Redox disproportionation

Another method for producing petoxycatboxyhc acids is by autoxidation of aldehydes (168). The reaction is a free-radical chain process, initiated by organic peroxides, uv irradiation, o2one, and various metal salts. It is terrninated by free-radical inhibitors (181,183). In certain cases, the petoxycatboxyhc acid forms an adduct with the aldehyde from which the petoxycatboxyhc acid can be hberated by heating or by acid hydrolysis. If the petoxycatboxyhc acid remains in contact with excess aldehyde, a redox disproportionation reaction occurs that forms a catboxyhc acid ... 

Shaw, C.F. Ill, Eldridge, J. and Cancro, M.O. (1981) Carbon-13 NMR studies of aurothioglucose ligand exchange and redox disproportionation reactions. Journal of Inorganic Biochemistry, 14, 267-274. 

B. Redox Disproportionation of Mixed-Valence Tetranuclear and Octanuclear Compounds... 

A solution of the isolated platinum blue compound usually contains several chemical species described in the previous section. Such complicated behaviors had long been unexplored, but were gradually unveiled as a result of the detailed equilibrium and kinetic studies in recent years. The basic reactions can be classified into four categories (l)HH-HT isomerization (2) redox disproportionation reactions (3) ligand substitution reactions, especially at the axial coordination sites of both Pt(3.0+)2 and Pt(2.5+)4 and (4) redox reactions with coexisting solvents and atmosphere, such as water and 02. In this chapter, reactions 1-4 are summarized. 

Clays may also promote electron transfer between adsorbed organic reactants. This process is termed redox disproportionation if the electron transfer occurs between two identical species. The formation of p-cymene and p-menthene from p-menthene is an example (56). In the presence of polymers were the main products. 

Redox disproportionation increased with the acidity of the clay and may be Br nsted acid-catalyzed. The mechanism was not established, however. 

Os (Tp)(OTf)(Cl)2] can abstract a nitrogen atom from MeCN upon heating to give the osmium nitrido compound [Os (N)(Tp)(Cl)2] (Equation (75)). The suggested mechanism is hydrolysis at Os followed by redox disproportionation to Os and Os ... 

Aldehydes with no H on the a C undergo self-redox (disproportionation) in hot concentrated alkali. 

Schaefer and Zimmermann (82) reported chemical evidence that the red color is caused by a base-induced redox disproportionation in which both leuco MB (colorless) and an oxidized imino form are produced (eq. 33 cf. Scheme 3). Hydrolysis of the imino material can demethylate the dye to afford a new colored species (eq. 34, Scheme 3) whose absorption is blue-shifted relative to MB. The role of the amine (or phosphine) in this scheme was not elaborated. 

A compelling conclusion is that the reaction and the product are the same for both TEA and TMBS. We suggest that the function of the added activator is to initiate redox disproportionation similar to that suggested by Schaefer and Zimmermann (82). The reaction is not, however, dependent on the presence of base. 

Other examples concern the interaction between iron carbonyles and potassium alkylthiolates that is accompanied by disproportionation. The anion radicals Fe2(CO)g, Fe3(CO)fi, Fe4(CO)i3, and Fe(CO)2 are formed (Belousov et al. 1987). The interaction of iron carbonyls Fe(CO)5, Fe2(CO)9, and Fe3(CO)i2 with (CH3)3NO occurs according to a one-electron redox-disproportionation scheme, giving rise to iron carbonyl anion radicals Fe2(CO)s Fe3(CO)n, l e3(CO)i2, and Fe4(CO)ii (Belousov Belousova 1999). 

This redox disproportionation of non-enolizable aldehydes to carboxylic acids and alcohols is conducted in concentrated base. 

Kovtun G, Kameneva T, Hladyi S et al (2002) Oxidation, redox disproportionation and chain termination reactions catalysed by the Pd-561 giant cluster. Adv Synth Catal 344(9) 957-964... 

Eventually we formed carbonyls in the liquid phase by redox disproportionation of nickel and cobalt derivatives of organic thioacids. In the reaction between nickel(II) dithiobenzoate and carbon monoxide in the presence of HS ion we assumed the formation of a sulfur-bridged nickel(IV) complex (VII, 32). More recent investigations (84), however, have shown that half the nickel appears as a monomeric nickel(II) complex of the same empirical formulation, formed by insertion of a sulfur atom in the dithio ligand, the other half of the nickel being reduced to nickel(O) by the sulfide. 

This difference has one irritating consequence the isomerization of 1-butene — 2-butene would change the oxidation numbers of two atoms. This isomerization thus would constitute a redox reaction or, more specifically, a redox disproportionation. That result, however, is not compatible with good common sense. ... 

In the case of transition metal compounds such as LaMn03 d-level splitting can be so pronounced that both valence and conduction band are derived from d-orbitals. For LaMnOj, e.g. Eq. (12) has to be interpreted as a redox disproportionation... 

Alkyl and aryl fluorophosphines, R PF3. (R = hydrocarbon group n = 1,2) are known to undergo spontaneous redox disproportionation in accord with... 

The polyimides were soluble in dipolar solvents such as NMP. Interestingly, the polyimides were readily transformed to non-hydroxylated polymers via a redox disproportionation as illustrated below. 

As indicated in equation 65 H2—formed by redox disproportionation, for example, by /3-oxidation of fatty acids such as CH3CH2CH2COO" + H2O = 2CH3COO -I- 2H2(g) + H —acts as a reductant of CO2 ... 

Alcohol fermentation may be exemplified by redox disproportionation of CH2O... 

As we have shown, the fixation of solar energy by photosynthesis causes a redox disproportionation. Abiotic photochemical processes can similarly induce redox disproportionation. Photochemical reactions produce highly reactive radicals and unstable redox species, which are important in the euphotic zone of natural waters. This will be discussed more in Chapter 12. 

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