Iron-induced reactions

An excess of a standard solution of iron(II) must therefore be added and the excess back-titrated with standard cerium(IV) sulphate solution. Erratic results are obtained, depending upon the exact experimental conditions, because of induced reactions leading to oxidation by air of iron(II) ion or to decomposition of the persulphate these induced reactions are inhibited by bromide ion in concentrations not exceeding 1M and, under these conditions, the determination may be carried out in the presence of organic matter. 

INDUCED REACTIONS CAUSED BY ARSENIC(lv) INTERMEDIATES 2.2.1 Iron II)-arsenic III)-peroxydisulphate system In the absence of oxygen... 

The stoichiometry of the induced reaction depends, as in the Fe(II)-S20 system, on the iron(II)/iron(III) ratio and on the pH. Therefore, it can be expected that under identical experimental conditions (actor, inductor, and hydrogen ion concentration) the induction factors for the two systems should be identical. The data obtained show that this expectation is fulfilled. For the photo-induced oxidation of arsenic(III) the value of ks /k -j was found to be 2, while in the present system k Jk -j = 4. (Comparing these values with the value of k jk = 21, it can be concluded that the SO4 radical, formed by reaction (43), is not removed by the reaction... 

It was found that the value of F, is markedly increased by ions which are effective catalysts of oxidation reactions of peroxydisulphate. These are silver(I) copper(n), and iron(III). Cobalt(II) and nickel(II) ions, although they are good catalysts for the decomposition of hydrogen peroxide, exert their effect merely as inert electrolytes in the induced reaction. Therefore it can be concluded that, in this process, activation of the rather less reactive 8203 is more important than that of hydrogen peroxide . ... 

Induced reactions involving hydrogen peroxide can be observed with hydrogen peroxide derivatives, as well. For instance, the reaction between cumene hydroperoxide and iron(IT), in the absence of oxygen, results in a considerable induced decomposition of the peroxy compound, while, in the presence of oxygen, a marked oxidation of iron(II) takes place s . 

During the induced reactions involving peroxydisulphate in the presence of oxygen, the induced oxidation of iron(II) by oxygen can be observed just as with the hydrogen peroxide-iron(ll) system. Chloride and particularly bromide ions are effective inhibitors in the iron(II)-peroxydisulphate system. 

The nonacarbonyldiiron-induced transformation of oxazabicyclo[2.2.2] octenes (12) into condensed azetidinones is intriguing mechanistically but will obviously have limited synthetic application (Scheme 15).37 The /(-lactam (14a), among other products, is isolated directly from the iron carbonyl reaction but the dimethyl analog (14b) is obtained by pyrolysis of an isolable intermediate <7-7r-allyl complex (13b). 

It must be noted that the inhibitory effects of flavonoids and other antioxidants in nonhomogenous biological systems can depend not only on their reactivities in reactions with free radicals (the chain-breaking activities) but also on the interaction with biomembranes. Thus, Saija et al. [137] compared the antioxidant effects and the interaction with biomembranes of four flavonoids quercetin, hesperetin, naringen, and rutin in iron-induced... 

Although thermodynamically favorable, reductive dissolution of Fe(III)(hydr)oxides by some metastable ligands (even those, such as oxalate, that can form surface complexes) does not occur in the absence of light. The photochemical pathway is depicted in Fig. 9.3e. In the presence of light, surface complex formation is followed by electron transfer via an excited state (indicated by ) either of the iron oxide bulk phase or of the surface complex. (Light-induced reactions will be discussed in Chapter 10.)... 

The synthesis of metal-coordinated 1-azirines and the reactions of azirines induced by metals have opened a new area in the chemistry of this small ring heterocycle. Many of the reactions encountered bear resemblance to previously discussed thermally and photo-chemically induced reactions of 1-azirines. The reaction of a series of diiron enneacarbonyls in benzene results in coupling and insertion to give diimine complexes and ureadiiron complexes as well as pyrroles and ketones (76CC191). A mechanism for the formation of these products which involves initial 1,3-bond cleavage and generation of a nitrene-iron carbonyl complex as an intermediate was proposed. 

The difficulty in removing metal residues from the product induced the search for iron-catalyzed reactions [77]. However, iron complexes can play different roles in catalytic processes ... 

Plant use of iron depends on the plant s ability to respond chemically to iron stress. This response causes the roots to release H+ and deduct ants, to reduce Fe3+, and to accumulate citrate, making iron available to the plant. Reduction sites are principally in the young lateral roots. Azide, arsenate, zinc, copper, and chelating agents may interfere with use of iron. Chemical reactions induced by iron stress affect nitrate reductase activity, use of iron from Fe3+ phosphate and Fe3+ chelate, and tolerance of plants to heavy metals. The iron stress-response mechanism is adaptive and genetically controlled, making it possible to tailor plants to grow under conditions of iron stress. 

A variety of synthetic routes to monoene and polyene tri-fluorophosphine-transition metal complexes have been devised. Direct photochemically induced reaction of a metal-PF3 complex with an activated alkene or diene (method A) has proved useful only for iron, the products being either [Fe(PF3)4(alkene)J or [Fe(PF3)3(diene)] (194). Mixed carbonyl-trifluorophosphine complexes of the type [Fe(PF3)x(CO)3 x(diene)] result from either thermal or photochemical reactions of dieneiron carbonyl complexes and PF3 (52, 53) (method B). The compounds are fluxional. 

A similar reaction with iron(IIl) nitrate (nonahydrate) in dimethylformamide with molecular sieves yields a bicyclic methyl ketone in moderate yield.This might be obtained by hydrogen atom abstraction of the similarly formed cyclized radical from the solvent. A variety of 4-substituted 2-cyclohexenones can be prepared based on the iron(III) chloride induced reaction of 3-alkyl-l-siloxybicyclo[3.1.0]hexanes. ... 

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