Irradiation cyclohexane

Lepine, F., Milot, S., and Vincent, N. Formation of toxic PCB congeners and PCB-solvent adducts in a sunlight irradiated cyclohexane solution of Aroclor 1254, Bull. Environ. Contam. Toxicol, 48(1) 152-156, 1992. 

Chemical evidence for the existence of electrons in irradiated cyclohexane was obtained from pulse radiolysis studies of solutions containing aromatic solutes27. Because of the lifetime of the pulse these experiments only allowed the determination of ions still surviving after 10 6 sec. With benzophenone and anthracene as scavengers transient absorption peaks at 700 nm and 730 nm respectively, were obtained. These were consistent with the known spectra of the benzophenone and anthracene radical ions and are most simply accounted for by assuming direct electron capture by these solutes. Positively charged ion radicals may also be produced since these are likely to have similar spectra. Ion yields can be calculated since the absorption coefficients are known, but these yields necessarily represent the sum of the positive and negative ion yields. Some results are shown in Fig. 3. 

Recent synchrotron radiation experiments showed that the probability of the energy deposition on the alkane molecules was the highest at about 16 18 eV [95]. With the energies above 16 eV, excited states of alkane radical cations can be produced efficiently. In irradiated cyclohexane, for example, the following reactions were considered to be the formation reactions of alkyl radical. 

We briefly consider cyclohexane as another example in order to illustrate the effect of density on the fragmentation. In Table 5 we show product yields obtained for pulse-irradiated (high dose rate) cyclohexane at 55 torr (a) and for gamma-irradiated cyclohexane at densities varying from 0.004 kg dm to the liquid density (b-d). 

Within the cubane synthesis the initially produced cyclobutadiene moiety (see p. 329) is only stable as an iron(O) complex (M. Avram, 1964 G.F. Emerson, 1965 M.P. Cava, 1967). When this complex is destroyed by oxidation with cerium(lV) in the presence of a dienophilic quinone derivative, the cycloaddition takes place immediately. Irradiation leads to a further cyclobutane ring closure. The cubane synthesis also exemplifies another general approach to cyclobutane derivatives. This starts with cyclopentanone or cyclohexane-dione derivatives which are brominated and treated with strong base. A Favorskii rearrangement then leads to ring contraction (J.C. Barborak, 1966). 

A solution of 7-bromo-2-(fV-methylanilino)hept-2-enenitrile (145 mg, 0.52 mmol) in cyclohexane (60 ml) was placed in a quartz tube and purged with oxygen. The sample was irradiated for 8h in a Rayonet Model RPR-100 Reactor using 254 nm light. An oxygen atmosphere was maintained during... 

Irradiation of the substituted pyrazole (523) gave the imidazoles (524) and (525). The amount of each isomer formed is solvent dependent. In ethanol 7% of (524) was formed together with 2% of (525). In cyclohexane, however, isomerization was more efficient, the percentages of the two isomers being 20% and 10%, respectively. 

The cyclohexylpyrazole (376) and the azlrlne (377) are formed by irradiation of 3-dlazo-4-methyl-5-phenylpyrazolenine (378) in cyclohexane (Scheme 35) (77JA633). The former is the result of carbene insertion into cyclohexane followed by a [1,5] hydrogen shift, whereas the latter arises by ring cleavage of nltrene (379) or by a concerted pathway. 

The photochemical behavior of the isomeric 3-methyl-2-phenyl-2-allyl-l-azirine (66) system was also studied. Irradiation of (66) in cyclohexane gave a quantitative yield of azabicyclohexenes (67) and (68). Control experiments showed that (65) and (66) were not interconverted by a Cope reaction under the photolytic conditions. Photocycloaddition of (66) with an added dipolarophile afforded a different 1,3-dipolar cycloadduct from that obtained from (65). The thermodynamically less favored endo isomer (68b) was also formed as the exclusive product from the irradiation of azirine (66b). 

Heating or irradiating alkenes in the presence of sulfur gives relatively low yields of thiiranes. For example, a mixture of sulfur and norbornadiene in pyridine-DMF-NHa at 110 °C gave a 19% yield of the monoepisulfide of norbornadiene as compared with a 78% yield by the method of Scheme 120 (79JCS(Pi)228). Often 1,2,3-trithiolanes are formed instead of thiiranes. The sesquiterpene episulfides in the essential oil of hops were prepared conveniently by irradiation of the terpene and sulfur in cyclohexane (Scheme 135) (80JCS(Pl)3li). Phenyl, methyl or allyl isothiocyanate may be used as a source of sulfur atoms instead of elemental sulfur. 

NBS can also be used to brominate alkanes. For example, cyclopropane, cyclopentane, and cyclohexane give the corresponding bromides when irradiated in a solution of NBS in dichloromethane. Under these conditions, the succinimidyl radical appears to be involved as the hydrogen-abstracting intermediate ... 

Benzylenol ethers rearrange in an apparently similar fashion via photolytic fission of the benzyl-oxygen bond and subsequent recombination steps. Irradiation in quartz of a cyclohexane solution of 3-benzyloxycholesta-3,5-diene (250) leads to 23% (251), 13% (252) [presumably formed from (251) during workup] and 10% (253). ... 

