Salt Catalysts Research Articles

Unlocking the Anion Effect on Steerable Production of 5‐Hydroxymethylfurfural

AbstractHomogeneous metal salt catalysts play a pivotal role in industrial production of 5‐hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3 (74.0 mol %)>AlCl3 (60.8 mol %)>Al2(SO4)3 (35.2 mol %)>Al(NO3)3 (14.9 mol %). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close‐range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno‐economic process, we expect to provides theoretical guidance for high‐throughput screening of metal salt catalysts in industrial biorefinery.

Unlocking the Anion Effect on Steerable Production of 5-Hydroxymethylfurfural.

Homogeneous metal salt catalysts play a pivotal role in industrial production of 5-hydroxymethylfurfural (HMF). Herein, we first proposed the anion effect on steerable production of HMF using metal salts with different anions as catalyst in a biphasic system of tetrahydrofuran (THF)/NaCl aqueous solution (NaCl aq). Notably, the anions affected the catalytic activity of the metal salts, leading to an order of magnitude difference in the HMF yields, i.e., AlBr3 (74.0 mol %)>AlCl3 (60.8 mol %)>Al2(SO4)3 (35.2 mol %)>Al(NO3)3 (14.9 mol %). The anion effect on steerable production of HMF could be attributed to the proximity effect and electron tension. Anions form close-range interactions with glucose molecules by proximity effect to promote electron transfer, facilitating the isomerization of glucose to fructose. Besides, anions induce a reduction of the electron cloud density of glucose carbon atoms, generating electron tension that rapidly transforms glucose from the ground state to the transition state, thereby increasing the HMF yield. Based on the revelation of anions effect and evaluation of techno-economic process, we expect to provides theoretical guidance for high-throughput screening of metal salt catalysts in industrial biorefinery.

Influence of Reaction Conditions on the Yield of Supercritical Multicomponent Thermal Fluids

Supercritical multicomponent thermal fluid (scMCTF) is a novel medium with great potential for heavy oil thermal recovery. The production rate of scMCTF will affect the injection efficiency of thermal fluid, and then affect the development effect of thermal recovery. However, at present, there are few reports on the production rate of each component of scMCTF, and their understanding is not clear. According to the existing production rate data of supercritical water (scH2O) gasification products, based on the generation mechanism of scMCTF, the production rate of thermal fluid generation products under different generation conditions was calculated, and its influencing factors were identified. The results show the following: (1) The factors affecting the production rate of scMCTF generation products can be divided into three categories: reaction raw material factors, reaction condition factors, and catalytic factors. (2) The hydrocarbon number of raw material, reaction temperature, reaction time, and catalyst concentration were positively correlated with the production rate of the product. (3) The concentration of the reaction raw material is negatively correlated with the production rate of the product. The higher the concentration of the raw material is, the lower the concentration of H2O is, and the steam reforming reaction is inhibited, which leads to the decrease in the production rate. (4) The effect of reaction pressure and catalyst load on the product is not significant. (5) The reaction product production rate increased first and then decreased with the ratio of H2O to oil in the raw material emulsion and the ratio of preheated H2O to raw material discharge. (6) The effect of metal salt catalysts is relatively stable, and the catalytic effect of simple metal catalysts is significantly different under the action of different types of accelerators, so it is necessary to study the degree of synergization of different accelerators on the catalytic effect. The results can lay a foundation for the subsequent experimental and theoretical research design.

