Photolysis procedure

Photolysis Procedure. The solvent-cleaned Kevlar-29 fabric swatch (2.5 cm x 18 cm) was placed around the outside quartz tube inside the photolysis chamber, which was subsequently evacuated, before - - 02 (99%) was introduced to 0.2 atm. The photolysis chamber was preheated to the specified photooxidation temperature, before the Hg-Xe lamp was turned on. The temperature, which was held constant in the chamber by adjusting the air flow around the lamp, was monitored by a thermocouple placed next to the fabric sample inside the chamber. After the photooxidation had continued for the specified... 

In HFP, where trinitromethanide is 3000 times less reactive than in acetonitrile, a weak signal of (N02)3C-PBN is still obtained by the photolysis procedure (Eberson et al., 1996a). Evidently, some nucleophilic reactivity is retained by trinitromethanide ion in HFP. 

It would appear from these data that the a-hydrogen abstraction process is more important to the yield of photolytic cleavage than the process of nitro group photoexcitation in the overall photolysis procedure. 

The photolysis procedure follows that given in the chloro derivative synthesis (Section 11-A). During irradiation, a white precipitate of [ReI(CO)5] appears in the violet solution. The reaction is terminated when the IR bands due to [Re2(CO)i0] (2073, 2016, and 1976 cm-1) disappear (about 140 min).t... 

Quantum yields for ethene hydrogenation under these ambient temperature conditions exceeded 20. The photolysis procedure generated a reservoir of Fe(CO)3(ethene)2 which is very labile and dissociates to give the active, unsaturated species Fe(CO)3(ethene). Added CO as well as photoliberated CO inhibits catalysis due to the back reaction to form the stable Fe(CO)4(ethene) [65]. 

The reactions that the vinyl cations can undergo are nucleophilic substitution and rearrangement, similar to those of solvolytically generated vinyl cations (Equation 11.3). The photolysis procedures have the advantage that they can be applied to a wide variety of substrates. 

Ring expansion of haloalkyloxiranes provides a simple two-step procedure for the preparation of azetidin-3-ols (Section 5.09.2.3.2(f)) which can be extended to include 3-substituted ethers and O-esters (79CRV331 p. 341). The availability of 3-hydroxyazetidines provides access to a variety of 3-substituted azetidines, including halogeno, amino and alkylthio derivatives, by further substitution reactions (Section 5.09.2.2.4). Photolysis of phenylacylamines has also found application in the formation of azetidin-3-ols (33). Not surprisingly, few 2-0-substituted azetidines are known. The 2-methoxyazetidine (57) has been produced by an internal displacement, where the internal amide ion is generated by nucleophilic addition to an imine. 

There are therefore two ways in which lasers may be used to bring about photon-assisted film formation. If the laser emits radiation in the near-ultra-violet or above, photochemical decomposition occurs in the gas phase and some unabsorbed radiation arrives at the substrate, but this latter should be a minor effect in die thin film formation. This procedure is referred to as photolysis. Alternatively, if the laser emits radiation in the infra-red, and tire photons are only feebly absorbed to raise the rotational energy levels of the gaseous... 

During 1961-2 four independent groups almost simultaneously reported the first syntheses of D-norsteroids, based on the photolysis of 16-diazo-17-ketones. In a typical procedure. Cava and Moroz ° convert the 16-oximino-17-one (93) derived from estrone methyl ether (92) to the diazoketone (94)... 

The following reactions share only the feature that they are structural isomerizations. They incorporate a variety of reagents and procedures from acid catalysts to photolysis. 

H-Azepines 2 by Photolysis of 2,1-Renzisoxazoles 1 in MeOH General Procedure 65... 

Interestingly, photolysis of phenyl azide in liquid ammonia yields 3//-azepin-2-amine (39)35 (see experimental procedure in Houben-Weyl, Vol.4/5b, pi268). 

Alkoxy-3//-azepines 87 by Photolysis of Esters and Amides of 2-Azidobenzoic Acid in Alcohol/THF Solution General Procedure 74... 

Dccalin (decahydronaphthalene),benzene, 1,4-dioxane, and ethanol may be used as solvents for the photolysis. In an alternative procedure, volatile materials swept from the photolysis vessel are condensed in a dry ice trap. This cold mixture is added to a flask containing a magnetically stirred solution of dimsyl anion in dimethyl sulfoxide, and fractionation at reduced pressure provides a solution of bicyclopentene in tetrahydrofuran. 

