Glasses photolysis

The glass photolysis cell has a radius of. 75 cm and an active length of 10 cm. The CaF2 windows of the cell are protected from photoproducts by a curtain of rare gas which flows over the windows and out the exhaust ports without mixing with the sample gases. 

Fig. 5. Pyrex glass photolysis vessel with water-cooled quartz probe.

The KG-33 glass photolysis vessels effectively filter the spectrum below 290 nm, eliminating photosensitization complications caused by mercury vapor introduced from the Toepler pump. During irradiation the samples were maintained at 304 1 K by means of air circulation provided by a blower mounted at the base of the lamp housing. Individual samples were photolyzed for 12-24 h with photochemical conversions never exceeding 2%. 

XSiOjCCHj (X=Vycor glass) ) Photolysis of acetylated Vycor glass/ Vycor glass EPR/ 133---323 2 H (a) a 2.0 73Mell... 

Examples include luminescence from anthracene crystals subjected to alternating electric current (159), luminescence from electron recombination with the carbazole free radical produced by photolysis of potassium carba2ole in a fro2en glass matrix (160), reactions of free radicals with solvated electrons (155), and reduction of mtheiiium(III)tris(bipyridyl) with the hydrated electron (161). Other examples include the oxidation of aromatic radical anions with such oxidants as chlorine or ben2oyl peroxide (162,163), and the reduction of 9,10-dichloro-9,10-diphenyl-9,10-dihydroanthracene with the 9,10-diphenylanthracene radical anion (162,164). Many other examples of electron-transfer chemiluminescence have been reported (156,165). 

Direct proof of an oxaziridine intermediate was achieved in photolysis experiments in an organic glass at 77 K (80JA5643). Oxaziridine (75), formed by photolysis of A/-oxide (74) and evidenced by UV spectroscopy under the above conditions, decomposed at higher temperature to form the imino ether (76) by N—O bond cleavage and C -> O migration of an aryl group. 

A more concentrated (1000 ppm) solution of dibenzo-p-dioxin in methanol was irradiated for 1.5 hours under a 450-watt lamp fitted with a borosilicate glass filter while nitrogen was bubbled continuously through, the solution. Unchanged starting material was recovered to the extent of 85%. The principal photolysis product again was a dark brown insoluble gum similar to that described above. Its mobility on thin layer chromatography (TLC) was very low in the benzene/ethyl acetate (4 1) solvent used to separate the other products. 

The results of low-temperature matrix-isolation studies with 6 [41a] are quite consistent with the photochemical formation of cyclo-Cif, via 1,2-diketene intermediates [59] and subsequent loss of six CO molecules. When 6 was irradiated at A > 338 nm in a glass of 1,2-dichloroethane at 15 K, the strong cyclobut-3-ene-1,2-dione C=0 band at 1792 cm in the FT-IR spectrum disappeared quickly and a strong new band at 2115 cm appeared, which was assigned to 1,2-diketene substructures. Irradiation at A > 280 nm led to a gradual decrease in the intensity of the ketene absorption at 2115 cm and to the appearance of a weak new band at 2138 cm which was assigned to the CO molecules extruded photo-chemically from the 1,2-diketene intermediates. Attempts to isolate cyclo-Cig preparatively by flash vacuum pyrolysis of 6 or low-temperature photolysis of 6 in 2-methyltetrahydrofuran in NMR tubes at liquid-nitrogen temperature have not been successful. 

Final resolution of these problems, particularly the complications from multiple matrix sites, came from investigations using spectroscopic methods with higher time resolution, viz. laser flash photolysis. Short laser pulse irradiation of diazofluorene (36) in cold organic glasses produced the corresponding fluorenylidene (37), which could be detected by UV/VIS spectroscopy. Now, in contrast to the results from EPR spectroscopy, single exponential decays of the carbene could be observed in matrices... 

Thus, we considered a number of examples of application of the sensor technique in experiments on heterogeneous recombination of active particles, pyrolysis and photolysis of chemical compounds in gas phase and on the surface of solids, such as oxides of metals and glasses. The above examples prove that, in a number of cases, compact detectors of free atoms and radicals allow one to reveal essential elements of the mechanisms of the processes under consideration. Moreover, this technique provides new experimental data, which cannot be obtained by other methods. Sensors can be used for investigations in both gas phase and adsorbed layers. This technique can also be used for studying several types of active particles. It allows one to determine specific features of distribution of the active particles along the reaction vessel. The above experiments demonstrate inhomogeneity of the reaction mixture for the specified processes and, consequently, inhomogeneity of the... 

A few other routes to new silenes involving photochemical processes have been reported, most of which have the structure RR Si=CH2110-112 and are listed in Table I. Photolysis of l,l-dimethyl-2-phenyl-l-silacyclo-but-2-ene 22 in a glass at 77 K led to the siladiene 23, which absorbed at 338 nm,113 as shown in Eq. (17) ... 

These reactions, while not very important for high-energy donors in the absence of azulene, do help define what the potential energy diagrams should look like, that is, the fram-stilbene triplet is a discrete intermediate while the cij-stilbene triplet is a high vibrational form of the phantom triplet. Herkstroeter and McClure(13> have been able to observe the fro/w-stilbene triplet via flash photolysis using low-temperature glasses however, no similar triplet was observed for cfr-stilbene. Only when they studied cfr-stilbene-like... 

