Ethylene irradiation

Wiesner and coworkers have emphasized that while the equilibrium constants between the two diastereomeric photoexcited states and anionic intermediates respectively should be similar, there is no reason to expect that they must be numerically identical. Small differences in equilibrium constants could in some cases reverse the stereoselectivity of photocycloaddition with respect to metal reduction. The group of Cargill94 examined the validity of Wiesner s models by the photoaddition of tert-butylcyclohexenone 178 with ethylene. Irradiation at low temperature (—78 °C) afforded a mixture of three isomers 179-181, in which the photoproduct 179 is the major product while isomer 180, expected to be the major one based on the first model, was obtained as the minor isomer. This result seems to rule out the first model (it does not take into consideration the reversibility of the first bond formation in the intermolecular photoadditions), however, it is consistent with the second model (Scheme 39). 

Let us also mention that, at — 80°C., various ethylene irradiations were carried out by gamma rays in the absence of any microporous solid. No polymerization occurred. The microporous solid is thus seen to take a prominent part in the polymerization phenomenon. 

Phenols are stronger AO/AR than HAS. Contrary to the transformation of phenols into quinone methides, discoloration-free products are formed from HAS. Combinations HAS/phenol are, therefore, used to obtain protection at minimum discoloration. The efficient protection of PP or of a block copolymer of propylene with 1.5% ethylene irradiated with a dose of 5 Mrad was reached with 0.1% 28, R = H and 0.05% Irganox 1076. Moreover, it was found that hindered phenolic AO prevent radiolysis of the ester type HAS (e.g. 28) [226]. Combinations of HAS with phenolic AO may, therefore, be recommended for commercial stabilization of y-irradiated hydrocarbon polymers [227]. 

The gas cell used for the ethylene irradiations was baked at 550°C. in air after each irradiation to remove the polymer formed. 

Ethylene Irradiations. The hydrogen yields from single pulse irradiations of ethylene are given in Table III. The hydrogen yields vary with pressure from G(H2) = 1.9 at 1 atm. to G(H2) = 1.0 at 10 atm. At... 

Table III. Hydrogen Yields from Ethylene Irradiations...

Ethylene does not appear to be a good choice for a dosimeter at very high dose rates. Although the hydrogen yield is independent of temperature and pressure (12, 15) at normal dose rates, this does not appear to be the case for the present study. The small hydrogen yield and the inherent difficulties of ethylene irradiations do not encourage a more careful study at the present time. 

With ethylene, irradiation of cyanoacetylene yields 1-cyanocyclobutene ... 

Poly(ethylene) unirradiated Poly(ethylene) irradiated with 260 kGy... 

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 ... 

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). 

Carbon monoxide also reacts with olefins such as ethylene to produce high molecular weight polymers. The reaction of CO with ethylene can be initiated by an x-ray irradiator (62) or transition-metal cataly2ed reactions (63). The copolymeri2ation of ethylene with carbon monoxide is cataly2ed by cationic Pd (II) complexes such as Pd[P(CgH )2] (CH CN) (BF 2 where n = 1-3. With this catalyst, copolymeri2ation can be carried out at 25°C and pressures as low as 2.1 MPa. 

CP grade ethylene (Matheson) was used without purification. A flow of ca. 100 raL/min of ethylene for 2-3 hr is adequate for saturation. Gas flow is continued throughout the irradiation in order to maintain a high concentration of ethylene and for stirring. 

Although photochemical cycloadditions have gained acceptance in synthetic chemistry, most such reactions are limited to a relatively small scale. The use of a 1000-watt street lamp permits the irradiation of up to 1 mol of substrate in less time than 0.2 mol can be irradiated with the conventional 450-watt lamps. Thus, under optimum conditions, the submitters were able to add ethylene to 3-methylcyclohexenone on a 20-g scale in 48 hr (801) with a 450-watt lamp with the apparatus described here 94 g of this enone was condensed with ethylene in 8 hr (91%). 

Fumigation with ethylene oxide does indeed lead to a considerable reduction in the germ count (and at the same time destruction of insects), but the process, because of the formation of toxic reaction products (ethylene chlorhydrin, ethylene glycol) has been banned throughout the European Community since 01.01.1990 Ionizing irradiation a declaration of the treatment is obligatory, but such drugs find little acceptance by the public who expect nature s products as such. 

A solution of 5 g of (267) in 140 ml of benzene is irradiated for 24 hr at 15-20° with a 70-W Hanau Q81 high pressure mercury lamp in a central pyrex immersion well. A stream of ethylene is bubbled through the solution during the irradiation. After evaporation of the solvent the residue is... 

When formation of either the five- or six-membered ring was possible for N-chloroamine 37, only the five-membered ring was conducive under the Hofmann-Ldffler-Freytag reaction conditions, forming exclusively 6-ethyl-6-aza-bicyclo[3.2.1]-octane (38). No 2-ethyl-2-aza-bicyclo[2.2.2]-octane (39) was observed. On the other hand, 2-methyl-2-aza-bicyclo[2,2.2]octan-6-one (41) was installed by UV irradiation of a solution of A -chloroamine 40 in TFA. Ironically, when the ketone functionality on 40 was protected as its ethylene ketal group, the resultant steric interactions completely prohibited the classic Hofmann-Loffler-Freytag reaction. 

The irradiation of the thiophene in gas phase yields ethylene, allene, methyl-acetylene, carbon disulfide, and vinylacetylene. No Dewar thiophene or cyclo-propene derivatives were isolated (69CJC2965). The irradiation in liquid phase gave the Dewar thiophene which can be trapped as a Diels-Alder adduct with furan (85JA723). The Dewar thiophene and cyclopropene-3-thiocarbaldehyde can be obtained by irradiation in argon matrices at 10 K (86JA1691). 

It was found out that when the bisfuranones 299 (R = H, Me, CMc3, TMS) were irradiated in a solution of acetone saturated with ethylene (medium pressure, 125 W, mercury lamp at —78°C), the biscyclobutane adducts 300, 301, and 302... 

The cross-sectional area per chain in the hexagonal lattice of irradiated PE varies between 20.6 and 22.0 A. It is, thus, always greater than the cross-sectional area in the rotator phase in paraffins (19.5-20.0 A ), but on average somewhat smaller than that in constrained PE fibers above 7, /, (21.4-22.7 A ). An ethylene-propylene diene copolymer with approximately 64%, 32%, and 4% by weight of each component, respectively, was found to contain hexagonal crystals with a cross-sectional area per chain of 20.3 A". 

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