain in solution, i.e. within a reasonable time scale - because they react - and so there is no, Ce couple in solution. 

After the end point, all of the ferrous ions will have been consumed and converted to ferric ions, i.e. there is no longer a Fe, couple in solution. However, after the end point, the ceric ions added to the solution will not react because there is nothing left to oxidize, so Ce and Ce reside together as a new, different redox couple with its own electrode potential, Ece >+.Ce +-... 

IVe need to think in terms of both kinetics and thermodynamics when considering restrictions on the choice of redox systems. For simplicity, we will continue to employ the case where ferrous ion is titrated with ceric ion. 

There are two thermodynamic factors that must be considered. The first thing to remember is that the product of the redox reaction must be. soluble and electroactive. This is an obvious point, since both the oxidized and reduced forms of the titrant need to comprise a redox couple. Ceric ion, is therefore a good choice of oxidant, since Ce and its Ce ... 

Secondly, if the volume of ceric ion is to be an acceptable measure of the quantity of ferrous material in solution, then the reaction needs to go to completion, that is, the equilibrium constant K of the redox reaction (e.g. equation (4.1)) must be high. 

Redox initiation is often an efficient method for graft polymerization. Hydroxyl-containing polymers such as cellulose and poly(vinyl alcohol) undergo redox reaction with ceric ion or other oxidizing agents to form polymer radicals capable of initiating polymerization... 

Other typical reagents generated for coulometric titrations are hydrogen and hydroxyl ions, redox reagents such as ceric, cuprous, ferrous, chromate, ferric, manganic, stannous, and titanous ions, precipitation reagents such as silver, mercurous, mercuric, and sulfate ions, and complex-formation reagents such as cyanide ion and EDTA [8-10]. 

The hydroxyl radicals can react with cellulose, initiating graft copolymerization, or react with monomer, resulting in homopolymerization. A similar redox system is based on the use of ceric ions, which produce radicals by direct oxidation of the cellulose chains and thus initiate graft polymerization ... 

As a new approach to the preparation of water-soluble polymers in inverse miniemulsions, a redox initiation system consisting of ceric ions and carbohydrate-based surfactant Span 60 as a reducing agent has been successfully used for the... 

This paper summarizes chemical grafting techniques explored in this laboratory that have potential biomedical application. These reactions, initiated by ceric ions, persulfate-bisulfite redox systems, or the presence of comonomers forming donor-acceptor complexes, were carried out in an aqueous environment under conditions which, with suitable modifications, might be tolerated in vivo. Grafting onto tissue surfaces by means of ionizing radiation will not be discussed since techniques for avoiding undesirable side reactions have not yet been developed. 

A number of studies to determine the mechanisms of grafting onto collagen initiated by CAN, including characterization of the reaction products, have been reported (5, 8, 9, 53, 62). Ceric ammonium nitrate forms an effective redox system with alcohols, aldehydes, amines, and thiols. Alcohols form a ceric ion-alcohol complex, and the dissociation of this complex is the rate-determining step 63) ... 

A homogeneous catalyst exists in the same phase as the reactants. Ceric ion, Ce4+, at one time was an important laboratory oxidizing agent that was used in many redox titrations (Section 11-8). For example, Ce + oxidizes thallium(I) ions in solution this reaction is catalyzed by the addition of a very small amount of a soluble salt containing manganese(II) ions, Mn +. The Mn + acts as a homogeneous catalyst. 

Surface grafting of barium sulfate is interesting Ifom the point of view of the kinetics of such reactions. Barium sulfate like calcium carbonate, is an inert filler. So it is necessary to modify its surface. First, barium chloride is reacted with sodium sulfate in the presence of a small amount of sodium 12-hydroxystearate. This introduces a controlled number of hydroxyl stearate sites onto the barium sulfate surface. The reaction is followed by a redox graft polymerization of acrylamide initiated by the hydroxyl stearate groups and ceric ion as a catalyst. Figures 6.9 to 6.11 show the effect of reaction substrates concentrations on polymerization rate. 

The analyst has little choice in the selection of a redox analytical method. In acid solution ceric ion is the most effective oxidant however, in acid solution there is possibility of analytical error because of the volatility ofhydrazoic acid. In alkaline solution, reduction of the azide ion by homogeneous or heterogeneous reduction methods results in variable stoichiometry and cannot be used. The argentometric determination of azide ion in neutral solution is satisfactory but has one serious drawback the manipulation of silver azide, a high cxplosix c. Two basic approaches have evolved for the assay of azide ion ... 

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