Disproportionation A reaction

Disproportionation A reaction in which a species undergoes oxidation and reduction simultaneously, 547-548 cooper, 547-548... 

Disproportionation A reaction in which a molecule reacts with itself. 

Disproportionation A reaction in which transfer of an atom from one growing polymer chain to another terminates both. 

The head element nitrogen does not react. White phosphorus, however, reacts when warmed with a concentrated solution of a strong alkali to form phosphine, a reaction which can be regarded as a disproportionation reaction of phosphorus ... 

Any substance capable of reacting with free radicals to form products that do not reinitiate the oxidation reaction could be considered to function as free-radical traps. The quinones are known to scavenge alkyl free radicals. Many polynuclear hydrocarbons show activity as inhibitors of oxidation and are thought to function by trapping free radicals [25]. Addition of R to quinone or to a polynuclear compound on either the oxygen or nitrogen atoms produces adduct radicals that can undergo subsequent dimerization, disproportionation, or reaction with a second R to form stable products. 

In reaction (19) the iodine shown on the left has an oxidation number of zero. After the reaction, some of the iodine atoms have oxidation number +5 and some —1. In other words, the iodine oxidation number has gone both up and down in the reaction. This is an example of selfoxidation-reduction, sometimes called disproportionation. It is a reaction quite typical of, but not at all restricted to, the halogens. 

The allyltin halides can then be obtained by a disproportionation reaction between tetraallyltin and tin tetrachloride or tetrabromide, a reaction that is exothermic (143,144). 

The sum of these reactions yields a reaction termed disproportionation ... 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

Both catalytic reactions were investigated in the gas phase under atmospheric pressure using a glass fixed bed micro-reactor Prior to the reaction given amount of the catalyst (fraction 0.5-0.71 mm) was in situ activated at 500 °C for 2 h (N2 stream 40 ml min"1) In the case of toluene disproportionation the reaction temperature was 500 °C, WHSV 2-20 h"1, concentration of toluene in a stream was 18.5 mol%. Toluene alkylation was studied at the reaction temperature 250 °C. WHSV related to toluene was 10 h"1, concentration of toluene was 18.5 mol% and toluene to isopropyl alcohol molar ratio was 9.6. 

Experiments carried out by feeding TBPE only over H-MWW, showed that the O-alkylated product do not rearrange to C-alkylated phenol derivatives in our conditions, but it is hydrolysed to phenol. So, TBPE is not a reaction intermediate and perforce O-and C-alkylation are parallel reactions. Also o-TBP and p-TBP were fed each of them alone over our catalysts. As it could be observed in Fig. lb, o-TBP convert to p-TBP (by transalkylation) and in minor extent 2,4-DTBP (by disproportionation), while p-TBP (results not shown here) convert to 2,4-DTBP (by disproportionation). Because the transalkylation and disproportionation are bimolecular reactions and need large spaces, it is plausible to suppose that the alkylation could not take place in the pores, but on the external surface of H-MWW zeolites. 

The effect of the H-Beta ratio (y in wt%) in the dual-bed Pt/Z12(x) HB(y) catalyst system on the benzene purity at a reaction temperature (Tr) of 623 K is shown in Fig. 1. It is evident that the benzene purity gradually increased with increasing H-Beta ratio (Fig. la), eventually reaching a plateau value which meets the industrial specification of 99.85% at y 40 wt%. The effects of catalyst bed ratio on product yields are shown in Fig. lb. Comparing to the single-bed catalyst Pt/Z 12 (i.e., y = 0), the overall premium product yields of benzene and xylene (A68 yield) over the dual-bed catalyst Pt/Z12(x) HB(y) system reached an maximum at y 10 wt%. That the A68 yield dwindled and tetramethylbenzene (TEMB) increased with further increase in the H-Beta ratio may be attributed to the larger pore opening possessed by the bottom (H-beta) catalyst, which may provoke disproportionation of TMB to form tetramethylbenzene (TEMB) [8],... 

Since peroxyl radicals are also removed as a result of disproportionation, the reaction conditions are quasi-stationary for which the equality Vj = 2fc7[InH] [R02 ] I 2A 6[R02 ]2 is more appropriate. In this case, the rate of initiated chain oxidation of RH is equal to ... 

Diffusion of particles in the polymer matrix occurs much more slowly than in liquids. Since the rate constant of a diffusionally controlled bimolecular reaction depends on the viscosity, the rate constants of such reactions depend on the molecular mobility of a polymer matrix (see monographs [1-4]). These rapid reactions occur in the polymer matrix much more slowly than in the liquid. For example, recombination and disproportionation reactions of free radicals occur rapidly, and their rate is limited by the rate of the reactant encounter. The reaction with sufficient activation energy is not limited by diffusion. Hence, one can expect that the rate constant of such a reaction will be the same in the liquid and solid polymer matrix. Indeed, the process of a bimolecular reaction in the liquid or solid phase occurs in accordance with the following general scheme [4,5] ... 

The fact that 4-hydroxycyclohexene can be formed both by a reaction in which two radicals disappear16 and in a reaction which does not consume radicals complicates the calculation of the yield of radicals in the /-radiolysis (continuous radiolysis) of N2O-saturated aqueous solution of 1,4-cyclohexadiene. Von Sonntag and coworkers14 wrote that the yield of radical 4 is 0.31 pmolJ-1. From their data it must be concluded that 4-hydroxycyclohexene (yield of 0.25 pmolJ-1) is formed solely by reaction 15, neglecting its formation by disproportionation (reaction 16). However, they found a yield of... 

Aside from the mixture of species 4 resulting from disproportionation, the reaction of LAH with highly hindered alcohols (or phenols) may lead to unexpected products. Refluxing a THF solution of lithium bis(2,6-di-/-butylphe-noxy)aluminum hydride (7) resulted in the reduction of THF to 1-butanol (41). 

The absence of dimer radical cation formation by diphenyl selenide under the pulse radiolysis conditions is in contrast to bimolecular reactions believed to occur under electrochemical conditions/ In these experiments, a rotating disk electrode was used in combination with commutative voltammetry under anhydrous conditions. The results led to the conclusion that reversible one-electron oxidation is followed by disproportionation, then reaction of the resulting dication with diphenyl selenide or an external nucleophile, with the likely intermediacy of the dimer dication (Fig. 33). As expected, the dihydroxy selenane is formed when water is present. Based on the kinetics of the electrochemical reaction, the authors believe the diselenide dication, not the radical cation, to be the intermediate that reacts with the nucleophile. 

Disproportionation A chemical reaction in which a single compound serves as both an oxidizing and reducing agent. It converts to a more oxidized and a more reduced derivative. 

Hampton et al. [23-24] activated the Mg Ni and Mg Ni alloys (Hy-Stor 301 by Ergenics slightly enriched in Mg to prevent disproportionation of Mg Ni to Mg and MgNij) by a reaction with liquid water or water vapor for hydrogen uptake. 

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