Triphasic Reaction Research Articles

Triphasic Hydroxysilylation of Alkenes by Mechanically Piezoelectric Catalysis

AbstractThe 1,2‐hydroxysilylation of alkenes is crucial for synthesizing organosilicon compounds which are key intermediates in material science, pharmaceuticals, and organic synthesis. The development of strategies employing hydrogen atom transfer pathways is currently hindered by the existence of various competing reactions. Herein, we reported a novel mechanochemical strategy for the triphasic 1,2‐hydroxysilylation of alkenes through a single‐electron‐transfer pathway. Our approach not only circumvents competitive reactions to enable the first‐ever 1,2‐hydroxysilylation of unactivated alkenes but also pioneers the research in mechanic force‐induced triphasic reactions under ambient conditions. This gentle method offers excellent compatibility with various functional groups, operates under simple and solvent‐free conditions, ensures rapid reaction time. Preliminary mechanistic investigations suggest that silylboronate can be transformed to a silicon radical by highly polarized Li2TiO3 particles and oxygen under ball‐milling condition.

Triphasic Hydroxysilylation of Alkenes by Mechanically Piezoelectric Catalysis.

The 1,2-hydroxysilylation of alkenes is crucial for synthesizing organosilicon compounds which are key intermediates in material science, pharmaceuticals, and organic synthesis. The development of strategies employing hydrogen atom transfer pathways is currently hindered by the existence of various competing reactions. Herein, we reported a novel mechanochemical strategy for the triphasic 1,2-hydroxysilylation of alkenes through a single-electron-transfer pathway. Our approach not only circumvents competitive reactions to enable the first-ever 1,2-hydroxysilylation of unactivated alkenes but also pioneers the research in mechanic force-induced triphasic reactions under ambient conditions. This gentle method offers excellent compatibility with various functional groups, operates under simple and solvent-free conditions, ensures rapid reaction time. Preliminary mechanistic investigations suggest that silylboronate can be transformed to a silicon radical by highly polarized Li2TiO3 particles and oxygen under ball-milling condition.

Understanding and Controlling Reactivity Patterns of Pd1@C3N4-Catalyzed Suzuki-Miyaura Couplings.

Using heterogeneous single-atom catalysts (SACs) in the Suzuki-Miyaura coupling (SMC) has promising economic and environmental benefits over traditionally applied palladium complexes. However, limited mechanistic understanding hinders progress in their design and implementation. Our study provides critical insights into the working principles of Pd1@C3N4, a promising SAC for the SMC. We demonstrate that the base, ligand, and solvent play pivotal roles in facilitating interface formation with reaction media, activating Pd centers, and modulating competing reaction pathways. Controlling the previously overlooked interplay between base strength, reagent solubility, and surface wetting is essential for mitigating mass transfer limitations in the triphasic reaction system and promoting catalyst reusability. Optimum conditions for Pd1@C3N4 require polar solvents, intermediate base strength, and increased water content. Our investigations reveal that high selectivity requires minimizing competitive coordination of bases and phosphine ligands to the Pd centers, to avoid homocoupling and alternative reductive elimination mechanisms giving rise to phosphonium side-products. Furthermore, in situ XAS investigations probing electronic structures and coordination environments of Pd sites further rationalize the base and ligand coordination, confirming and expanding upon previous computational hypotheses for Pd1@C3N4. This understanding allows for designing a more selective ligand-free reaction pathway using the solvent and base to modulate the chemical environment of the active sites. We highlight the importance of environment-compatible surface tension, the creation of coordinatively available active sites, and the stabilization of partially reduced Pd centers, emphasizing the importance of mechanistic studies to advance the design of SACs in organic liquid phase reactions.

The fabrication and application of a triphasic reaction interface based on superwettability for improved reaction efficiency

This review concentrates on recent developments in the application of triphasic systems based on superwettability in photocatalysis, electrochemistry, and bioelectronics.

Photoactive cobalt-bipyridine electron mediator promotes reversible Li2O2 formation in irradiated Li-O2 battery

Photo-assisted charge/discharge has witnessed marked success in Li-O2 batteries (LOBs) to overcome the sluggish kinetics of triphasic reactions at the cathode, but challenges remain to develop high-efficiency but low-cost photocathode catalysts. Herein, a photoactive electron mediator is applied, for the first time, as bifunctional photocathode catalyst in solar-assisted LOBs. The facilely synthesized tris(2,2-bipyridine) cobalt(II) complex (Co-bpy) manifests good electrocatalytic activity in dark and high photoactivity under illumination, concertedly affording an superior charge/discharge voltage gap of 0.12 V and round-trip efficiency of 97%. Moreover, a significantly enhanced charge/discharge reversibility was attained under illumination and attributed to the light-induced amorphization of Li2O2 that further extends the cycle life. A two-circuit model is proposed to rationalize the better reduction of charge/discharge polarization at lower operating current density. This work not only extends the family of photocathode catalysts to small-molecule complexes, but also offers new insights into the mechanism of photoenergy storage in LOBs.

