Disproportionation with hydrogen

The three saturated long-chain tert-butyl peresters are members of a homologons series, and as such, the weighted least-squares regression analysis of the enthalpies of formation V5. number of carbons yields a methylene increment of —26.7 kJmol , a typical valne for liquids. The methylene increment for the terf-butyl esters of the Cg, Cjo, Cn and C14 acids is —28.0 kJmol. The closeness of these two values ensures that the enthalpies of formal reaction 16 will be nearly constant. For the three pairs from Table 3, the value is —70.3 8.1 kJmol. The standard deviation from the mean is quite large because the arithmetic difference for the C12 ester and perester, —79.5 kJmol, is quite a bit more negative than the differences for the Cio and C14 pairs, —64.4 and —66.9 kJmol, respectively. Unfortunately, the acids and esters are in different phases and so we are reluctant to attempt any comparison between them, such as a formal hydrolysis reaction or disproportionation with hydrogen peroxide. 

Disproportionation, with hydrogen abstraction from one end to give an unsaturated group and two dead polymer chains. 

Doubleday C, J Mclver, M Page and T Zielinski 1985. Temperature Dependence of the Trcinsition-State Structure for the Disproportionation of Hydrogen Atom with Ethyl Radical. Journal of Pie American Chemical Society 107 5800-5801. 

The dioxides of molybdenum (violet) and tungsten (brown) are the final oxide phases produced by reduction of the trioxides with hydrogen they have rutile structures sufficiently distorted to allow the formation of M-M bonds and concomitant metallic conductivity and diamagnetism. Strong heating causes disproportionation ... 

Purely parallel reactions are e.g. competitive reactions which are frequently carried out purposefully, with the aim of estimating relative reactivities of reactants these will be discussed elsewhere (Section IV.E). Several kinetic studies have been made of noncompetitive parallel reactions. The examples may be parallel formation of benzene and methylcyclo-pentane by simultaneous dehydrogenation and isomerization of cyclohexane on rhenium-paladium or on platinum catalysts on suitable supports (88, 89), parallel formation of mesityl oxide, acetone, and phorone from diacetone alcohol on an acidic ion exchanger (41), disproportionation of amines on alumina, accompanied by olefin-forming elimination (20), dehydrogenation of butane coupled with hydrogenation of ethylene or propylene on a chromia-alumina catalyst (24), or parallel formation of ethyl-, methylethyl-, and vinylethylbenzene from diethylbenzene on faujasite (89a). 

Some limitations of the method arise due to side reactions involving the nitroxide. However, such problems can usually be avoided by the correct choice of nitroxide and reaction conditions. Nitroxides, while stable in the presence of most monomers, may act as oxidants or rcductants under suitable reaction conditions.516 The induced decomposition of certain initiators (e.g. diacyl peroxides) can be a problem (Scheme 3.94).166 177 There is some evidence that nitroxides may disproportionate with alkoxy radicals bearing a-hydrogens,123 Side reactions with thiols have also been identified.4 18... 

Catalase is a heme protein belonging to the class of oxidoreductases with ferripro-toporphyrin-IX at the redox center, and it catalyzes the disproportionation of hydrogen peroxide into oxygen and water without the formation of free radicals. 

Olas and Wachowicz (2002) investigated the effects of tranx-resveratrol and vitamin C on oxidative stress in blood platelets. The level of 02 in control blood platelets and platelets incubated with resveratrol or vitamin C was recorded using a chemiluminescence method. On the other hand, Oh and others (2006) reported the x02 quenching activities of various freshly squeezed fruit and vegetable juices by measuring their inhibitory effects on the rubrene oxidation induced by x02 from disproportionation of hydrogen peroxide by sodium molybdate in a microemulsion system. 

The superoxide ion is a very weak hydrogen atom abstractor, which cannot continue the chain, and is destroyed via disproportionation with any peroxyl radical. So, the studies of the mechanisms of cyclic chain termination in oxidation processes demonstrate that they, on the one hand, are extremely diverse and, on the other, that they are highly structurally selective. The 20 currently known mechanisms are presented in Table 16.6. 

The chloroacetonyl radicals formed in the hydrogen abstraction reactions are also shown to combine and disproportionate, or combine and disproportionate with acetonyl radicals. 

Tetrasubstituted 4//-pyrans 153 and 431 were found to disproportionate with trifluoroacetic acid359 and with boron trifluoride-hydrogen bromide reagent360 to mixtures of pyrylium salts 395a,b and tetrahydro-pyrans 432359 or 433,360 respectively. 

The only significant ring transformation affording a thiopyrylium salt is closely related to the route outlined above via the disproportionation of a thiopyran. Treatment of alkyl or aryl substituted 4//-pyrans with hydrogen sulfide in the presence of acid leads to a mixture of tetrahydrothiopyrans and thiopyryliums (75ZOR1540)... 

The persulfate ion S2OI-, with or without various transition metal ions, is a particularly effective oxidant, especially for the decarboxylation of carboxylic acids.535 In the presence of silver(I), persulfate oxidation to silver(II) readily occurs and for aliphatic carboxylic acids the decarboxylation mechanism given in Scheme 4 has been established. The aliphatic radicals produced may then disproportionate, abstract hydrogen or be further oxidized to an alcohol. In... 

In the same way as intramolecular displacement leads to particularly stable atomic groupings within a molecule, the disproportionation reactions between several molecules are attributable to the tendency for the more stable compound with the higher fluorine content to form. Reactions of this kind are sometimes used to obtain highly fluorinated compounds from products with lower fluorine contents, for example, the catalytic fluorination of chloroalkanes with hydrogen fluoride or with fluorination agents such as antimony(V) fluoride or antimony(III) fluoride. The chlorine compound formed as the second product of the disproportionation process is reused as the starting material for the preparation of the compound to be dispropor-tionated. 

Exchange of halogen with hydrogen atoms on aluminum is also quite rapid since solutions of aluminum hydride and aluminum chloride readily form hydridoaluminum halides 302). The ether and trialkylamine addition compounds disproportionate upon distillation or sublimation 10, 306). 

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