Unexpected Artifact Formation in Mass Spectrometric Analysis of Aniline under Atmospheric-Pressure Chemical Ionization

Atmospheric-pressure chemical ionization mass spectrometry (APCI-MS) is a widely used technique for the analysis of a diverse range of analytes. Under APCI conditions, a nonthermal plasma, rich in highly oxidative species such as H2O2, O3, atomic O, and radicals such as HO•, is created. These oxidants trigger unanticipated and often undesirable chemical reactions within the ion source. For example, when aniline was introduced into this environment, it initially underwent oxidative dimerization forming hydrazobenzene (m/z 185). However, with prolonged exposure, there was a marked increase in total ion abundance and the generation of additional artifact ions such as protonated azobenzene (m/z 183) and protonated azoxybenzene (m/z 199). The emergence of these artifacts was found to be highly dependent on the corona-current magnitude. Moreover, the desorption-gas temperature significantly influenced the rate of artifact generation. Recognizing and acknowledging the formation and presence of such artifacts in an ion source is paramount in conducting validated chemical analysis. The existence of artifacts can complicate mass spectral interpretation, potentially leading to erroneous conclusions and misinterpretations of both qualitative and quantitative data. Thus, understanding the intricacies of nonthermal plasma-driven artifact formation is critical for accurate analytical outcomes.

A Dual CQD-Catalysis and H-Bond Acceptor for Controlling Product Selectivity and Regioselectivity in Symmetric/Unsymmetric Azoxy Arenes

Azoxy arenes are valuable compounds in different areas of chemistry, such as organic chemistry, medicinal chemistry, and natural product chemistry. Despite their value, the regioselective synthesis of unsymmetric azoxybenzenes has remained a real challenge in the field. Herein, the product selectivity in oxidative homocoupling of anilines into symmetric azoxybenzenes was first achieved by an asparagine-functionalized CQD catalyst. Subsequently, in the cross-coupling of anilines into the unsymmetric azoxybenzenes via an ortho H-bond acceptor (HBA) on one of the coupling anilines, the regioselectivity was effectively controlled. It was demonstrated that ortho-HBA could mechanistically establish a six-membered intramolecular hydrogen-bonded ring on an N,N'-dihydroxy intermediate. The formed hydrogen bond makes the nearby nitrogen eminently suitable for the slow dehydration step. As a result, the functional oxygen of the azoxy compound is placed far from the HBA. The o-HBA mechanism also controls the regioselectivity ratio in which 1:0 (with an intramolecular H-bonded hexagonal ring), 2:1 (with an intramolecular H-bonded pentagonal ring), and 1:1 (without an ortho-HBA) isomeric mixtures could be achieved. The HBA mechanism was exploited by different substituted anilines, and various unsymmetric azoxybenzenes were synthesized. Finally, with the aid of mechanistic studies, a plausible mechanism for the reaction was proposed.

Controllable Selective Oxidation of Anilines to Azoxybenzenes and Nitrobenzenes by Regulating the Base

The importance of selectively oxidizing aniline into value-added chemicals azoxybenzene and nitrobenzene is well-recognized in organic synthesis. However, the lack of control over selectivity and the complex synthesis of costly catalysts significantly hinder these reactions' industrial applications. In this work, an environmentally friendly approach was developed for the selective oxidization of substituted anilines. This method involves adjusting the strength of alkalinity with peroxide as the oxidant, without the addition of any metals or additives. A mild base (NaF) facilitated azoxybenzene formation, while a stronger base (NaOMe) enabled the synthesis of nitroaromatics. These protocols are user-friendly and scalable, accommodating various substitution patterns and functional groups, yielding products with high to excellent yields. The findings of this work present a framework for investigating base catalysis in organic synthesis and provide a viable and effective approach for selectively oxidizing aniline.

A Direct Method for the Efficient Synthesis of Hydroxyalkyl-Containing Azoxybenzenes

Reaction of nitrobenzyl alcohol with glucose (200 mol%) in the presence of NaOH in water-ethanol medium gave 1,2-bis(4-(hydroxymethyl)phenyl)diazene oxide, 1,2-bis(2-(hydroxymethyl)phenyl)diazene oxide and 1,2-bis(4-(1-hydroxyethyl)phenyl)diazene oxide in 76%, 76% and 72% yields, respectively.

Catalytic selective oxidation of aromatic amines to azoxy derivatives with an ultralow loading of peroxoniobate salts

Tartaric acid-coordinated peroxoniobate salts demonstrate an exceptionally high TOF value (up to 4435 h−1) even at an ultralow catalyst loading for the oxidation of aromatic amines to azoxy compounds under green and very mild conditions.

Convergent Paired Electrochemical Synthesis of Azoxy and Azo Compounds: An Insight into the Reaction Mechanism

A convergent paired electrochemical method was developed for the synthesis of azoxy and azo compounds starting from the corresponding nitroarenes. We propose a unique mechanism for electrosynthesis of azoxy and azo compounds. We find that both anodic and cathodic reactions are responsible for the synthesis of these compounds. The synthesis of azoxy and azo derivatives have been successfully performed in an undivided cell, using carbon rod electrodes, by constant current electrolysis at room temperature.

1,2-Bis(4-(1,3-dioxolan-2-yl)phenyl)diazene Oxide

A simple approach to synthesizing 1,2-bis(4-(1,3-dioxolan-2-yl)phenyl)diazene oxide was developed in this study, based on glucose as an eco-friendly reductant.