Organic Acid Catalyst Research Articles

Tropylium-promoted prenylation reactions of phenols in continuous flow

2-Dimethylchroman framework occurs in many complex natural and synthetic compounds which show various types of biological activities such as antitumor, anticancer, antihypertensive, antioxidant and antithrombotic. Herein, we report an organocatalytic approach to the synthesis of 2,2-dimethylchromans where tropylium tetrafluoroborate was used as an organic Lewis acid catalyst for metal-free prenylation reactions of phenols. This method was amenable to continuous flow chemistry to enable an inexpensive pathway to access 2,2-dimethylchromans on multiple-gram scale with short reaction times, high efficiencies and simple product purification.

Unique acrylic resins with aromatic side chains by homopolymerization of cinnamic monomers

Cinnamic monomers, which are useful chemicals derived from biomass, contain α,β-unsaturated carbonyl groups with an aromatic ring at the β-position. Homopolymers synthesized by addition polymerization of these compounds are expected to be innovative bio-based polymer materials, as they have both polystyrene and polyacrylate structures. However, polymerization of these compounds by many methods is challenging, including by radical methods, owing to steric hindrance of the substituents and delocalization of electrons throughout the molecule via unsaturated π-bonding. Herein we report that homopolymers of these compounds with molecular weights (Mn) of ~18,100 g mol−1 and controlled polymer backbones can be synthesized by the group-transfer polymerization technique using organic acid catalysts. Additionally, these homopolymers are shown to have high heat resistance comparable to that of engineering plastics. Overall, these findings may open up possibilities for the convenient homopolymerization of cinnamic monomers to produce high-performance polymer materials.

Advances in nano-catalysts based biodiesel production from non-food feedstocks

This paper aims to examine the influence of various catalysts on biodiesel production, especially from non-food feedstocks with an ambition to optimize the catalytic biodiesel production. Homogenous acid catalysts are mainly used in biodiesel production, but they cannot be recovered and demand costly fuel purification as being corrosive. Similarly, enzyme catalysts are expensive in industrial-scale production of biodiesel. However, heterogeneous catalysts simplify the easy separation of product and by-products from the catalyst along with catalyst reusability and reduction of waste. Solid acid and base catalysts offer more advantages due to their non-toxicity, high surface area, reusability, higher stability, and the simplicity of purification. Solid base catalysts yield better activity than solid acid catalysts, however, they cannot esterify large amounts of free fatty acids (FFAs) in non-food feedstocks. The solid acid catalysts have the added advantages of being more tolerant to high amounts of FFAs and being able to simultaneously esterify FFAs and transesterify triglycerides in cheap feedstocks like waste cooking oil. Recently, an array of inorganic, organic and polymeric solid acid and nanomaterial-based catalysts have been developed using cheap feedstocks. However, the issues of low reactivity, small pore sizes, low stabilities, long reaction times, and high reaction temperatures still need to be solved. The developments of producing efficient, cheap, durable, and stable solid acid and nanomaterial-based catalysts have been critically reviewed in this study. Furthermore, the challenges and future perspectives of production of biodiesel and its industry growth have also been discussed.

Liquefaction of Kraft lignin using polyhydric alcohols and organic acids as catalysts for sustainable polyols production

In this work, three different organic acid catalysts, (acetic acid, lactic acid and citric acid), are proposed as an alternative to common catalysts used in the liquefaction process of Kraft lignin. These organic acids can easily be obtained from renewable resources and their application as a catalyst could allow the development of more environmentally friendly process in the production of biopolyols. The main objective of the present work was to study the influence of these organic acids catalysts and their concentration (3%, 6% and 9%, w/w) on the yield and properties of the obtained liquefied products. The results demonstrated that the type of the organic catalysts (85–88%) has not influenced the liquefaction yield of Kraft lignin. The highest hydroxyl number was obtained with lactic acid at 3% (660.08 mg KOH.g−1), whereas acetic acid provided the lowest acid number (0.80 mg KOH.g−1). The viscosity varied with catalysts (114.5–345.8-mPa.s) and the molecular weights of the liquefied products were in the range of 1459-1990 g.mol−1, lower than Kraft lignin (3866 g.mol−1). Moreover, volatile compounds showed traces of lignin derivatives and a few intermediate products from solvents. The low lignin signals observed by ATR-IR in the solid residue as well as the obtained liquefaction yields, suggested that most of the Kraft lignin has reacted during liquefaction process. The obtained results showed the potential value of these organic compounds to be used as renewable and more environmentally friendly catalysts in the liquefaction of Kraft lignin.

