Real-time monitoring as a tool for comparison of electrochemical advanced oxidation processes for the decolourisation of azo and indigoid dyes.

The widespread use of synthetic dyes has led to the release of substantial amounts of dye-contaminated wastewater, posing significant environmental and health concerns. This study focuses on the use of anodic and electrochemically activated persulfate oxidation for the degradation of organic contaminants. Specifically, the structural variations of nine dyes in the indigoid and azo families, and their impact on the efficiency of electrochemical oxidation were analysed.

Scale-up of Sodium Persulfate Mediated, Nitroxide Catalyzed Oxidative Functionalization Reactions.

Background: Oxidation is a valuable tool in preparative organic chemistry. Oxoammonium salts and nitroxides have proven valuable as reagents and catalysts in this endeavor.

Objective: The objective of this study is to scale up the oxidative amidation, ester formation, and nitrile formation using nitroxide as an organocatalyst.

Acetamido-TEMPO mediated electrochemical oxidation of alcohols to aldehydes and ketones.

A protocol for the oxidation of alcohols to aldehydes and ketones employing an electrochemical aminoxyl-mediated reaction is presented. The approach employs a catalytic amount of the radical and the use of a base is not required. It is performed using readily available electrodes in a commercially available electrochemistry apparatus and does not require a reference electrode.

Solvent- and additive-free oxidative amidation of aldehydes using a recyclable oxoammonium salt.

A range of acyl azoles have been prepared from aromatic, heteroaromatic, and aliphatic aldehydes by means of an oxidative amidation reaction. The methodology employs a substoichiometric quantity of an oxoammonium salt as the oxidant. It avoids the need for additives such as a base, is run solvent-free, and the oxoammonium salt is recyclable.

Preparation of nitriles from aldehydes using ammonium persulfate by means of a nitroxide-catalysed oxidative functionalisation reaction.

A methodology for the preparation of nitriles from aldehydes by means of an oxidative functionalisation reaction is reported. It employs ammonium persulfate as both the primary oxidant and the nitrogen source, and a catalytic amount of a nitroxide. It is applicable to a range of structurally diverse (hetero)aromatic aldehydes furnishing the nitrile products in 30-97% isolated yield.

Preparation of hexafluoroisopropyl esters by oxidative esterification of aldehydes using sodium persulfate.

A simple, metal-free route for the oxidative esterification of aldehydes to yield hexafluoroisopropyl esters is reported. The methodology employs sodium persulfate and a catalytic quantity of a nitroxide and is applicable to aromatic, heteroaromatic, and aliphatic aldehydes.

Using experimental and computational approaches to probe an unusual carbon-carbon bond cleavage observed in the synthesis of benzimidazole -oxides.

Experimental and computational studies have been performed in order to investigate an unusual carbon-carbon bond cleavage that occurs in the preparation of certain benzimidazole N-oxides from anilines. The key factor determining the outcome of the reaction was found to be the substituents on the amine functionality of the aniline.

Oxidative Amidation of Amines in Tandem with Transamidation: A Route to Amides Using Visible-Light Energy.

A methodology is reported for preparing amides using amines as an acyl source. The protocol involves the visible-light-promoted oxidative amidation of amines with pyrazole to synthesize -acyl pyrazoles followed by transamidation. By combining photoredox catalysis with oxoammonium cations in the presence of sodium persulfate as a terminal oxidant, the -acyl pyrazoles could be prepared efficiently and effectively using blue LEDs.

One-Pot Two-Step Synthesis of 2-Aryl benzimidazole -oxides Using Microwave Heating as a Tool.

A methodology is reported for the preparation of 2-aryl-benzimidazole-3-oxide derivatives. By means of a one-pot two-step protocol, a library of 42 new compounds has been prepared. Reactions were performed in a total time of 40 min using microwave heating as a tool.

Visible-light-driven catalytic oxidation of aldehydes and alcohols to nitriles by 4-acetamido-TEMPO using ammonium carbamate as a nitrogen source.

A mild and efficient route to prepare nitriles from aldehydes by combining photoredox catalysis with oxoammonium cations is reported. The reaction is performed using ammonium carbamate as the nitrogen source. The practicality of the method is increased by the extension of the dual catalytic system to one-pot two-step conversion of alcohols to nitriles.

Oxidation of α-trifluoromethyl and non-fluorinated alcohols via the merger of oxoammonium cations and photoredox catalysis.

We present an alcohol oxidation strategy to access α-trifluoromethyl ketones (TFMKs) merging catalytic oxoammonium cation oxidation with visible-light photoredox catalysis. This work uses 4-acetamido-(2,2,6,6-tetramethyl-piperidin-1-yl)oxyl as an organic oxidant capable of generating TFMKs in good yields. The methodology serves as an improvement over previous reports of an analogous oxidation strategy requiring superstoichiometric quantities of oxidant.

Oxidative functionalisation of alcohols and aldehydes via the merger of oxoammonium cations and photoredox catalysis.

