7-Irradiation unsaturated hydrocarbons

Reactions, under irradiation, involving the addition to unsaturated hydrocarbons of nitrogen and phosphorus compounds and of silanes have been summarized by Spinks and Woods (1990). Some cycloaddition reactions have also been reviewed. These will not be detailed here. 

Before ozone - and PAN were identified as specific phytotoxic components of the photochemical complex, researchers used a number of artificial chemical reaction systems to simulate the ambient photochemical-oxidant situation. These efforts involved a number of irradiated and nonirradiated reaction systems unsaturated hydrocarbon-ozone mixtures, unsaturated hydrocarbon-NOx mixtures, and dilute auto exhaust). Most research before 1960 involved one or more of these reaction systems. This research has been well reviewed " - 451.459.488.505 extenslvely covered here. Although the... 

The incorporation of 14C in unsaturated hydrocarbons on irradiation in the presence of 14CH3I is most easily explained by recombination of radicals produced by the radiation87... 

Photochemical activation of transition metal carbonyls has been used as a preparative tool for substitution of carbonyl ligands by donor molecules or unsaturated hydrocarbons for many years (7-6). The advantage of photochemical activation in comparison with thermal activation is the possibility of conducting reactions at fairly low temperatures. Hence even thermolabile products can be prepared and isolated by appropriate treatment of the reaction mixtures. However, due to the various activation modes of transition metal carbonyls by UV light, often more than one product is obtained, and chromatographic separation is necessary. Limitations are set primarily by the amount of substance which can be irradiated in solution at one time. 

Aromatic, olefinic, and acetylenic hydrocarbons, but especially saturated hydrocarbons belong to persistent pollutants difficult to eliminate from the troposphere. The only exceptions are some aromatic compounds that undergo direct photodegradation in result of solar irradiation. Alkanes are undoubtedly much less reactive than other organic compounds including unsaturated hydrocarbons, surely because they are more completely saturated and their activation involves cleavage of the relatively strong C—H bond (s = 415 kJ). 

UV irradiation of Ti02 containing a sufficient amount of H2O in the presence of unsaturated hydrocarbons such as CsHg and C4H6 leads to the formation of hydrogenolysis reaction products and oxygen-containing products (214, 242, 243). As shown in Fig. 52, the rates of these photocatalytic reactions increase when the ionization potential of the reactants decreases (224). 

Hydrosilylation of unsaturated hydrocarbons is the most essential procedure for creating Si-C bonds. It is an addition of Si-H units across ir-systems such as C=C double or C=C triple bonds and may occur on two different reaction modes. Radical hydrosilylation is initiated with ultraviolet (UV) hght, y-irradiation, or radical starters such as azobis(isobutyronitrile) (AIBN) or peroxides. However, there are some drawbacks which have to be taken into account, such as competition of... 

The phenylcyclopropylcarbene generated upon irradiation of phenylcyclopropyl-diazomethane (166) in benzene, hexafluorobenzene or saturated and unsaturated hydrocarbons leads to 1-phenylcyclobutene (167) in nearly quantitative yield on the other hand, the cyclopropylcarbene formed on irradiation of 2,3-biscyclopropylstilbene oxide (168) leads to secondary photo-products of higher molecular weights (equation 115). ... 

Absolute rate constants have been measured for silylone reactions with hydrocarbons ah .98 K and these show that si lyl ene reacts rapidly but unselective.ly with unsaturated hydrocarbons however, si lyl ene is unreactive towards al kanes- Dimethylsilylene has been produced by y-irradiation of benzene solutions of dodecamethylcyclohexasilane. Relative rate constants for the reactions of methylphenylsilylene generated by photolysis of the Si-bridged arene ( .) with KhOH, Kt-3SiH, and... 

The irradiation of aromatic compounds results in considerably lower yields of radiolysis products than does irradiation of aliphatic compounds of similar molecular weight and functional group composition. This has been attributed to effectiveness of the delocalized 7t-orbitals in accommodating excitation energy without permitting the molecule to dissociate. Nevertheless, some radiolysis does occur. Benzene is known to yield biphenyl, phenylcyclohexadiene, and a polymeric material of average composition (C6H7) which behaves as if it were an unsaturated hydrocarbon. Dimerization and polymer formation are also characteristic of the radiation... 