Succinyl-β-cyclodextrin–driven synthesis of a nitrogen-fused five-ring heterocycle using GBB-based [4 + 1] cycloaddition via supramolecular host–guest interactions

We synthesized a mono-succinyl-β-cyclodextrin (Suc-β-CD) and used it as a supramolecular organic acid catalyst for the synthesis of the therapeutically relevant indazolo[3′,2':2,3]imidazo[1,5-c]quinazolin-6(5H)-one (IIQ) via the Groebke–Blackburn–Bienaymé reaction (GBB). The Suc-β-CD was characterized using MALDI-TOF mass spectrometry, NMR spectroscopy, FT-IR spectroscopy, and SEM. A possible reaction mechanism via molecular complexation is suggested, based on 2D NMR (ROESY) spectroscopy, FT-IR spectroscopy, FE-SEM, and DSC analysis. The significant advantages of this atom-economical method include the simple single-step preparation of the catalyst, tolerance of a wide range of functional groups, easy catalyst recyclability, and absence of a tedious workup or purification; moreover, this method eschews the use of hazardous reagents/solvents.

Synthesis of Silica Xerogels Obtained in Organic Catalyst via Sol Gel Route

Citric acid is an organic acid catalyst and content carbon that is templated into silica network. The mixture between these materials is gratefully useful to tailor pore size of silica-carbon mixtures in the form of silica-carbon sols which robust and good hydrostability properties. This fabricated materials is applied for coated membrane layers (thin film) coated onto membrane substrates for water desalination. This study was aimed to utilize sol gel process to synthesize the functionalization of organic catalyst in silica matrices. Silica xerogels was prepared from TEOS (Tetraethyl orthosilicate) with a two-step organic acid and base catalyst via sol gel method. The hydrolysis and condensation reactions were applied within 3 hours at 50 °C. IR spectra shows that.

Synthesis of High Molecular Weight Poly(L-Lactic Acid)s by Direct Polycondensation with Organic Acids as Catalyst

In this study, high molecular weight (HMW) poly (l-lactic acid)s (PLLAs) were synthesized by direct polycondensation using organic acid catalysts alone in a nitrogen-controlled environment. The melting point and enthalpy of the pre-polymer produced by melt polycondensation increased as molecular weight grew during solid-state polycondensation. It was observed that the nitrogen-controlled external environment had lower molecular weight than air, but the low molecular weight tail was significantly reduced, as indicated by gel permeation chromatography. This is because it inhibited the reverse reaction by preventing the penetration of water inside the reactor. Also, the control of moisture improved the color of PLLA. The amount of organic acid catalyst used was 1 wt%, which was favorable for achieving HMW. Both p-toluenesulfonic acid and 4-ethylbenzenesulfonic acid are examples of organic acids that were able to produce HMW PLLA.

Effect of organic solvents and acidic catalysts on biodiesel yields from primary sewage sludge, and characterization of fuel properties

ABSTRACTBiodiesel is considered the most convenient biofuel, due to its direct use in existing combustion engines; however, its production is not economically optimal due to processes that utilize costly substrates, require high energy expenditure or achieve low biodiesel yields. We used primary sewage sludge for the production of biodiesel and compared yields at different temperatures (40, 50 and 60 °C) and with different organic solvents (chloroform, toluene and hexane), acid catalysts (HCl and H2SO4) and catalyst concentrations (3, 5 and 7%). A maximum of 18 wt% biodiesel was obtained using chloroform with 3% H2SO4 at 40 °C. The conversion efficiency of the primary sludge to biodiesel under these conditions was 86.4%. Based on the fatty acid methyl ester composition of the obtained biodiesel and measured fuel properties, it was deduced that fuel from primary sludge is more suitable for areas with warmer climates than ones that reach temperatures close to 0 °C. However, the fuel properties of the produced biodiesel were within the limits of accepted international standards. We conclude that production of biodiesel from primary sewage sludge under optimized conditions reduces the impact of the feedstock on the environment, decreases overall costs and produces fuel with acceptable properties.

