Vapor-Phase Radiolysis of Cyclohexane and Mixtures of Benzene and Cyclohexane

Abstract

T h e vapor-phase radiolysis o f cyclohexane and benzene-cyclohexane mixtures has been studied with isotopic tracer techniques using CsDlr and CGDG. Benzene does not quench the molecular detachment o f hydrogen, CGDI? D! +. CGDIo, but interacts with the secondorder processes giving I-ID in CGD1?-Cr,H1? mixtures. T h~s ~nteraction is not H-atom scavenging and an ionic mechanism is preferred. T h e radiolysis o f all these systenls is very different from their liquid-phase radiolysis.'The low radiolytic yields in liquid benzene-cyclohexane mixtures are a classic example of 'protection'. T h e interactions causing these low yields are physical; they do not involve the ma1;ing or breaking of chemical bonds. This has been shown in two ways: by complete product analysis (1) and by techniques using isotopically labelled hydrocarbons (2). These isotopic techniques have revealed similar interactions in alkane mixtures (3) which are, however, absent in the vapor phase (4). As a result, we expect the vapor-phase radiolysis of benzene-cyclohexane inixtures to show marked differences froin the liquid-phase radiolysis.We have applied our isotopic techniques t o the vapor-phase radiolysis. In the liquid, benzene quenches both the first-order process, which gives D2 by molecular detachment from CGDl?, and the second-order processes which give HD in C G H~~-C G D~~ mixtures. I n the vapor, however, the D2 yield is reduced much more sloivly than would be expected if I-I-atom scavenging were occurring and so we favor an ionic mechanism for this interaction. Physical interactions quenching the first-order processes are absent. 1;isher 'Spectranalyzed' cyclohesane and benzene and Merck benzene-dG and benzene-free cyclohexane-d,z were used as received. T o minimize air contamination the sa~nple vessels (volume about 330 m l ) were evacuated t o 5x10-"mm Hg at 500' C for at least 24 hours before being filled and irradiated. Even so, the gaseous radiolytic products contained about 3% air. T h e vessels were sealed t o a grease-and mercury-free preparation line; the sample (about 2 1111 o f liquid) was degassed b y repeated freezing, pumping, and thawing and was then distilled into the irradiation vessel. During irradiation in our Co60 source, t h e vessels were kept at a constant temperature ( 2~2 ' C ) in a n electric furnace. Using the techniques already described ( 4 ) , we found t h e dose rate t o be 4.S7XlOL6 ev/sec g cyclohexane; the dose in most experiments was 3.61 X 101%v/g organic vapor.After

The X-radiolysis of water vapor containing methanol. Effects of some electron and hydrogen atom scavengers

“…Experiments with water vapor C,H6+ will also be present as ion clusters, containing propylene (but no methanol) gave clustering of the ions will probably not have a G(H,) = 0.6, independent of propylene con-marked effect on the enthalpy changes in recentration over a factor of 10. This, together actions [9] Previous results (4-6) have shown nitrous oxide and sulfur hexafluoride to be efficient scavengers of electrons in water vapor.…”

“…Reactions [9] and [lo] are both endothermic, where AG = the reduction in hydrogen yield on addition of propylene and g(H), = the total [9] CH30HZ+ + C3H6 -> CH30H + C3H7+…”

“…Corrections for products produced by direct absorption of energy by methanol were made using the experimentally determined values of G(H2) = 11.5, G(CH4) = 0.7, G(C0) = 1.8 for methanol vapor irradiated at 125 "C and 320 Torr. Corrections for other additives were made using G(N2),,, = 11.0 (a), G(H2)cyclohexanc = 5.3 (9), and G(Hz)proPylene = 1.2 (10). In correcting, it was assumed that the product yields from each component in a mixture were the same as those in the pure component.…”

The γ-radiolysis of cyclohexane with electron scavengers. V. C6F12 as an electron scavenger in the vapor phase

“…The radiolysis of liquid cyclohexane produces largely hydrogen, cyclohexene, and bicyclohexyl (7) but the radiolysis of cyclohexane vapor produces a wider variety of products (8,9). Since we were primarily concerned with the neutralization processes, as outlined in the Introduction, we were interested mainly in those products derived directly from cyclohexyl radicals.…”

“…Since there seems to be some uncertainty about the product yields from the radiolysis of pure cyclohexane vapor, yields of the products studied are given in Table I. The results of Theard (8) and of Blachford and Dyne (9) are included for comparison. In general, our results are in better agreement with those of Theard than of Blachford and Dyne, allowing for the increased cyclohexene yields at higher temperatures found by the latter workers.…”