Reinvigorating aza-Michael reactions under ionic liquid catalysis: a greener approach

Cholinium α-amino carboxylates, which debuted in the ionic liquid arena over a decade ago, exhibit superior stability and suitable physical properties relative to other RTILs. Although synthetic pursuits in such media, leveraging their dual role as solvents and catalysts, have been scarce so far, we herein illustrate their catalytic advantage in aza-Michael reactions in terms of low loading, acceleration and improved yields with respect to conventional conditions and other imidazolium-based ILs. These highly structured salts most likely act through multiple and cooperative non-covalent interactions. These mechanistic features have also been investigated through high-level computational analyses as well.

The vital use of isocyanide-based multicomponent reactions (MCR) in chemical synthesis

Multicomponent (MCRs) reactions are classified as one-pot reaction where more than two starting materials are employed to form a single product that contains the building blocks of the starting components. MCRs are considered a convenient approach in synthetic chemistry and have many advantages over the traditional one or two-component reaction, by reducing the number of sequential multiple steps required and often producing better yields. This chapter dissects the use of isocyanide-based MCRs and the elegant chemistry that they offer to build useful scaffolds in the chemical synthetic field. In addition MCRs are considered as one of the recognisable options for increasing “greenness” during the synthesis of pharmaceutical and industrial products.

Ammonium 2,2'-thiodiacetates - Selective and environmentally safe herbicides

2,2'-Thiodiacetic acid derivatives have a wide application potential, mainly in coordination chemistry. This research indicates that quaternary ammonium 2,2'-thiodiacetate salts may also be potent herbicidal agents used in agriculture. To provide a rationale for this statement, the toxic effect by a alkyl and aryl quaternary ammonium salts (QASs) on plant growth was investigated. The phytotoxicity of these compounds was tested against cultivated monocotyledonous (spring barley) and dicotyledonous (common radish) plants, whereas herbicidal activity was investigated in relation to popular weeds species (white goosefoot, sorrel and gallant-soldier). The results showed that aliphatic QASs possessed a low phytotoxicity to food crops and that some of them (in particular triethylammonium salt) had potent and selective herbicidal properties against common weeds, such as sorrel and gallant-soldier. However, the investigated compounds appeared to be ineffective herbicides against white goosefoot.

Ammonium haloacetates - An alternative to glyphosate?

This study shows the design, synthesis and evaluation of eco(phyto)toxic and herbicidal activities of quaternary ammonium salts (QASs), derived from haloacetic acids, in context of the search for safer alternatives to the commonly used herbicide, N-(phosphonomethyl)glycine (glyphosate). The structure of the investigated QASs refers to the heteroatom sequence in the anion of glyphosate in which the (P-C)-N nitrogen atom was replaced by one or more halogens (F, Cl). The ecotoxicity of the synthesized QASs was tested against luminescent marine bacteria Vibrio fischeri (Microtox® test) and the crustaceans Heterocypris incongruens (Ostracodtoxkit F™). The phytotoxic effect of QASs was also studied with respect to spring barley (Hordeum vulgare) and common radish (Raphanus sativus L. radicula Pers.), whereas herbicidal activity was investigated in relation to popular weeds species gallant soldier (Galinsoga parviflora Cav.) and common sorrel (Rumex acetosa L.). The results showed that toxicity of the synthesized QASs depends on a number of halo-substituents, especially for bioluminescent bacteria Vibrio fischeri for which EC50 values were those varying the most. Phytotoxicity tests proved that the investigated QASs had a similar high, toxic effect both on monocotyledonous and dicotyledonous plants with exception of DIPA - DCA. Moreover, their herbicidal activity against common sorrel was comparable to glyphosate.

Experimental and Theoretical Investigation of the Reaction of Secondary Amines with Maleic Anhydride

The reaction of secondary amines, namely 1-methylpiperazine, pyrrolidine, morpholine, 2-methylpiperidine, and diethylamine, with maleic anhydride has been investigated experimentally and theoretically at the DFT level. Under kinetic control, i.e. at −78°C or −15°C, amines add across the C=O functionality exclusively and the initially formed addition products isomerize to the corresponding N-substituted maleimic acid derivatives. In contrast to the acyclic α,β-unsaturated carbonyl compounds, amine does not add across the C=C functionality in maleic anhydride even under thermodynamic control. This behaviour of maleic anhydride can be rationalized on the basis of the local condensed Fukui functions, which reveal that the carbonyl carbon atoms in maleic anhydride are much harder than in an acyclic α,β-unsaturated carbonyl compound, such as acrolein. This prompts the amines to attack the carbonyl group in maleic anhydride exclusively.

Hantzsch Reaction Starting Directly from Alcohols through a Tandem Oxidation Process

A Brønsted acidic ionic liquid, 3-(N,N-dimethyldodecylammonium) propanesulfonic acid hydrogen sulphate ([DDPA][HSO4]), has been successfully applied to catalyze sequential oxidation of aromatic alcohols with NaNO3 followed by their condensation with dicarbonyl compound and ammonium acetate. The corresponding pyridine analogues of Hantzsch 1,4-dihydropyridines could be obtained as a major product with high yields by the multicomponent reaction. The present work utilizing alcohols instead of aldehyde in Hantzsch reaction is a valid and green alternative to the classical synthesis of the corresponding pyridine analogues of Hantzsch 1,4-dihydropyridines.

Ionic liquid/water mixture promoted organic transformations

Wet ILs constitutes a new class of solvents with their own new and interesting properties. The IL–water mixing makes it easy to control the properties of the solution and the formation of these ionic liquid mixtures increases synthetic flexibility.

Ionic Liquids: Synthesis and Applications in Catalysis

Ionic liquids have emerged as an environmentally friendly alternative to the volatile organic solvents. Being designer solvents, they can be modulated to suit the reaction conditions, therefore earning the name “task specific ionic liquids.” Though primarily used as solvents, they are now finding applications in various fields like catalysis, electrochemistry, spectroscopy, and material science to mention a few. The present review is aimed at exploring the applications of ionic liquids in catalysis as acid, base, and organocatalysts and as soluble supports for catalysts.