Photolyzing

Cyclopropenones and cyclobutendiones can be photolyzed or thermolyzed (FVP) to give acetylenes. 

One potential approach extends the idea of chemical amplification introduced in our preceding description of dry-film resists. In 1982, Ito and co-workers (37,38) recognized that if a photosensitizer producing an acidic product is photolyzed in a polymer matrix containing acid-labile groups, the acid will serve as a spatially localized catalyst for the formation or cleavage of chemical bonds. 

The reaction mechanisms by which the VOCs are oxidized are analogous to, but much more complex than, the CH oxidation mechanism. The fastest reacting species are the natural VOCs emitted from vegetation. However, natural VOCs also react rapidly with O, and whether they are a net source or sink is determined by the natural VOC to NO ratio and the sunlight intensity. At high VOC/NO ratios, there is insufficient NO2 formed to offset the O loss. However, when O reacts with the internally bonded olefinic compounds, carbonyls are formed and, the greater the sunshine, the better the chance the carbonyls will photolyze and produce OH which initiates the O.-forming chain reactions. 

In the mid-1970s, it was realized that the CFCs in widespread use because of their chemical inertness, would diffuse unaltered through the troposphere and into the mid-stratosphere where they, too, would be photolyzed by uv (<240 nm) radiation. For example, CFC-12 can photolyze ... 

Hydrogen peroxide is photolyzed slowly to hydroxyl radicals, which decompose ozone. 

Although inert in the lower atmosphere (troposphere), the hilly halogenated CFCs and Halons diffuse into the upper stratosphere where they are photodissociated, ie, photolyzed, by the intense ultraviolet radiation. 

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

Protonated /V-chloroalkyl amines under the influence of heat or uv light rearrange to piperidines or pyrroHdines (Hofmann-Lriffler reaction) (88). The free-radical addition of alkyl and dialkyl-/V-chloramines to olefins and acetylenes yields P-chloroalkji-, P-chloroalkenyl-, and 8-chloroalkenylamines (89). Various N-hiomo- and N-chloropolyfluoroaLkylarnines have been synthesized whose addition products to olefinic double bonds can be photolyzed to fluoroazaalkenes (90). 

Photolysis of 1,2,3-thiadiazole (35) gives thiirene (36) which can be trapped by an alkyne (70AHC(ll)l). 4,5-Diphenyl-l,2,3-thiadiazole (37) is photolyzed at low temperatures to the thiobenzoylphenylcarbene triplet (38). Diphenylthioketene (39) is formed on warming (81AHC(28)231). 

Photodecomposition of A -l,2,3-triazolines gives aziridines. In cyclohexane the cis derivative (304) gives the cis product (305), whereas photolysis in benzene in the presence of benzophenone as sensitizer gives the same ratio of cis- and trans-aziridines from both triazolines and is accounted for in terms of a triplet excited state (70AHC(ll)i). A -Tetrazo-lines are photolyzed to diaziridines. 

The isoxazole (19a) when photolyzed produced two oxazoles (20) and (21) which were not interconvertable under the reaction conditions. The corresponding esters (19b) and (19c) gave (20b) and (20c), respectively. These studies were instrumental in establishing the photointerconversion of 4- and 5-acylisoxazoles (76HCA2074). 

Phenyldiazonium salts react with malonaldioxime to produce a 2-isoxazoline (7 IGEPl 920245), and the diazo ketone (484) when photolyzed gave a mixture of 2-isoxazoline and an isoxazole by a 1,5 carbon-hydrogen insertion. A phenyl migration was apparently not involved (Scheme 124) (66CC689). 

Many azo compounds also generate radicals when photolyzed. This ean oeeur by a thermal decomposition of the c -azo compounds that are formed in the photoehemieal... 

Applicabdity Limitations Photolysis is appropriate for difficult-to-treat chemicals (e.g., pesticides, dioxins, chlorinated organics), nitrated wastes, and those chemicals in media which permits photolyzing the waste. The waste matrix can often shield chemicals from the light (e.g., ultraviolet light absorbers, suspended solids, solid wastes). The photolysis process typically requires pretreatment to remove suspended materials, and the by-products formed may be more toxic than the parent molecules. 

It has been reported recently that 17/ -acetoxy-5a,14a-androstan epimerizes at C-14 when photolyzed in cyclohexane solution in the presence of mercuric bromide. When the reaction is carried out in perdeuterated cyclohexane, the product consists of 55 % d - and 12% d2-labeled species. This reaction may develop into an interesting deuteration technique if the incorporated deuterium can be securely assigned to the epimerized position. 

