Benzenes photochemical decomposition

The thermal, but not the photochemical, decomposition of ferro-cenylsulphonyl azide (14) in benzene gave some intermolecular aromatic substitution product FCSO2NHC6H5 (6.5%) but no intermolecular cyclization product (17). Contrariwise, photolysis of 14 in benzene gave 17 but no anilide 1 ). 

Photochemical decomposition of diazomethane yields methylene, which reacts with benzene to form toluene and cycloheptatriene (via norcaradiene) (Scheme 5).65 66... 

Photolysis of l-methylnaphtho[l,8-de]triazine (32, R = Me) also results in extrusion of nitrogen and formation of a diradical intermediate (167). Thus, reaction in cyclohexane as solvent gives, among other products, bicyclohexyl and 1-methylaminonaphthalene, while 8-phenyl-1-methylaminonaphthalene is the only product formed when benzene is used as solvent. Photochemical decomposition of 32, R = Me, in the presence of olefins results in an unusual ring transformation, and with a-methylstyrene, for example, the triazine is converted into the dihydroazaphenalene derivative (168). When vinyl bromide and trans-... 

Highly selective formation of phenyl acetate was observed in the oxidation of benzene with palladium promoted by heteropoly acids.694 Lead tatraacetate, in contrast, usually produces acetoxylated aromatics in low yields due to side reac-tions. Electrochemical acetoxylation of benzene and its derivatives and alkoxylation of polycyclic aromatics789 790 are also possible. Thermal or photochemical decomposition of diacyl peroxides, when carried out in the presence of polycyclic aromatic compounds, results in ring acyloxylation.688 The less reactive... 

The decomposition of benzene-1.4-diazooxide might be expected to give as an intermediate (XI) which could possibly polymerize to a polyphenylene ether. In 1956, Sus studied the photochemical decomposition of benzene-1.4-diazooxide (79). He states... 

The photochemical decomposition of 2,2-diphenyl-5-(diphenyl-methylene)-l,3,4-oxadiazoline (73) is solvent-dependent.63 In benzene,... 

The photochemical decomposition of the same diazo compound in ferf-butanol/benzene generated five products, in which either one or two alcohol molecules are incorporated and which are obviously derived from diazosilene and bissilene intermediates. 

The success of the fluidized bed in eliminating interference from thermal or photochemical decomposition products is evident in the spectra characterizing benzene adsorbed in Fl-USY zeolite shown in Fig. 6. The strong peak at 990 cm in liquid benzene (6a) is assigned to a symmetric ring-breathing mode. This band is... 

Other aminoferrocene precursors are Af-ferrocenyl phthalimide, which can be converted to FC-NH2 by N2H4 H2O in boiling ethanol (82% yield) [16, 44], and ferrocenyl azide, FC-N3, which has been reduced with LiAlH4 (72% yield) (cf. Scheme 5-6) [45]. Ferrocenyl amine, FC-NH2, is generally formed among other products in the thermal or photochemical decomposition of FC-N3 [56] and in the thermolysis of ferrocenyl isocyanate, Fc-NCO [57], in solvents such as cyclohexane, cyclohexene and benzene, probably by reaction of the intermediate nitrene, [Fc-N], with the solvent [56, 57]. The reduction of nitroferrocene, FC-NO2, provides another route to aminoferrocene, FC-NH2 [58 — 61] however, FC-NO2 is not an easily accessible starting material. 

Both N-N and N-C bond fission occurs on irradiation of the hydrazone derivatives (191). The photodegradation of the phenylhydrazone and the hydrazone of benzil have also been described. a-Ketoiminyl radicals are formed on irradiation of oximino ketones at low temperature. A study of the photochemical decomposition of sulfamic esters and their use as initiators of cross-linking of a melamine resin have been described. The bispyridinyl radical (192) is formed by one electron reduction of the corresponding pyridinium salts. The irradiation of this biradical at 77 K results in C-N bond fission with the formation of benzene-1,3-diyl. The predominant products from the irradiation (X,> 340 nm) of (193) in methanol were identified as A -hydroxy-2-pyridone and (194) from the fission of the C-O bond. Other products were 2-pyridone, (195) and (196) that arise from O-N bond fission. The reaction is to some extent substituent dependent and a detailed analysis of the reaction systems has identified an intramolecular exciplex as the key intermediate in the C-O bond heterolysis. 

