Isomerization, radiation-induced

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. 

Various other radiation-induced reactions have been studied for potential use in the industry on a pilot-plant scale. Among these may be mentioned hydrocarbon cracking (i.e., production of lower-molecular-weight hydrocarbons from higher-molecular-weight material), isomerization of organic molecules, and synthesis of labeled compounds with radioactive nuclei. When organic compounds are irradiated in the pure state or in aqueous solution, dimeric... 

Materials and Methods. The isomeric compositions of the four polybutadienes used are listed in Table I. Samples were prepared for infrared measurement from solutions of the polymer without further purification. Most films were cast from carbon disulfide solutions on mercury or on glass plates, but a few films were cast from hexane solutions to determine whether or not the solvent affected the radiation-induced behavior. No difference was observed for films cast from the different solvents. The films were cured by exposure to x-rays in vacuum. (Doses were below the level producing detectable radiation effects.) They were then mounted on aluminum frames for infrared measurements. The thicknesses of the films were controlled for desirable absorbance ranges and varied from 0.61 X 10 s to 2 X 10 3 cm. After measuring the infrared spectrum with a Perkin-Elmer 221 infrared spectrophotometer, the mounted films were evacuated to 3 microns and sealed in glass or quartz tubes (quartz tubes only were used for reactor irradiations). 

Isomerization must occur during the radiation-induced degradation, either of the initially produced 1-butene as a radiation-induced secondary... 

In 1937 Arnow showed that tyrosine could be converted into DOPA by ultraviolet radiation51 and that the DOPA produced in this manner was subsequently destroyed by further irradiation, the solutions becoming red-brown in color (presumably due to the formation of dopachrome).51 In 1939 Konzett and Weis reported that the blood pressure-raising effect of adrenaline solutions was lost on ultraviolet irradiation and that the solutions became colored and fluorescent the initial red color fades to reddish yellow.62 This phenomenon suggests the initial formation of adrenochrome, followed by its isomerization to adrenolutin, both of these compounds being virtually void of pressor activity. Similarly to the radiation-induced hydroxylation of tyrosine mentioned above, synephrine was first... 

The presence of double-bonded fatty acids in proteins and their isomerization was found to help some bacteria to adapt to ambient temperature changes62. The alteration of C=C bonds in liposomes plays a role in protection against radiation-induced damage63. 

Mizuta et al. (1993) have reported that a single-layer photoreceptor containing 9-isopropylcarbazole-3-carbaldehyde-N,N-diphenylhydrazone is fatigued on exposure to ultraviolet radiation. The results were interpreted by a mechanism where radiation induces isomerization of the anti- to the -isomer. The latter has a lower ionization potential and is a hole trap. In the single-layer configuration, hole trapping near the free surface results in the creation of volume space charges, which cause decreased sensitivity. 

Among the very few reported cases of radiation induced isomerizations in sulfur compounds is that of JV-alkyl-iV-vinyl-sulfonamides. The products of the reaction are 2-sulfonyl vinyl amines, viz. 

In later studies, Golub and Danon [329, 330] reported that, in addition to loss of unsaturation, polybutadiene and polyisoprene films and solutions undergo radiation-induced cis-trans isomerization. 

The radiation induced cis-trans isomerization of 2-butene in benzene, benzene-dr, toluene, and pyridine has been studied. The triplet yield in benzene is 4.7 molecules per 100 e.v. benzene-dr, is similar. The yield in toluene is 6 molecules per 100 e.v. Nitrous oxide reduces the isomerization yield by about 40%. This indicates a G value of about 2 for excited states produced by the recombination of benzene ions with electrons. Xenon and krypton (up to 1M) increase the isomerization yield from 2.4 to 3.1 and 2.9 respectively, whereas argon has no effect. From the effect of xenon, which is attributed in part to enhanced intersystem crossing, it is estimated that the yield of singlet states which do not cross to the triplet in unperturbed benzene solutions is 1.3 molecules per 100 e.v. 

Polysulfones have found use as resists in the area of mierolithography since the polysulfones are unstable toward radiation and heat below their melting points and the SO2 and olefin degradation products are volatile. It is interesting to note that some olefins undergo isomerization during the radiation induced degradation step [9c]. 

