Irradiation of hydrocarbons

The formation of polymers upon irradiation of hydrocarbons through the ionic mechanism, of course, will belong to this class of reactions. 

Irradiation of Hydrocarbon Polymers in Nitrous Oxide Atmosphere... 

The use of pulse radiolysis and scavenging techniques has identified the electron in liquid hydrocarbons [116]. In these non-polar media, interaction between the electron and the solvent is, of course, very small and it is doubtful whether such electrons can properly be described as solvated. The pulse radiolysis of hexane or 3-methyl hexane gave rise to a short lived transient species absorbing at Xm ax = 1500 nm. Rate coefficients for reaction in hydrocarbon solutions at 193°K are given in Table 10. Baxendale et al. [117] have studied the pulse radiolysis of liquid methylcyclohexane and obtained rate coefficients for the reactions of the electron with carbon tetrachloride and pyrene at 293° K. Relative rate coefficients have been obtained by irradiation of hydrocarbons containing two electron scavengers [118]. 

G-Values of Products by Gamma Irradiation of Hydrocarbons Containing Six Carbons... 

A few illustrative examples are the following. Photohydrogenation of acetylene and ethylene occurs on irradiation of Ti02 exposed to the gases, but only if TiOH surface groups are present as a source of hydrogen [319]. The pho-toinduced conversion of CO2 to CH4 in the presence of Ru and Os colloids has been reported [320]. Platinized Ti02 powder shows, in the presence of water, photochemical oxidation of hydrocarbons [321,322]. Some of the postulated reactions are ... 

The irradiation of tetra-/-butylcyclopentadienone with 254 nm light at 77 K produced a tricyclopentanone which, upon extended irradiation, lost carbon monoxide. Tetra-f-butyltetrahedrane was formed. This derivative of the second fundamental hydrocarbon of molecular formula (CH), namely tetrahedrane, is stable at room temperature and could be isolated after chromatography on silica gel in crystalline form (G. Maier, 1978). 

Fig. 20. Proposed photochemical mechanisms for the generation of acid from sulfonium salt photolysis. Shown ate examples illustrating photon absorption by the onium salt (direct irradiation) as well as electron transfer sensitization, initiated by irradiation of an aromatic hydrocarbon.

In contrast, the ultrasonic irradiation of organic Hquids has been less studied. SusHck and co-workers estabHshed that virtually all organic Hquids wiU generate free radicals upon ultrasonic irradiation, as long as the total vapor pressure is low enough to allow effective bubble coUapse (49). The sonolysis of simple hydrocarbons (for example, alkanes) creates the same kinds of products associated with very high temperature pyrolysis (50). Most of these products (H2, CH4, and the smaller 1-alkenes) derive from a weU-understood radical chain mechanism. 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

The solvent is then evaporated, and the unconverted sterol is recovered by precipitation from an appropriate solvent, eg, alcohol. The recovered sterol is reused in subsequent irradiations. The solvent is then evaporated to yield vitamin D resin. The resin is a pale yeUow-to-amber oil that flows freely when hot and becomes a brittie glass when cold the activity of commercial resin is 20 30 x 10 lU/g. The resin is formulated without further purification for use in animal feeds. Vitamin D can be crystallized to give the USP product from a mixture of hydrocarbon solvent and ahphatic nitrile, eg, benzene and acetonitrile, or from methyl formate (100,101). Chemical complexation has also been used for purification. 

Hoijtink and co-workers (13) found that with some hydrocarbons, a concentration of radical cations can be enhanced by the uv irradiation of the reaction mixture, under which a fission of the addition complex to the radical cation occurs. Further progress in preventing reaction (2) could be achieved by sterically hindered oxidizing agents. 

