Natural polyphenols as safe alternatives to hydroquinone for the organocatalyzed reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA)

Abstract

Reduction of dioxygen dissolved in water by diethylhydroxylamine (DEHA) in the presence of hydroquinones or quinones as organocatalysts is investigated with regard to reaction rate and catalyst turnover. Eleven p-benzoquinone derivatives bearing various electron-donating, electron-withdrawing and bulky substituents are studied. The catalytic activity of four benzenediols (hydroquinone, resorcinol, catechol and 4-tert-butylcatechol) and of four benzenetriols (hydroxyquinol, phloroglucinol, pyrogallol and 5-tert-butylpyrogallol) is compared. Mechanistic and kinetic studies indicate that the rate-determining step is the regeneration of hydroquinones through the reduction of the corresponding benzoquinones by DEHA. Then, eight natural polyphenols are tested as alternative catalysts to the potential carcinogen hydroquinone. Four of them ( purpurin, myricetin, gallic acid and propyl gallate) exhibit some catalytic activity and gallic acid is shown to be even more efficient than hydroquinone itself. A further improvement of the catalytic system is achieved by adding catalase to disproportionate the generated hydrogen peroxide, which is detrimental for the catalyst. Thus, the oxygen scavenging system DEHA-gallic acid-catalase is found to be not only greener but also more efficient than the current system DEHA-hydroquinone since it gives water instead of hydrogen peroxide as the final reduction product of dioxygen. † Electronic supplementary information (ESI) available. See

Cellular Metabolomics by a Universal Redox-Reactive Nanosensors Array: From the Cell Level to Tumor-on-a-Chip Analysis

“…The 9,10-dihydroxyanthracene/9,10-anthraquinone (DHA/AQ) redox reversible system was selected as the sensing moiety on the SiNW FET array due to the rapid oxidation of the reduced form DHA in the presence of metabolic products such as H 2 O 2 and ROS via conversion to the oxidized state AQ, Figure b. However, AQ in aqueous solution can be reversibly reduced back to DHA in the presence of mild chemical reductants such as N , N -diethylhydroxylamine (DEHA), or by applying electric potential . Therefore, by covalently binding this redox system to a SiNW FET device’s array surface via a short linker, a novel configuration of redox-reactive SiNW FET nanodevices was achieved, Figure a.…”

Redox-Reactive Field-Effect Transistor Nanodevices for the Direct Monitoring of Small Metabolites in Biofluids toward Implantable Nanosensors Arrays

“…The surface of the nanowires is covalently modified with a redox reversible system, 9,10-dihydroxyanthracene/9,10-anthraquinone (DHA/AQ). The reversible redox transformation of the surface-confined DHA molecules can occur by alternatively applying chemical reductants and oxidants, such as N , N -diethylhydroxylamine (DEHA), and hydrogen peroxide, respectively. , DHA tends to selectively react with oxygen reactive species (ROS) or with H 2 O 2. , Therefore, by introducing a metabolite, glucose, for example, to a specific oxidase enzyme, such as glucose oxidase, the coproduction of H 2 O 2 will occur.…”

Dramatic synergistic effects between hydroquinone and resorcinol derivatives for the organocatalyzed reduction of dioxygen by diethylhydroxylamine

“…However, with methoxy and chlorine substituents, the reactions run faster, albeit without improving the TON because of degradation of the catalysts. 11 A first approach to improve the catalytic system was to find more active polyphenols that led to the identification of gallic acid as a safer alternative to hydroquinone. 11,12 Alternatively, antioxidants are well-known to present synergistic effects in radical trapping chain transfer reactions, like the combination of 2,5-di-tert-butyl-3-methylphenol (BHT) with 2-tert-butyl-4-hydroxyanisole (BHA), 13 or tocopherol with ascorbic acid.…”

“…11 A first approach to improve the catalytic system was to find more active polyphenols that led to the identification of gallic acid as a safer alternative to hydroquinone. 11,12 Alternatively, antioxidants are well-known to present synergistic effects in radical trapping chain transfer reactions, like the combination of 2,5-di-tert-butyl-3-methylphenol (BHT) with 2-tert-butyl-4-hydroxyanisole (BHA), 13 or tocopherol with ascorbic acid. 14 Such synergies between dioxygen scavengers have however, to the best of our knowledge, not been reported yet.…”

“…The mechanism of the binary DEHA-H 2 Q catalytic system (eqn (1)) has already been discussed in detail. 11 The rate limiting step is believed to be the regeneration of hydroquinone H 2 Q or its conjugated base HQ À , either through disproportionation of the semiquinone radical HQ into H 2 Q and benzoquinone Q (Scheme 1, pathway A), or its direct reduction by DEHA (Scheme 1, pathway B).…”