Poly (lactic acid)/Poly (butylene adipate-co-terephthalate) Films with Simultaneous High Oxygen Barrier and Fast Degradation Properties

Although poly (lactic acid) (PLA) is a good environmentally-friendly bio-degradable polymer which is used to substitute traditional petrochemical-based polymer packaging films, the barrier properties of PLA films are still insufficient for high-barrier packaging applications. In this study, oxygen scavenger hydroxyl-terminated polybutadiene (HTPB) and cobalt salt catalyst were incorporated into the PLA/poly (butylene adipate-co-terephthalate) (PLA/PBAT), followed by melting extrusion and three-layer co-extrusion blown film process to prepare the composite films. The oxygen permeability coefficient of the composite film combined with 6 wt% oxygen scavenger and 0.4 wt% catalyst was decreased significantly from 377.00 cc∙mil∙m-2∙day-1∙0.1MPa-1 to 0.98 cc∙mil∙m-2∙day-1∙0.1MPa-1, showing a remarkable enhancement of 384.69 times compared with the PLA/PBAT composite film. Meanwhile, the degradation behavior of the composite film was also accelerated, exhibiting a mass loss of nearly 60% of the original mass after seven days of degradation in an alkaline environment, whereas PLA/PBAT composite film only showed a mass loss of 32%. This work has successfully prepared PLA/PBAT composite films with simultaneously improved oxygen barrier property and degradation behavior, which has great potential for high-demanding green chemistry packaging industries, including food, agricultural, and military packaging.

Ketalization mechanism of glycerol to biobased glycerol levulinate ketal over HZSM-5: A combined experimental and theoretical study

Methyl levulinate ketal (MLK) is a novel biobased chemical derived from glycerol via ketalization, and exploring its synthesis mechanism is of great significance for the high-value utilization of biomass resources. In this study, the ketalization reaction of glycerol was evaluated using the MLK yield calculated by the GC internal standard method. The acidity of HZSM-5 was determined by NH3-TPD. The catalyst screening experiments demonstrated that HZSM-5 in zeolites and AlCl3 in metal salts exhibited high catalytic activity in the synthesis of MLK. Furthermore, the kinetic results indicated that the HZSM-5 zeolite catalyst exhibited a lower apparent activation energy in catalyzing the synthesis of MLK compared to the metal salt catalyst AlCl3. The ketalization reactions of levulinate and glycerol catalyzed by different types of acidic sites in HZSM-5 were then investigated using the density functional theory method. A comprehensive catalytic path, free energy changes, intermediates, and transition state structures were proposed. Furthermore, the free energy barriers of ethyl levulinate ketal and butyl levulinate ketal catalyzed by HZSM-5 were calculated, and the difference between the steric hindrance effect and the electronic effect of alkyl in levulinate was compared. This study enhances the understanding of ketalization reactions and will be useful in future catalyst design studies.

Insight into catalytic effects of alkali metal salts addition on bamboo and cellulose pyrolysis

Alkali metal compounds have vital influence on biomass pyrolysis conversion. In this study, cellulose, and bamboo catalytic pyrolysis with different alkali metal salts catalysts (KCl, K2SO4, K2CO3, NaCl, Na2SO4, and Na2CO3) were investigated in the fixed-bed reaction system. The effects of cations (K+ and Na+) and anions (Cl-, SO42−, and CO32-) on the evolution properties of biochar, bio-oil, and gas products were explored under both in-situ and ex-situ catalytic pyrolysis. Results showed that alkali metal salts facilitated the yields of biochar and gases at the expense of that of bio-oil. Alkali metal chloride and sulfate showed a weaker catalytic effect, while alkali metal carbonate greatly promoted the generation of gas products and increased the condensation degree of biochar. With the addition of K2CO3 and Na2CO3, cyclopentanones content was over 50% from cellulose catalytic pyrolysis, and phenols content (mainly alkylphenols) reached over 80% from bamboo catalytic pyrolysis. Moreover, solid-solid catalytic reactions with K2CO3 and Na2CO3 catalysts had an important role in strikingly promoting conversion of pyrolysis products, and the solid-solid and gas-solid catalytic reactions with alkali metal carbonate catalysts were stronger than those with alkali metal chloride and sulfate catalysts. Furthermore, the possible catalytic pyrolysis mechanism of alkali metal salts on biomass pyrolysis was proposed, which is important to the high-value utilization of biomass.

