A mechanistic study on the oxidative photodegradation of 2,6-dichlorodiphenylamine-derived drugs: Photo-Fenton versus photocatalysis with a triphenylpyrylium salt

Photoredox catalysis for environmental and chemical applications. A mechanistically-based approach.

“…The redox potential measurement for TCA was carried out according to 9.3.3. Under this context, TPP + looks as an appropriate candidate to be used as a model to provide direct evidence for the electron transfer mechanism in a photoredox process for several reasons: i) its photophysical properties are deeply described in the literature, see Table 1 in the Preamble of Part I; ii) it has demonstrated to be a good oxidant from its excited states, see results described in Chapter 3 and previous results of the group; [82,85,103,111] and iii) the spectra of its triplet excited state and the corresponding reduced species (pyranyl radical) after the redox process are well reported in the literature and have been experimentally obtained in Chapter 3.…”

“…[82,103] or emerging pollutants, such as drugs in wastewaters effluents. [109][110][111] One of the main advantages of organic photocatalysts is that they exhibit absorption bands in the UV-vis region, which can be excited to generate transient species able to interact with the substrates. [70,112] Among them, solar-driven ones are particularly interesting since they could be considered as green methodologies.…”

“…Their photophysical properties are shown in Table 1. [103,111,116,117] A) B) ii) In the second study, direct detection of all the TPP + derived short-lived intermediates in the photocatalyzed oxidation of a mixture of pollutants using TPP + was proposed as a methodology to assess the photodegradation extent. iii) In the last study, the role of singlet and triplet excited states in the photocatalytic treatment of a mixture of pollutants, at different concentrations, was evaluated using TPTP + as photocatalyst.…”

“…The fast degradation in the case of CLOF could be attributed to the formation of stable byproducts that may favour the degradation reaction or to direct photolysis, seeFigure 28B.Direct photolysis control experiments (in the absence of TPTP + ) showed almost no reaction apart from CLOF, which suffered some direct photodegradation although much more slowly (Figure 28B). Plot of the relative concentration of ACF (■), ACP (■), CAF (■), CBZ (■)and CLOF (■) at Co= 5 mg L -1 each (1.3x10 -4 M global concentration)in aerated acidic 3) media, vs. time under solar simulated irradiation, in the presence of 10 mg L -1 (2x10 -5 M) of TPTP + (A) and in the absence of photocatalyst (B).The next step was the evaluation of the electron transfer from the singlet and from the triplet excited states of TPTP + and the formation of photoactive ground-state complexes, since previous studies have demonstrated that this photocatalyst is also able to act through all those pathways[103,111,116,117,140]. Therefore, every potential species that may participate in the photodegradation has to be evaluated for every pollutant and the combined results have to be analysed for each pollutant at different concentrations.First, fluorescence experiments (steady-state and time-resolved) were performed in deaerated acetonitrile to investigate the involvement of 1 (TPTP + ) * in the photodegradation of the pollutants, (Figure 29).…”

“…All these examples deal with the oxidation of the substrates, but little attention has been paid to the potential of RF as a reductant in either water remediation or organic synthesis.It is worth mentioning that reductive dehalogenation methods are used in a wide variety of synthetic contexts and these procedures have already been optimized using visible-light photocatalysts such as Ru(bpy)3Cl2 [211][212][213][214][215][216][217][218][219][220][221][222]. However, many of the recent publications lack a kinetic study of the involved excited states; therefore, a deeper mechanistic understanding of the processes based on time-resolved techniques could help to broaden the substrate scope of the photocatalyzed organic reactions [70,103,104,111,140,167]. Under this context, the objective of the present chapter is to perform reductive dehalogenation of different bromo-derivatives using RF as a metal-free photocatalyst upon visible light irradiation (460 nm), in the presence of amines and isopropanol as eand H-donors, respectively.…”