Excited states of hydrocarbon molecules often undergo nondissociative transformation, although dissociative transformation is not unknown. In the liquid phase, these excited states are either formed directly or, more often, indirectly by electron-ion or ion-ion recombination. In the latter case, the ultimate fate (e.g., light emission) will be delayed, which offers an experimental window for discrimination. A similar situation exists in liquid argon (and probably other liquefied rare gases), where it has been estimated that -20% of the excitons obtained under high-energy irradiation are formed directly and the rest by recombination (Kubota et al., 1976). 

Chlorination reactions. Chlorination of hydrocarbons has been carried out in Japan, chlorination of toluene in the United States, chlorination of tetrachloropentane in the former U.S.S.R. to give octachlorocy-clopentane, and chlorination of propanoic acid in France to give chloro-propanoic acid. Chlorination of methane by irradiation to give lower halomethanes was found to be cost-effective. Chlorination of various amorphous polymers such as polypropylene, polybutadiene, and PVC, has also been carried out. 

The main products of the irradiation of beef fat at high doses are such hydrocarbons as alkanes, alkenes, alkynes, and alkadienes. Of these, the alkanes and alkenes consitute the most significant part of the volatile products. 

When the irradiation of SP-A in hydrocarbon solvents is performed in an external electric field, thread-like structures are formed... 

The results from a series of early studies of the products formed from irradiation of DAX appeared to show that XA does not react with hydrocarbons or simple olefins (Reverdy, 1976a,b,c.). However, later reports (G. W. Jones et al., 1978, 1979) seemed to contradict many of these claims. Our more recent investigation of XA resolves the apparently conflicting results and provides further information on the forces that relate structure to reactivity for aromatic carbenes (Lapin and Schuster, 1985). 

Peduoropolyethers, which constitute special class of fluoropolymer, are useful as lubricants,1 elastomers,2 and heat-transfer fluids under demanding conditions. Several commerical products are available, which are generally prepared by ring-opening polymerization of hexafluoropropylene oxide or by the random copolymerization oftetrafluoroethylene and hexafluoropropylene with oxygen under ultraviolet irradiation.3 Direct fluorination of hydrocarbon ethers has been reported4 but must be done very slowly under carefully controlled... 

This is supported by the absence of hydrocarbons in the volatile products after irradiation at 150°C. Similarly, the water observed in the volatile products after irradiation at ambient temperature... 

Detection of irradiated food containing fat - Gas chromatographic analysis of hydrocarbons... 

Irradiation of mixtures of hydrocarbons and chlorine at suitable wavelengths leads to chlorination of the organic molecule (Scheme 1.3). Reactions have overall quantum yields in excess of 106 (>106 propagation cycles for each termination step). 

Irradiation of mixtures of halogen and hydrocarbons at suitable wavelengths can lead to halogenation of the hydrocarbon by a free-radical chain reaction. 

Several examples of aromatic hydrocarbon sensitized additions of NNP to the same arenes were demonstrated to occur if an acid is present this is in contrast to the failure of benzophenone to sensitize the photoreactions. Irradiation of anthracene in the presence of NNP and hydrochloric acid gives 308 in 70% yield and a small amount of 309 derived from the acid-catalysed elimination of piperidinium ion and addition of ethanol165 (equation 147). Anthracene possesses Es = 76.3 kcal mol 1,

[Pg.813]

The direct irradiation of 1,3,5-cyclooctatriene (184) in ether or hydrocarbon solvents leads to the slow formation of two stable isomers corresponding to disrotatory 47T-electrocyclization (185) and bicyclo[3.1.0]pentene (186) formation along with small amounts of the reduced product 187 (equation 69)279-281. Conventional flash photolysis experiments later showed that, in fact, the main primary photochemical process is the formation of a short-lived stereoisomer (r = 91 ms)282, most likely identifiable as ,Z,Z-184. The transient decays to yield a second transient species (r = 23 s) identified as Z,Z-l,3,5,7-octatetraene (188), which in turn decays by electrocyclic ring closure to regenerate 184282 (equation 70). The photochemistry of 184 has been studied on the picosecond timescale using time-resolved resonance Raman spectroscopy49. 

---