Formation of Sulfonyl Aromatic Alcohols by Electrolysis of a Bisazo Reactive Dye

María Elizalde-González,Ignasi Sirés,Martín Dávila-Jiménez,Enric Brillas,Uriel Arroyo-Abad,Esmeralda García-Díaz

doi:10.3390/molecules171214377

María Elizalde-González, Ignasi Sirés + Show 4 more

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https://doi.org/10.3390/molecules171214377

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Abstract

Five sulfonyl aromatic alcohols, namely 4-((2-hydroxyethyl)sulfonyl)phenol, 4-((2-(2-((4-hydroxyphenyl)sulfonyl)ethoxy)vinyl)sulfonyl)phenol, 4-(ethylsulfonyl)phenol, 4-(vinylsulfonyl)phenol and 5-((4-aminophenyl)sulfonyl)-2-penten-1-ol were identified by LC-ESI-Qq-TOF-MS as products formed by electrolysis of the bisazo reactive dye Reactive Black 5 (RB5). Since electrolyses were performed in an undivided cell equipped with Ni electrodes in alkaline medium, amines like 4-(2-methoxyethylsulfonyl)benzene-amine (MEBA) with m/z 216 were also suspected to be formed due to the plausible chemical reaction in the bulk or the cathodic reduction of RB5 and its oxidation by-products. Aiming to check this hypothesis, a method was used for the preparation of MEBA with 98% purity, via chemical reduction also of the dye RB5. The logP of the synthesized sulfonyl aromatic compounds was calculated and their logkw values were determined chromatographically. These data were discussed in regard to the relationship between hydrophobicity/lipophilicity and toxicity.

Highlights

Electrolysis can be considered as a physicochemical method for both the decomposition of environmental pollutants and the production of new chemical compounds
Only some few reports have dealt with the identification of the Reactive Black 5 (RB5) electrolysis products [7,8,18], which is mainly due to the lack of proper analytical equipment and standard reagents
The electrolysis using RB5 solutions was performed at room temperature with a conventional threeelectrode system under potentiostatic conditions with a Volta Lab PGZ301 potentiostat/galvanostat using an undivided cell of 50 cm3 capacity

Summary

Introduction

Electrolysis can be considered as a physicochemical method for both the decomposition of environmental pollutants (electrodegradation) and the production of new chemical compounds (electrosynthesis). According to this point of view, a target pollutant functioning as remediation object, may serve as reagent in a synthesis of new products. Electro-oxidation with anodes like Pt, platinised Ti, BDD, Ni, RuO2 and IrO2 has been the most applied electrochemical technology for the decolorization and mineralization of such dye solutions [5,6,7]. The identification of the reaction products has been most typically performed by means of chromatographic techniques coupled to mass spectrometry [2,3,4,6,7,8]

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