Synthesis of Terpineol from α-Pinene Using Low-Price Acid Catalyst

This study aims to produce terpineol from α-pinene by direct one-stage hydration reaction mechanism. The study was focused to investigate the influence of organic acids and mixture acid catalyst between organic acid and phosphoric acid. Based on the experimental results and depending on the acid strength and affinity of catalyst to the carbocation mechanism, p-toluensulfonic acid was shown to have a better result compared to acetic and formic acid. The presence of phosphoric acid could boost the performance of acetic acid in term of acidity strength that increased the conversion of the reaction. The highest yield of terpineol from α-pinene in this hydration reaction in this study was 53.5 wt% using mixed phosphoric and acetic acid.

Tropylium cation now serves as an organocatalyst

The tropylium ion is a curious seven-membered aromatic ring (C7H7+) used in organic synthesis and as a ligand for metal complexes. Chemists led by T. Vinh Nguyen of the University of New South Wales Sydney have shown for the first time that tropylium salts can act as organic Lewis acid catalysts (Green Chem. 2017, DOI: 10.1039/c7gc01519d). Carbonyl compounds used in multistep reactions are often temporarily functionalized via acetalization reactions to mask their reactivity. This protection step typically relies on a metal salt Lewis acid catalyst. But residual metal can pose problems in purifying pharmaceutical products, leading to excessive use of solvents and generating waste. Organocatalysts that avoid metals are often a greener option. Building on their prior research on tropylium chemistry, Nguyen and coworkers reasoned that the carbocation with one positive charge delocalized over the conjugated seven-membered ring could serve as a “soft Lewis catalyst” for protective acetalizations of aldehydes

Exploring Closed-Shell Cationic Phenalenyl: From Catalysis to Spin Electronics.

The odd alternant hydrocarbon phenalenyl (PLY) can exist in three different forms, a closed-shell cation, an open-shell radical, and a closed-shell anion, using its nonbonding molecular orbital (NBMO). The chemistry of PLY-based molecules began more than five decades ago, and so far, the progress has mainly involved the open-shell neutral radical state. Over the last two decades, we have witnessed the evolution of a range of PLY-based radicals generating an array of multifunctional materials. However, it has been admitted that the practical applications of PLY radicals are greatly challenged by the low stability of the open-shell (radical) state. Recently, we took a different route to establish the utility of these PLY molecules using the closed-shell cationic state. In such a design, the closed-shell unit of PLY can readily accept free electrons, stabilizing in its NBMO upon generation of the open-shell state of the molecule. Thus, one can synthetically avoid the unstable open-shell state but still take advantage of this state by in situ generating the radical through external electron transfer or spin injection into the empty NBMO. It is worth noting that such approaches using closed-shell phenalenyl have been missing in the literature. This Account focuses on our recent developments using the closed-shell cationic state of the PLY molecule and its application in broad multidisciplinary areas spanning from catalysis to spin electronics. We describe how this concept has been utilized to develop a variety of homogeneous catalysts. For example, this concept was used in designing an iron(III) PLY-based electrocatalyst for a single-compartment H2O2 fuel cell, which delivered the best electrocatalytic activity among previously reported iron complexes, organometallic catalysts for various homogeneous organic transformations (hydroamination and polymerization), an organic Lewis acid catalyst for the ring opening of epoxides, and transition-metal-free C-H functionalization catalysts. Moreover, this concept of using the empty NBMO present in the closed-shell cationic state of the PLY moiety to capture electron(s) was further extended to an entirely different area of spin electronics to design a PLY-based spin-memory device, which worked by a spin-filtration mechanism using an organozinc compound based on a PLY backbone deposited over a ferromagnetic substrate. In this Account, we summarize our recent efforts to understand how this unexplored closed-shell state of the phenalenyl molecule, which has been known for over five decades, can be utilized in devising an array of materials that not only are important from an organometallic chemistry or organic chemistry point of view but also provide new understanding for device physics.

