Quantitative photolysis

Quantitative Photolysis. Photolysis experiments were performed by exposing samples to a 450 Watt medium pressure mercury lamp. A shutter was placed between the samples and the lamp so that the exposure time could be accurately controlled. Unless otherwise stated, the samples were placed 4 inches from the lens. Filters (254 nm, 280 nm and 366 nm) when used, were placed immediately in front of the shutter. Sample holders were available for 1" x 1" quartz plates, NaCl windows and quartz UV cuvettes, and samples of each type were utilized. 

Hydroxy-1,2,2-triphenylethanone based carboxylic esters upon irradiation with a medium pressure mercury lamp resulted in a rapid and quantitative photolysis to afford the carboxylic acid and benzo[ft]phenanthro[9,10-tf]furan. No yield was reported for this synthetic transformation <03TL3151 >. 

Alanine was initially incorporated in the C-terminal position as a dummy amino acid to act as a substrate for the enzyme. The transacylation was carried out in EDTA buffer at pH 6.0 and the yield was essentially quantitative. Photolysis was carried out in methanol solution containing aqueous sodium bisulfite at pH 9.5 at 20 cm from a mercury SP 200 lamp filtered... 

Irradiation of (h -CsHjIjM CCO) (M = Mo, W) in gives h -C5H5M(CO)3Cl quantitatively photolysis of the Mo dimer with CHBrj yields h -CjHjMoCCOjBr. Homolytic cleavage of the M—M bond is the primary photoprocess, a fact further supported by ... 

In this section, we apply the phase-change rule and the loop method to some representative photochemical systems. The discussion is illustiative, no comprehensive coverage is intended. It is hoped that the examples are sufficient to help others in applying the method to other systems. This section is divided into two parts in the first, loops are constructed and a qualitative discussion of the photochemical consequences is presented. In the second, the method is used for an in-depth, quantitative analysis of one system—photolysis of 1,4-cyclohexadiene. 

Nitrile ylides derived from the photolysis of 1-azirines have also been found to undergo a novel intramolecular 1,1-cycloaddition reaction (75JA3862). Irradiation of (65) gave a 1 1 mixture of azabicyclohexenes (67) and (68). On further irradiation (67) was quantitatively isomerized to (68). Photolysis of (65) in the presence of excess dimethyl acetylenedicar-boxylate resulted in the 1,3-dipolar trapping of the normal nitrile ylide. Under these conditions, the formation of azabicyclohexenes (67) and (68) was entirely suppressed. The photoreaction of the closely related methyl-substituted azirine (65b) gave azabicyclohexene (68b) as the primary photoproduct. The formation of the thermodynamically less favored endo isomer, i.e. (68b), corresponds to a complete inversion of stereochemistry about the TT-system in the cycloaddition process. 

Aziridinimine derivatives are also accessible by the photochemically induced extrusion of nitrogen and ring contraction of simple alkylidene tetrazolines (424) <75AG(E)428). Thus, Pyrex-filtered photolysis of (424) at -60 °C quantitatively afforded the aziridinimines (425). 

Benzylsulfonamides, prepared in 40-70% yield, are cleaved by reduction (Na, NH3, 75% yield H2, Raney Ni, 65-85% yield, but not by H2, Pt02) and by acid hydrolysis (HBr or HI, slow). They are also cleaved by photolysis (2-4 h, 40-90% yield). The similar p-methylbenzylsulfonamide (PMS—NR2) has been prepared to protect the e-amino group in lysine it is quantitatively cleaved by anhydrous hydrogen fluoride/anisole (—20°, 60 min). Another example of this seldom used group is illustrated below... 

This derivative, synthesized by a silver oxide-promoted condensation of pyrenylmethyl chloride and a dialkyl phosphate (92% yield), is quantitatively cleaved by photolysis at >300 nm in 60 min. ... 

Pyridinium ylide is considered to be the adduct car-bene to the lone pair of nitrogen in pyridine. The validity of this assumption was confirmed by Tozume et al. [12J. They obtained pyridinium bis-(methoxycarbonyl) meth-ylide by the photolysis of dimethyl diazomalonate in pyridine. Matsuyama et al. [13] reported that the pyridinium ylide was produced quantitatively by the transylidalion of sulfonium ylide with pyridine in the presence of some sulfides. However, in their method it was not easy to separate the end products. Kondo and his coworkers [14] noticed that this disadvantage was overcome by the use of carbon disulfide as a catalyst. Therefore, they used this reaction to prepare poly[4-vinylpyridinium bis-(methoxycarbonyl) methylide (Scheme 12) by stirring a solution of poly(4-vinylpyridine), methylphenylsulfo-nium bis-(methoxycarbonyl)methylide, and carbon disulfide in chloroform for 2 days at room temperature. 

A comparison of the photolysis of 2-azidophenyl methyl ketone and 3-methyl-2,1-benzisoxazole in piperidine reveals that whereas the former gives a mixture of isomeric 3//-azepines the latter furnishes 3-acetyl-2-piperidino-3/7-azepine (4) in almost quantitative yield.124... 

An essentially quantitative yield (98%) of the thermally stable hexafluoro-2-aza-bicyclo[3.2.0]hepta-3,6-diene 18 is obtained from the small-scale photolysis of the hexafluoro-l//-azepine 17.230 Hexafluoro-l//-azepine-l-carbonitrileand-l-carboxamidebehave similarly. On scaling up the process for the l-(ethoxycarbonyl) derivative 17, however, a much lower yield (59%) of bicycle 18 resulted, although this was improved to 81% by carrying out the photolysis in hexane or rm-butyl alcohol in the presence of a triplet sensitizer, e. g. ben-zophenone. 