Arylthallium bis(trifluoroacetates) (see 12-21) can be converted to aryl nitriles by treatment with copper(I) cyanide in acetonitrile. Another procedure uses excess aqueous KCN followed by photolysis of the resulting complex ion ArTl(CN)3 in the presence of excess KCN. Alternatively, arylthallium acetates react with Cu(CN)2 or CuCN to give aryl nitriles. Yields from this procedure are variable, ranging from almost nothing to 90 or 100%. 

In another reductive coupling, substituted alkenes (CH2=CH Y Y = R, COOMe, OAc, CN, etc.) can be dimerized to substituted alkanes (CH3CHYCHYCH3) by photolysis in an H2 atmosphere, using Hg as a photosensitizer. Still another procedure involves palladium-catalyzed addition of vinylic halides to triple bonds to give 1,3-dienes. ... 

For example, photolysis of a suspension of an arylthallium ditrifluoro-acetate in benzene results in the formation of unsymmetrical biphenyls in high yield (80-90%) and in a high state of purity 152). The results are in full agreement with a free radical pathway which, as suggested above, is initiated by a photochemically induced homolysis of the aryl carbon-thallium bond. Capture of the resulting aryl radical by benzene would lead to the observed unsymmetrical biphenyl, while spontaneous disproportionation of the initially formed Tl(II) species to thallium(I) trifluoroacetate and trifluoroacetoxy radicals, followed by reaction of the latter with aryl radicals, accounts for the very small amounts of aryl trifluoroacetates formed as by-products. This route to unsymmetrical biphenyls thus complements the well-known Wolf and Kharasch procedure involving photolysis of aromatic iodides 171). Since the most versatile route to the latter compounds involves again the intermediacy of arylthallium ditrifluoroacetates (treatment with aqueous potassium iodide) 91), these latter compounds now occupy a central role in controlled biphenyl synthesis. 

The kinetics of the various reactions have been explored in detail using large-volume chambers that can be used to simulate reactions in the troposphere. They have frequently used hydroxyl radicals formed by photolysis of methyl (or ethyl) nitrite, with the addition of NO to inhibit photolysis of NO2. This would result in the formation of 0( P) atoms, and subsequent reaction with Oj would produce ozone, and hence NO3 radicals from NOj. Nitrate radicals are produced by the thermal decomposition of NjOj, and in experiments with O3, a scavenger for hydroxyl radicals is added. Details of the different experimental procedures for the measurement of absolute and relative rates have been summarized, and attention drawn to the often considerable spread of values for experiments carried out at room temperature (-298 K) (Atkinson 1986). It should be emphasized that in the real troposphere, both the rates—and possibly the products—of transformation will be determined by seasonal differences both in temperature and the intensity of solar radiation. These are determined both by latitude and altitude. 

A closely related procedure results in formation of y-lactones. Amides are converted to AHodoamidcs by reaction with iodine and /-butyl hypochlorite. Photolysis of the AHodoamides gives lactones via iminolactone intermediates.372... 

Alkoxy radicals are also the active hydrogen-abstracting species in a procedure that involves photolysis of nitrite esters. This reaction was originally developed as a method for functionalization of methyl groups in steroids.379... 

The disilene synthesis by the photolysis of linear trisilanes proceeds via initial formation of a silylene followed by its dimerization (Eq. 1). Disilene 1 has now become a common organometallic reagent. A detailed synthetic procedure employing photolysis of the corresponding linear trisilane is described in Inorganic Syntheses (Eq. 2).6... 

A very interesting technique for radical generation is flash photolysis, which employs a very intense pulse of radiation (visible or u.v.) of very short duration. This produces a very high immediate concentration of radicals, which may be detected—and whose fate may be followed—by spectroscopy through one or more subsequent pulses of lower intensity radiation of suitable wavelength. This is, of course, primarily a technique for the study of radicals rather than for their use in preparative procedures. Radicals may also be generated, in suitable cases, by irradiation of neutral molecules with X-rays or with y-rays radiolysis. 

The synthetic procedures applied utilize the photochemical generation of the solvent stabilized 16e -species [(ij5 -H3CC5H4)Mn(CO)2 x THF] 6 by photolysis of (7j5-H3CC5H4)Mn(CO)3 5. [(t/5-... 

A similar procedure allows us to assign the additional peaks produced on ArF photolysis as being due to Cr(C0>3 and Cr(C0>2 [9]. The frequencies of the gas phase absorptions for these coordinatively unsaturated fragments is presented in table II. Data for the rates of reaction of each of these species with CO is summarized in table I. 

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