Tropylium salts as efficient organic Lewis acid catalysts for acetalization and transacetalization reactions in batch and flow

Tropylium salts were reported as organic-Lewis acids to efficiently catalyze acetalization reactions in batch and flow.

The Furfurylation of Wood: A Nanomechanical Study of Modified Wood Cells

Furfurylation of wood is of interest worldwide as an environmentally friendly modification process. It is widely assumed that low-molecular weight furfuryl alcohol (FA) can penetrate into wood cells and polymerize in-situ during the process, resulting in substantial improvement in the physical-mechanical properties and durability of wood. In this study, confocal laser scanning microscopy (CLSM) was used to visualize the microscopic distribution of polymerized FA resin in the Masson pine wood cavities, and a Nanoindenter was used to probe the mechanical properties of modified wood cells. The effects of catalysts (maleic anhydride and a mixed organic acid catalyst), FA concentration, curing time, and curing temperature on the nanomechanical properties of wood cell walls were investigated. An improvement in the indentation modulus and hardness of modified wood cells demonstrated indirectly but strongly that FA indeed penetrated wood cells during the modification process. Based on the results of the cell wall nanoindentation test, a combination of 50% furfuryl alcohol, 8 h curing time, and 95 °C curing temperature were proposed as the starting processing parameters for the development of a more practical and effective wood furfurylation process using a mixed organic acid catalyst.

Development of new high-throughput screening method to compare and to detect efficient catalysts for adhesive materials

Organotin compounds particularly dibutyltin dilaurate, are commonly used as catalysts in coatings or adhesive materials to crosslink silyl modified polymers. However, environmental concerns should lead before 2020 to ban organotin compounds due to their high toxicity. Thus new catalysts must be developed. According to the different types of catalytic systems, i.e. acid, basic or metal containing catalysts, a large variety of candidates should be tested. Thus a high-throughput screening (HTS) method could be an interesting tool for the detection of new efficient catalysts to substitute organotin compounds. We report a global HTS method, compatible with organic amino or acid catalysts libraries, as well as with metal-containing libraries.

Asymmetric Latent Carbocation Catalysis with Chiral Trityl Phosphate.

Stable carbocations such as tritylium ions have been widely explored as organic Lewis acid catalysts and reagents in organic synthesis. However, achieving asymmetric carbocation catalysis remains elusive ever since they were first identified over one century ago. The challenges mainly come from their limited compatibility, scarcity of chiral carbocations, as well as the extremely low barrier to racemization of chiral carbenium ions. We reported here a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation (e.g., acid, H-bonding, polar substrates) to form a catalytically active chiral ion pair for substrate activation and chiral induction. The latent strategy provides a solution for the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations.