Production of diphenolic acid from bio-levulinic acid over MCF supported bimetallic phosphotungstic acid as catalyst: Enhancement in rate and selectivity under microwave irradiation

The para-isomer of diphenolic acid is widely accepted as a bio-based polymer precursor and a sustainable substitute for bisphenol A (BPA). In the current work, a bimetallic dodecatungstophosphoric acid salt catalyst supported on mesocellular foam (MCF) was employed to condense bio-derived levulinic acid and phenol under solvent-free conditions in the presence of microwaves to enhance rates of reaction, conversion and selectivity. Various parameters affecting conversion and selectivity were systematically studied. A study was done to investigate the factors that affect the reaction rate. A kinetic model was derived, and reaction mechanism proposed. The reaction proceeds with a second-order kinetics with an activation energy of 10.17 Kcal/mol and exhibits the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism. The catalyst was robust and could be repeatedly used. The overall process showed microwaves coupled with the new catalyst improved efficiency, selectivity, and sustainability in synthesizing diphenolic acid (DPA), offering new insights into the process.

Organocatalyzed Asymmetric Conjugate Addition of Alcohols to β-Fluoroalkyl Vinylsulfones by Bifunctional Phosphonium Salt Catalyst.

Chiral secondary alcohols, serving as essential structural motifs, hold significant potential for diverse applications. The exploration of effective synthetic strategies toward these compounds is both attractive and challenging. Herein, we present an asymmetric oxa-Michael reaction involving aliphatic alcohols as nucleophiles and β-fluoroalkyl vinylsulfones catalyzed by bifunctional phosphonium salt (BPS), achieving high yields and excellent enantioselectivities (up to 98 % yield and 98 % ee). Additionally, a sequential process including asymmetric oxa-Michael and debenzylation, facilitated by BPS/Lewis acid cooperation, was revealed for synthesizing diverse chiral secondary alcohol compounds in high yields (81-88 %) with consistent stereoselectivities. Furthermore, mechanistic explorations and subsequent results unveiled that the enantioselectivity originates from hydrogen-bonding and ion-pair interactions between the BPS catalyst and the substrates.

2-Pyridone-Directed CuII-Catalyzed General Method of C(sp2)-H Activation for C-S, C-Se, and C-N Cross-Coupling: Easy Access to Aryl Thioethers, Selenide Ethers, and Sulfonamides and DFT Study.

We have demonstrated N-substituted 2-pyridones as an N,O-directing group for selective C(sp2)-H-activated thiolation, selenylation, and sulfonamidation of ortho C-H bonds of benzamides. This method utilizes a cost-effective Cu(II)-salt catalyst instead of precious metal catalysts, achieving high yields, including gram-scale synthesis and excellent functional group tolerance. We applied this protocol to access 30 different compounds with high yields, demonstrating thiolation of fluorine-substituted benzamides as well. Density functional theory (DFT) calculations support the mechanism, including acetate-supported concerted metalation deprotonation (CMD) steps and the unique role of dimethyl sulfoxide (DMSO) solvent. The facile synthesis of pharmaceutically important sulfonamides and other compounds highlights the method's potential in chemistry and medicinal chemistry.

Chiral Quaternary Ammonium Salt‐Catalyzed Enantioselective Addition Reactions of Hydantoins

AbstractWe herein report a protocol for the asymmetric 1,4‐addition of hydantoins to various Michael acceptors by utilizing Cinchona alkaloid‐based chiral quaternary ammonium salt catalysts. Various products were obtained with moderate to good enantioselectivities and accompanying computational investigations helped to identify key interactions responsible for the observed selectivity. DFT calculations along with non‐covalent interaction plots reveal the presence of numerous stabilizing non‐classical hydrogen bonding interactions along with other non‐covalent interactions between the chiral quaternary ammonium salt and hydantoin molecule in the C−C bond forming transition states leading to the formation of the products. In addition, a first proof‐of‐concept for an analogous a‐sulfanylation reaction, albeit with poor selectivity, is reported as well.

