Protons extraction

The number of protons extracted from the film during coloration depends on the width of the potential step under consideration. As can be seen in the formulation of Fig. 26 an additional valence state change occurs at 1.25 Vsce giving rise to another proton extraction. The second proton exchange may explain the observation by Michell et al. [91] who determined a transfer of two electrons (protons) during coloration. Equation (5) is well supported by XPS measurements of the Ir4/ and Ols levels of thick anodic iridium oxide films emersed at different electrode potentials in the bleached and coloured state. Deconyolution of the Ols level of an AIROF into the contribution of oxide (O2-, 529.6 eV) hydroxide, (OH, 531.2 eV) and probably water (533.1 eV) indicates that oxide species are formed during anodization (coloration) on the expense of hydroxide species. The bleached film appears to be pure hydroxide (Fig. 27). 

D2EF1PA is thus a poor extractant for nickel as this shows a preference for a pseudo-octahedral structure in which two axial ligands are either fully protonated extractant molecules, fully protonated extractant dimers, or water molecules depending on extractant concentration, and four equatorial sites are occupied by deprotonated isolated D2EHPA molecules. 

In many reactions, transfer of the anion across the interface and subsequent diffusion into the bulk of the organic phase will not be the rate-determining step when lipophilic catalysts are used, but the effect of less lipophilic catalysts may be influenced more by the anion and the mechanism of the transfer process. Thus, for example, the reactive anion is frequently produced in base-initiated reactions by proton extraction from the substrate at the two-phase interface and diffusion of the ion-pair contributes to the overall kinetics of the reaction. Additionally, the reactivity of the anion depends on its degree of hydration and on its association with the quaternary ammonium cation. In most situations, the activity of the transferred anion is enhanced, compared with its reactivity in aqueous media, as its degree of hydration is reduced, whereas a relatively weak electrostatic interaction between the two ions resulting from the bulkiness of the cation enhances the reactivity of the anion by making it more available for reaction and will be a major factor in the ratedetermining step. 

The mechanism in Fig. 14 applies equally well to both PVC and HPll. However, an unusual bond between the imidazole ring of His392 and the p-carbon of Tyr415 on the proximal side of the HPll heme has been identified (Fig. 13) (93), and subsequently its presence was correlated with heme oxidation. The apparent correlation between heme oxidation and His-Tyr bond formation suggested a mechanistic linkage between the two modifications and an alternate mechanism imique to HPll was proposed (Fig. 15). As with the first mechanism, the reaction assumes the formation of compound I that is available for reduction. Formation of the His-Tyr bond, involving a base catalyzed proton extraction from the... 

Examples for electrochromic behavior upon electrochemical oxidation can be found among group VIII metal oxides. Thin films of transparent hydrated iridium oxide turn blue-black, whereas nickel oxide switches from pale green to brown-black, possibly due to the absorbance of Ni3+ centers [26]. The systems are much less thoroughly investigated and a detailed mechanistic explanation is not known. However, proton extraction and anion insertion have been suggested. 

An important development in the use of superoxide as an EGB was the realisation that, if an excess of dioxygen is maintained during electrolysis, many carbanions formed by proton extraction by superoxide will rapidly react with the excess of dioxygen. 

This has been studied much less frequently and appears to be a rather more complex reaction. The first results obtained, for the butyl-lithium, styrene reaction in benzene have already been described. In a similar way the addition of butyllithium to 1,1-diphenylethylene shows identical kinetic behaviour in benzene (26). Even the proton extraction reaction with fluorene shows the typical one-sixth order in butyllithium (27). It appears therefore that in benzene solution at least, lithium alkyls react via a small equilibrium concentration of unassociated alkyl. This will of course not be true for reactions with polar molecules for reasons which will be apparent later. No definite information can be obtained on the dissociation process. It is possible that the hexamer dissociates completely on removal of one molecule or that a whole series of penta-mers, tetramers etc. exist in equilibrium. As long as equilibrium is maintained, the hexamer is the major species present and only monomeric butyllithium is reactive, the reaction order will be one-sixth. A plausible... 

