Investigation of the degradation of cresols in the treatments with ozone

Abstract

The reaction between ozone and the three cresol isomers was investigated in pure water. Cresols were selected as model substrates representing an important component of humic material.Cresols carry both a hydroxyl and a methyl group, each theoretically increasing the reactivity of ozone with the aromatic ring. Direct comparison of the aromatic ring and the methyl group reactivities was made possible by the analysis of reaction products. The substrate degradation kinetics was studied by preparing aqueous solutions of each cresol and treating them with ozone for increasing time periods. It had been hypothesized that hydroxybenzaldehydes and hydroxybenzoic acids could be possible degradation intermediates of cresols. To verify this hypothesis, the degradation kinetics of three hydroxybenzaldehydes and two hydroxybenzoic acids were also studied. The reaction products were studied using gas chromatography (GC)-electron capture negative ionization (ECNI)-mass spectrometry (MS) analysis after direct derivatization of the samples with 5-chloro-2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate (ClOFPCF). This new analytical approach enables the extraction and analysis of highly polar polycarboxylic and hydroxycarboxylic acids, as well as highly polar aldehydes and hydroxy aldehydes that are difficult to extract and measure using conventional methods. As such, this new approach offered insights into ozone reaction intermediates that had been previously hypothesized, but not confirmed.Several highly hydrophilic degradation intermediates were identified, including malic, citraconic, itaconic, malonic, methylmuconic, and tartronic acid, but no hydroxybenzaldehydes were observed.The results support a 3-stage mechanism previously hypothesized, which involves ring-opening of the phenolic group, followed by the generation of several intermediates of increasing oxidation state, finally leading to relatively stable products, such as malonic and oxalic acids. We demonstrated that oxidation of the methyl group does not occur during cresol degradation. Graphical abstractHighlights ► Reaction of O3 with three cresol isomers used as model compounds for humic material. ► Ozone reacts preferentially with the aromatic ring, not the methyl group. ► Highly hydrophilic reaction byproducts are formed from cresols after ring-opening. ► Chloroformate derivatives of degradation intermediates are identified by GC-ECNI-MS.

Kinetics and Mechanism of the Ozone Reaction with Alcohols, Ketones, Ethers and Hydroxybenzenes

“…The ozonation of phenol, pyrocatechol, resorcinol and hydroquinone has been studied in different solvents -aqueous and organic, aimed at the deriving of the kinetic parameters and product composition [21][22][23][24][80][81][82][83][84][85][86]. The rate constants of phenol and resorcinol ozonation in water at room temperature are 1.…”

Light-Absorbing Products Form during the Aqueous Phase Reaction of Phenolic Compounds in the Presence of Nitrate and Nitrite with UV Illumination

“…Interestingly, the spectral data suggests the color faded for the catechol and guaiacol reaction solutions, but the syringol solution optical depth increased during ozone treatment. The color fading might be expected since degradation of aromatics, such as cresols have been observed through ozone treatment [22]. Destruction of the aromatic ring would shift light absorption to deeper UV wavelengths and a reduction of visually perceived color would occur.…”

Transformation of pharmaceuticals during oxidation/disinfection processes in drinking water treatment

“…Another common derivatization reagent, N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA), converts hydroxyl, phenol, amine, and carboxylic acid groups to trimethylsilyl groups that are amenable to GC-MS analysis [20]. Another newly-developed derivatizing reagent involves the use of 5-chloro-2,2,3,3,4,4,5,5-octafluoro-1-pentyl chloroformate (ClOF-PCF), which enables the extraction and analysis of highly polar polycarboxylic and hydroxycarboxylic acids, as well as highly polar aldehydes and hydroxy aldehydes that are difficult to extract and measure using conventional methods [21].…”