Catalytic effect of metal salts on deoxygenation and aromatization reaction during pressurized pyrolysis of corncob waste at mild temperatures

Converting biomass to high quality bio-char with high carbon solidification at low energy consumption can greatly promote the application of biomass to alternative coal. Metal salts have been confirmed to enhance carbonization and dehydration during traditional pyrolysis and hydrothermal conversion, whereas the catalytic deoxygenation and aromatization mechanisms during dry mild pyrolysis in the presence of pressure are currently unclear. A mild gas-pressurized pyrolysis assisted by metal salts catalysts at 200–300 °C was proposed in this work. The effects of catalysts on three-phase products as well as synergistic catalytic reaction mechanism were studied. Results indicated that CaCl2, ZnCl2 promoted carbon fixation rates by 19.77 % and 26.89 %, and ZnCl2, KCl could remove oxygen content by 11.45 % and 6.56 % (wt.%, dry ash free basis). ZnCl2 exhibited the best deoxygenation and aromatization effect. With ZnCl2 catalysis at 280 °C, the volatile content reduced to 37.25 %, and O/C, H/C values decreased by 19.05 % and 11.25 %, achieving coking coal-like quality. FTIR and NMR results implied that oxygen-containing functional groups were removed even more rapidly under the catalysis of ZnCl2, facilitating the rearrangement of O-alkyl C and aliphatic C into aromatic C, exhibiting a higher aromatization degree in semi-char. Moreover, CH4 and H2 increased in gas products catalyzed by ZnCl2, while C2H4 and C2H6 decreased. Pressure inhibited the escape of small molecule gas volatiles, making them easily adsorbed on surfaces of molecular structures for secondary reactions. Under the action of the [ZnOZn]2+ acid sites, alkanes underwent dehydrogenation activation to yield H2, and demethylation activation to generate CH4, followed by cyclization reaction. The upgrading promotions of biomass were caused by the synergistic effect of pressure and ZnCl2 catalysis.

Efficacy of the Ionic Liquid 1,4-Bis(carboxymethyl)piperazine-1,4-diium Chloride as a Catalyst for Xanthenes/Acridines Synthesis: Spectral Characterization, X-ray Structure, and Nematicidal Activity

In this research paper, a straightforward and efficient approach for synthesizing the 1,4-bis(carboxymethyl)piperazine-1,4-diium chloride [BCMPZ][2Cl] ionic liquid salt (IL) catalyst is introduced. The morphology, thermal stability, and functionality of the synthesized [BCMPZ][2Cl] IL were characterized using spectroscopic, electron microscopy, and thermal analysis. A density functional theory (DFT) study, including infrared spectroscopy (IR), powder X-ray diffraction (PXRD), Thermogravimetric analysis (TGA), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM with EDX), were employed. The well-characterized ionic liquid (IL) assisted as a catalyst in the synthesis reaction involving aldehydes, dimidone, and arylamine to yield 1,8-dioxo-octahydroxanthene and 1,8-dioxo-9-aryl-10-aryl-decahydroacridine derivatives (3a-i and 4a-b) with high yields, getting up to 97%. The structure of the synthesized molecules was confirmed through various physicochemical techniques, including 1H and 13C NMR, IR, elemental analysis, and MS. X-ray single crystal diffraction techniques were also used to elucidate the geometry of one of the synthesized molecules (3f). The heterogeneous catalyst (IL) used in the synthesis of the molecules was successfully recycled and reused without additional treatment of purification. The synthesized xanthines were found to inhibit nematode activity, thus they may act as potential nematicides for crop protection. The present study also identified five different compounds that were effective against Meloidogyne incognita. Compound 3a reduced nematode egg hatching by 65% at a concentration of 2000 ppm, which was the highest efficacy in tested compounds. Compound 3c had a mortality rate of 80% against nematodes. Overall, the developed method has many advantages, including fast reaction time, economic efficiency, and minimal catalyst loading, making it a promising method for future research in the field of heterocycle synthesis and crop protection.