In the oxidation of indene [39] and of 1,2-diphenylcyclobutene [25] with singlet oxygen generated by irradiation of the solutions of the compounds in the presence of sensitizers, dioxetanes are the probable intermediates in the conversion of the unsaturated hydrocarbons into dialdehydes and diketones, respectively. Different products may be formed depending on the solvents used (equation 65) [25]. 

Unsaturated hydrocarbons with tetrasubstituted double bonds are cleaved to ketones by ozonolysis followed by reduction with zinc in acetic acid [HOT], by oxygen sensitized with methylene blue under irradiation [25,1109], by chromium trioxide and sulfuric acid at low temperature [564], or by sodium periodate [760] (equations 105-107). 

Polypropylene. In the thermal and photothermal degradations of PP as prepared as well as In the thermal degradation of the pre-irradiated polymer, the general patterns of volatile products are similar and are qualitatively accounted for In terms of the mechanism of Tsuchlya and Suml ( ), which proposed that the complex mixture of saturated and unsaturated hydrocarbons Is formed in a free radical process in which Inter and Intramolecular transfer play a predominating role. In the photothermal reaction, however, in addition to those products, a very much higher relative concentration of methane and an appreciable amount of... 

Although electrochemical CO2 incorporation into unsaturated hydrocarbons is a significant advancement, it is not economical to fix CO2 in this manner. We are interested in using Ni(bpy)3 to photochemically reduce CO2. We have found that when an MeCN solution containing Ni(bpy)3, triethylamine (TEA), and CO2 is irradiated at 313 nm, it produces CO with a quantum yield of-0.1% (defined as CO produced/photons absorbed). Here we present results on photochemical CO2 reduction using Ni(bpy)3 and discuss the nature of the various intermediates studied by electrochemistry, flash photolysis, and pulse radiolysis. 

Azide R-N3 is easily decomposed by UV light. Azide benzene is decomposed and produces nitrene by UV irradiation (Equation (1.111)). The produced nitrene reacts with unsaturated hydrocarbon (Equation (1.113)) ... 

The irradiation environment plays an important role in the evolution of polymer stability. While unsaturated hydrocarbon like acetylene [61] or divinyl benzene [62] is present in the material surrounding and provides radicals for the formation of intermolecular bridges, oxidative atmosphere, oxygen or air, promotes oxidation as the result of diffusion inside the polymer matrix. The distribution profile for carbonyl products that generated during irradiation takes a parabolic form [63]. The source of radicals may be one of the components of blends, which presents a lower stability. This case can be illustrated by various blends, EPDM/PP [64], EPDN-NR [65]. These polymer mixture show the maximum level of crosslinking at about 120-150 kGy. 

The improvement in the quality of recycled polymers can be achieved by the accomplishment of high energy irradiation in hydrocarbon atmospheres [62, 145, 146], because the scission of n component of double bonds or the opening of cycles provides radicals, which crosslink polymer molecules. An example of mechanistic scheme applied in the irradiation of unsaturated structures is presented in Fig. 8. 

Thermal decomposition of a y-irradiated poly( vinyl fluoride) occurred in two main steps firstly, elimination of hydrogen fluoride and secondly, main chain scission to yield unsaturated hydrocarbons." Polytetrafluoroethylene and the copolymer of tetrafluoroethylene and hexafluoropropene were degraded in various atmospheres and the decomposition products analysed." - For an inert atmosphere over twenty different fluorinated products were identified. For air the major products were COF, CF , and COj with minor amounts of fluorocarbons. The gaseous and solid decomposition products have also been analysed from the thermal degradation of poly(carbon monofluorides) containing different proportions of fluorine. Kinetic data were also obtained. 

On irradiation of olefinic bond with a light of suitable frequency, the unsaturated hydrocarbon get electronically excited. Beyond physical phenomena, excited olefinic bond produces following chemical changes ... 

Reactions involving lithium appear to be particularly good candidates for ultrasonic acceleration. The reduction of some highly unsaturated cyclic hydrocarbons by lithium was not only accelerated but pushed to completion by ultrasonic irradiation(19) ... 

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