Catalytic Reductive Alkylation of Amines in Batch and Microflow Conditions Using a Silicon-Wafer-Based Palladium Nanocatalyst.

We describe the development of the catalytic reductive alkylation of amines with aldehydes under the atmospheric pressure of H2 using a brush-like silicon-nanostructure-supported palladium nanoparticle composite (SiNS–Pd) as a silicon-wafer-based reusable heterogeneous catalyst. The present reaction of primary and secondary amines with various aliphatic and aromatic aldehydes in the presence of the catalyst (0.02–0.05 mol % Pd) gave the corresponding secondary and tertiary amines including Lomerizine and Aticaprant in a 68% quantitative yield without overalkylation. We also designed and fabricated a flow device equipped with SiNS–Pd for microflow reactions, which was applied to the gas–liquid–solid triphasic reaction system (i.e., H2 gas, a substrate solution, and a solid catalyst). A multigram-scale reaction of aniline and benzaldehyde was demonstrated to obtain N-benzylaniline (ca. 4 g/day), in which the internal volume of the flow channel was 43 μL, the residence time was approximately 1 s, and the turnover number (TON) reached 4.0 × 104 in a continuous 24 h run (1.7 × 103 h–1; 0.50 s–1).

One-step eantioselective bioresolution for (S)-2-chlorophenylglycine methyl ester catalyzed by the immobilized Protease 6SD on multi-walled carbon nanotubes in a triphasic system

(S)-2-chlorophenylglycine methyl ester ((S)-1) is a key chiral building block of clopidogrel, which is a widely administered antiaggregatory and antithrombotic drug. Herein, Protease 6SD was covalently immobilized on multi-walled carbon nanotubes (MWCNT), and the as-prepared immobilizate P-6SD@NH2-MWCNT was applied in the enantioselective resolution of (R,S)-1 to yield (S)-1. In order to overcome the poor solubility of (R,S)-1 in aqueous solution, a novel triphasic reaction system constituting P-6SD@NH2-MWCNT, aqueous phase and methyl tert-butyl ether (MTBE) as the organic phase was constructed, which simultaneously improved the substrate solubility and the immobilizate recyclability. Under the optimized reaction conditions, P-6SD@NH2-MWCNT catalyzed 10 mM (R,S)-1 for 2 h, yielding optically pure (S)-1 (>99.0 % ees) with 70.74 % conversion of the (R,S)-1. Moreover, P-6SD@NH2-MWCNT can be reused for 15 batches, displaying an exquisite recycling performance. It is for the first time that enantiomerically pure (S)-1 was successfully synthesized by protease-catalyzed one-step resolution.

Formalization of the kinetics for autocatalytic dissolutions. Focus on the dissolution of uranium dioxide in nitric medium

Uranium dioxide dissolution in nitric acid is a complex reaction. On the one hand, the dissolution produces nitrous oxides (NOX ), which makes it a triphasic reaction. On the other hand, one of the products accelerates the kinetic rate; the reaction is hence called autocatalytic. The kinetics for these kinds of reactions need to be formalized in order to optimize and design innovative dissolution reactors. In this work, the kinetics rates have been measured by optical microscopy using a single particle approach. The advantages of this analytical technique are an easier management of species transport in solution and a precise following of the dissolution rate. The global rate is well described by a mechanism considering two steps: a non-catalyzed reaction, where the catalyst concentration has no influence on the dissolution rate, and a catalyzed reaction. The mass transfer rate of the catalyst was quantified in order to discriminate when the reaction was influenced by catalyst accumulated in the boundary layer or uncatalyzed. This first approximation described well the sigmoid dissolution curve profile. Moreover, experiments showed that solutions filled with catalyst proved to lose reactivity over time. Results pointed out that the higher the liquid-gas exchanges, the faster the kinetic rate decreases with time. Thus, it was demonstrated, for the first time, that there is a link between catalyst and nitrous oxides. The outcome of this study leads to new ways for improving the design of dissolvers. Gas-liquid exchanges are indeed a lever to impact dissolution rates. Temperature and catalyst concentration can be optimized to reduce residence times in dissolvers.

Molecular Transformation, Diffusion, and Assembling into Three-Dimensional Freestanding Tube Arrays via a Triphasic Reaction.

Converting nitrobenzene to freestanding polyaniline tube arrays has been successfully carried out in a "water-oil-water" triphasic reaction system, where catalytic reduction of nitrobenzene to aniline and aniline polymerization reactions were synergistically integrated. With optimized control over molecular diffusion and reaction at separate solid/liquid and liquid/liquid interfaces, polyaniline nanostructures could be synthesized with different morphologies. The paired molecular diffusion and reaction rate is revealed as the dominating factor that determines the feasibility of the reaction system to produce a patterned array structure. Slow molecular diffusion leads to a better ordered three-dimensional (3D) assembling structure. This work demonstrates a new approach to control 3D assembling structures with integrated control on diffusion and reaction across multiple liquid/liquid interfaces.