Radiation-induced isomerization is most pronounced in high-viscous oils with high contents of heavy aromatic compounds. The favorable conditions for isomerization are lowered dose rates of ionizing irradiation and lowered temperatures. 

The observed changes in isoalkane concentration in gasoline extracted from gas condensate are shown in Figure 15.5. These data demonstrate a strong effect of aromatics addition on radiation-induced isomerization. 

Evaluation of the effects of radiation-induced isomerization and polymerization is important for obtaining high yields and quality of the commodity oil products produced by radiation processing of heavy oil feedstock. 

The content of gasoline produced by RTC essentially differs from that obtained by the thermocatalytic method (Figure 15.13). Concentration of isoparaffins after TCC is almost twice lower than that of n-paraffins due to the highly pronounced effect of radiation-induced isomerization. In the case... 

Zaikin, Y.A. and Zaikina, R.F. 2007. Effect of radiation-induced isomerization on gasoline upgrading. In Proceedings of the 8th Topical Meeting on Nuclear Applications and Utilization of Accelerators AAAPP 07, Pocatello, ID, July 29-August 2, pp. 993-998. 

A particularly informative set of experiments which reveal the extent of initial bond cleavage has been conducted by Busfield and co-workers (35-38). They have studied the radiation-induced changes in the stereochemistry of isotactic polypropylene (iPP). The changes in the stereochemistry are a result of initial chain scission, isomerization, and rehealing of the broken bond, as shown below in Figure 1. 

The cationic cyclization of polyisoprene with acid catalysts is well documented. The same reaction in polybutadienes requires much more severe conditions, higher temperatures and more acidic catalysts, and until recently has received much less attention. A cyclized polymer with a reduction of 35—40% of the initial unsaturation, can be prepared by treating cis-l,4-polybutadiene with an alkyl aluminium chloride-organic halide catalyst in xylene solution at >100 C."- Such polymers, containing polycyclic sequences apparently at random within the chains, have better skid resistance and tensile properties than the parent polymer. Cyclization has been reported to accompany other reactions in polydienes, for example the radiation-induced addition of carbon tetrachloride to 1,2-polybutadiene, and the direct addition of a o j unsaturated carboxylic acids (acrylic and cinnamic) to polydienes and polypentenamers. It is reported that the thermal isomerization of cis-transoidal poly(phenylacetylene) is accompanied by cyclization, and additionally chain scission and aromatization at temperatures >120°C. ... 

Figure 1.44 Radiation-induced gelation via isomerization of a cinnamic acid derivative. Reproduced from Ref [129] with permission of The Royal Society of Chemistry.

Adhikari S, Sprinz H, Brede 0 (2001) Thiyl radical induced isomerization of unsaturated fatty acids determination of equilibrium constants. Res Chem Intermed 27 549-559 Adhikary A, Bothe E, Jain V, von Sonntag C (2000) Pulse radiolysis of the DNA-binding bisbenzimid-azole derivatives Hoechst 33258 and 33342 in aqueous solution. Int J Radiat Biol 76 1157-1166 Akhlaq MS, von Sonntag C (1986) Free-radical-induced elimination of H2S from dithiothreitol. A chain reaction. J Am Chem Soc 108 3542-3544... 

Hankiewicz E (1995) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis II. Reactions of primary radicals with oxidants. Bull Pol Acad Sci Chem 43 41-49 Hankiewicz E (1996) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis - Part III. Consecutive reactions. Radiat Phys Chem 47 61-65 Hankiewicz E (1998) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis. IV. Reactions of primary radicals with reductants. Bull Pol Acad Sci Chem 46 455-464 Hankiewicz E, Bothe E, Schulte-Frohlinde D (1992) Hydroxyl radical-induced reactions in polyadenylic acid as studied by pulse radiolysis, part. I. Transformation reactions of two isomeric OH-adducts. Free Rad Res Commun 16 391-400... 

Photochromism is a reversible transformation of a single chemical species between two states, the absorption spectra of which are clearly different, the transition in at least one direction being induced by electromagnetic radiation [1], The widest and most important group of the photochromic system is based on electrocyclic reactions [2,3] a few have been commercially successful (polymer-based photochromic eyewear, novelty items and security printing inks). Several other photochromic systems based on E,Z-isomerization, cycloaddition reaction, electron or proton transfer have potential industrial applications [4],... 

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