Azoxy Products Research Articles

Unspecific peroxygenase enabled formation of azoxy compounds

Enzymes are making a significant impact on chemical synthesis. However, the range of chemical products achievable through biocatalysis is still limited compared to the vast array of products possible with organic synthesis. For instance, azoxy products have rarely been synthesized using enzyme catalysts. In this study, we discovered that fungal unspecific peroxygenases are promising catalysts for synthesizing azoxy products from simple aniline starting materials. The catalytic features (up to 48,450 turnovers and a turnover frequency of 6.7 s–1) and substrate transformations (up to 99% conversion with 98% chemoselectivity) highlight the synthetic potential. We propose a mechanism where peroxygenase-derived hydroxylamine and nitroso compounds spontaneously (non-enzymatically) form the desired azoxy products. This work expands the reactivity repertoire of biocatalytic transformations in the underexplored field of azoxy compound formation reactions.

Enhanced reductive degradation of chloramphenicol by sulfidated microscale zero-valent iron: Sulfur-induced mechanism, competitive kinetics, and new transformation pathway

Crystalline iron sulfide (FeSx, i.e., FeS or FeS2) minerals as sulfur sources were used to prepare the mechanochemically sulfidated microscale zero-valent iron ((FeSx+ZVI)bm). Metastable FeS and FeS2 precursors were generated via aqueous coprecipitation and applied to fabricate FeSx@ZVI samples. (FeSx+ZVI)bm and FeSx@ZVI exhibited better chloramphenicol (CAP) degradation than ZVI due to the increase in specific surface areas, the decrease of electrochemical impedance, the formation of galvanic cells, and sulfur-induced pitting and local acidity. (FeSx+ZVI)bm had better CAP removal capacity than FeSx@ZVI under different S/Fe molar ratios, initial pH, and oxygen conditions. At the same time, FeSx@ZVI showed better electron utilization under oxic conditions, related to their Fe0 and sulfur spatial distribution. Nitro reduction and dechlorination of CAP by (FeSx+ZVI)bm produced nitroso, azoxy, amine, and monodechlorination products, while dechlorination was not involved in the degradation process of CAP by FeSx@ZVI. A new transformation pathway of nitroso-CAP to amine-CAP mediated by azoxy products is proposed via coupling a chain decay multispecies model and DFT calculations. The larger competitive reaction rates among O2, CAP, and its degradation products was determined by their lower LUMO energy. The contribution of direct electron transfer to nitro reduction was greater than that of atomic hydrogen, but the opposite was true for dechlorination. FeSx@ZVI had a larger DET contribution than (FeSx+ZVI)bm, and FeS2 promoted the DET contribution better than FeS. Toxicity assessment indicated that the rapid transformation of nitroso and azoxy products was crucial for eliminating the biotoxicity of CAP.

Tungstate-Catalyzed Biomimetic Oxidative Halogenation of (Hetero)Arene under Mild Condition.

SummaryAryl halide (Br, Cl, I) is among the most important compounds in pharmaceutical industry, material science, and agrochemistry, broadly utilized in diverse transformations. Tremendous approaches have been established to prepare this scaffold; however, many of them suffer from atom economy, harsh condition, inability to be scaled up, or cost-unfriendly reagents and catalysts. Inspired by vanadium haloperoxidases herein we presented a biomimetic approach for halogenation (Br, Cl, I) of (hetero)arene catalyzed by tungstate under mild pH in a cost-efficient and environment- and operation-friendly manner. Broad substrates, diverse functional group tolerance, and good chemo- and regioselectivities were observed, even in late-stage halogenation of complex molecules. Moreover, this approach can be scaled up to over 100 g without time-consuming and costly column purification. Several drugs and key precursors for drugs bearing aryl halides (Br, Cl, I) have been conveniently prepared based on our approach.

ChemInform Abstract: Identification and Biosynthetic Characterization of Natural Aromatic Azoxy Products from Streptomyces chattanoogensis L10.

Abstractisolation, structural elucidation and biosynthetic pathway of three novel aromatic azoxy compounds, azoxymycins A, B, and C

Room temperature selective reduction of nitrobenzene to azoxybenzene over magnetically separable urchin-like Ni/Graphene nanocomposites

Magnetically recyclable Ni/Graphene (Ni/G) nanocomposites were synthesized via an in situ reduction growth process for selective reduction of nitroarenes into corresponding azoxybenzene at room temperature and at atmospheric pressure. Here, hydrazine hydrate (N2H4⋅H2O) is used as the reducing agent which generates harmless by-products such as N2 and water. The catalyst, when used under controlled reaction conditions, exhibits a 100% conversion and selectivity to the target product without the use of any external additives (turnover number 36.2). Under the optimized conditions, a variety of structurally different nitroarenes were selectively transformed to their corresponding azoxy products in high conversions. Furthermore, a high stability and recyclability of the catalyst were also observed under the investigated conditions (93% conversion, 100% selectivity after the 4th reuse).

