Journal of Organic Chemistry p. 534 - 540 (1989)
Update date:2022-08-02
Topics:
Bortolus, Pietro
Monti, Sandra
Albini, Angelo
Fasani, Elisa
Pietra, Silvio
The quenching rate constants of singlet oxygen liefetime by dialkylamino azo dyes 1 and tautomeric azo dyes 2 and 5 (as well as azo- and hydrazone-model methylated derivatives 3 and 4) were determined by measuring the 1.27-μm 1O2 emission lifetime, and the values obtained are in the range 106 - 108 M-1 s-1.The quenching involves a charge-transfer interaction, and different correlations with the oxidation potentials of the two classes of azo dyes are observed.Chemical reactions take place with a rate in the range 103 - 104 M-1 s-1 and are rationalized as a secondary pathway for the charge-transfer complex between 1O2 and the azo dye.Products include dealkylated amino azo dyes 6 from 1; compounds arising from the fragmentation of the aryl-azo bond, viz., benzenes 7 and phenoles 8 from 1 and 2; and 1,4-naphthoquinone 10 as well as the dimer 9 and the oxidized cyclic derivative 11 from 2.The methoxy derivative 3 yields an endoperoxide, which rearranges to a 1,2-naphthoquinone derivative 14.The results are discussed in comparison with the currently accepted mechanism for the reaction of 1O2 with azo dyes.
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