Starting from (2-oxoalkylidene)sulfur-5, triacylcyclopropanes are often the dominant products, regardless of the decomposition mode of the sulfonium ylide. . In fact, no example of an efficient alkene cyclopropanation using these synthetic equivalents of oxocar-benes is yet known. The photochemical decomposition (2> 300nm) of (2-oxo-2-phenylethylidene)sulfur-5" in cyclohexene yielded only a minor amount of 7-benzoyl-bicyclo[4.1.0]heptane (2, 5%) in addition to tranj-l,2,3-tribenzoylcyclopropane (3, 40%), acetophenone (37%), bicyclohex-2-enyl (38%), and propiophenone (3%). In an inert solvent (benzene, chloroform) without an additional trapping reagent,, 2,3-tribenzoylcyclo-... 

Thermal, or photochemical, decomposition of certain polycyclic diazines yields seven-membered rings. Thus, enr/o-10,ll-diazatetracyclo[4.3.2.0 .0 ]undec-10-ene rearranges to bicy-clo[5.2.0]nona-2,5-diene at 180°C (Section 2.4.1.5.2.8.). Substituted 9,10-diazatetracyclo-[3.3.2.0. 0 - ]dec-9-enes, e.g. 3, rearrange to give mixtures of bicyclo[5.1.0]octa-2,5-dienes and tetracyclo[3.3.0.0 . 0 ]octanes when photolyzed in methanol or benzene. ... 

More detailed investigations by Rabek and Pajak [508] show that DPPH (concentration 10-3—10-4 mole l-1) added to a solution of cis-l,4-polyisoprene in benzene or n-heptane accelerates the photodegradation in the presence as well as in the absence of oxygen. It was discovered that the products of photochemical decomposition of DPPH have stronger sensitizing properties with respect to the photodegradation of diene polymers than has the undecomposed DPPH. 

The photochemical decomposition of the thiazete 207 in benzene at 30 °C affords carbazole 208190. The reaction presumably involves the formation of a biradical by S—N bond fission which, on loss of S02, undergoes cyclization to yield the final product. Loss of sulphur dioxide also occurs on irradiation of the sultam 209 yielding the quinomethane imine 210, which ring closes to the azetidine 211181. Irradiation of the sulphobenzimide 212 in benzene yields the amide 213 by a free radical reaction path182. 

Quantum yields for photochemical decomposition of Cp2M (M = Fe, Ru, Ni, or Co), (benzene)aCr, and their cations have been measured.188 The 18-electron compounds were found to be photostable. 

The reaction rate of photochemical decomposition at room temperature in the presence of oxygen and nitric oxides is lower for benzene than for other hydrocarbons [82]. In photochemical reactions, acrolein and glyoxal [83, 84] and primarily nitrobenzene and nitrophenols [85, 86] are formed from benzene in the presence of nitric oxides, with o- and p-nitrophenol being formed from nitrobenzene as intermediate [87]. If benzene is exposed to light in the presence of carbon monoxide and nitric oxides, then p-nitrophenol, 2,6-dinitrophenol and 2,4-dinitrophenol are formed [88]. 

When, phenylazide and 3-methyl-1-butene are mixed in benzene and kept standing for a couple of days, triazoline is formed and it gives aziridine by thermal or photodecomposition. However, when the mixture is irradiated as soon as they are mixed, the aziridine which is found in the solution is the one formed, not by the decomposition of the triazoline but, by direct photochemical reaction of phenylnitrene with 3-methy1-1-butene. 

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