Novelties of selective triphasic synthesis of bis-(p-chlorobenzyl) sulfide using hydrogen sulfide and reusable phase transfer catalyst

The present investigation is based on the advancement in hydrogen sulfide (H2S) capture and utilization (HSCU). Commercially H2S is absorbed efficiently using alkanolamines such as methyldiethanolamine (MDEA). Aqueous H2S-rich MDEA is proposed to act as a sulfiding agent for aromatic halides such as p-chlorobenzyl chloride (p-CBC) to synthesize value-added thioethers. The objective of the present investigation is to synthesize bis-(p-chlorobenzyl) sulfide (BPCBS), a value-added thioether, selectively using p-CBC and H2S-laden aqueous MDEA. For the immiscible bi-phasic system, reusable solid phase transfer catalyst, polymer-bound tributylmethylammonium chloride (PBTBMAC) was employed under liquid-liquid-solid (L-L-S) mode in the presence of solvent toluene to enhance the reaction rate and product selectivity. Full conversion of p-CBC was obtained with 100% selectivity towards the desired product BPCBS at optimized specific level of process parameters. The catalyst has shown substantial activity even after three times of reuse, which leads to waste minimization and economic benefits. A generalized empirical kinetic model was developed and successfully validated against the experimental results. The triphasic reaction thus leads to process intensification, waste minimization and selectivity enhancement. The process can be utilized as an alternative to many other HSCU processes to utilize the sour gas in synthesizing value-added chemicals.

Confined molecular motion across liquid/liquid interfaces in a triphasic reaction towards free-standing conductive polymer tube arrays

Freestanding conductive polymer tube arrays can be synthesized by synergistically integrating diffusion and reaction control at separate liquid/liquid interfaces without using substrates or templates.

Vacuum gas oil hydrocracking performance of bifunctional Mo/Y zeolite catalysts in a semi-batch reactor

A new approach has been developed to characterize bifunctional catalysts in a complex matrix of hydrotreated vacuum gas oil using a batch reactor test. Triphasic reactions were carried out in a reactor equipped with a stationary basket, hydrogen injection and products sampling systems. Bifunctional catalysts containing different relative amounts of alumina-supported NiMo sulfide and zeolite were tested at 400°C under 120 bars over different reaction times. The repeatability of the test conditions was validated and the lack of mass transfer limitations at phase interfaces was confirmed. Gas and liquid samples were analyzed by one and two-dimensional gas chromatography (GC×GC) respectively to obtain quantitative distributions of linear and branched paraffins, naphthenes and aromatics. The details of the products distribution provided by chromatography were explained using mechanisms of bifunctional catalysis. It has been established that the limiting step defining the total conversion is the scission of the hydrocarbon chains on acid sites of the zeolite. The increase of the molybdenum to zeolite ratio provided an improvement of middle distillate selectivity.

Process intensification and waste minimization in liquid–liquid–liquid phase transfer catalyzed selective synthesis of mandelic acid

Conversion of biphasic reactions into triphasic reactions can lead to process intensification, waste minimization and selectivity enhancement. Unlike liquid–liquid (L–L) PTC, the Liquid–Liquid–Liquid phase transfer catalysis (L–L–L PTC) offers high order of intensification of rates of reaction and catalyst reuse. The rate of reaction is remarkably enhanced by the catalyst-rich middle phase, which is the main reaction phase. Separation of catalyst can be done easily and the separated catalyst can be reused several times by using L–L–L PTC. This leads to waste minimization and other benefits of Green Chemistry. Mandelic acid and its derivatives are used for their dual activities as antibacterial and anti-aging agents. In this work, mandelic acid was produced by L–L–L PTC reaction of dichlorocarbene with benzaldehyde. Dichlorocarbene was generated in situ by the reaction of chloroform and sodium hydroxide in the presence of poly ethylene glycol (PEG) 4000 as the catalyst. The selectivity to mandelic acid was 98%. The reaction mechanism and kinetics model were established to validate the experimental data.

ChemInform Abstract: Heterogeneous Catalytic Hydrogenation Reactions in Continuous‐Flow Reactors

AbstractReview: 232 refs.

Heterogeneous Catalytic Hydrogenation Reactions in Continuous‐Flow Reactors

Microreactor technology and continuous flow processing in general are key features in making organic synthesis both more economical and environmentally friendly. Heterogeneous catalytic hydrogenation reactions under continuous flow conditions offer significant benefits compared to batch processes which are related to the unique gas-liquid-solid triphasic reaction conditions present in these transformations. In this review article recent developments in continuous flow heterogeneous catalytic hydrogenation reactions using molecular hydrogen are summarized. Available flow hydrogenation techniques, reactors, commonly used catalysts and examples of synthetic applications with an emphasis on laboratory-scale flow hydrogenation reactions are presented.

