UV light, initiation

Some other processes are known for sulfoxidation but have no technical importance. The acetic anhydride process has attracted some interest because it does not need exposure to light and enables conversion rates up to 15% of paraffin feedstock. Once started by peroxide or UV light initiation, it propagates without further radical-forming initiation steps. The addition of some 2.5% acetic anhydride to the reacting alkane is crucial to form a mixed anhydride of par-... 

Figure 5.36 ASBA contains a primary amine group that may be conjugated to carboxylate compounds using the carbodiimide EDC. Subsequent exposure to UV light initiates the photoreaction leading to covalent crosslinks.

Lee and coworkers report on a photo-initiated polymerization for the preparation of poly(butyl methylacrylate-co-ethylene dimethylacrylate) within fused silica capillaries. UV light-initiated polymerization is well suited to monolith formation in restricted spaces since polymer forms only in those areas that are exposed to irradiation. This leads to far greater control over the length and size of the monolithic column formed. The resulting columns are robnst since their separation ability does not deteriorate with time or number of injections and their reprodncibility is excellent. ... 

Aniline is a compound used in the synthesis of insecticides, chemical brighteners, and dyes and is a by-product of the petroleum, paper, and coal industries. The photocatalytic oxidation of aniline was studied by Sanchez et al. (1997). The reaction was found to follow Langmuir-Hinshelwood kinetics. The adsorption rate constant and the reaction rate constants were also reported. Higher yields were reported for acidic conditions and values near the pH at the point of zero charge (pHpZC) of Ti02. The rate of photocatalytic oxidation was also found to increase with the addition of small amounts of Fe. Hydroquinone is the main intermediate formed from the reaction. Photocatalytic reactions were carried out in a 130-cm3 cylindrical Pyrex cell. Medium-pressure mercury lamps provided UV light. Initial concentrations of 1.0 x 104 and 2 g/L were prepared. The pH of the solutions was adjusted and reactions were carried out for 15 min. Concentrations of aniline and byproducts formed were determined by HPLC. 

UV-light initiation is used for the perfluoroalkyl iodide addition to more fragile alkenes. The synthesis of 3-trifluoromethyl-substituted steroids is an example of such a photochemical addition. In the addition of trifluoroiodomcthanc to 5a-pregn-3-en-20-one. only one product 4 was isolated from the reaction mixture although eight isomeric adducts might be formed from this reaction. ... 

Jl < 500 nm) In a 19- pm-thick KVV40 film (B) the same. In a 3 m-thick film, induced by UV light (initial birefringence of the film induced by preliminary illumiRation with polarized blue- en light)... 

The same pathway was assumed to be responsible for the reduction of Tl(III) and the oxidation of 2-propanol to acetone in deaerated aqueous perchloric acid solution, where the UV-light-initiated formation of Tl(II) in the primary process was demonstrated by flash photolysis... 

Noteworthy, very few reports can be found on UV light-initiated cycloaddition of carbonyl compounds to tetrafluoroethylene (TFE). " The yields of oxetanes in these processes are generally low due to facile polymerization of TFE under the reaction conditions. 

Scott, G., UV-light initiated deep curing of epoxy potting compounds (pp. 803-812), Proc. RadTech America, 2002. 

Secondary Initiation is operative when the UV light initiating the photooxidation is absorbed by oxidation products of the substrate (peroxides and carbonyls) or other impurities pre nt. 

Figure2.30 UV-light-initiated polymerization of an urethane-acrylate system (a) and an acrylate/epoxide blend (1 1, w/w) ...

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