Ab initio study of the formation and degradation reactions of chlorinated phenols

Abstract

The formation, stability, and reactivity of chlorinated phenoxyl radicials was studied using ab initio methods. All 19 congeners from mono- to penta-chlorinated species were considered. The radical species are formed in combustion reactions via unimolecular scission of the phenoxyl-hydrogen bond or hydrogen atom abstraction by hydrogen atom or hydroxyl radical. The resulting radicals are stable with respect to unimolecular decomposition and reaction with molecular oxygen is relatively slow. Activation energies are similar to those of the phenoxyl radical for both the decomposition pathway and the reaction with molecular oxygen at the more reactive para-position. Calculations were performed with the model chemistries B3LYP/6-31G(d,p), BHandHLYP/6-31G(d,p), BHandHLYP/aug-cc-pVDZ and QCISD(T)/6-31G(d,p)//BHandHLYP/6-31G(d,p) (for selected reactions.) The results suggest the radicals are sufficiently stable and unreactive to be moderately persistent in the atmosphere, especially when associated with some types of particulate matter. An additivity analysis is made to decompose the relative energetics of the congeners into contributions from hydrogen bonding, resonance stabilization, and repulsive interactions. The results of this analysis correlate well with the results of the calculations.

Environmentally Persistent Free Radicals (EPFRs)-2. Are Free Hydroxyl Radicals Generated in Aqueous Solutions?

“…Association with the surfaces of fine particles imparts additional stabilization to these radicals such that they can persist almost indefinitely in the environment 2, 4 . A mechanism of chemisorption and electron transfer from the molecular adsorbate to a redox-active transition metal or other receptor is shown through experiment, and supported by molecular orbital calculations, to result in EPFR formation 2, 3, 5 . Both oxygen-centered and carbon-centered EPFRs are possible, the exact structure of which can significantly affect their environmental and biological activity 6, 7 .…”

Highly efficient extraction of phenolic compounds by use of magnetic room temperature ionic liquids for environmental remediation

“…Chlorinated phenols are toxic chemicals frequently found in hazardous wastes at superfund sites. Upon heating or burning they can be converted into even more toxic polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) by both gas-phase and metal catalyzed pathways [44]. Pentachlorophenol is a manufactured chemical which is restricted in use as a pesticide and is used industrially as a wood preservative for utility poles, railroad ties, and wharf pilings.…”

Bond dissociation enthalpies in chlorinated benzenes and phenols and enthalpies of formation of their free radicals: A Gaussian-4 prediction

“…O H BDEs of 2-C 6 H 4 ClO-H and 2,4,6-C 6 H 2 Cl 3 O-H can be obtained from the predicted enthalpies of formation of phenols and radicals using empirical [13] or G3MP2B3 calculations [14] and of the complete set of chlorophenols using density functional theory (DFT) methods [15,16]. C H/C Cl BDEs in chlorobenzenes have also been predicted by using the DFT method of B3LYP/6-311G(d,p) [17,18].…”

“…C H/C Cl BDEs in chlorobenzenes have also been predicted by using the DFT method of B3LYP/6-311G(d,p) [17,18]. However, DFT methods tend to greatly underestimate the BDEs, e.g., DFT calculations have predicted D 0 (C 6 H 5 -H) of 447.4 kJ/mol at B3LYP/6-311G (d,p), and D 298K (C 6 H 5 O-H) of 340.2, 350.6, and 352.7 kJ/mol at levels of B3LYP/6-31G(d) [15], MWB1K/6-311+G(3df,2p) [16], and B3LYP/CBS [19], all being significantly lower than the best experimental values of 465.9 ± 0.6 and 364.8 ± 0.5 kJ/mol [5,10].…”