Photo-accelerator

Merlic A, Xu D (1991) J Am Chem Soc 113 7418. For photo accelerated classical Dotz benzannulations see Choi YH, Rhee KS, Shin GP, Shin SC (1995) Tetrahedron Lett 36 1871 Weyershausen B, Dotz KH (1999) Synlett 231... 

For light-cured materials, the initiator system can be based on camphorquinone, so that cements can be cured with a conventional dental cure lamp emitting at a maximum wavelength around 470nm. Unlike formulations of composite resin, these materials cannot deploy amines as activators, because they would react with the carboxylic acid groups on the polymer, forming salts. Instead, a substance such as sodium p-toluene sulfinide is used as the activator. In addition, a photo-accelerator such as ethyl 4-NJ -dimethylamino benzoate is included [10]. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

N3-coordination by monomeric and dimeric Zn2+-cyclen derivatives has also been shown to both inhibit the photo [2+2] cycloaddition of thymidilyl(3 -5 )thymidine, d(TpT), and to accelerate the photosplitting process of the [T-cis,syn-T] dimer (78% after 1 h of UV exposure) (38). 

In our study we have found that UV-light greatly accelerates the rate of ozone attack at the polypropylene surface. Presented results were undertaken to determine mechanism of the photo-oxidation of polypropylene surface upon UV-irradiation of polymer films in ozone. 

Photo-excitation and de-excitation are basic processes in nuclear reactions. A Japanese-Hungarian cooperation investigating these processes has yielded good results during the past few years [21-26], These studies used weighable amounts of "Tc to look at the (y, y ) reaction that leads to the production of the nuclear isomer "mTc by electron linear accelerator irradiation. 

Water, methanol, and n-hexane do not influence the photooxidation of PVC (43), but the photodegradation is accelerated by ferric chloride (70,71) and certain other compounds containing iron (70,71,72). Purification of the polymer might be expected to enhance its photostability by removing deleterious impurities such as iron compounds that are derived from metal equipment. This type of result was obtained in one recent study (58) but not in others (30,59). In contrast, the photo-oxidative degradation of PVC should be enhanced by admixture of the polymer with materials that are unusually susceptible to photooxidation themselves. Such behavior has been observed for impact-modified PVC containing polybutadiene-based polyblends (69,73). 

For Schiff base being a derivative of gossypol and R-( I )-2-amino-3-benzyloxy-1-propanol, the conditions of the atropisomerisation were determined on the basis of the NMR spectra.37 The ratio of the diastereomers was established on the basis of the integrals of selected H signals (H-l and H-ll). The atropisomerisation of the gossypol Schiff base took place even if the samples were not exposed to the sunlight, however, this process was slower in the dark. The diastereopure Schiff bases were converted into a racemic mixture after ca. 12-14 h in the dark and ca. 3-3.5 h after irradiation of monochromatic light. The addition of a drop of water to acetonitrile solution accelerated the atropisomerisation. In this case, the 1 1 ratio of diastereomers was achieved after 45 min. The results obtained indicated that the atropisomerisation process cannot be considered as a simple photo-atropisomerisation. 

The thiolate species (182) and (183) do not require photo excitation in order to initiate polymerization (182) consumes 200 equivalents MMA in 18 h at 35 °C (Mn = 22,000, Mn(calc) = 20,000, Mw/ Mn= 1.12) 446 The propagating species is again believed to be an enolate.447 Propagation is accelerated upon addition of (185), with 100 equivalents of MMA requiring just 90 seconds for full conversion. The steric bulk of the Lewis acid prevents scrambling of the propagating enolate between the two aluminum centers.448 Hence, for aluminum diphenolates, ortho substitution is essential, whilst smaller Lewis acids such as Me3Al may only be used successfully at low temperatures, e.g., —40 °C. 

Discharge tubes have an excellent detectivity and are solar-blind. These technological advantages have to be balanced against the need for acceleration voltage of some 100 V and complicated readout electronics. These requirements make sensing systems based on discharge tubes much more expensive than those based on photo-... 

This method is similar to continuous flow method except that the rate of flow is continuously varied and the analysis is made at a fixed point along the observation tube. Since the rate of flow changes with time, the reaction mixtures arriving at observation point have different time. In the accelerated flow method the output from a photo electric colorimeter is fed to a cathode-ray oscilloscope, which sweeps out a complete time-concentration record which may be photographed. The method is useful for very rapid enzyme reactions and requires only small quantities of reactants. 

Jang and McDow (1997) studied the photodegradation of benzo[a]anthracene in the presence of three common constituents of atmospheric aerosols reported to accelerate benzo [a] anthracene, namely 9,10-anthroquinone, 9-xanthone, and vanillin. The photo-degradation experiments were conducted using a photochemical reactor equipped with a 450-W medium pressure mercury arc lamp and a water bath to maintain the solution temperature at 16 °C. The concentration of benzo [a] anthracene and co-solutes was 10" M. Irradiation experiments were conducted in toluene, benzene, and benzene-c/e- Products identified by GC/MS, FTIR, and NMR included benzo[a]an-thracene-7,12-dione, phthalic acid, phthalic anhydride, 1,2-benzenedicarboxaldehyde, naphtha-lene-2,3-dicarboxylic acid/anhydride, 7,12-dihydrobenzo[a]anthracene, 10-benzyl-10-hydroan-thracen-9-one, benzyl alcohol, and 1,2-diphenylethanol. 

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