Cuprous oxide redox reaction

By-products from capture of nucleophilic anions may be observed.53 Phenols can be formed under milder conditions by an alternative redox mechanism.98 The reaction is initiated by cuprous oxide, which effects reduction and decomposition to an aryl radical, and is run in the presence of Cu(II) salts. The radical is captured by Cu(II) and converted to the phenol by reductive elimination. This procedure is very rapid and gives good yields of phenols over a range of structural types. 

By-products from capture of nucleophilic anions may be observed.79 Phenols can be formed under milder conditions by an alternative redox mechanism.90 91 The reaction is initiated by cuprous oxide, which effects reduction and decomposition to an aryl radical. 

The nature of a transition metal is not essential for this redox reaction. However, one of the reaction products, namely, anion radical SOJ, can be complexed by a transition metal in a higher oxidation state. This leads to some stabilization of SOJ and increases its effective concentration. In other words, further reactions with organic substrates are facilitated (Fristad Peterson 1984). Cuprous and ferrous salts are preferable. 

Catalysis by Cu(NH3)4S04 has been examined by Nikolev (98) who found a maximum rate at pH 8.5 to 9.0. The reaction is strictly first order in peroxide up to 0.25 M peroxide but decreases to zero order at 0.5 M. Addition of ammonium hydroxide at first increases the rate but ultimately depresses it, an effect also noted by Bobtelsky and Kirson (99). Unfortunately the experiments are not very extensive, and it is impossible to separate the effect of ammonia in complexing from the effect of the accompanying pH increase. Information on the relative activities of the complexes with various amounts of coordinated ammonia would be interesting. The only indication from this work is that the depressing effect of high ammonia concentrations supports the authors view that the hexammine probably formed in these conditions is less active than the tetrammine. One other point of interest is that it seems probable that radicals are formed in the reaction, possibly in conjunction with a cupric ammine-cuprous ammine redox system, since organic substances can be oxidized by the cuprammonium-peroxide mixtures. 

Chemical or photochemical oxidation of a nucleic acid is accomplished very efficiently by a variety of metal complexes. In the presence of hydrogen peroxide and thiol, bis(phenanthroline) cuprous ion very efficiently cleaves DNA (26). Tris(phenanthroline) complexes of cobalt(IIl) or rhodium(III) promote redox reactions in their excited states (27, 28). These photoac-tivated probes bind to the DNA helix in a fashion comparable to the spectroscopic probes described above and then, upon photoactivation, promote DNA strand cleavage. 

The catalyst is cuprous chloride and the reaction is actually a redox reaction which occurs in two steps. The first step is the oxidation of cuprous chloride to cupric methoxychloride as shown in Eq. (47) ... 

As the examination of this equation shows, this is not a simple redox reaction. There is also a precipitation reaction together with the redox one. Half of the iodide ions added are indeed oxidized into iodine, while the other half remains at state-I. The part that the latter plays is to precipitate Cu +1 as cuprous iodide. Cu +1 is formed by the redox reaction between Cu + and I ... 

We remark that this reaction is also a redox one. The precipitation of Hg2Cl2 induces the reduction of Hg+ to the stage Hg+ . It is interesting to notice that the redox reaction between 8n + and Fe + given above allows the determination of 8n + through that of Fe +. This is an example of a titration by substitution. We also notice that the reduction of Fe + may also be achieved with solid cuprous oxide Q12O (it is very poorly soluble). The occurring redox reaction is... 

Fig. 14. Redox cycling in the uptake of copper and iron. The lower valent state species is substrate for uptake of copper and iron. The system in the yeast Saccharomyces cerevisiae is diagrammed. The Frel protein reduces environmental Cu " and Fe +. The cuprous ion is substrate for the copper permease, Ctrip. Fe + is substrate for Fet3p its oxidation to Fe + is an obligate step in iron uptake through Ftrlp. Exogenous ferric iron is not taken up by yeast cells unless it is cycled through the ferrireduction-ferrox-idation reactions catalyzed by Frelp and FetSp.

Figure 13.9(b) also illustrates analogies between CcO and peroxidases and catalases, which we discuss next, in terms of both oxygen—oxygen bond cleavage chemistry and the nature of the products of the reactions. In CcO, the enzyme extracts three electrons from metals in the active site — two from haem 03 as it goes from the +2 to the +4 state and one from Cub as it is oxidized from cuprous to cupric — and one electron from a redox-active protein side... 

As was reported by Romano et aL, cuprous chloride is an effective catalyst for selective dimethyl carbonate synthesis. The reaction proceeds at 90—100 C at >20 bar of CO and can be either separated into an oxidation and a reduction step, or carried out in a one-pot redox system [71]. Dimethyl carbonate is a versatile reagent which can replace phosgene and dimethyl sulfate as carbonylating and methylating agents, respectively. 

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