Solvent effect on the sensitized photooxygenation of 2,3-dihydropyrazine derivatives

Else Lemp, Antonio L. Zanocco, German Günther, Nancy Pizarro

Research output: Contribution to journalArticlepeer-review

6 Citations (Scopus)


Detection of O2(1Δg) phosphorescence emission, λmax = 1270 nm, following laser excitation and steady-state methods was employed to determine the total rate constant, kT, and the chemical reaction rate constant, kR, for reaction between 5,6-disubstituted-2,3-dihydropyrazines and singlet oxygen in several solvents. Values of kT ranged from 0.26 × 105 M-1 s-1 in hexafluoro-2-propanol to 58.9 × 105 M-1 s-1 in N,N-dimethylacetamide for 5,6-dimethyl-2,3-dihydropyrazine (DMD) and from 5.74 × 105 M-1 s-1 in trifluoroethanol to 159.0 × 105 M-1 s-1 in tributyl phosphate for 5-methyl-6-phenyl-2,3-dihydropyrazine (MPD). Chemical reaction rate constants, kR, for DMD are similar to kT in polar solvents such as propylencarbonate, whereas for MPD in this solvent, the contribution of the chemical channel to the total reaction is about of 4%. Dependence of the total rate constant on solvent microscopic parameters, α and π*, for DMD can be explained in terms of a reaction mechanism that involves formation of a perepoxide exciplex. Replacement of the methyl by a phenyl substituent enhances dihydropyrazine ring reactivity toward singlet oxygen and modifies the dependence of kT on solvent parameters, specially on the Hildebrand parameter. These results are explained in terms of an additional reaction path, involving a perepoxide-like exciplex stabilized by the interaction of the negative charge on the terminal oxygen of the perepoxide with the aromatic π system.

Original languageEnglish
Pages (from-to)3009-3016
Number of pages8
JournalJournal of Organic Chemistry
Issue number8
Publication statusPublished - 18 Apr 2003

ASJC Scopus subject areas

  • Organic Chemistry


Dive into the research topics of 'Solvent effect on the sensitized photooxygenation of 2,3-dihydropyrazine derivatives'. Together they form a unique fingerprint.

Cite this