Butene radiolysis

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

Enhancement of the total butene yield is observed when various additives whose ionization potential falls below about 9.4 e.v. are present during ethylene radiolysis (35). This is consistent with the above interpretation (Figure 2). In the vacuum ultraviolet photolysis of cyclobutane the yield of butenes varies with the ionization potential of the additives in the same way as observed here (12). The maximum enhancement corresponds closely to the yield of C4H8+, as expected from our mechanism. 

Considerable support exists for Reaction 18a (35). The application of an electrostatic field during radiolysis of ethylene-nitric oxide (I.P. 9.25 e.v.) mixtures showed no enhancement of the butene yields, consistent with an ionic mechanism. When mixtures of C2D4 and C2H4 are irradiated in the presence of nitric oxide, product butene consists almost entirely of C4H8, C4D4H4, and C4D8—evidence for a molecular association mechanism. 

Table I. Isotopic Composition of Butenes Produced in Radiolysis of C2H4-C2D4 Nitric Oxide Mixtures...

OH radicals react very fast (almost in a diffusion-controlled rate) with simple alkenes (k = 7.0 x 109 for 1-butene or cyclopentene and 8.8 x 109 M 1 s 1 for cyclohexene) and there is almost no change for 1,3- or 1,4-cyclohexadiene. Cycloheptatriene reacts very fast with all the three radicals formed in the radiolysis of water k = 6 x 109 with eaq, 8 x 109 with H atoms and 1 x 101CI M 1 s 1 with hydroxyl radicals13. 

Because 1,2-diphenylcyclo-l-butene (DPCB) has a rigid planar structure with the c-St-chromophore structurally constrained by the cyclobutene ring, and because it is stable for geometrical isomerizations, TPCB" is expected to have the same rigid planar structure. Pulse radiolysis of DPCB in DCE produces DPCB, which shows bands at... 

Similarly, fluorescence detected magnetic resonance effects observed during the pulse radiolysis of anthracene-dio in the presence of 2,3-dimethyl-l-butene support the presence of 8 equivalent methyl groups. Because the splitting, Odi = 0.82 mT, was approximately one-half that of the monomer splitting, Omon =1.71 mT, the sandwich dimer 91 + was invoked. ... 

Table II. Yields of Butene Isomers from the Radiolysis of Poly (1-Butene Sulfone) at 30 °C...

We have studied the alkane and alkene yields from the radiolysis of copolymers of ethylene with small amounts of propylene, butene and hexene. These are examples of linear low density polyethenes (LLDPE) and models for LDPE. Alkanes from Ct to C6 are readily observed after irradiation of all the polymers in vacuum. The distribution of alkanes shows a maximum corresponding to elimination of the short-chain branch. This is illustrated in Figure 8 for the irradiation of poly (ethylene-co-1-butene) containing 0.5 branches per 1,000 carbon atoms at 20 C. 

Radiolysis of ZSM-5 containing 2,2,3-trimethylbutane (5) at 77 K yielded a six-line spectrum characteristic of 5 + (a = 3.1 mT, 5H) [76]. Upon raising the temperature, in the range 120-200 K, the well known 2,3-dimethyl-2-butene radical... 

The radiolysis of ethane has been studied almost exclusively in the gas phase. The products of reaction are mainly hydrogen, n-butane, ethylene, propane and methane with smaller quantities of acetylene, isobutane and isopentane - °°. When the radiolysis is conducted with NO added as a radical scavenger, the hydrogen and n-butane yields are reduced and propene and butene are observed as products > The radiolysis of ethane with iodine vapor has shown that the radicals H, C2H5, and CH3 along with smaller quantities of C3H7, C4H9 and CH2 are present . 

The effect of electrical fields on the radiolysis of ethane has been examined by Ausloos et and this study has shown that excited molecules contribute a great deal to the products. The experiments were conducted in the presence of nitric oxide, and free-radical reactions were therefore suppressed. The importance of reactions (12)-(14) was clearly demonstrated by the use of various isotopic mixtures. Propane is formed exclusively by the insertion of CH2 into C2H6 and the yield is nearly equal to the yield of molecular methane from reaction (14). Acetylene is formed from a neutral excited ethane, probably via a hot ethylidene radical. Butene and a fraction of the propene arise from ion precursors while n-butane appears to be formed both by ionic reactions and by the combination of ethyl radicals. The decomposition of excited ethane to give methyl radicals, reaction (15), has been shown by Yang and Gant °° to be relatively unimportant. The importance of molecular hydrogen elimination has been shown in several studies ° °. ... 

