Solute Competition for Thermal Electrons in Gamma-Irradiated Organic Glasses at -196°C

Tert-butyl halides and carbon tetrachloride, neopentane and carbon tetrachloride binary mixtures were irradiated at 77 "K and electron spin resonance spectra mere recorded at increasing temperatures until the radicals disappeared.Even at high concentrations of tert-butyl halides, the radicals obtained from CC1, predominate, indicating that CCI, has a high efficiency for electron capture. Maximum radical yields and the appearance of a narrow line spectrum with rising temperature uere observed in (CH,),C-X -CCI, mixtures (X = C1, Br, I) in concentration ranges where only a single phase exists. This spectrum consists of 17 lines which appear to belong to one odd-numbered spectrum (7 lines due to (CH,),C-X radical) and two evennumbered snectra (4 and 10 lines. the last being due to iCH,),C radical). The disanvearance of the CCld broad band'and thk appearance of these radicals mith increasing temperature cad be interpreted as due to charge transfer from carbon tetrachloride cation to tert-butyl halide, facilitated by greater freedom of movement in the solid solutions. In contrast, neopentane and carbon tetrachloride lnixtures do not display these features.Des melanges binaires d'haloginures de tertiobutyl et neopentane dans le CCI, on1 ete irradies a 77 "K. Les spectres de resonance paramagnttiquc indiquent que la concentration des radicaux issm du tetrachlorure de carbone est preponderante, meme aux fortes concentrations en halogenures de tertiobutyl, ce qui fait ressortir la haute efficacite de capture d'electrons thermiques par les molecules de CCI,.Lorsque les deux substances fornlent Line solution solide B basse ternperaturc, on constate un n~axin~uln dans les valeurs des rendenients radicalaires et l'apparition d'un tres beau spectre par elevation de temperature. Ce dernier comprend 17 raies appartenant a 3 especes radicalaires differentes. La disparition de la bandc attribuee a l'ion-radical CCI, + et l'apparition de nouvellcs especes radicalaires par elevation de temperature peuvent &tre intcrpretees par le transfert de charge de CC1,' sur l'halogenure de tertiobutyl. Celui-ci est favorise par la libbration progressive des mouvements moleculaires dans les solutions solides etudiees. Par contre, les nlelanges de neopentane et tetrachlorure de carbone ne presentent pas ces particularites.Canadian Journal of Chemistry, 47, 273 (1969) Hntrodoetion or neopentane -carbon tetrachloride solid soluxf,ork (11, ethyl iodide and carboll tions are compared with those of ethyl iodidetetrachloride mixtures were irradiated ; radio-carbon tetracllloride mixtures (X = Cl, Br, I). chemical yields obtained by electron spin resonance (e.s.r.) and analysis of reaction products enabled us to show that electron capture mas very efficient in alkyl halides and in carbon tetrachloride. Hamill and his co-workers (2) have also reached this conclusion in work describing the relative efficiency of electron capture for a series of solutes dissolved in suitable solvents. It ought to be interesting to study the effects of irradiation on so...

Section: Discussionmentioning

confidence: 99%

“…[3]) (2). Minor colltributions of tert-butyl radical are observable at high conce~ltrations in halides a t 77 'K.…”

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Electron spin resonance study of tert-butyl halides and carbon tetrachloride, neopentane and carbon tetrachloride binary mixtures irradiated at 77 °K

Thyrion¹

1969

“…spectra of the ionic species in organic glasses at -196 O C (1). In the same way, Hamill and his co-workers (1) have established a scale of relative efficiency of electron capture for a whole series of solutes dissolved in suitable solvents; these measurements were based on competitive reaction abilities of solutes for thermalized electrons produced within the medium; however, they were confined to low solute concentrations.…”

Section: Introductionmentioning

confidence: 99%

Radiolysis of ethyl iodide and carbon tetrachloride mixtures at 77°K

Leblanc¹,

Thyrion²,

Herman³

1968

The radical yields of C2H5' and CCI,' observed by electron spin resonance of CCI4 + C,H51 mixtures irradiated by y rays at 77 "K are compared with yields of HCI, I,, and HI measured after thawing. The dissociative capture of thermalized electrons by CC14 is extremely effective and accounts for most of the observed radicals. The difference between yields of HC1 and CCI3' results from charge transfer from C2H51' to CC1,'. The formation of iodine proceeds both from neutralization processes of C1-ions with positive ions formed from C2H51, and from ion-molecule reactions.On compare les rendements radicalaires observes par la resonance tlectronique paramagnttique aux rendements en HCI, I, et H I observes apris rkchauffement de melanges de CC14 et de C2H51 soumls aux irradiations des rayons y. La capture d'electrons thermalids est tris efficace dans le cas du CC14 et fournit la plus grande partie des radicaux observts. L'Ccart entre les rendements en HCI et CCI,' est dii au transfert de charge que subit C2H51+ avecCCI,'. Les reactions de neutralisation de C1-avec une entit6 positive issue de C2H51 et les reactions ion-molCcule sont a la base de la production d'iode. IntroductionIt has been shown that some y-irradiated halogenated alkanes form anions efficiently by electron capture, as indicated by the corresponding visible and U.V. spectra of the ionic species in organic glasses at -196 O C (1). In the same way, Hamill and his co-workers (1) have established a scale of relative efficiency of electron capture for a whole series of solutes dissolved in suitable solvents; these measurements were based on competitive reaction abilities of solutes for thermalized electrons produced within the medium; however, they were confined to low solute concentrations.It seems worthwhile to extend such a study over a wider range of concentration in a mixture of two solutes chosen from the Hamill scale. However, at high concentration the technique of measuring the optical spectrum of organic glasses at 77 OK does not give sufficient precision, therefore another experimental approach was preferred: the e.s.r. spectrum of radicals in frozen solutions and the subsequent chemical analysis of reaction products enabled us to establish a reaction scheme in such a system. In addition, irradiation in the solid phase has the advantage of limiting the reactions, especially of formed products, by preventing diffusion of bulky fragments in the solid.

“…From the results of experiments with very dilute solutions of iodine in cyclohexane, Schuler (20) suggested that solutes a t low concentration can act as energy sinks and thus protect the solvent molecules although they inay themselves decompose as a result of this absorption of energy. A similar conclusion was reached by us to explain the effect of dilute solutions of benzene on the radiolysis of cyclohexane (4).…”

mentioning

confidence: 99%

Radiation Chemistry of Cyclohexane: Vi. Dilute Solutions of Carbon Tetrachloride and Chloroform in Cyclohexane

Stone¹,

Dyne²

1964

A study of the effect of the addition of small amounts (<3.5%) of the halogenated compounds CC14, CHC13, and CDC13 on the radiolysis of cyclohexane has shown that processes other than rad~cal scavenging occur. A t the lowest concentrations of solute that it was practical t o employ (0.004 1M) cyclohexyl radicals were scavenged without a corresponding reduction in the hl-drogen yield. A t higher solute concentrations G(H2) was reduced by a physical process which did not involve the scavenging of thermal hydrogen atoms but did lead to chemical reaction involving the solute.