Disproportionation reaction, copper

This is a disproportionation reaction, and is strongly catalysed by light and by a wide variety of materials, including many metals (for example copper and iron) especially if these materials have a large surface area. Some of these can induce explosive decomposition. Pure hydrogen peroxide can be kept in glass vessels in the dark, or in stone jars or in vessels made of pure aluminium with a smooth surface. 

In most redox reactions, one substance is oxidized and a different substance is reduced. In a disproportionation reaction, however, a single element undergoes both oxidation and reduction in the same reaction. For example, a copper(I) solution undergoes disproportionation in the following reaction. 

The copper disproportionation reaction suggests that M + (aq) ions of the transition elements might undergo the same fate ... 

Two ascorbate radicals can react with each other in a disproportionation reaction to give ascorbate plus dehydroascorbate. However, most cells can reduce the radicals more directly. In many plants this is accomplished by NADH + H+ using a flavoprotein monodehydroascorbate reductase.0 Animal cells may also utilize NADH or may reduce dehydroascorbate with reduced glutathione.CC/ff Plant cells also contain a very active blue copper ascorbate oxidase (Chapter 16, Section D,5), which catalyzes the opposite reaction, formation of dehydroascorbate. A heme ascorbate oxidase has been purified from a fungus. 11 1 Action of these enzymes initiates an oxidative degradation of ascorbate, perhaps through the pathway of Fig. 20-2. 

Superoxide dismutases are found widely in nature where a variety of redox metals (copper, nickel, iron, and manganese) are used to catalyze the disproportionation reaction 202 + 2H+ > 02 I H202.66 The copper/zinc and manganese-... 

Since Cu(I) ions are usually powerful electron donors, the reaction with H202 to give OH radicals is highly probable. However, the reaction [4.13] is less useful as a method of inducing oxidation because the disproportionation reaction to give Cu(II) and copper metal ensures that [Cu(I)] is always low. 

CIDNP studies have proven to be a valuable tool in investigating the mechanisms of decarbonylation and disproportionation reactions in micelles27 29). Since the mechamisms involve the formation of triplet radical pairs, nuclear polarization of the protons near the radical centers occurs and results in the observation of emission or enhanced absorption in the NMR spectra of products of the radical pairs. For example, the photolysis of di-t-butyl ketone (11) in HDTCI yields both decarbonylation and disproportionation products (Scheme VII)27,29). The CIDNP spectra (Fig. 12) taken at various concentrations of copper chloride (free radical scavenger) illustrates that the intramicellar product is isobutylene (72), while 2,2,4,4-tetramethylbutane (13) and 2-methyl-propane (14) are the extramicellar products. 

Kunkely and Vogler have shown " that Cu(hfacac)(cod) in hexane undergoes photochemical release of cod, indnced by a Cu(I) r (cod) MLCT excitation, with formation of Cu(hfacac), which rapidly disproportionates to copper metal and copper(II), a well known reaction in the field of copper(I) chemistry and especially easy to carry out in the case of copper(I) flnoro-snbstimted diketonates . 

The equilibrium between the Cu(II) and Cu(I) ions and metallic copper is also important. It is described by the disproportionation reaction (21)... 

Reaction of amines with alkyldiphenylbismuthane in the presence of a stoichiometric amount of copper diacetate afforded mixtures of the corresponding mono- and di-substituted amines, the alkyl group being first transferred, followed by the phenyl group. The transfer of two different substituents was explained by a disproportionation reaction of the alkyldiphenylbismuthane into trialkylbismuthane and triphenylbismuthane.m ... 

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