Radiolysis compounds

Direct observations of the decompositions of a wide range of inorganic compounds [231—246], which are unstable in the electron beam, particularly azides and silver halides, have provided information concerning the mechanisms of radiolysis these are often closely related to the processes which operate during thermal decomposition. Sample temperatures estimated [234] to occur at low beam intensity are up to 470 K while, at higher intensity, 670 K may be attained. 

Cooper and coworkers30 measured also the absorption spectrum of transient species produced in the radiolysis of pure liquid DMSO-d6 and found the same absorption of the first two bands, however, the intensity of the absorption is about 30% larger in the case of the deuterated compound for both of the absorption bands. The intensity of the absorption is given by Ge, but as the same change was found for both bands it seems most reasonable that the 30% difference arises from a change in G rather than in e. This is similar to water, where the fraction of ions which become free ions is substantially larger for the deuterated compound32. 

If reaction 49 is responsible for the high decomposition yield of ASCO, it can be understood why it does not occur for PSCO, since the C—H bond strength in the allyl compound is weaker than in the propyl derivative due to the resonance stabilization of the radical60. However, the yield of alanine was found to be 1.97 in the case of radiolysis of PCSO and almost zero for ACSO. Thus reaction 49 does not occur for the case of ACSO. Since only the yields of cysteine (0.98 for ACSO and 0 for PCSO) are given, no explanation can be proposed for the high decomposition yield of ACSO. 

This review is concerned with the formation of cation radicals and anion radicals from sulfoxides and sulfones. First the clear-cut evidence for this formation is summarized (ESR spectroscopy, pulse radiolysis in particular) followed by a discussion of the mechanisms of reactions with chemical oxidants and reductants in which such intermediates are proposed. In this section, the reactions of a-sulfonyl and oc-sulfinyl carbanions in which the electron transfer process has been proposed are also dealt with. The last section describes photochemical reactions involving anion and cation radicals of sulfoxides and sulfones. The electrochemistry of this class of compounds is covered in the chapter written by Simonet1 and is not discussed here some electrochemical data will however be used during the discussion of mechanisms (some reduction potential values are given in Table 1). 

Field and Lampe (23) established the occurrence of the hydride transfer reaction in the gas phase in 1958 by detecting secondary ions of mass one unit lower than the parent compound. Subsequently, Futrell (24, 25) attempted to account for most lower hydrocarbon products formed in the radiolysis of hexane and pentane by assuming that hydride transfer reactions play a dominant role in radiolysis. More recently, Ausloos and Lias (2) presented experimental evidence which indicated that some of the products in the radiolysis of propane are, in... 

M is an unsaturated hydrocarbon or an organic compound such as CH3OH, CH3I, CH3N02, (CH3)2CO, CH3NH2, etc. When M is an olefin, Reaction 27 or 28 will compete with a hydride transfer process (see earlier discussion) and a condensation process. For instance, in the radiolysis of C3D8-CH3CHCH2 mixtures (9), the relative rates of Reactions 29, 30, 31, and 32... 

Solutions of Cd(II) compounds can be reduced to Cd(I) by hydrated electrons formed by pulse radiolysis ... 

The origin of these radical species is also not known. It is often considered that they may result from recoil, either from the original molecule or from fragments of other molecules following collision Perhaps the most commonly assumed, and the most likely, source of free radicals is radiolysis of the target compound The pre-... 

Physical properties of carbon black-filled EPR and EPDM elastomers have been found to be comparable with the suUur-cured analogues [372]. Aromatic oils increase the optimum dose requirement for these compounds due to the reaction of the transient intermediates formed during radiolysis of the polymer with the oil as well as energy transfer which is particularly effective when the oil contains aromatic groups. The performance and oxidative stability of unfilled EPDM as well as its blend with PE [373], and the thermal stabdity and radiation-initiated oxidation of EPR compounds are reported by a number of workers [374,375]. 

The results of this study show (99) the involvement of fragments such as Cr(CO) , (3 < jc < 6) which react with CO molecules which come from any of several sources fragmentation of the original molecules, bulk radiolysis of the compound, application of an external atmosphere, or perhaps from intermolecular exchange. It was concluded from the data that diffusion processes are involved and that the relative rates of reaction and of diffusion away are important in determining the height of the annealing plateaus. 