We present a new paradigm for nitroxyl-mediated processes via the merger of oxoammonium cation-mediated oxidation with visible-light photoredox catalysis. The integration of these two forms of catalysis has been realised for the oxidative amidation of aldehydes, furnishing N-acylated heterocycles. Extension of this process to the oxidative amidation of alcohols via the intermediacy of an aldehyde was successfully pursued, thus proffering a general oxidation platform.

Oxidation of terminal diols using an oxoammonium salt: a systematic study.

A systematic study of the oxidation of a range of terminal diols is reported, employing the oxoammonium salt 4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate (4-NHAc-TEMPO BF) as the oxidant. For substrates bearing a hydrocarbon chain of seven carbon atoms or more, the sole product is the dialdehyde. A series of post-oxidation reactions have been performed showing that the product mixture resulting from the oxidation step can be taken on directly to a subsequent transformation.

Accessing N-Acyl Azoles via Oxoammonium Salt-Mediated Oxidative Amidation.

An operationally simple, robust, metal-free approach to the synthesis of N-acyl azoles from both alcohols and aldehydes is described. Oxidative amidation is facilitated by a commercially available organic oxidant (4-acetamido-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) and proceeds under very mild conditions for an array of structurally diverse substrates. Tandem reactions of these activated amides, such as transamidation and esterification, enable further elaboration.

A combined computational and experimental investigation of the oxidative ring-opening of cyclic ethers by oxoammonium cations.

The propensity of oxoammonium cations to facilitate the oxidative ring-opening of cyclic ethers to their corresponding distal hydroxy ketones is investigated. The reaction has been evaluated using experimental and computational methods to gain deeper insight into trends in reactivity.

Rules of Macrocycle Topology: A [13]-Macrodilactone Case Study.

Shape is an inherent trait of a molecule that dictates how it interacts with other molecules, either in binding events or intermolecular reactions. Large-ring macrocyclic compounds in particular leverage their shape when they are selectively bound by biomolecules and also when they exhibit macrocyclic diastereoselectivity. Nonetheless, rules that link structural parameters to the conformation of a macrocycle are still rudimentary.

Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example.

By using inline monitoring, it is possible to optimize reactions performed using continuous-flow processing in a simple and rapid way. It is also possible to ensure consistent product quality over time using this technique. We here show how to interface a commercially available flow unit with a Raman spectrometer.

Toward a Unified Mechanism for Oxoammonium Salt-Mediated Oxidation Reactions: A Theoretical and Experimental Study Using a Hydride Transfer Model.

A range of oxoammonium salt-based oxidation reactions have been explored computationally using density functional theory (DFT), and the results have been correlated with experimentally derived trends in reactivity. Mechanistically, most reactions involve a formal hydride transfer from an activated C-H bond to the oxygen atom of the oxoammonium cation. Several new potential modes of reactivity have been uncovered and validated experimentally.

Oxidative cleavage of allyl ethers by an oxoammonium salt.

A method to oxidatively cleave allyl ethers to their corresponding aldehydes mediated by an oxoammonium salt is described. Using a biphasic solvent system and mild heating, cleavage proceeds readily, furnishing a variety of α,β-unsaturated aldehydes and ketones.

Access to nitriles from aldehydes mediated by an oxoammonium salt.

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4-acetylamino-2,2,6,6-tetramethylpiperidine-1-oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl-imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.

Methylenation of perfluoroalkyl ketones using a Peterson olefination approach.

An operationally simple, inexpensive, and rapid route for the olefination of a wide array of trifluoromethyl ketones to yield 3,3,3-trifluoromethylpropenes is reported. Using a Peterson olefination approach, the reaction gives good to excellent yields of the alkene products and can be performed without purification of the β-hydroxysilyl intermediate. The reaction can be extended to other perfluoroalkyl substituents and is easily scaled up.

Opening an Aladdin's cave: the Suzuki coupling in a room-temperature ionic liquid.

This viewpoint will discuss the impact of the 2000 Chem. Commun. report that the palladium-catalysed Suzuki coupling can be performed quickly and easily in a room-temperature ionic liquid.

Trifluoromethyl ketones: properties, preparation, and application.

Trifluoromethyl ketones (TFMKs) are exceedingly valuable synthetic targets in their own right and as synthons in the construction of fluorinated pharmacons. This Feature Article provides an overview of the properties of TFMKs, an in-depth discussion of the methods available for their synthesis, and two illustrative examples of their application as key intermediates in medicinal chemistry.

Raman spectroscopy as a tool for monitoring mesoscale continuous-flow organic synthesis: Equipment interface and assessment in four medicinally-relevant reactions.

An apparatus is reported for real-time Raman monitoring of reactions performed using continuous-flow processing. Its capability is assessed by studying four reactions, all involving formation of products bearing α,β-unsaturated carbonyl moieties; synthesis of 3-acetylcoumarin, Knoevenagel and Claisen-Schmidt condensations, and a Biginelli reaction. In each case it is possible to monitor the reactions and also in one case, by means of a calibration curve, determine product conversion from Raman spectral data as corroborated by data obtained using NMR spectroscopy.