Photoperoxidation reaction

C. Kinetics of photoperoxidation reaction. In the sensitized photooxygenation by Type lib mechanism the 02 (JAg) acts as dienophile and adds to give the endoperoxide in concerted addition reaction similar to Diels-Alder... 

The quantum yield for photoperoxidation reaction of anthracene in CC14 is expressed by (Sec 11.3.1)... 

The reaction mechanism for the aerobic oxidation of the pz to seco-pz can be attributed to a formal 2 + 2 cycloaddition of singlet oxygen to one of the pyrrole rings, followed by cleavage (retro 2 + 2) of the dioxetane intermediate to produce the corresponding seco-pz (160). This mechanism is shown in Scheme 29 for an unsymmetrical bis(dimethylamino)pz. Further photophysical studies show that the full reaction mechanism of the photoperoxidation involves attack on the reactant by singlet oxygen that has been sensitized by the triplet state of the product, 159. As a consequence, the kinetics of the process is shown to be autocatalytic where the reactant is removed at a rate that increases with the amount of product formed. 

The reaction has been studied for the photoperoxidation of hydrocarbon l-methyl-2 pentene in MeOH -f EtOH solution using (3-carotene as the quencher of the reaction. For estimation of rate constants, following procedure has been followed i... 

These data do not apply directly for anthracene + CC14 reactions, but just give a procedure to obtain the photoperoxidation rates. The lifetime of Ot Ag) in CC14 = 700 ps.M The flow sheet for the photoreaction between anthracene and solvent CC14 is summarised as given on page 345. 

On kinetic grounds it is not possible to distinguish between the schemes (1) and (2) since both give the same type of dependence on [A]. Some information can be obtained by using suitable quenchers for the reaction. These quenchers may either be competitors and undergo photoperoxidation themselves (chemical type) or quench the reaction by deactivating the intermediates (physical type).1840... 

The role of exciplexes in self-sensitized photo-oxidations has been further investigated by Stevens and co-workers.273 - Photoperoxidation of 1,3-diphenyl-isobenzofuran in solution proceeds at a rate which is independent of acceptor concentration when this is very low, and this observation has been interpreted in terms of a re-encounter of x02 and ground-state acceptor molecules generated in the same triplet-triplet annihilation act. This interpretation accounts for the failure of tetramethylethylene to inhibit the reaction completely. Processes 1—3 in Scheme 8 account for the observations if re-encounter effects are included,... 

A novel triglyceride-based a, p-unsaturated ketone, obtained by photoperoxidation from high oleic sunflower oil, can be cross-linked with diamino diphenyl methane through the aza-Michael addition reaction. The reaction of p-toluidine with either enone-containing methyl oleate or epoxidised methyl oleate, produces an alternative to amine-cured epoxidised vegetable oil thermosets. ... 

The photoperoxidation of high oleic sxmflower oil with singlet oxygen is an efficient reaction for the synthesis of functionalized triglyceride derivatives. In this reaction, high oleic sunflower oil and oxygen are the only reactants, which makes this transformation very attractive from an environmental point of view (74). 

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