Redox potentials chlorins

Such informations can be correlated with those coming from standard chemical monitoring systems (conductivity, acid conductivity, pH, redox potential, chlorine, sodium and oxygen concentration, etc.). 

When either hydrogen ions or hydroxide ions participate in a redox half-reaction, then clearly the redox potential is alTected by change of pH. Manganate(Vir) ions are usually used in well-acidified solution, where (as we shall see in detail later) they oxidise chlorine ions. If the pH is increased to make the solution only mildly acidic (pH = 3-6), the redox potential changes from 1.52 V to about 1.1 V, and chloride is not oxidised. This fact is of practical use in a mixture of iodide and chloride ions in mildly acid solution. manganate(VII) oxidises only iodide addition of acid causes oxidation of chloride to proceed. 

Thus under standard conditions chloride ions are not oxidised to chlorine by dichromate(Vr) ions. However, it is necessary to emphasise that changes in the concentration of the dichromate(VI) and chloride ions alters their redox potentials as indicated by the Nernst equation. Hence, when concentrated hydrochloric acid is added to solid potassium dichromate and the mixture warmed, chlorine is liberated. 

Many of the reactions of halogens can be considered as either oxidation or displacement reactions the redox potentials (Table 11.2) give a clear indication of their relative oxidising power in aqueous solution. Fluorine, chlorine and bromine have the ability to displace hydrogen from hydrocarbons, but in addition each halogen is able to displace other elements which are less electronegative than itself. Thus fluorine can displace all the other halogens from both ionic and covalent compounds, for example... 

DCE interface in the presence of TPBCl [43,82]. The accumulation of products of the redox reactions were followed by spectrophotometry in situ, and quantitative relationships were obtained between the accumulation of products and the charge transfer across the interface. These results confirmed the higher stability of this anion in comparison to TPB . It was also reported that the redox potential of TPBCP is 0.51V more positive than (see Fig. 3). However, the redox stability of the chlorinated derivative of tetra-phenylborate is not sufficient in the presence of highly reactive species such as photoex-cited water-soluble porphyrins. Fermin et al. have shown that TPBCP can be oxidized by adsorbed zinc tetrakis-(carboxyphenyl)porphyrin at the water-DCE interface under illumination [50]. Under these conditions, the fully fluorinated derivative TPFB has proved to be extremely stable and consequently ideal for photoinduced ET studies [49,83]. Another anion which exhibits high redox stability is PFg- however, its solubility in the water phase restricts the positive end of the ideally polarizable window to < —0.2V [85]. 

When there is a peak flow of chlorine in the feed-stream the redox potential decreases and the amount of caustic that is dosed increases automatically. Caustic is fed to the jet-loop and its flow is regulated by the measurement of the redox potential. When the lead time is long there is a shortage of caustic, which results in a lower level of free caustic that leads to a higher chlorine concentration. This chlorine subsequently reacts with the chlorite in the hypochlorite solution to form chlorine dioxide. The absorption of chlorine dioxide by the caustic is then very limited in step one and is hardly absorbed at all in the caustic present in step two of the production and is emitted with the inert gas stream. 

Halo-de-diazoniations are a series of reactions in which the replacement of the dia-zonio group changes from a heterolytic de-diazoniation in the case of the fluorination (Balz-Schiemann reaction) to transition metal-catalyzed chlorination and bromination (Sandmeyer reaction) and finally to iodination and astatination where no catalyst is necessary due to the favorable redox potentials of I and At- (I- E° = 1.3 V). 

In contrast to the case of ZnCh-Ceo, no transient formation of Ceo" was detected at 1000 nm for any other dyad in Scheme 4b [65]. In each case, only the triplet-triplet absorption due to the chlorin or porphyrin moiety was observed due to the higher energy of the radical ion pair as compared to the triplet excited state as is expected from the redox potentials. Thus, the energy level of the radical ion pair in reference to the triplet energy of a component is an important factor in determining the lifetime of the radical ion pair. 

The most common valence state of indium is +3. However, +2 and -i-l valence states also exist. Chemical properties of indium are similar to aluminum. Its redox potential is -0.34V. When heated with chlorine at 200°C, indium becomes a dichloride ... 

