Role of TEMPO in Enhancing Permanganate Oxidation toward Organic Contaminants

Abstract

Permanganate (Mn(VII)) has been widely applied as an oxidant in water treatment plants. However, compared with ozone, Fenton, and other advanced oxidation processes, the reaction rates of some trace organic contaminants (TrOCs) with Mn(VII) are relatively low. Therefore, further studies on the strategies for enhancing the oxidation of organic contaminants by Mn(VII) are valuable. In this work, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), as an electron shuttle, enhanced Mn(VII) oxidation toward various TrOCs (i.e., bisphenol A (BPA), phenol, estrone, sulfisoxazole, etc.). TEMPO sped up the oxidative kinetics of BPA by Mn(VII) greatly, and this enhancement was observed at a wide pH range of 4.0−11.0. The exact mechanism of TEMPO in Mn(VII) oxidation was described briefly as follows: (i) TEMPO was oxidized by Mn(VII) to its oxoammonium cation (TEMPO + ) by electron transfer, which was the reactive species responsible for the accelerated degradation of TrOCs and (ii) TEMPO + could decompose TrOCs rapidly with itself back to TEMPO or TEMPOH (TEMPO hydroxylamine). To further illustrate the interaction between TEMPO and target TrOCs, we explored the transformation pathways of BPA in Mn(VII)/ TEMPO oxidation. Compared to Mn(VII) alone, adding TEMPO into the Mn(VII) solution significantly suppressed BPA's selfcoupling and promoted hydroxylation, ring-opening, and decarboxylation. Moreover, the Mn(VII)/TEMPO system was promising for the abatement of TrOCs in real waters for humic acid, and ubiquitous cations/anions had no adverse or even beneficial impact on the Mn(VII)/TEMPO system.

The role of trace N-Oxyl compounds as redox mediator in enhancing antiviral ribavirin elimination in UV/Chlorine process

“…This phenomenon may be attributed to two mechanisms. One mechanism is that TEMPO tends to be oxidized into TEMPO + by the radicals generated in UV/Chlorine process, which could oxidize the secondary alcohol hydroxyl group into carbonyl group to promote the degradation of RBV [19] , [38] . The other mechanism is that high concentration of TEMPO could act as a radical scavenger, which consumes radicals generated in UV/Chlorine process and inhibits the degradation of RBV [12] , [39] , [40] .…”

“…(1) ). After oxidation, TEMPO + was reduced into TEMPOH, which is unstable and could be immediately transformed into TEMPO to take part in another TEMPO/TEMPO + cycle (as shown in Fig.S13) [38] , [53] . …”

“…One mechanism is that DOM could interfere with the photolysis of chlorine by inner filter effect, which would inhibit the generation of radicals by UV/Chlorine process [59] . The other mechanism is that SRNOM could compete with RBV for radicals and oxidative species (e.g., HO•, RCSs, TEMPO + and PINO) in the UV/chlorine system [38] , [60] . Therefore, the enhancement on RBV degradation by UV/Chlorine/Redox mediator process was weakened as the SRNOM concentration increased.…”

The Utility of Oxoammonium Species in Organic Synthesis: Beyond Alcohol Oxidation

“…After this report, this type of oxidation (that is oxygenation of phenol) has been reported by several researchers. 85,178,179 Scheme 27. Formation of o-quinone from phenols using oxoammonium species Another important transformation of phenols mediated by oxoammonium species is the oxidative phenol coupling reaction.…”

New Insights into the Actual H-Abstraction Activities of Important Oxygen and Nitrogen Free Radicals: Thermodynamics and Kinetics in Acetonitrile

“… 5 − 7 2,2′,6,6′-Tetramethylpiperidine 1-oxyl (TEMPO • ) and its derivatives are popular in radical reactions and academic research studies. 8 , 9 Alkoxy radicals such as the cumyloxyl radical (CumO • ) 10 and tert -butoxyl radical ( t BuO • ), 11 alkyl peroxy radicals (ROO • ) 12 such as CumOO • and t BuOO • , and phenol radicals (ArO • ) 13 are all important oxygen-centered radicals that are involved in a variety of chemical and biological processes. The nitrogen-centered radical 2,2-diphenyl-1-picrylhydrazyl (DPPH • ) is a relatively stable neutral radical and is frequently used as a reactive oxygen species (ROS) model to evaluate the radical-scavenging activity of an antioxidant.…”