If the source of anions A is a mineral acid, a competitive proton-extraction reaction might occur, which will decrease the affinity of the neutral solvation agent for the target trivalent elements ... 

The rate retarding role of water in radiation induced ionic polymerizations was visualized as proton extraction by water from the growing carbonium ion and hydronium ion formation (101). The formation of solvated hydronium ions is greatly favored energetically. 

In the 1,4-dihydropyridine series, there has been much discussion on detailed mechanism. In a study of reduction of-cyanocinnamates with a 4,4-dideutero Hantzsch dihydropyridine, a product that was singly deuterated at only the benzylic position together with the oxidized pyridine product 503 was obtained. This seems to show that the mechanism involves hydride transfer from the 4-position of the 1,4-dihydropyridine followed by proton extraction from the nitrogen of the dihydropyridine <2000J(P2)1857>. 

Scheme 4 Racemization of a A-Acyl Amino Acid Mixed Anhydride by Proton Extraction from the a-Carbon...

Iodide anation studies showed that substitution at this hydroxide CB did not in fact occur, water being a better leaving group than OH". Complications of the kinetics at high pH were more likely to be due to proton extraction from the Et4-dien (86). 

All the plants in operation use extractants of the ortAo-hydroxyoxime type, the active component being the anti isomer (14), in which R = alkyl, phenyl or hydrogen, and R = alkyl. These reagents (HA, where H denotes the replaceable, phenolic proton) extract copper by a pH-dependent cation-exchange mechanism ... 

The reduction of the pyrrolo[3,4-A]indol-3(2//)-ones 462 with LAH in toluene at reflux temperatures gave the expected 1,2,3,4-tetrahydro derivative 463 in 45% yield. However, the dihydropyrrolo[3,4-6]indole 464 was also isolated. The yield of this latter product was increased from 27 to 42% when the reduction was carried out in the presence of l-ethylpiperidine. This was interpreted as increasing the propensity toward C-1 proton extraction from the aluminum-oxygen complex 465. 

The mechanism of the Swem oxidation has been studied in depth and the formation of an initial adduct 7 from the reaction between dimethyl sulfoxide and oxalyl chloride which then collapses to give a dimethylchlorosulfonium species 8 is clearly indicated by mechanistic studies.3,8 Reaction of 8 with an alcohol then produces the alkyoxysulfonium ion 9 which upon treatment with an amine base gives the ylide 10. Subsequent proton extraction gives the carbonyl product 2 with the release of dimethyl sulfide. 

Sodium cyclononatetraenide was also prepared, in lower yield, by proton extraction from bicyclo[6.1.O]nonatriene with the methyl-sulphinyl carbanion in dimethyl sulphoxide [66],... 

A typical example of anodic ECMs is iridium oxide which may be rapidly and reversibly coloured in aqueous solutions containing sulphuric acid. The exact type and mechanism of the ion insertion process in this oxide are still uncertain [17]. In aqueous H2SO4, the most commonly used electrolyte, two mechanisms have been proposed, i.e. a cation mechanism involving coloration via proton extraction ... 

Figure 2. D iee of tiiennal coagulation of protons extracted firom mechanically separated seal meat (MSSM, H) and mechanically separated duckm meat (MSCM, by S% NaCl in 0.003M NaHC03 solution. Results are mean values of 4 detominations and standard deviations did not exceed 3.7% of the recmded mean values.

All efforts were therefore concentrated on examining the potential of a-phenylglycidate as an afiinity label. Structurally it is very similar to mandelate. Moreover, the-CHz-group of the epoxide ring seemed strategically placed to intercept the key basic group postulated to be involved in the a-proton extraction process associated with enzymic catalysis ... 

Uses Protonic extraction agent, bleach bath stabilizer, sequestrant, wetting agent for variety of bleaching applies, incl. continuous, pad-batch, and pkg. bleaching Environmentai Biodeg. 

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