Phase-Vanishing Reactions with PTFE (Teflon) as a Phase Screen

Phase-vanishing reactions are triphasic reactions, which involve a reagent, a liquid perfluoroalkane, and a substrate. In a phase-vanishing reaction with PTFE tape as the phase screen instead of a liquid perfluoroalkane, there is no limitation related to the density of a phase and the denser phase can be in the top layer. The reactions were faster compared to traditional PV reactions, and it was possible to carry out sequential and tandem reactions and reactions under a reflux.

Toward charge-neutral ‘soft scorpionates’: Coordination chemistry and Lewis acid promoted isomerization of tris(1-organo-imidazol-2-ylthio)methanes

Two tris(1-organo-imidazol-2-ylthio)methanes, HC(S-tim R) 3 (R = organo = methyl, tert-butyl), have been prepared by a triphasic reaction between chloroform, the appropriate heterocycle, and saturated aqueous solutions of Na 2CO 3, in the presence of a phase transfer agent, (NBu 4)(Br). These ligands have been characterized both spectroscopically and by single crystal X-ray diffraction. The reaction chemistry of these potentially N,N,N-tripodal ligands with AgBF 4 was also explored where simple 1:1 coordination complexes could be isolated from reactions performed in THF solution at room temperature. The derivative {Ag[HC(S-tim Me) 3]}(BF 4) was structurally characterized which showed that the ligand binds in a μ –κ 2 N, κ 1 N-mode to give a coordination polymer with an interesting layered supramolecular structure. Surprisingly, heating CH 3CN solutions of the silver complexes at reflux resulted in decomposition of the complex and concomitant isomerization of the ligands to give metal-free tris(3-organo-1-imidazole-2-thione)methane, HC(N-imt R) 3; the heretofore elusive charge-neutral analogues of the well-studied ‘soft scorpionate’ Tm R− anions. The solution isomerization of HC(S-tim R) 3 to HC(N-imt R) 3 was found to be general, occurring in a variety of solvents with any of a host of different Lewis acids [ para-toluenesulfonic acid, KPF 6, and M(CO) 5Br (M = Mn, Re)] but did not occur by heating in the absence of Lewis acid. The compound HC(N-imt Me) 3 exhibited unusually low solubility in common organic solvents. Single crystal X-ray diffraction of HC(N-imt Me) 3 revealed a remarkable honeycomb supramolecular structure with ca. 5 Å channels filled with solvent. The robust nature of this solid is a result of strong dipolar stacking interactions of molecules into polymer chains bolstered by concerted π–π and CH–π interactions involving the heterocycles, holding the chains together in the remaining two dimensions.

Thieme Chemistry Journal Awardees - Where are They Now? Catalytic Transport with an Amine Carrier in a Fluorous Triphasic Reaction

Several aromatic aldehydes are transported by a fluorous amine from one organic phase through a fluorous phase to another organic phase. The derived imines react with phenylhydrazine to immobilize the transported product as a hydrazone and release the amine for reuse. In this way, catalytic transport is accomplished for the first time.

The role of neat substrates in phase-vanishing and tandem phase-vanishing reactions

Phase-vanishing reactions are triphasic reactions, which involve a reagent, a liquid perfluoroalkane as a phase screen and a substrate. Aromatization, isomerization and halogenation of neat substrates under phase-vanishing conditions gave the expected products in good to excellent yields. In tandem single-phase–phase-vanishing reaction, two reactants, placed in the top phase, afforded the intermediate, which in a subsequent phase-vanishing reaction reacted with the reagent from the bottom phase to give the final product. The reaction worked well under solvent-free conditions on liquid substrates and intermediates. With solids, results were better if an additional solvent was employed.

Phase-vanishing halolactonization of neat substrates

Phase-vanishing reactions are triphasic reactions which involve a reagent, a liquid perfluoroalkane as a phase screen and a substrate. The perfluoroalkane does not dissolve any of the reactants and is used to separate them. Halolactonization of neat substrates under phase-vanishing conditions avoids use of both solvents and basic reaction conditions. Both γ,δ-alkenoic acids as well as the corresponding methyl esters are suitable substrates for phase-vanishing halolactonizations. The reaction works well both on solid and liquid substrates and the products are obtained in good to excellent yields, particularly in the case of rigid bicyclic systems. Bromine (Br2) and iodine monochloride (ICl) are suitable electrophiles for bromolactonization and iodolactonization, respectively. Although in some cases iodine gave satisfactory yields of the corresponding iodolactone, it is generally inferior to iodine monochloride.