This nitrite (5 g) is dissolved in 200 ml of toluene and photolyzed For 2 hr at 20° as described above. Without further treatment the solution is chromatographed on 100 g of alumina and eluted with methylene dichloride containing increasing proportions of methanol. The first fraction gives 0.6g prednisolone BMD. The latter fractions afford 17,20 20,21-bismethylenedioxy-llj5-hydroxy-18-oximinopregna-l,4-dien-3-one (3 g) mp 270-274° [oc]d 0°, after crystallization from ethyl acetate-hexane. 

The same product ratio is obtained when (267) is photolyzed under the same conditions in the presence of P flfn -dichloroethylene. 

The elimination of sulfur dioxide is apparently more difficult than that of either carbon monoxide or carbon dioxide When fluorosulfonyldifluoroacetyl halide (chloride, bromide, or iodide) is photolyzed, carbon monoxide is quantitatively eliminated to give halodifluoromethanesulfonyl fluonde with increasing ease from chloride to bromide to iodide [95, 100] (equation 67)... 

Poly-1,2-1//-azepines, produced by gas-phase photopolymerization of aryl azides yield, after oxidation, electrically conducting films.103 By photolyzing 4-(pcntyloxy)phenyl azide in the gas phase, a flexible polyazepine is produced which can be deposited directly as a thin polymer film onto a suitable surface. 

A solution of ethyl azidoformate (10 g, 87 mmol) in anhyd benzene (250 mL) was photolyzed at 60-70 C for 60 h, using a high-pressure Hg ultraviolet lamp, whereupon N2 was evolved and the solution became yellow. The benzene and remaining azido ester were removed under reduced pressure, and the yellow-brown oily residue distilled under high vacuum to give a yellow oil yield 8.35 g (67%) bp 46-47 C/5 x 10"3 Torr bp 130 C/0.2 Torr. 

A solution of the 2-azido ester or amide (ca. 2 g) in a mixture of MeOII (95 mL) and sodium-dried THF (95 mL) was photolyzed under N2 in a Hanovia photochemical reactor (110-W medium-pressure Hg lamp with a Pyrex filter). The reaction was monitored by observing the rate of disappearance of the absorption band (Nf) at 2140 cm 1 (irradiation times of 3-5 h were generally required). When the reaction was complete the solvent was removed in vacuo and the brown residual oil chromatographed on alumina [petroleum ether (bp 60-803C)/benzene 7 3]. Further elution with benzene followed by removal of the solvent gave the product (the esters as pale yellow oils, the amides as crystalline solids), which were further purified by vacuum distillation or by recrysiallization. 

Similarly, allylbromide reacts to give the hexabutenyl complex. The latter can be photolyzed. The new hexabutenylbenzene ligand is recovered in the recycling reaction [77] Scheme XI. 

Margerum et al (Ref 9) photolyzed solns of aromatic nitrocompds in 95% ale using an unfiltered 400 watt mercury lamp. No compd was found to be phototropic which did not have a nitrogroup ortho to a benzyl hydrogen. They hypothesized that an intramolecular process involving an H-atom transfer was operative ... 

Wettermark (Refs 10, 11 12) studied o-nitrotoluene and dinitrotoluene, flash photolyzed in w and ale. He observed transients, and noted that the absorption spectra was a function of pH. He concluded that intramolecular H-atom transfer was involved... 

Tench and Coppens (Ref 13) photolyzed o-nitrobenzaldehyde, nitrobenzene, and nitroben-zoic acid with light > 3500A. ESR measurements revealed the presence of radicals for o-nitrobenzaldehyde (in solns and powder), with no radicals observed with nitrobenzene and... 

Ambroz and Kemp (1979 a, 1982 a, b) photolyzed benzenediazonium salts with donor substituents in the 4-position (2,5-di- -butoxy-4-morpholine-, 2,5-diethoxy-4-H-butylthio-, and 2,4,5-trimethoxy-benzenediazonium hexafluorophosphate in LiCl - H20 - acetone matrices at low temperatures, 77-130 K). Under these conditions the aryl cation formed is sufficiently stable to be identified spectroscopically. It is a triplet, a result that is consistent with earlier ab initio calculations by Dill et al. (1977), and with earlier observations by Lee et al. (1961), also at low temperature (77 K). 

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