Nitronium salts as mild and inexpensive oxidizing reagents toward designing efficient strategies in organic syntheses; A mechanistic investigation based on the DFT insights

Today, introducing and evaluating the performance of novel reagents are an undeniable part of designing a successful synthetic strategy. Herein, we study the efficiency and mechanism of recently synthesized nitronium salts (e.g., NO2FSO3, NO2CF3SO3, NO2HS2O7, NO2BF4, NO2PF6, and NO2HSO4) in the oxidation reaction of ethanol to acetic acid, as a model of the primary alcohol transformations to linear carboxylic acid. An aldehyde molecule is the first produced species in this reaction which is converted to the acetic acid molecule in the presence of in situ-produced nitric acid. Concerning the proposed mechanism, among the studied nitronium salts, two different behaviors can be observed in the transition state of the step in which the aldehyde molecule is formed. The calculated barrier energies of this step have been scrutinized by powerful descriptors such as Quantum Theory of Atoms in Molecules (QTAIM), Natural Bond Orbital (NBO), Electrostatic Potential (ESP) surfaces, and Activation Strain Model (ASM). The outcomes of the studied descriptors illustrate that nitronium salts have different performances in progressing the formation of the aldehyde molecule. Indeed, the likeness of the transition state of this step to the products for NO2FSO3, NO2CF3SO3, and NO2HS2O7 species is more significant than the others. Accordingly, these reagents have more potential to apply as oxidizing agents in the primary alcohol transformations to linear carboxylic acid.

Automated summary

In this study, the efficiency and mechanism of recently synthesized nitronium salts in the oxidation reaction of ethanol to acetic acid were investigated. The results showed that different nitronium salts have varying performances in the formation of the aldehyde molecule, with NO2FSO3, NO2CF3SO3, and NO2HS2O7 showing the most promising results. This study is important for designing successful synthetic strategies.