Progress in thermoregulated liquid/liquid biphasic catalysis

Ionic Liquids: Advances and Applications in Phase Transfer Catalysis

Ionic liquids are a family of liquids that are composed entirely of ions and usually have melting points lower than 100 °C. Extensive research, along with the ever-growing interest of the scientific community, allowed for the development of a multitude of ionic liquids with low melting points. Such compounds are considered neoteric materials as well as ideal, custom-made solvents for a variety of different chemical transformations. In this regard, the importance of phase transfer catalysis is evident in a diversity of substrates and reactions. The use of phase transfer catalysts allows the reaction to proceed, facilitating the transfer of otherwise insoluble reactants to the desired phase. Recent scientific advances led to the emergence of ionic liquids, which are excellent candidates as phase transfer catalysts. The inherent fine-tuning capability of these molecules, along with the potential of phase transfer catalytic reactions, epitomize the sustainable aspect of this field of research. Herein, a cohesive report of such applications will be presented, including the period from the last decade of the 20th century up to date.

Recent development towards alkene hydroformylation catalysts integrating traditional homo- and heterogeneous catalysis

This mini-review provides the recent progress towards catalysts for the hydroformylation of catalysts that bridge traditional homo- and heterogeneous catalysis, highlighting the future development of heterogeneous catalysts in hydroformylation.

Effect of Particle Wettability and Particle Concentration on the Enzymatic Dehydration of n-Octanaloxime in Pickering Emulsions

Pickering emulsion systems have emerged as platforms for the synthesis of organic molecules in biphasic biocatalysis. Herein, the catalytic performance was evaluated for biotransformation using whole cells exemplified for the dehydration of n-octanaloxime to n-octanenitrile catalysed by an aldoxime dehydratase (OxdB) overexpressed in E. coli. This study was carried out in Pickering emulsions stabilised solely with silica particles of different hydrophobicity. We correlate, for the first time, the properties of the emulsions with the conversion of the reaction, thus gaining an insight into the impact of the particle wettability and particle concentration. When comparing two emulsions of different type with similar stability and droplet diameter, the oil-in-water (o/w) system displayed a higher conversion than the water-in-oil (w/o) system, despite the conversion in both cases being higher than that in a "classic" two-phase system. Furthermore, an increase in particle concentration prior to emulsification resulted in an increase of the interfacial area and hence a higher conversion.

Designing a robust recyclable tricopolymer poly(ionic liquid) macroligand for copper-mediated atom transfer radical polymerization in non-aqueous biphasic systems

Herein, a robust thermoregulated poly(ionic liquid) macroligand was designed, synthesized and applied in an ICAR-based ATRP-TPSC system with efficient recycling/reuse.

Recent Advances Utilized in the Recycling of Homogeneous Catalysis

Homogeneous catalysts often show high activity and selectivity towards the various chemical transformations. Most of the transition metal-based active catalysts are expensive, rare, and have strict regulations for their use in pharmaceutical products. Hence, there is a requirement to develop suitable technologies for the practical separation and recycling of metal complex catalysts along with the sustainability of the process. This review focuses on the recent techniques used for the catalyst separation, their recovery, and recyclability of the homogeneous form of catalysts based on their economic compatibility and industrial applications. Various homogeneous catalysts have been reviewed on the basis of their support or media, active centres and recyclability aspects of the catalysts. This review gives brief insights into the varied examples of different recycling techniques utilized in the past 6-7 years.

New developments in liquid-liquid extraction, surface modification and agglomerate-free processing of inorganic particles

This review describes new methods for the particle extraction through liquid-liquid interface (PELLI). The discovery of new surface modification techniques, advanced extractors and new adsorption mechanisms enabled novel applications of PELLI in nanotechnology of metals, quantum dots, oxides and hydroxides. Colloidal and interface chemistry of PELLI is emerging as a new area of technological and scientific interest. The progress achieved in the understanding of particle behavior and interactions at the liquid-liquid interface, phase transfer and interface reactions allowed for the development of new extraction mechanisms. An important breakthrough was the development of surface modification techniques for extraction of functional oxides. Especially important is the possibility of particle transfer from the synthesis medium to the device processing medium, which facilitates agglomerate-free processing of functional nanoparticles. Multifunctional extractor molecules were discovered and used as capping and reducing agents for particle synthesis or dispersing and charging agents for colloidal processing. The progress achieved in the development of extractors and extraction mechanisms has driven the advances in the surface modification and functionalization of materials. New PELLI techniques were used for the development of advanced materials and devices for optical, photovoltaic, energy storage, electronic, biomedical, sensor and other applications.