A liner containing glass wool was installed in the injection port of the GC to trap polymer residues. A solution containing a known amount of the carbamate in THF along with sulfolane as an internal standard was used to establish the concentration of carbamates in the PMMA and PPMA matrix. Quantum yields were then determined. Product ratios were calculated from UV difference spectra (taken on a Beckman DK-2A spectrometer) of films before and after photolysis. 

Spatial electrochromism has been demonstrated in metallopolymeric films.28 Photolysis of poly-[Run(L10)2(py)2]Cl2 thin films on ITO glass in the presence of chloride ions leads to photochemical loss of the photolabile pyridine ligands, and sequential formation of po/y-[RuII(Llt))2(py)Cl]Cl and po/y-[Run(L10)2Cl2] (Scheme 1). 

The Pl Sn- radical has also been generated by photolysis of PhsSn in THF and 2-methyl THF glasses at 93 K42. The radical was identified by ESR spectroscopy, and its signal was found to disappear on warming the glass to 150 K. A similar reaction has been studied by Mochida and coworkers, who looked at the photolysis of PhKMe3 E (n = 1-3, E = Si, Ge n = 3, E = Sn)43. Continuous photolysis of the anions in THF solution results in the formation of the respective dimers, presumably via the radical intermediate (reaction 29). 

Photolysis of vinyldiazomethane in an organic glass at 6 K leads to vinylcarbene in its triplet ground state,14,56,57 which — as is indicated by the ESR spectra — forms a pair of the s-cis and s-trans isomer. The delocalization of one unpaired electron in the rr-system is similar to that of the allyl radical, while the other unpaired electron is localized in a sp2-orbital at the carbenic C atom (see formula T-33 ).58... 

The chemical properties of BA have been studied in detail (Lapin et al., 1984). Low temperature epr spectroscopy shows clearly that the ground state of BA is the triplet (3BA). The zero field parameters (Table 3) reveal some details of this structure. When the irradiation is performed at 4.6 K in a 2-methyltetrahydrofuran glass no epr signals from radical species are apparent. The optical spectrum under these conditions shows absorptions (Table 4) which disappear when the glass is warmed. From these findings the absorption bands are assigned tentatively to 3BA. This conclusion is strongly supported by results from laser flash photolysis experiments. 

Photolysis of DAX in a methylcyclohexane glass at 77 K creates a metastable species detected by its optical absorption spectrum (Table 4). This solution does not exhibit an epr spectrum characteristic of a triplet carbene, nor is one observed when DAX is irradiated in Fluorolube (where triplet carbenes are generally more stable). Warming the frozen solution causes the reaction of the metastable transient and the formation of dimeric xanthone azine. 

Dioxin half-life period under photolysis is on glass - 6 days, in methanol - 6 hours, in hexane - 1 hour. [3, 8],... 

Photolysis at 254 nm of phenylbutazone (220) in aqueous solution raised to pH 8 to 9 with sodium hydroxide gave a mixture of ring-opened products. Reisch etal. identified samples of aniline, the malonamides (221) and (222) and the 2-oxohexanamide (225). When the solution was basified with diethylamine, the amino diamide (223) was produced in addition to (222) and (225). In methanol solution the malonamides (221) and (224) were obtained [132]. In an older study by Pawelczyk and Wachowiak, a 20% solution (pH 10.5) of phenylbutazone sodium was kept in a clear glass bottle in diffused daylight for 2 years. 

Photolysis of PATE Films. PATE films (5 n to 20 n thick) were obtained by casting on glass 10-20% solids aqueous solutions containing 0.02% wetting agent. The resultant films, heated in a drying oven at 100 °C for four minutes, were quite water soluble. 

Photolysis of PATE Films. Photolysis of 2-8 micron films of PATE on glass or steel under the full arc of a focused 450 Watt medium pressure mercury lamp for 10 minutes yields totally insoluble films in water and a variety of organic solvents. These include ethyl ether, MEK, MIBK, THF, carbon tetrachloride, cyclohexane, pyridine, methylene chloride, methoxy ethanol, benzene, xylenes and acetone. DMSO alone swelled the film. Upon soaking in warm water for 10 minutes, the films could be removed intact. 

The identity of methoprene photoproducts has been studied from aqueous emulsions, thin films on glass or silica gel, and in methanolic solution (Figures 3 and 4, 40). As a thin film (0.1 ym) on glass, the half-life of methoprene was about 6 hr. After 93% degradation of parent, more than 50 photoproducts were observed, only five of these present in 3% or higher yield 7-methoxycitronellic acid (4%), 7-methoxycitronellal (4%), the 4,5-epoxide of methoprene (6%), a C12 methyl ketone (3%), and 14C02 (6%). Similar products were encountered on photolysis of a 100 ppm aqueous emulsion of methoprene, except that methoxy-citronellal was isolated only as its dimethyl acetal (9% yield), a presumed artifact of work-up. In addition to the same products identified from thin film studies, at least forty-six other discrete products were detected, but not identified (40). 

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