Ionic Liquid as Catalyst and Reaction Medium – A Simple, Efficient and Green Procedure for Knoevenagel Condensation of Aliphatic and Aromatic Carbonyl Compounds Using a Task-Specific Basic Ionic Liquid

Recent development in functionalized ionic liquids as reaction media and promoters

The recent development in the use of functionalized ionic liquids as both reaction media and promoters is reviewed. Ionic liquids designed with special functionality can enhance the reaction rate, selectivity, and productivity in various chemical reactions. In this context, some important chemical reactions involving C–C, C–O, C–N, and C–S bond formation in functionalized ionic liquids are discussed. These functionalized ionic liquids were found to provide distinct advantages over conventional organic solvents in these catalytic reactions.

Zirconium oxide nanoparticles coated on sepiolite by sol–gel process — Their application as a solvent-free catalyst for condensation reactions

An inorganic nanocomposite made of zirconia nanoparticles coated on the external surfaces of the fibrous clay mineral sepiolite was prepared by using the sol–gel process under soft conditions using zirconium(IV) propoxide in 1-propanol as the precursor. The resulting materials were characterized by X-ray diffraction (XRD), thermal gravimetric analyses (TGA) and differential thermal analyses (DTA), microporosimetry, 29Si magic-angle spinning (MAS) nuclear magnetic resonance (NMR), and high-resolution transmission electron microscopy (HR-TEM). The organic material from the precursor was fully removed after calcination at 450 °C, concurrently with the crystallization of the cubic phase of zirconium oxide. The coordinated water molecules of sepiolite were fully removed and its symmetrical layered structure was folded after calcination at 650 °C, as observed by XRD and 29Si cross-polarization (CP) / MAS NMR. The arrangement of the nanoparticles of zirconium oxide on the sepiolite external surfaces maintains a fibrous morphology for the nanocomposite. This material was applied as a catalyst for the Knoevenagel condensation reaction of benzaldehyde and malononitrile under solvent-free conditions. Strongly improved yields of reaction, attributed to larger catalytically active surfaces, were obtained compared with either the sepiolite clay mineral or the zirconium oxide tested individually.

Synthesis of diphenylamine-based novel fluorescent styryl colorants by Knoevenagel condensation using a conventional method, biocatalyst, and deep eutectic solvent

Novel Y-shaped acceptor-pi-donor-pi-acceptor-type compounds, synthesized from 4,4'-hexyliminobisbenzaldehyde as electron donors and different active methylene compounds as electron acceptors, were produced by conventional Knoevenagel condensation alone, with a deep eutectic solvent, or with a lipase biocatalyst to compare the yield and recyclability among the three methods. Yield, reaction time, reaction temperature, and recyclability were compared among the three methods. The photophysical properties and thermal stability of the products were also investigated.

A nonaqueous lyotropic liquid crystal fabricated by a polyoxyethylene amphiphile in protic ionic liquid

The aggregation behaviors of oleyl polyoxyethylene (10) ether, Brij 97, in room temperature ionic liquids, ethylammonium nitrate (EAN), pyrrolidinium nitrate ([Pyrr][NO(3)]), ethylammonium butyrate (EAB), 1-butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PF(6)]), and 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]), have been investigated. Only in the Brij 97/EAN binary system is the hexagonal liquid crystalline phase formed, and its ordering is found to decrease with increasing temperature. The lattice spacing values measured from the small-angle X-ray scattering (SAXS) shrink with reduction of ionic liquid content at room temperature. The general rules for aggregate formation in these ionic liquids are discussed and compared with that in water. A degraded ability to produce the ordered self-assembly of Brij 97 from H(2)O to EAN to [Bmim][PF(6)], [Bmim][BF(4)], [Pyrr][NO(3)], and EAB is found and analyzed based on the molecular packing and Gordon parameters and also hydrogen-bonding or solvophobic interactions. Steady-shear rheological measurements combined with the frequency sweep data indicate the highly viscoelastic nature of this liquid crystalline phase.

L-Arginine as a Cost-Effective and Recyclable Catalyst for the Synthesis of α,β-Unsaturated Nitriles and Ketones in an Ionic Liquid

L-Arginine catalysed the Knoevenagel condensations of aromatic, heteroaromatic and α,β-unsaturated aldehydes with malononitrile and acetylacetone to afford α,β-unsaturated nitriles and ketones. The reactions were carried out at room temperature in the ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate. Moderate to excellent yields (45–100%) were achieved. The L-arginine/ionic liquid combination was successfully recycled for five runs without significant loss of activity.

Ultrasound-promoted synthesis of oximes catalyzed by a basic ionic liquid [bmIm]OH

The basic ionic liquid 1-butyl-3-methylimidazolium hydroxide, [bmIm]OH, efficiently catalyzes the condensation reaction of aldehydes and ketones with hydroxylamine hydrochloride under ultrasound irradiation. Compared with conventional methods, the main advantages of the present procedure are milder conditions, shorter reaction time and higher yields.

Sustainable chemistry metrics

Green chemistry has developed mathematical parameters to describe the sustainability of chemical reactions and processes, in order to quantify their environmental impact. These parameters are related to mass and energy magnitudes, and enable analyses and numerical diagnoses of chemical reactions. The environmental impact factor (E factor), atom economy, and reaction mass efficiency have been the most influential metrics, and they are interconnected by mathematical equations. The ecodesign concept must also be considered for complex industrial syntheses, as a part of the sustainability of manufacturing processes. The aim of this Concept article is to identify the main parameters for evaluating undesirable environmental consequences.