Degradation and determination of 4-Chloro-2-methylphenol

Introduction

4-Chloro-2-methylphenol (Figure 1) is an important chemical raw material for organic synthesis and fine chemical intermediates, and is widely used in various fields such as pharmaceuticals, pesticides, solvents, dyes, pigments, mildew inhibitors, surfactants, and fragrances. This paper mainly focuses on the research related to its degradation and determination.

Degradation of 4-chloro-2-methylphenol

Report 1:The Gram-negative strain S1, isolated from activated sludge, metabolized 4-chloro-2-methylphenol by an inducible pathway via a modified ortho-cleavage route as indicated by a transiently secreted intermediate, identified as 2-methyl-4-carboxymethylenebut-2-en-4-olide by gas chromatography/mass spectrometry. Beside 4-chloro-2-methylphenol only 2,4-dichlorophenol and 4-chlorophenol were totally degraded, without an accumulation of intermediates. The chlorinated phenols tested induced activities of 2,4-dichlorophenol hydroxylase and catechol 1,2-dioxygenase type II. Phenol itself appeared to be degraded more efficiently via a separate, inducible ortho-cleavage pathway. The strain was characterized with respect to its physiological and chemotaxonomic properties. The fatty acid profile, the presence of spermidine as main polyamine, and of ubiquinone Q-10 allowed the allocation of the strain into the alpha-2 subclass of the Proteobacteria. Ochrobactrum anthropi was indicated by fatty acid analysis as the most similar organism, however, differences in a number of physiological features (e.g. absence of nitrate reduction) and pattern of soluble proteins distinguished strain S1 from this species.[1]

Report 2: 4-Chloro-2-methylphenoxyacetic acid (MCPA) is a widely used herbicide across the world. MCPA is persistent and easily transports into anoxic environment, such as groundwater, sediments and deep soils. However, little research on anaerobic microbial degradation of MCPA was carried out. The functional microorganisms as well as the catabolic pathway are still unknown. In this research, an anaerobic MCPA-degrading bacterial consortium was enriched from the river sediment near a pesticide-manufacturing plant. After about 6 months' acclimation, the MCPA transformation rate of the consortium reached 4.32 μmol g-1 day-1, 25 times faster than that of the original sludge. 96% of added MCPA (2.5 mM) was degraded within 9 d of incubation. Three metabolites including 4-chloro-2-methylphenol (MCP), 2-methylphenol (2-MP) and phenol were identified during the anaerobic degradation of MCPA. An anaerobic catabolic pathway was firstly proposed: firstly, MCPA was transformed to 4-chloro-2-methylphenol via the cleavage of the aryl ether, then 4-chloro-2-methylphenol was reductively dechlorinated to 2-MP which was further demethylated to phenol. The 16S rRNA gene amplicon sequencing revealed a substantial shift in the bacterial community composition after the acclimation. SBR1031, Acidaminococcaceae, Aminicenantales, Syntrophorhabdus, Acidaminobacter, Bacteroidetes_vadinHA17, Methanosaeta, Bathyarchaeia, KD4-96, Anaeromyxobacter, and Dehalobacter were significantly increased in the enriched consortium after acclimation, and positively correlated with the anaerobic degradation of MCPA as suggested by heat map correlation analysis. This study provides a basis for further elucidation of the anaerobic catabolism of MCPA, and contributes to developing efficient and low-cost anaerobic treatment technologies for MCPA pollution.[2]

Determination of 4-chloro-2-methylphenol

Report 1: The development and application of a polyaniline/carbon nanotube (CNT) cyclodextrin matrix (PANI-β-CD/MWCNT)-based electrochemical sensor for the quantitative determination of the herbicide 4-chloro-2-methylphenoxyacetic acid (MCPA) and its main transformation product 4-chloro-2-methylphenol in natural waters are described. A simple cyclic voltammetry-based electrochemical methodology, in phosphate buffer solution at pH 6.0, was used to develop a method to determine both MCPA and 4-chloro-2-methylphenol, without any previous extraction or derivatization steps. A linear concentration range (10 to 50 μmol L(-1)) and detection limits of 1.1 and 1.9 μmol L(-1), respectively, were achieved using optimized cyclic voltammetric parameters. The proposed method was successfully applied to the determination of MCPA and 4-chloro-2-methylphenol in natural water samples with satisfactory recoveries (94 to 107%) and in good agreement with the results obtained by an established high-performance liquid chromatography technique, no significant differences being found between the methods. Interferences from ionic species and other herbicides used for broad-leaf weed control were shown to be small. The newly developed methodology was also successfully applied to MCPA photodegradation environmental studies.[3]