The radiolysis of propane has been studied extensively in experiments that have included a wide range of techniques. The gas-phase radiolysis in the absence of inhibitors yields the products hydrogen, ethane, propene, 2,3-dimethylbutane, methane, ethylene, isobutane, acetylene, isopentane and n-butane as well as small quantities of butene-1, -pentane, 2-methylpentane and -hexane ° ° . At high conversions the yield of ethylene, propene, 2,3-dimethylbutane and isobutane are all reduced. The reduction in ethylene arises from hydrogen atom addition, while the reduction in the other products may arise from the reaction of propyl ions with propene to remove both C3H6 and the source of isopropyl radicals. 

Among the products of the radiolysis of 2-pentanone and 2-hexanone, ethylene and propene were found in considerable amounts . The distribution of the butenes in the radiolysis of 4-methyl 2-hexanone (both in the vapour and in the liquid phase) was very much similar to that observed in fhe photolysis at short wavelengths . 

Lipsky (237), Sandros (181), and Russian workers (238,239) observed triplet energy transfer from benzene to biacetyl for dilute benzene solutions. This indicates that the triplet lifetime in solution is also concentration dependent as is the case for o-xylene (240) where the lifetime Increased from a few nanoseconds to microseconds or more, on dilution. This has been confirmed for benzene (175,189) and further, additional evidence from photochemical (173) and pulse radiolysis (241) systems demonstrate the very short lifetime of the triplet state in pure benzene liquid. It is believed (175) that decay proceeds via the triplet excimer which is only inefficiently quenched by butene-2. Results of electron impact excitation (242) and pulse radiolysis (243) have indicated a triplet lifetime of 500 ps for gaseous benzene at low and high pressures. 

Infrared studies of the radiation-induced degradation of PMPS by Bowden et al. (19) supports the oligomerization process and also shows that the oligomers can be removed by post-exposure baking. These effects have not been seen for other poly (olefin sulfone)s (2.3). Figure 8 and Figure 9 show the yield versus dose curves for irradiation of poly(l-butene sulfone) and poly (cyclohexene sulfone) respectively (20). No comparable shift of the S02/olefin ratio towards unity is observed in the radiolysis of these polymers. 

Ion—molecule reactions in olefins, especially in those higher than ethylene, are characterized by their complexity due to multiple products from a given reactant and multiple reactants for a given product. Thus, even restricting ourselves to reactions of parent ions with parent molecules, at least five reactions in propene, eight reactions in 1-butene, and nineteen reactions in 1-pentene are observed. Occurrence of several primary fragment ions in ordinary electron impact and radiolysis systems makes the situation more complicated. 

Brown and J.H. O Donnell, y radiolysis of poly(butene 1 sulfone) and poly(hexane 1 sulfone), Macromolecules 5, 109 (1972). 

Recently, Chaudhari has compared the activity of dispersed nanosized metal particles prepared by chemical or radiolytic reduction and stabihzed by various polymers (PVP, PVA or poly(methyl vinyl ether)) with that of conventional supported metal catalysts in the partial hydrogenation of 2-bu1yne-l,4-diol in butene-1,4-diol. Several transition metals such as Pd, Pt, Rh, Ru and Ni were prepared according to conventional methods and investigated [17]. Generally, the catalysts prepared by the chemical reduction method were more active than those prepared by radiolysis and, in aU cases, aqueous colloids showed a higher catalytic activity (up to 40 times more) in comparison with the corresponding conventional supported catalysts. The results obtained with Rh and Ru species are reported in Table 11.2. 

We have cited several examples which illustrate characteristic ionic polymerization reactions of unsaturated compounds, which may be contrasted with the behavior of alkanes, for which the initial ion-molecule reactions usually lead to stable ion products which do not react further. It was therefore of interest to investigate ionic reactions in cyclobutane, the saturated hydrocarbon isomeric with the unsaturated butenes, to establish whether cyclanes could properly be classified in either of these categories. Additional impetus for such a study was provided by radiolysis data on cyclobutane which suggested that the cyclobutane parent ion rearranges prior to reaction. ... 

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