Oxidation of telluropyrylium dyes with ozone, chlorine, and bromine. Differing regiochemical and kinetic behavior with respect to oxidations of oxygen-, sulfur-, and selenium-containing dyes

Abstract

Oxidations of telluropyrylium dyes 1-3 with ozone in water, chlorine in carbon tetrachloride, or bromine in carbon tetrachloride gave second-order rate constants of greater-than-or-equal-to 10(9) L mol-1 s-1 using stopped-flow techniques to measure rates of oxidation. Aqueous ozone gave initial oxidation of the tellurium atoms of 1-3 to produce hydroxytelluranes 4-6, respectively. Oxidative addition of chlorine or bromine across a tellurium atom of 1-3 gave the corresponding tellurium(IV) dihalides. With excess ozone, a second oxidation was observed with a second-order rate constant of (1.3 +/- 0.1) X 10(6) L mol-1 s-1. Chalcogenopyrylium dyes 7-10 which contain only oxygen, sulfur, and/or selenium heteroatoms reacted with smaller rate constants for oxidation. Chlorine and bromine gave second-order rate constants within 1 order of magnitude of those of telluropyrylium dyes for reactions with 7-10. Ozone was more than 100 000 times less reactive toward chalcogenopyrylium dyes 7-9 relative to telluropyrylium dyes 1-3 with second-order rate constants (1.1 +/- 0.1) X 10(4) L mol-1 s-1 for 7, (8.5 +/- 0.9) X 10(3) L mol-1 s-1 for 8, and (5.4 +/- 0.6) X 10(3) L mol-1 s-1 for 9. With dyes 7-10, ozone destroyed the pi-framework of the dye while chlorine and bromine gave mono- and dihalogenation of the trimethine bridge of the dye.