The only respect in which the hot atom chemistry of organometallic compounds has so far been applied to other fields of study is in the area of isotope enrichment. Much of this has been done for isolation of radioactive nuclides from other radioactive species for the purpose of nuclear chemical study, or for the preparation of high specific activity radioactive tracers. Some examples of these applications have been given in Table II. The most serious difficulty with preparation of carrier-free tracers by this method is that of radiolysis of the target compound, which can be severe under conditions suited to commercial isotope production, so that the radiolysis products dilute the enriched isotopes. A balance can be struck in some cases, however, between high yield and high specific activity (19, 7J),... 

Ito and Matsuda studied the y-radiolysis of 2-methyltetrahydrofuran (MTHF) solutions of diphenyl sulfone and dibenzothiophene-S,S-dioxide (DBTSD) at 77 K. They found that the radical anions of these sulfone compounds are formed and have intense absorption bands at 1030 nm and 850 nm, respectively. The blue glassy solution of y-irradiated diphenyl sulfone has absorption bands at both 1030 nm and 360 nm while the absorption spectrum of the benzenesulfonyl radical formed by UV irradiation of diphenyl sulfone solution at 77 K showed only a peak at 382 nm. Gamma-irradiated phenyl methyl sulfone solution showed an absorption band only at 385 nm. Consequently the appearance of the absorption bands in 800-1030 nm of diphenyl sulfone and DBTSD may suggest that the unpaired electron is delocalized on two phenyl rings. The same authors studied the radiolysis of MTHF solutions of disulfones (diphenyl and dihexyl disulfones). They found a blue coloring of the solution by the y-radiolysis of diphenyl disulfone and dihexyl disulfone due to absorption peaks at 695 nm and 690 nm respectively, besides smaller absorptions at 300-400 nm. Comparing these results to the previous observation, that phenyl methyl sulfone solution absorbs only at 398 nm, results in the conclusion that the absorption band at 690 nm is due to the linked two sulfone moieties. The authors found that substituents on the phenyl ring lead to shifts in the absorption maxima of the... 

Hydrogen halides will easily add to unsaturated compounds under radiolysis or photolysis. The free-radical chain reaction process is initiated by the dissociation of the halide or by the radiolytic production of radicals from the halide or the organic compound. Thus, for the radiolysis of a mixture of HBr and ethene the postulated initiation is... 

Rate Constants for Reaction of Superoxide with Flavonoids and Related Compounds (Pulse-Radiolysis Experiments)... 

Finally, radical cations can be generated in solution by different types of pulse radiolysis225. Like PET, this is inherently a method for transient spectroscopic observations, but it has proved to be invaluable in investigations of dimer cations, e.g of polyenes, which form spontaneously upon diffusion of radical cations in the presence of an excess of the neutral parent compound, but a discussion of the electronic structure of such species is beyond the scope of this review. Pulse radiolysis is of interest in the present context because it allows the observation of large carotenoid radical cations which are difficult to create in solid-state or gas-phase experiments... 

Shevlin and coworkers30 studied the radiolysis-induced addition of the a-hydroxy isopropyl radical to substituted 1,6-heptadienes and analogs containing a heteroatom. The radical was generated by /-irradiation of propanol solutions of various 1,6-heptadienes. It was found that the adduct to the double bond decomposed to give a compound containing a five-membered ring (equation 26). 

Cyclopentadiene behaves differently than the cyclohexadienes in that its radiolysis leads to high molecular weight polymer via a cationic mechanism89, whereas such compounds are not formed in high yield from cyclohexadienes irradiated in the liquid phase. 

Plutonium nitride, 19 691 Plutonium oxalates, 19 691 Plutonium(IV) oxide, 19 669 Plutonium oxides, 19 688-689 Plutonium oxyhalides, 19 689-690 Plutonium pnictides, 19 691 Plutonium-producing reactors, storage of radioactive waste from, 25 855 Plutonium radioisotopes, 21 319 Plutonium refractory compounds, 19 687 Plutonium reprocessing plants, 19 686 Plutonium silicides, 19 690-691 Plutonium solutions, self-radiolysis of, 19 694... 

The importance of track structure, the migration of species, the role of oxygen, the study of model compounds and the use of pulse radiolysis techniques are discussed. 

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. 

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