Carbocation Lewis Acid Catalyzed Redox-Neutral α-C(sp3)H Arylation of Amines

The α-substituted nitrogen-containing heterocycles (N-heterocycles) like tetrahydroisoquinolines (THIQs) and piperidines are common in nature and are present as the key functional group in bioactive and pharmacologically active compounds. The two traditional approaches for the synthesis of α-substituted N-heterocycles are Pictet-Spengler condensa- tion and hydrogenation of the α-substituted cyclic imines. Recently, direct C(sp 3 )-H functionalization of N-heterocycles with various nucleophiles catalyzed by transition metal complex under the oxidants presents an atom-economic protocol without prior installation of activating group. However, new catalytic strategy or catalysts are still desirable in order to further address the use of excess oxidants and expensive transition metal complex. Stable carbocations, such as tritylium ions, have been widely used as organic Lewis acid catalysts and reagents in organic synthesis. In our studies, it was found that tritylium salts (Ph3C)(BArF) (10 mol%) in situ generated by Ph3CBr (0.02 mmol) and NaBArF (0.02 mmol) could promote the three com- ponent redox-neutral α-arylation of amines reaction with tetrahydroisoquinoline 2 (0.3 mmol), aldehyde 3 (0.2 mmol) and indole 4 (0.3 mmol) in toluene (1.0 mL) to afford the desired α-substituted N-heterocyclic compounds 5 in good yields (up to 99% yield) at ambient temperature to 50 ℃. To our satisfaction, a variety of differently substituted indoles 4a~4i could work well with tetrahydroisoquinoline 2 and 2,6-dichlorobenzaldehyde 3a to provide the corresponding α-substituted N-heterocyclic compounds 5a~5i in good to excellent yields at room temperature. When other substituted benzaldehydes 3b~3f were used, the reactions could also proceed smoothly to give the compounds 5j~5o with moderate yield (up to 66% yield) at 50 ℃. Moreover, we have also developed redox-neutral α-arylation of tetrahydroisoquinoline 2 with other aromatic nucleophile such as substituted phenol, β-naphthol and pyrrole under the optimal reaction conditions. Importantly, the model reaction, conducted in the presence of Na2CO3(1.0 equiv.) or 2,6-bis(tert-butyl) pyridine (0.5 equiv.) at room temperature in toluene also proceeded smoothly to give the desired adduct 5a with comparable yields (82% and 92% yield, respectively), which could exclude the possibility of free acid catalysis in this reaction.

Conversion of bamboo fiber into 5-hydroxymethylfurfural catalyzed by sulfamic acid with microwave assistance in biphasic system

The present work reports the conversion of lignocellulosic biomass into 5-hydroxymethylfurfural (HMF) catalyzed by solid organic acid catalyst with microwave heating in H2O/THF biphasic system. The 52.2% yield of HMF was achieved from the bamboo fiber degradation using NH2SO3H as catalyst at 180°C for 40min with 500Hz microwave heating. The results showed that HMF yield increased significantly with adding NaCl, which not only could effectively increase the HMF distribution coefficient between organic phase and water phase, but also can separate HMF from water phase to organic phase continuously. Moreover, the catalytic system also showed effectiveness to convert other raw lignocellulosic variants to HMF, including softwood, hardwood, and cotton in the optimal biphasic system.

ChemInform Abstract: Organic Acid Catalysts in Reactions of Lactones with Silicon Enolates.

By choosing the organic acid catalysts, the reaction of lactones with ketene silyl acetals results in selective formation of simple Mukaiyama aldol adducts or olefination products, which are formed by the subsequent elimination of a silanol from the adducts. That is, in the presence of acidic zwitterions, the reaction of lactones with ketene silyl acetals gives simple Mukaiyama aldol adducts in excellent yields. In contrast, the same reaction in the presence of a carbon acid catalyst brings about the formation of olefination products in a Z-selective manner.

Synthesis and Characterization of Poly(L-Lactic acid)/Clay Nanocomposite via Metal-Free Process

Biopolymer nanocomposite was synthesized using metal-free catalyst which is Montmorillonite-K10 as organic filler and acid catalyst for polymerization of L-Lactic acid. To evaluate the effect of Montmorillonite onto polymer properties, 1, 3 and 5% clay were used. Products were characterized using X-ray diffraction and transmission electron microscopy. Thermal parameters of products were investigated via differential scanning calorimeter and thermo-gravimetric analyzer. Thermal stability, degree of crystallinity, temperatures for glass transition, crystallization and melting of the nanocomposites were studied. Effect of clay onto molecular weight was investigated via gel permeation chromatography. It was found that properties of polymer were influenced by addition of clay.

Organic Acid Catalysts in Reactions of Lactones with Silicon Enolates

AbstractBy choosing the organic acid catalysts, the reaction of lactones with ketene silyl acetals results in selective formation of simple Mukaiyama aldol adducts or olefination products, which are formed by the subsequent elimination of a silanol from the adducts. That is, in the presence of acidic zwitterions, the reaction of lactones with ketene silyl acetals gives simple Mukaiyama aldol adducts in excellent yields. In contrast, the same reaction in the presence of a carbon acid catalyst brings about the formation of olefination products in a Z‐selective manner.