Report 2: A rapid and sensitive LC-electrospray tandem mass spectrometry method has been developed for the quantitation of 4-chloro-2-methylphenoxyacetic acid (MCPA) and 4-chloro-2-methylphenol in both water and soil samples. Soil samples were extracted in alkaline media and cleaned-up by solid-phase extraction with C18 cartridges before LC-MS analysis. The selectivity and sensitivity offered by the triple quadrupole allowed the direct injection of the water samples rendering a sample throughput of around 100 samples per day, without any sample pretreatment, rendering for MCPA a limit of detection of 40 ng/l. In order to increase the method sensitivity, mainly for metabolite, a previous solid-phase extraction step was also performed. The method was validated by means of recovery experiments using fortified water and soil samples, obtaining satisfactory recoveries for both compounds in water and for MCPA in soil. The validated procedures can be used for the specific monitoring of residues of MCPA and its main metabolite in environmental samples, as ground and surface waters and soils, providing more selectivity and sensitivity than the current UV-based methodology. Besides, sample manipulation is greatly reduced in comparison to other GC-MS based methods which require a previous derivatization.[4]

The case of 4-chloro-2-methylphenol and of its nitroderivative

A field monitoring campaign for pesticides and their transformation intermediates was carried out in the Rhône delta (Southern France). It was evidenced the following transformation sequence: MCPA-->4-chloro-2-methylphenol (CMP)-->4-chloro-2-methyl-6-nitrophenol (CMNP). Interestingly 4-chloro-2-methylphenol disappeared about as quickly as MCPA, while CMNP was environmentally more persistent than the parent molecules. This is very relevant to the environmental risk associated with the occurrence of these compounds, because the nitration of chlorophenols reduces their acute toxicity but the nitroderivatives could have more marked long-term effects, associated with their genotoxicity. Irradiation experiments suggested that the photonitration of 4-chloro-2-methylphenol into CMNP involves nitrogen dioxide, generated from the photolysis of nitrate and from the photooxidation of nitrite by OH. The photochemistry of Fe(III) species could also play a significant role, but its contribution is still difficult to be quantified. Another important intermediate of 4-chloro-2-methylphenol transformation is methylnitrophenol (MNP), produced via a dechlorination/nitration pathway, with ortho-cresol as the most likely reaction intermediate.[5]

References

[1] Lechner U, Baumbach R, Becker D, Kitunen V, Auling G, Salkinoja-Salonen M. Degradation of 4-chloro-2-methylphenol by an activated sludge isolate and its taxonomic description. Biodegradation. 1995;6(2):83-92. doi:10.1007/BF00695339

[2] Zhang X, Geng K, Wu N, et al. Sustained anaerobic degradation of 4-chloro-2-methylphenoxyacetic acid by acclimated sludge in a continuous-flow reactor. Chemosphere. 2023;330:138749. doi:10.1016/j.chemosphere.2023.138749

[3] Rahemi V, Garrido JM, Borges F, Brett CM, Garrido EM. Electrochemical sensor for simultaneous determination of herbicide MCPA and its metabolite 4-chloro-2-methylphenol. Application to photodegradation environmental monitoring. Environ Sci Pollut Res Int. 2015;22(6):4491-4499. doi:10.1007/s11356-014-3693-y

[4] Pozo O, Pitarch E, Sancho JV, Hernández F. Determination of the herbicide 4-chloro-2-methylphenoxyacetic acid and its main metabolite, 4-chloro-2-methylphenol in water and soil by liquid chromatography-electrospray tandem mass spectrometry. J Chromatogr A. 2001;923(1-2):75-85. doi:10.1016/s0021-9673(01)01006-8

[5] Chiron S, Comoretto L, Rinaldi E, Maurino V, Minero C, Vione D. Pesticide by-products in the Rhône delta (Southern France). The case of 4-chloro-2-methylphenol and of its nitroderivative. Chemosphere. 2009;74(4):599-604. doi:10.1016/j.chemosphere.2008.09.012

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