A solution of 1 g of (239) in 80 ml cyclohexane is irradiated as described above. After 3 hr e reaches a constant value of 4700. The solvent is evaporated and the residue chromatographed on alumina (40 g). Elution with pentane-benzene (3 1) gives 0.14 g unreacted starting material... 

This is most readily studied with cyclohexane- /n in which 11 of the 12 protons are replaced with deuterium. The spectrum of cyclohexane- /n resembles the behavior shown in Fig. 4-8 at about — 100°C (the slow exchange regime) two sharp lines are seen these broaden as the temperature is increased, reaching coalescence at — 61.4°C, and becoming a single sharp line at higher temperatures. (The deuterium nuclei must be decoupled by rf irradiation.) Rate constants t for the conversion were measured over the temperature range — 116.7°C to — 24.0°C by Anet and Bourne. It is probable that the chair-chair inversion takes place via a boat intermediate. 

A solution of quinoline 1-oxide (0.29 g, 2 mmol) in cyclohexane (1 L) was dehydrated by azeotropic distillation in the reaction vessel. The solution was purged with dry N2 and irradiated with a Hanau high-pressure Hg lamp. The resulting solution was evaporated and the residue was extracted with a little cyclohexane. The insoluble part contained carbostyril (3). The cyclohexane extract was evaporated and the residue purified by short-path distillation at 50°C/0.1 Torr yield 0.174g (60%) moisture-sensitive oil. 

A solution of a phenantbridine 5-oxide (0.20 g) in benzene (200 mL) was irradiated at 17 C with a Helios Italquartz 125-W medium-pressure arc until TLC showed that the reaction was complete. The solution was evaporated under reduced pressure and the residue was chromatographed (silica gel, cyclohexane/ EtOAc then CHCl,). 

A solution of the quinoxaline 1-oxide (4 mmol) in cyclohexane was degassed by boiling and passing N2 through and irradiated with a medium-pressure water-cooled Hg lamp (Hanau TQ 150), equipped with a Pyrex filter, until conversion was complete. The solvent was evaporated in vacuo at 20 C and the residue was extracted with a small amount of cyclohexane. The product was deposited on strong cooling. Attempted chromatography resulted in the formation of AfW-diacylbenzene-l,2-diamines. 

Photolysis of several 2-azidophenazines has been shown to afford quinoxahnes. Thus irradiation of 2-azidophenazine (576, R = H) in cyclohexane or acetonitrile gave, among other products, 3-(2-cyanovinyl)-2-quinoxalmecarbaldehyde (577) in <17% yield and irradiation of 2-azido-l-methoxyphenazine in degassed benzene or acetonitrile gave, among other products, a separable mixture of cis- and frawi-isomers of methyl 3-(2-cyanovinyl)-2-quinoxalinecarboxylate (578), each in low yield. 3 ... 

Note Chloramines do not require exposure to chlorine gas before application of o-toluidine. A range of halogen-containing substances (e.g. bromazine, hexachloro-cyclohexane isomers) can be detected with o-toluidine (1 % in ethanol) after subsequent irradiation with UV light (k = 254 or 366 nm 10-15 min) [1, 8]. 

It seems that deep-seated cleavage of the dioxin nucleus must accompany dechlorination in methanol. When pure dibenzo-p-dioxin (II) was irradiated in cyclohexane solution in a quartz cuvette, it darkened in color, and a precipitate of intractable dark brown material was collected and was insoluble in the common solvents except for methanol. 

Upon irradiation of (dimesityl)(trimethylsilyl)silylazide at 254 nm in a cyclohexane/t-butanol or a cyclohexane/ethanol solution, migration of the trimethylsilyl group to the nitrene center is observed (Eq. 2). The products are equivalent to the addition products mentioned above. 

According to Ludwig (1968), there is a some similarity between UV- and high-energy-induced luminescence in liquids. In many cases (e.g., p-ter-phenyl in benzene), the luminescence decay times are similar and the quenching kinetics is also about the same. However, when a mM solution of p-terphenyl in cyclohexane was irradiated with a 1-ns pulse of 30-KeV X-rays, a long tail in the luminescence decay curve was obtained this tail is absent in the UV case. This has been explained in terms of excited states produced by ion neutralization, which make a certain contribution in the radiolysis case but not in the UV case (cf. Sect. 4.3). Note that the decay times obtained from the initial part of the decay are the same in the UV- and radiation-induced cases. Table 4.3 presents a brief list of luminescence lifetimes and quantum yields. 

Rzad et al.( 1970) compared the consequences of the lifetime distribution obtained by ILT method (Eq. 7.27) with the experiment of Thomas et al. (1968) for the decay of biphenylide ion (10-800 ns) after a 10-ns pulse-irradiation of 0.1 M biphenyl solution of cyclohexane. It was necessary to correct for the finite pulse width also, a factor rwas introduced to account for the increase of lifetime on converting the electron to a negative ion. Taking r = 17 and Gfi = 0.12 in consistence with free-ion yield measurement, they obtained rather good agreement between calculated and experimental results. The agreement actually depends on A /r, rather than separately on A or r. 

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