The simple initiation process depicted in many standard texts is the exception rather than the rule. The yield of primary radicals produced on thermolysis or photolysis of the initiator is usually not 100%. The conversion of primary radicals to initiating radicals is dependent on many factors and typically is not quantitative. The primary radicals may undergo rearrangement or fragmentation to afford new radical species (secondary radicals) or they may interact with solvent or other species rather than monomer. 

The coordinated silylenes in both the iron and the chromium compounds can be photolytically activated Photolysis of the complexes in the presence of triphenylphosphine gives the trans-silylene-phosphine complex, which in a second step is transformed into the trnns-bisphosphine compound by excess phosphine. If the silylenes are not trapped, polysilanes are isolated in almost quantitative... 

Several studies of the application of the photoextrusion of S02 have been conducted in substituted analogs of the parent compounds above. For example, the photolysis of 2-phenylthietane 1,1-dioxides (34), in dichloromethane or methanol, at 254 nm affords the expected phenylcyclopropanes in almost quantitative yields68. The 2-phenyl substituent... 

Thiophenols may also be synthesized via the photochemical decomposition route 156). Thus, treatment of arylthallium ditrifluoroacetates with an aqueous solution of potassium Ar,AT-dimethyldithiocarbamate led in quantitative yields to the formation of the corresponding aryl AT,A -dimethyl-dithiocarbamates. Subsequent photolysis in aqueous acetone then led to disulfides which were reduced to the thiophenols. A small amount of aryldithiocarbamate formed as a by-product in the photolysis was converted to the same thiophenol by hydrolysis. The overall reaction sequence is illustrated in Eq. (18). 

The low-temperature photolysis of hexakis(2,4,6-triisopropylphenyl) cyclotristannane leads quantitatively to the corresponding distannene (Eq. 30).90 The distannene was found to be in equilibrium with the cyclotristannane over a wide range of temperatures. The simplest explanation for this is that the stannylene is formed as an intermediate from either the cyclotristannane or the distannene, but quickly adds to the distannene or dimerizes. This equilibrium can be followed by ll9Sn NMR spectroscopy at elevated temperatures.96... 

In 1959 Wheeler and Eastman reported that umbellulone quantitatively produced thymol upon photolysis at room temperature(B1) ... 

Photolysis in the gas phase leads to the quantitative production of nitrogen and methyl radicals. Photolysis in solution, however, results in a shift in the absorption spectrum to longer wavelengths due to the production of a new species, which is identified as the cw-azomethane (the trcms configuration is the normal isomer). Similarly, irradiation of tro/u-azoisopropane<3) results in trans-cis isomerization to the cis isomer ... 

Burdick and Jackson). All solutions were photolyzed to less than 5% conversion in a standard 3 ml capacity, 1-cm path length quartz cell. Samples were irradiated with a 450-Watt medium pressure, Hanovla mercury lamp focused through an appropriate band-pass filter (280 nm or 254 nm) onto the 1-cm quartz cell with the requisite solution. Test solutions could be purged with either helium or oxygen using a needle valve assembly attached to the tapered quartz cell neck. The loss of carbamate due to photolysis and the amounts of known photoproducts were determined quantitatively by GC using eicosane as an internal standard. The columns were 6 stainless steel containing Carbowax 20M on chromosorb G. 

The pyranofurooxazoline 109 can be prepared by a nitrene insertion reaction of the corresponding furan 110 upon treatment with ethyl azidoformate at — 50 °C under photolysis conditions. Compound 109 is moisture sensitive, and upon treatment with wet acidic THF was converted quantitatively to the more polar furanopyran 111. The structure and stereochemistry of 109 were proved unambiguously by X-ray diffraction, showing that the nitrene inserted anti to the bridgehead methyl group <1999JOC736> (Scheme 30). 

In this article we have summarized the use of both photochemical and more classical thermal kinetics techniques to deduce the nature of intermediates in the ambient temperature, fluid solution chemistry of several triruthenium clusters. In some cases the photochemically generated intermediates appear to be the same as those proposed to be formed along thermal reaction coordinates, while in other cases unique pathways are the results of electronic excitation. The use of pulse photolysis methodology allows direct observation, and the measurement of the reaction dynamics of such transients and provides quantitative evaluation of the absolute reactivities of these species. In some cases, detailed complementary information regarding... 

The steady-state charge-transfer photolysis of the yellow solution of [MV2+, Ar2C(0H)C02 ] leads to a quantitative yield of diarylketone200 (equation 68). 

Photolysis of the triazepine products produces 2,2-dimethylpropanenitrile and the corresponding pyrazole in quantitative yield <1997BSF927>. Reaction of sydnone 89 with fulvene 91 proceeds by [ji4s + jt6s]-cycloaddition followed by spontaneous loss of carbon dioxide and a molecule of dimethylamine or acetic acid from the pseudo-azulene , cyclopentaMpyridazine 92 (Equation 9) <1996CC1011, 1997T9921>. 

Chen, J., Quan, X., Yan, Y., Yang, F., Peijnenburg, W.J.G.M. (2001) Quantitative structure-property relationship studies on direct photolysis of selected polycyclic aromatic hydrocarbons in atmospheric aerosol. Chemosphere 42, 263-270. 

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