Oxidation of p-DHB

The next set of experiments involved the Fe-assisted PC oxidation of p-DHB and 1,4-BQ as the model pollutants. In these cases, similar patterns were observed leading to the conclusion that these two compoimds behave in a similar way to phenol and o-DHB with both exhibiting a series-parallel reaction scheme (Ortiz-Gomez et al., 2008)... 

THB as a model pollutant (results not shovm here), its reaction rate was very fast compared with the oxidation of the other aromatics. Moreover, the Fe-assisted PC reaction of 1,2,4-THB was even faster than the impromoted PC reaction. Thus, it can be expected that if 1,2,4-THB is formed in the Fe-assisted oxidation of p-DHB, it will disappear very quickly as well, keeping its concentration below the detectable limit. 

In this regard, the PC oxidation of phenol produces similar hydroxylated aromatics as reaction intermediates since the oxidation occurs via hydroxyl radical attack. These intermediates might be equally harmful than the parent species. Several authors report that during the oxidation of phenol, they identified various hydroxylated intermediates such as 1,2,3-trihydrox-ybenzene (1,2,3-THB), ortho- and parfl-dihydroxybenzene (o,p-DHB) (Al-Ekabi and Serpone, 1988), 1,2,4-THB and 1,4-benzoquinone (1,4-BQ)... 

Each of the series-parallel reaction schemes presented in the previous sections for the Fe-assisted oxidations of phenol, o-DHB, p-DHB, and 1,4-BQ, were established considering the chemical species detected in the bulk of the water solution. Given that o-DHB, p-DHB, and 1,4-BQ are intermediates in the Fe-assisted PC oxidation of phenol, an overall reaction scheme for the Fe-assisted PC oxidation of phenol can be formulated. This overall reaction network incorporates all the detected intermediaries. 

The underlying assumption in this reaction scheme is that all chemical species behave the same as a model pollutant or as an intermediate. To exemplify, o-DHB is an intermediate in the Fe-assisted oxidation of phenol and when used as a model reactant, o-DHB forms p-DHB. It is h)q)othesized therefore that o-DHB as an intermediate in phenol Fe-assisted PC conversion forms p-DHB. Hence, the same assumptions for the development of the overall reaction scheme in the unpromoted PC reaction are considered for the Fe-assisted PC system. 

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