Synergistically activating nucleophile strategy enabled organocatalytic asymmetric P-addition of cyclic imines.

Herein, we present an attractive organocatalytic asymmetric addition of P-nucleophiles to five-membered cyclic N-sulfonyl imines facilitated by phosphonium salt catalysis, enabling the highly enantioselective synthesis of tri- and tetra-substituted cyclic phosphorus-containing benzosultams. With this protocol, various cyclic α-aminophosphonates were efficiently synthesized with high yields and exceptional enantioselectivities (up to >99% ee) under mild reaction conditions. The utility and practicality of this method were demonstrated through gram-scale reactions and straightforward elaborations. Notably, the success of this approach relies on the deliberate selection of a synergistic organocatalytic system, which helps circumvent foreseeable side effects while handling secondary phosphine oxides (SPOs). Systematic mechanistic studies, incorporating experiments and DFT calculations, have revealed the critical importance of judiciously selecting bifunctional phosphonium salt catalysts for effectively activating P-nucleophiles while stereoselectively controlling the P-attack process.

Controlled ring-opening copolymerization of epoxides and cyclic anhydrides through bifunctional thiourea–quaternary ammonium salt catalysts

Bifunctional thiourea–quaternary ammonium salt catalysts exhibited significantly higher activity over a two-component system with a similar structure at a low catalyst loading for the ring-opening copolymerization of epoxides and cyclic anhydrides.

Towards an asymmetric β-selective addition of azlactones to allenoates.

We herein report the asymmetric organocatalytic addition of azlactones to allenoates. Upon using chiral quaternary ammonium salt catalysts, i.e., Maruoka's binaphthyl-based spirocyclic ammonium salts, the addition of various azlactones to allenoates proceeds in a β-selective manner with moderate levels of enantioselectivities (up to 83:17 er). Furthermore, the obtained products can be successfully engaged in nucleophilic ring opening reactions, thus giving highly functionalized α-amino acid derivatives.

Study on the Morphological Mechanism of MoS2 Growth by NaCl‐Assisted Chemical Vapor Deposition

AbstractMonolayer MoS2 is a two‐dimensional transition‐metal dichalcogenide (TMD), and its atomic‐level thickness makes it an appealing research target in beyond‐silicon devices. Future practical uses are intimately related to controllable synthesis of materials at present, and salt‐assisted chemical vapor deposition (SA‐CVD) offers a promising way. However, the specific growth mechanism of alkali metal salts on MoS2 crystal development and their influence on optoelectronic characteristics of the as‐grown MoS2 crystals is not fully identified. Here, based on large amount experiments, we present a vapor‐liquid‐solid (VLS) edge‐adsorbed growth model for synthesizing MoS2 nanoflakes, emphasizing the edge‐adsorbed phenomena of the alkali metal element Na in regulating MoS2 crystal shape. Through controlling flow rate of carrier gas, the MoS2 defective morphology can be effectively suppressed. This study contributes to a better understanding of the role of alkali metal halide salts in TMD development by providing experimental and theoretical evidence, which is critical for synthesizing high quality TMD by alkali metal halide salts catalyst.

