| Abstract |
In the first section of this Thesis we studied the ability of diaryl selenides and selenoxides, as well as their Tellurium analogs, to trap the intermediates in the photooxygenation of dialkyl sulfides. The results showed that the organoselenium compounds are very effective trapping reagents. More specifically, diaryl selenoxides are the most effective trapping reagents reported so far. Hammett kinetic experiments showed that the trapping reaction of diaryl selenoxides takes place via two different mechanisms: Nucleophilic attack of persulfoxide to the Se atom, or nucleophilic attack of the oxygen atom of selenoxide to the electrophilic S atom of persulfoxide, depending on the electronic nature of the para-substitutents of selenoxides. In contrast, tellurides cannot be used as trapping reagents, because they react with 3O2, while telluroxides decompose upon reaction with 1O2. In the second section, we studied, by means of Hammett kinetic experiments, the reaction of oxygen atom transfer from diaryl selenoxides and telluroxides to triaryl phosphites and phosphines. This study revealed that the reaction between selenoxides and phosphites takes place via a concerted mechanism, initiated by nucleophilic attack of the oxygen atom of selenoxide to the phosphorous. However, when the selenoxide possesses a strong electron donating para-substitutent (e.g., MeO), the transition state is late, while in the reactions of diphenyl selenoxide the transition state is early, which results in a modification of the sign of the ρ value. For the case of the reaction between telluroxides and phosphites, two possible mechanisms were proposed. A step-wise mechanism, in which nucleophilic attack of the O atom of the telluroxide to P atom takes place in the first slow step, and a concerted in which the transition state is early no matter if the substitutent is electron withdrawing or electron donating. Finally, the reaction between selenoxides or telluroxides with triaryl phosphines takes place in a concerted mechanism in which the transition state is late in nature.
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| Subject |
οξυγόνο απλής κατάστασης, φωτοξείδωση σουλφιδίων, οργανοσεληνιακές και οργανοτελλουριακές ενώσεις, αντιοξειδωτική δράση, αναγωγή σεληνοξειδίων και τελλουροξειδίων, singlet oxygen, photooxygenation of sulfides, organoselenium |
Αντιοξειδωτική δράση οργανικών ενώσεων του σεληνίου κατά τη φωτοξείδωση σουλφιδίων