Palladium-Catalyzed Hydroxycarbonylation of 1-Dodecene in Microemulsion Systems: Does Reaction Performance Care about Phase Behavior?

Catalysis, particularly metal-catalyzed reactions in microemulsion systems, offers a sustainable approach for organic reactions in water. However, it is still a challenging task because of the complex role of the nonionic surfactant in such a system and the interaction of the phase behavior and reaction performance. To get a profound knowledge of this role and interaction, a systematic study of the palladium-catalyzed hydroxycarbonylation of 1-dodecene in a microemulsion system is reported. The influence of the temperature, additives such as cosolvents, the catalyst concentration, and the hydrophilicity of the surfactant and its concentration has been investigated with regard to both the phase behavior and reaction performance. Interestingly, the investigations reveal that not the phase behavior of the microemulsion system but mainly the dimension of the oil-water interface and the local concentrations of the substrates at this interface, which is provided by the amount and hydrophilicity of the surfactant, control the reaction performance of hydroxycarbonylation in these systems. Moreover, it was found that the local concentration of the active catalyst complex at the interface is essential for the reaction performance. Dependent on the surface active properties of the catalyst complex, its bulk concentration, and the nature and amount of additives, the local concentration of the active catalyst complex at the interface is strongly influenced, which has a huge impact on the reaction performance.

Unsupported Micellar Palladium Nanoparticles for Biphasic Hydrogenation and Isomerization of Hydrophobic Allylic Alcohols in Water

This article presents the evaluation of water-soluble palladium nanoparticles with hydrophobic active sites that are ideal for the biphasic colloidal catalysis of water-insoluble organic substrates in aqueous solution. Palladium nanoparticles stabilized with ω-carboxylate-functionalized alkanethiolate are first synthesized using ω-carboxylate-S-alkylthiosulfate as their ligand precursor. The biphasic catalysis is carried out for the reaction of hydrophobic allylic alcohols without using any additional mixing solvent or surfactant, which results in the complete consumption of substrates under the atmospheric pressure of H₂ gas and at room temperature in less than 24 h. Systematic investigations on the influence of pH and substrate size are also performed to examine the utility of these thiolate-capped palladium nanoparticles as structurally stable and water-soluble micellar catalysts for the biphasic reaction.

Cooperative Reinforcement of Ionic Liquid and Reactive Solvent on Enzymatic Synthesis of Caffeic Acid Phenethyl Ester as an In Vitro Inhibitor of Plant Pathogenic Bacteria

It is widely believed that lipases in ionic liquids (ILs) possess higher enzyme activity, stability and selectivity; however, reaction equilibrium is always limited by product inhibition, and the product is difficult to separate from non-volatile ILs using distillation. To solve this problem, using trialkylphosphine oxide (TOPO) as a complexing agent, a novel biphase of reactive solvent and IL was firstly reported for caffeic acid phenethyl ester (CAPE) production from methyl caffeate (MC) and 2-phenylethanol (PE) catalyzed by lipase via transesterification. The effects of the reaction parameters and their action mechanism were investigated, and the inhibition of CAPE against bacterial wilt pathogen Ralstonia solanacearum was firstly measured. The MC conversion of 98.83% ± 0.76% and CAPE yield of 96.29% ± 0.07% were obtained by response surface methodology in the 25 g/L TOPO-cyclohexane/[Bmim][Tf₂N] (1:1, v/v); the complex stoichiometry calculation and FTIR spectrum confirmed that the reversible hydrogen-bond complexation between TOPO and caffeates significantly enhances the cooperative effect of two phases on the lipase-catalyzed reaction. The temperature was reduced by 14 °C; the MC concentration increased by 3.33-fold; the ratio of catalyst to donor decreased by 4.5-fold; and Km decreased 1.08-fold. The EC₅₀ of CAPE against R. solanacearum was 0.17–0.75 mg/mL, suggesting that CAPE is a potential in vitro inhibitor of plant pathogenic bacteria.

A pH-switched Pickering emulsion catalytic system: high reaction efficiency and facile catalyst recycling

A smart Pickering emulsion catalytic system is constructed, which not only exhibits fivefold reaction rate enhancement effects in comparison to the conventional biphasic system but also can be facilely demulsified by tuning pH, allowing for in situ recycling nanocatalysts.