Photochemical photodecomposition

Photochemical decomposition of riboflavin in neutral or acid solution gives lumichrome (3), 7,8-dimethyl all oxazine, which was synthesized and characterized by Karrer and his co-workers in 1934 (11). In alkaline solution, the irradiation product is lumiflavin (4), 7,8,10-trimethyhsoalloxazine its uv—vis absorption spectmm resembles that of riboflavin. It was prepared and characterized in 1933 (5). Another photodecomposition product of riboflavin is 7,8-dimethy1-10-foTmylmethy1isoa11oxazine (12). 

Anotlrer consideration in the production of thin fllms by photochemical processes is that the fraction of the beam which is not used in photodecomposition will heat any substrate on which it is desired to form the fllm. The power of tire light source which can be used for photodecomposition in the gaseous phase only is therefore limited by the transmission of energy. Clearly this transmitted beam represents a constant source of energy which... 

Diacyl peroxides have continuous weak absorptions in the UV to ca 280 nm (e ca 50 M cm 1 at 234 nm),147 Although the overall chemistry in thermolysis and photolysis may appear similar, substantially higher yields of phenyl radical products are obtained when BPO is decomposed photochemically. It has been suggested that, during the photodecomposition of BPO, (3-scission may occur in... 

Trichlorodibenzo-p-dioxin was sensitive to photodecomposition. When this compound was irradiated in TFMS acid by UV light, the upper spectrum in Figure 9 was obtained. However a new spectrum appeared after standing for a day, identical to the spectrum of the 1-chloro derivative. Further photochemical studies with this compound are being made. 

An interesting alternative mechanism of activation is the photochemical reduction of Pt(IV) to Pt(II) (Fig. 3). In addition to photoreduction, photosubstitution and photoisomerization can also occur, making the photochemistry of Pt complexes difficult to predict and a careful analysis of the photoproducts imperative (21). We have been involved particularly in the development of photochemotherapeutic agents based on Pt(IV) and the study of their photodecomposition and (subsequent) interactions with... 

Detailed photochemical studies of RBS and RRS have revealed that the photolysis of RRS produces RBS and NO quantitatively (Scheme 5.6) and the RBS produced undergoes further photodecomposition to generate NO and iron (III) [165, 168]. RBS has been tested as an NO delivery drug to the vascular and brain tissues by thermal as well as photochemical means [169, 170]. Due to the high solubilities in aprotic solvents, Roussin s salts are able to penetrate the endothelial cell membrane easily and deliver NO for hours [169]. RBS has been found to inhibit ADP-induced platelet aggregation [171] and Roussin s salts in general show a bacteriostatic effect, presumably due to the interaction of released NO and iron-sulfur proteins [172]. 

Because of the paucity of rate data for the reactions of F and FO one can only speculate on the course of the reaction subsequent to the initial dissociation. The results of photochemical studies398,399 give some guidance. The quantum yield F2o of photodecomposition is 1.0 at 3650 A, independent of temperature in the range 15-45 °C, pressure of F20 and pressure of oxygen398 the primary step is almost certainly as in (2)398,3". Thus, at room temperature at least, any contribution from... 

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. 

That chiral molecules can be produced in a CPL field, either from achiral precursors by photo-activated synthesis or by preferential chiral photodestruction of a racemic mixture, is now well demonstrated and has been reviewed. [46] In all cases currently known, however, such processes have proved very inefficient. For example, asymmetric photochemical ring-closures of achiral helicene precursors induced by CPL have produced only about 0.2% e.e. in the products. Likewise, the CPL-induced photolysis of racemic camphor produced about 20 % e.e., but only after 99% photodestruction, and photolysis of D.L-glutamic acid produced only 0.22 % e.e. after 52 % photodecomposition. [71]... 

In summary, photodecomposition of methoprene is facile and leads to a multiplicity of products. The lower photostability in sunlight of methoprene compared to epifenonane has been mentioned previously. Because of its photochemical lability and its ready microbial degradation (see below), methoprene is microencapsulated for aquatic use as a mosquito larvicide. 

Peltonen K, et ah Free radicals from photodecomposition of Bisphenol A. Photochem Photobiol 3-A8l, 1986... 

All the 1-pyrenylbismuthonium salts photochemically decompose (2ex > 320 nm / > 150 mW cm 2) to generate their respective protic acids, accompanied by the formation of bismuth(III) compounds and pyrene (Scheme 25). The quantum yields of the photodecomposition (<7>dcc) in acetonitrile were determined by chemical actinometry to be 0.20-0.22. These values are comparable to the values reported for the triarylsulfonium and diaryliodonium salts (dec = 0.17-0.22) [98, 99]. 

The photochemical stabihty of the molecules is characterized by the quantum yield of photodecomposition, (P = N/Q [69], where N and Q are the numbers of decomposed molecifles and absorbed photons, respectively. The photochemical properties of the fluorene derivatives were investigated in different organic solvents (hexane, CH2CI2, ACN, and polyTHF) at room temperature by the absorption and fluorescence methods and comprehensively described [70-72]. These methods are based on measurements of the temporal changes in the steady-state absorption and fluorescence spectra during irradiation. For the absorption method, the quantum yield of the photodecomposition under one-photon excitation, c >ipa, can be obtained by the equation [73] ... 

The published research on the photochemical decomposition of di-azonium salts suggests that the two processes, a heterocyclic and a homolytic process, analogous to those of the thermal decomposition may occur. Various workers 36 187 have reported that phenols are formed when diazonium salts are photolyzed in water and aryl ethers result when an alcohol replaces water as the solvent. Homer and Stohr122 report that a process analogous to reductive deamination occurs in preference to ether formation results in alcohols. The importance of free radical intermediates in the photodecomposition, based on magnetic susceptibility measurements, has been stressed.25 Lee and his co-workers171 have recently suggested that in ethanol the photodecomposition of a diazonium salt occurs via a radical intermediate while in water an ionic process predominates. Thus, photodecomposition of a nitrobenzene diazonium chloride in water yielded both a nitrophenol and a chloronitrobenzene in ethanol, on the other hand, the major product of photolysis was the reduction product, nitrobenzene. 

The photodecomposition of phthalic anhydride has received detailed attention132 and 8 has been shown to be a definite but minor product with irradiation at 308 nm the major path involves CO and C02 ejection to benzyne. Indeed, the use of low temperature photochemical methods to provide 8 has much appeal as equation 18 and the sequences of Scheme 11 attest. The deazetation133 of 84 probably proceeds via carbene 85 which under-... 

A number of reports of photochemical decomposition of heteroaromatic compounds have appeared in the literature during the past 50 or 60 years. A few of these undoubtedly involve photooxidative processes, whereas others have been examined in the vapor phase, often at elevated temperatures. Recent work includes the study of the photodecomposition of thiophene128 andpyrazine.129 Furans undergo... 

The photodecomposition of oxiran and alkyloxirans both in the gas phase and in solution has been extensively investigated. Processes arising by carbon-oxygen bond homolysis and hydrogen abstraction have been reported, and the subject has been reviewed in detail elsewhere.48 The most recent studies include the photoaddition of methanol to alicyclic epoxides, a process that appears to be promoted by acid,49 and the interesting if unusual photochemically induced conversion of the epoxyalcohol (56) to sugiresinol dimethyl ether (57).50... 

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