Aliphatic compounds, radiolysis

An additional contributing factor to the mechanism of the present grafting reaction is the role of radiolytically produced hydrogen atoms. In the radiolysis of binary mixtures of aromatic and aliphatic compounds such as styrene-methanol, the concentration of aromatic strongly influences the G(H2) obtained from the methanol. In the most extensively studied binary mixtures of benzene-methanol (11) and pyridine-methanol (10), it is found that the yield of H atoms is important in determining product yields and types. Small additions (5%) of benzene and pyridine significantly reduce G(H2) from the methanol by scavenging H atoms. Above 5% additive, G(H2) is reduced further, but at a slower rate. These data for benzene-methanol and pyridine-methanol can be extrapolated... 

Al-Sheikhly Ml, Schuchmann H-P, von Sonntag C (1985) y-Radiolysis of N20-saturated formate solutions. A chain reaction. Int J Radiat Biol 47 457-462 An bar M, Meyerstein D (1964) Isotope effects in the hydrogen abstraction from aliphatic compounds by radiolytically produced hydrogen atoms in aqueous solutions. J Phys Chem 68 3184-3167 Anbar M, Meyerstein D, Neta P (1966) Reactivity of aliphatic compounds towards hydroxyl radicals. J Chem Soc Perkin Trans 2 742-747... 

In the family of phosphonates (RO)2R PO, the aryl derivatives were more stable than the related alkyl compounds, and the benefit was higher than the effect observed from alkylphosphate to alkylphosphonate (96). The same tendency has been observed with dithiophosphinic acids (RO)R PSSH namely, aromatic ligands were more resistant to hydrolysis and radiolysis than aliphatic compounds (49, 61). It was noted that the introduction of chlorine into the phenyl rings reinforced the radiolytic stability of the extractant (49, 61). 

Irradiation of saturated aliphatic compounds typically results in imsaturation, polymerization, and isomerization. The radiolysis of cyclohexane illustrates all three of these processes. If the radicals are very energetic, cyclohexene can be formed by the abstraction of hydrogen from a cyclohexyl radical either by a hydrogen atom or by another cyclohexyl radical. If the radicals become thermalized, recombination of radicals can occur to give bicyclohexyl. A less frequent process is rearrangement, followed by hydrogen atom capture to yield methylcyclopentane. 

The irradiation of aromatic compounds results in considerably lower yields of radiolysis products than does irradiation of aliphatic compounds of similar molecular weight and functional group composition. This has been attributed to effectiveness of the delocalized 7t-orbitals in accommodating excitation energy without permitting the molecule to dissociate. Nevertheless, some radiolysis does occur. Benzene is known to yield biphenyl, phenylcyclohexadiene, and a polymeric material of average composition (C6H7) which behaves as if it were an unsaturated hydrocarbon. Dimerization and polymer formation are also characteristic of the radiation... 

ALIPHATIC CARBOXYLIC ACIDS The radiation chemistry of the simple aliphatic carboxylic acids has been widely investigated. The major products of gamma radiolysis of these compounds are typified by those found (1) for radiolysis of isobutyric acid at 273 K... 

For a wide variety of aliphatic carboxylic acids, including some with aromatic substituents, the product yields for CO and C02 are in an approximately constant ratio of 1 10 for radiolysis at 298 K. Values for some typical compounds are given below in Table II. 

As with the aliphatic carboxylic acid model compounds, the major volatile product observed on gamma radiolysis of the poly acids is carbon dioxide. However, the carbon dioxide yields are somewhat larger than those observed for the model compounds. 

In the poly carboxylic acids, carbon dioxide is the major product of radiolysis, but the carbon monoxide yields are greater than they are for the aliphatic carboxylic acids. However, the radical yields are not greater than expected on the basis of the model compounds, which suggests that excited states play an important role in the degradation of these poly acids. 

IV. RADIOLYSIS OF NITRO AND NITROSO COMPOUNDS A. Aliphatic Nitro Compounds... 

The principle of the method involves the exposure of a mixture of two compounds (A) and (B) to ionizing radiation when a number of cross-products are formed from the fragments of the parent compounds. If A or B is labeled with tritium prior to irradiation, then the cross-products from the radiolysis will contain tritium in specific parts of the molecule. Ideal systems for the present labeling method are those in which A is an aliphatic molecule and B is aromatic or heterocyclic. Benzene and pyridine are suitable B components since these compounds can be labeled with tritium to very high specific activities by catalytic... 

The addition of sodium to aromatic hydrocarbons produces only the corresponding radical anion [121]. Alkali metals, however, dissolve in aliphatic ethers, e.g. tetrahydrofuran, dioxan, producing the characteristic blue colour [122], The solutions are diamagnetic because of the formation of higher ion pairs. Flash photolysis of solutions of sodium in ethers forms the ion pair consisting of the solvated electron and a sodium cation [123]. Three transients are formed in the flash photolysis of sodium pyrenide in tetrahydrofuran [124]. These have been identified as the solvated electron, es"oiv. the ion pair, esoiv> Na, and the sodium atom, Na°. Rate coefficients of reactions of es ,iv with various compounds relative to the rate of reaction with NjO have been determined recently by the 7-radiolysis of 2-methyl-tetrahydrofuran [125]. 

A general review of pulse radiolysis studies on electron transfer in solution is presented together with some recent unpublished data. Electron transfer processes occurring in irradiated solutions of metal ions, inorganic anions, and various aliphatic and aromatic organic compounds are discussed with respect to general redox phenomena in radiation and free radical chemistry. Specific topics include the measurement of peroxy radical formation, the use of nitrous oxide in alkaline radiation chemistry, and cascade electron transfer processes. Some implications of the kinetics of electron transfer are discussed briefly. 

Aliphatic nitro compounds are characterized by another interesting and mechanistically important property. Based on tautomeric and protolytic equilibria the stable form of nitromethane in basic solution is that of a double bonded ac/-nitromethane anion, CH2=N02 , which becomes ready target for electrophilic radical additions. An example, studied by pulse radiolysis, is its reaction with hydroxyl radicals as formulated in eq. 3."... 

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