Identification and Biosynthetic Characterization of Natural Aromatic Azoxy Products from Streptomyces chattanoogensis L10.

Aromatic azoxy compounds recently attracted wide interest for their unique liquid crystalline properties. However, biosynthetic pathways of natural azoxy products have rarely been reported. Three novel aromatic azoxy compounds, azoxymycins A, B, and C, have been isolated and identified from Streptomyces chattanoogensis L10, and their biosynthetic pathways have been reported.

Exploring New Parameter Spaces for the Oxidative Homocoupling of Aniline Derivatives: Sustainable Synthesis of Azobenzenes in a Flow System

Aromatic azo compounds have countless applications, not merely in the chemical industry, but also in medicinal chemistry, biotechnology, and the field of renewable resources. However, in the synthetic batch routine, the synthesis of azobenzenes often constitutes a significant challenge, mainly because of the ease of overreaction leading to nonoptimal selectivity, and also because of reactivity issues necessitating long reaction times and special reaction conditions. We therefore exploited the benefits of continuous-flow processing for the copper-mediated oxidative homocoupling of arylamines to facilitate the time-, cost-, and atom-effective synthesis of azobenzenes. The novel process window of increased temperature and pressure ranges in combination with the application of overheated solvents afforded a remarkable chemical intensification. Precise control of the residence time restricted the possibility of undesired reaction pathways, such as overreaction to azoxy products, but at the same time ensured su...

Selective oxidation of primary substituted aromatic amines to azoxy products using lacunary catalyses

Some of the substituted anilines were selectively converted in to the corresponding azoxy and azobenzenes by oxidation with 30% aqueous hydrogen peroxide. The reactions were catalyzed by various heteropolyoxometalates, at boiling point of the used solvents. An improvement in the product yield and selectivity towards azoxybenzens was also observed. Azobenzenes was obtained as by-product. In the all similar cases, the highest yield of azoxy compounds was observed using K 5PW 11ZnO 39 as catalyst in N, N-dimethylformamide solvent.

Oxidation of Primary Aromatic Amines under Irradiation with Ultrasound and/or Microwaves

The oxidation of primary aromatic amines, p-methylaniline, p-ethylaniline and p-chloroaniline to the corresponding azo- and azoxy-compounds has been observed in ultrasound and/or microwaves systems. The individual irradiation of microwaves and its simultaneous irradiation with ultrasound obviously elevate the conversion of amines, as compared with the individual irradiation of ultrasound and the heating in a plain water bath. However, the formation of formamidine resulted in poor selectivity toward azo and azoxy products in the presence of dimethylformamide (DMF).

Role of hydroxylamine intermediates in the phytotransformation of 2,4,6-trinitrotoluene by Myriophyllum aquaticum.

Phytotransformation studies of 2,4,6-trinitrotoluene (TNT) were conducted using Myriophyllum aquaticum to clarify the role of initial intermediates of TNT transformation in the complex product distributions reported previously. 2-Hydroxylamino-4,6-dinitrotoluene (2HA46DNT) and 4-hydroxylamino-2,6-dinitrotoluene (4HA26DNT) were the initial intermediates of TNT phytotransformation. 2HA46DNT and 4HA26DNT were both abiotically transformed to 4,4',6,6'-tetranitro-2,2'-azoxytoluene (2,2'azoxy) and 2,2',6,6'-tetranitro-4,4'-azoxytoluene (4,4'azoxy) and also phytoreduced to the related amines 2-amino-4,6-dinitrotoluene (2A46DNT) and 4-amino-2,6-dinitrotoluene (4A26DNT). To further elucidate the initial steps of this TNT phytotransformation pathway, the transformations of known intermediates (including 2HA46DNT, 4HA26DNT, 2A46DNT, 4A26DNT, 2,2'azoxy, and 4,4'azoxy) were monitored in plant systems. The transformation rates were measured, and kinetic analysis using pseudo-first-order models was used to evaluate the relative rates of competing reactions. The formation of the azoxy products was determined to be more rapid than the formation of the amine products. Both the azoxy and amine products were subject to uptake and further transformation by the plant.

ChemInform Abstract: PHOTOCHEMICALLY INDUCED OXIDATION OF SOME STEROIDAL ISOXAZOLIDINES BY MOLECULAR OXYGEN

AbstractDie Belichtung des Isoxazolidins (Ia) ergibt in Aceton in Gegenwart von Sauerstoff ein Gemisch der Nitroverbindungen (II)‐(IV) und der Azoxyverbindungen (V) und (VI).

Photochemically induced oxidation of some steroidal isoxazolidines by molecular oxygen

U.v. irradiation of the steroidal isoxazolidines 5α,10α-imino-oxy-5(10 → 1βH)abeo-5α-cholestan-3β-olacetate (1a) and the corresponding N-methyl and N-acetyl derivatives (1b) and (1c) in various solvents in the presence of oxygen, gave the nitro products (2), (3), and (4) and the azoxy products (5) and (6); a mechanism involving exciplex formation followed by proton transfer from isoxazolidine to molecular oxygen is proposed.