Prospective life cycle assessment of poly (ethylene terephthalate) upcycling via chemoselective depolymerization

Chemical upcycling of non-biodegradable polymers can shift the current linear plastic economy towards circular patterns. This work studies the environmental impacts of poly(ethylene terephthalate) (PET) upcycling given its extensive use in packaging, textile and automotive industries. A prospective gate-to-gate life cycle assessment is applied to five PET upcycling processes representative of common chemoselective depolymerization strategies. Laboratory-scale upcycling is scaled-up for processes depolymerizing 1 kg of post-consumer PET. With a global warming potential from 4.3 to 5.8 kg·CO2 equiv. per kg of upcycled postconsumer PET, Glycolysis-PG using propylene glycol and a manganese acetate catalyst, Aminolysis and Hydrogenolysis processes bear the lowest global warming potential. On the contrary, the Glycolysis-EG process that uses ethylene glycol (EG) and a protic ionic salt catalyst has the largest global warming potential of 91.3 kg·CO2 equiv. per kilo of PET. These differences are driven by variabilities in the energy and solvent consumption, and the presence of catalysts. Two sensitivity analyses focused on EG recirculation and ethylene carbonate production are performed to explore environmentally friendlier processes. Overall, this work highlights the environmental hotspots during postconsumer PET upcycling, guiding the implementation of sustainable approaches in polymer recycling.

One‐pot Multicomponent Synthesis of Novel Chromene Derivatives Using New Organic Phosphate Salt Catalysts

AbstractA new method for synthesizing chromene derivatives as an essential class of heterocyclic compounds has been reported. This research described synthesizing and identifying three new organic salt catalysts based on phosphate moieties. Among the synthesized new phosphate‐based organic salt catalysts, disodium ethyl (phenyl) amino phosphate (DSEAP) plays an essential role and reusable catalyst for the preparation of chromene derivatives under different reaction conditions following the principles of green chemistry. Cost‐effectiveness, non‐toxicity and easy availability are among the salient features of this environmentally friendly catalyst. Furthermore, the catalyst was satisfactorily recycled up to four times without significant performance degradation in the yield of synthesized chromenes. X‐ray diffraction (XRD), infrared spectroscopy (FT‐IR), thermal gravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to illustrate the structural and morphologic characteristics of the catalysts. Some synthesized chromene derivatives, including 4I and 4P, showed good antibacterial and biological antioxidant activity compared to the standard drug, respectively. In this research, DSEAP was used as a heterogeneous catalyst in performing one‐pot 3MCRs of aryl aldehyde, an active methylene group e. g. ethyl acetoacetate or diethyl malonate and 5,5‐dimethyl‐1,3‐cyclohexanedione.

Chiral Hypoiodite Salt Catalysts for Enantioselective Oxidative Transformations

AbstractIodine and its hypervalent derivatives have emerged as versatile and environmentally friendly oxidative reagents in organic synthesis, offering efficient ways to form new bonds. However, the use of hypervalent iodine reagents is challenging, as they are unstable, potentially explosive, and costly. Therefore, hypoiodite species derived from onium iodites using safe and inexpensive oxidants are considered more promising for facilitating oxidative transformations. Nevertheless, applications of such catalytic systems are still limited in scope, especially for asymmetric reactions. In this concept paper, we described recent progress in chiral hypoiodite‐catalyzed enantioselective oxidative bond‐forming reactions, focusing on carbon–oxygen, carbon–nitrogen, and carbon–carbon bond formation reactions using ammonium and guanidinium salts as onium iodites.

Design and Application of Peptide‐Mimic Phosphonium Salt Catalysts in Asymmetric Synthesis

AbstractChiral phosphonium salt catalysis, traditionally classified as a type of phase transfer catalysis, has proven to be a powerful strategy for the stereoselective preparation of diverse optically active molecules. However, there still remain numerous forbidding issues of reactivity and selectivity in such well‐known organocatalysis system. Accordingly, the development of new and high‐performance phosphonium salt catalysts with unique chiral backbones is highly desirable, yet challenging. This Minireview describes the prominent endeavours in the development of a new family of chiral peptide‐mimic phosphonium salt catalysts with multiple hydrogen‐bonding donors and their applications in a plethora of enantioselective synthesis during the past few years. Hopefully, this minireview will pave a way for further developing much more efficient and privileged chiral ligands/catalysts featuring exclusively catalytic ability in asymmetric synthesis.