In situ redox manipulation (ISRM) is an in situ, groundwater remediation technology for manipulating the oxidation-reduction (redox) potential of an unconfined aquifer to immobilize inorganic contaminants (metals, inorganic ions, and radionuclides) and to destroy organic contaminants (primarily chlorinated hydrocarbons). 

With the redox potential of the aquifer reduced, ISRM could potentially treat a variety of metals, radionuclides, and chlorinated organic solvents. 

The results demonstrate that the rate of the chlorine abstraction reaction (Eq. (47)), which is usually the rate determining step in this process, is affected by (a) the redox potential of the Cun/IL couple (solvents such as acetonitrile, that form complexes with Cu1 and anodically shift its redox potential, decrease the reactivity),... 

The halogens and their oxyacids, particularly chlorine and hypochlorous acid, are widely used as oxidizing and bleaching agents. These properties are related to the variations of redox potentials.17... 

Hazardous waste could be successfully and mostly cheaply eliminated with those methods. Strong oxidizing materials (chlorine) could be applied when dealing with soluble matter. Ozone could be also used as oxidizing agent. Ozone has higher redox potential than chlorine so the oxidizing state in reactions could be much easier reached [ 1 ]. 

Thus the chloride/chlorine couple has a redox potential of 1.36 V and can be oxidised by myeloperoxidase and eosinophil peroxidase lactoperoxidase can oxidise bromide (E° = 1.07 V) whereas thyroid peroxidase can only oxidise thiocyanate (E° = 0.77 V) and iodide (E° = 0.54V). All these reactions are two-electron oxidations and there is no evidence for a stable one-electron intermediate, i.e., compound II does not build up as a stable intermediate, and in fact can be inhibitory if it does form in significant concentrations [21]. 

A method for the preparation of thin films of Fe4[Ru(CN)6]3 ( ruthenium purple ) involving electrochemical reduction of K3[Ru(CN)6] in a solution of Fe2(S04)3 has been developed.28 This ruthenium purple modified electrode is claimed to be one of the best catalysts for evolution of oxygen and chlorine. Electrochemical studies on polyammonium macrocyclic complexes of [Ru(CN)6]4 indicate a 1 1 stoichiometry with a monoelectronic, reversible, oxidation for these complexes this illustrates the control of redox potential of anions by complexation with appropriate receptor molecules.29 The kinetics of oxidation of [Ru(CN)6]4 by [Mn04] in HC104 have been investigated by stopped-flow techniques. It is found that [Ru(CN)6]4" is quantitatively oxidized to [Ru(CN)6]3 in accordance with equation (1) and that two protonated intermediates [RuH(CN)6]3 and [RuH2(CN)6]3 are involved in the oxidation process.30... 

By changing the 7r-electron distribution in the porphyrin ring, substantial changes in redox potential may be achieved. Chlorins, for example, are used as electron donors... 

Figure 5 Thermodynamic parameters associated with organohaUde reactivity (a) electon accepting species versus redox potential (b) relative importance of oxidation versus dechlorination rates as a function of number of chlorines [1-8] and (c) trend between energy difference of the HOMO and LUMO electron layers and Gibbs free energy of...

Example 8.13. Chlorine Redox Equilibria Summarize in a pc-pH diagram the information contained in the equilibrium constants, I — 0, 25°C, of the following three reactions involving Cl2(aq), Cl, OCl, and HOCl. [For convenience, in addition to the equilibrium constant, the standard redox potential. 

The reaction of sodium hydroxide with chlorine is strongly exothermic (AH = 103 kJ/mol). Production can be carried out discontinuously and is monitored by redox potential measurements. Since hypochlorite is easily converted to chlorate at high temperatures, the reaction temperature must be kept below 40°C, for which coolers constructed of titanium are used. The chlorination is generally carried out in such as way that a slight excess of alkali is retained so as to increase the stability of the... 

Elemental bromine and chlorine set iodine free from aqueous iodide solutions due to their higher redox potential ... 

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