Acid-catalyzed Conditions Research Articles

Acid-catalyzed conversion of sesamolin to sesamol: Kinetics and reaction mechanism based on density functional theory.

Sesamol is a significant lignan in sesame oil, which can be converted from sesamolin under acid-catalyzed conditions. The effects of several factors on the conversion of sesamolin to sesamol under acid-catalyzed conditions were investigated. The conversion kinetics were studied and the relevant conversion mechanism was revealed by density functional theory (DFT). The results indicated that catalyst dosage and substrate concentration had significant effects on the yield of sesamol. The conversion of sesamolin conformed to the characteristics of a first-order kinetics reaction within the range of 50-70°C. The activation energy of the reaction was 35.78±1.21kJ/mol. The energy barrier to be crossed for the formation of intermediates in generating sesamol was 237.83kJ/mol; the energy barrier to be overcome for the formation of intermediates in generating sesaminol was 266.95kJ/mol. This study provides information relevant to increasing the percentage of sesamol in processed sesame oil.

ЦИКЛИЧЕСКИЕ АЦЕТАЛИ И КЕТАЛИ – ЦЕННЫЕ ПРЕКУРСОРЫ В ОРГАНИЧЕСКОМ СИНТЕЗЕ

Acetals and ketals are a latent form of carbonyl compounds and important intermediates in synthetic and carbohydrate chemistry. There is probably not a single scheme for the synthesis of biologically active compounds in which the technique with diol protection of the carbonyl function has not been used at least once. This is due to the convenience of both setting up the protective group and removing it. Classical synthesis involves the addition of alcohols to aldehydes and ketones in slightly acidic or basic solutions. Before the stage of formation of hemiacetals, the reaction is catalyzed by both acids and bases. However, the conversion of a hemiacetal to an ace- tal occurs only under conditions of acid catalysis and proceeds via the SN1 mechanism through the stage of for- mation of a carbocation from the intermediate hemiacetal. Cyclic acetals and ketals can be classified according to the structure of the ketal center: external (1,3- dioxolane and 1,3-dioxane) and internal. Internal ketals and acetals are cyclic compounds formed from 1,4- and 1,5-oxyaldehydes and oxyketones in the presence of anhydrous acids. Prominent representatives of internal ketals and acetals are carbohydrates and bicyclic ketals containing an adjacent C-C bond at the site of which there is a ketal center, for example, chromanes – bicyclic ketals or hemiketals. Optically active cyclic acetals and ketals are prepared by reacting aldehydes or ketones with chiral diols in three ways. The classic method is to boil the corresponding aldehyde or ketone with alcohol, azeotropically re- moving water in a Dean-Stark apparatus. In α,-enones, to protect the keto group and eliminate the side reaction – migration of the double bond, an alternative approach is used, the Noyori method, which involves the use of disilyl ethers of chiral alcohols. In the case when the initial carbonyl compounds are unstable or are in the form of dimethoxyketals or acetals, the method of transketalization or acetalization is used. Chiral diols are used as alco- hol components, for example, 2,3-butanediols, 2,4-pentanediols, hydrobenzoins. They are capable of attaching nucleophiles and are prone to various rearrangements at acetal and ketal cen- ters. The value of bicyclic hemiketals lies in their use in the synthesis of lactones of various ring sizes. This re- view is devoted to these and some other chemical transformations of cyclic acetals and ketals.

Phenothiazine Embedded Dithiasmaragdyrins.

Two different types of novel phenothiazine-embedded dithiasmaragdyrins containing one phenothiazine ring, two thiophene rings and two pyrrole rings connected via three meso carbons and two direct bonds in the macrocyclic framework were synthesized over the sequence of synthetic steps starting with phenothiazine. Three examples of phenothiazine-embedded dithiasmaragdyrins were synthesized by condensing appropriate phenothiazine-based pentapyrrane with pentafluorobenzaldehyde and two examples of phenothiazine sulfone embedded dithiasmaragdyrins were synthesized by condensing phenothiazine-based diol with appropriate meso-aryl dipyrromethane under mild acid-catalysed conditions. 1D&2D NMR studies revealed that the thiophene rings adopted inverted orientation in phenothiazine sulfone embedded dithiasmaragdyrins whereas in phenothiazine-embedded dithiasmaragdyrins, the thiophene rings were in normal orientation. Both types of macrocycles exhibit nonaromatic absorption features and showed panchochromic absorption features in its neutral and protonated forms. The electrochemical studies indicated that the phenothiazine-embedded dithiasmaragdyrins were more electron-rich compared to phenothiazine sulfone embedded dithiasmaragdyrins. DFT studies revealed that both types of dithiasmaragdyrins exhibit significantly distorted structures and TD-DFT studies support the experimental observations.

Microwave-Assisted Synthesis of 5-Substituted 3-Amino-1,2,4-triazoles from Aminoguanidine Bicarbonate and Carboxylic Acids

The effect of the molar ratio between reagents, reaction time and temperature on the yield of 5-substituted 3-amino-1,2,4-triazoles obtained by the direct condensation of carboxylic acids with aminoguanidine bicarbonate under acid catalysis conditions was studied. As a result, a general green straightforward synthesis of the title compounds bearing aliphatic substituents or a phenyl ring was developed using sealed reaction vials under controlled microwave synthesis conditions that are suitable for the application of volatile starting carboxylic acids. Our straightforward synthetic method proposed in this work increases the synthetic accessibility of these widely used building blocks and therefore is able to significantly expand the structural diversity of compounds containing a triazole moiety for the needs of drug discovery.

Synthesis and Studies of Symmetrical DitelluraCalix[6]phyrin(1.1.1.1.1.1)s.

Rare examples of ditellura calix[6]phyrin(1.1.1.1.1.1)s containing two telluratripyrrin units connected via two sp3 carbons were synthesized by condensing 16-telluratripyrrane with a cyclic ketone in CH2Cl2 under acid-catalyzed conditions. The X-ray structure obtained for meso-cyclohexyl-substituted calix[6]phyrin revealed that the macrocycle resembles a roof-like shape with two telluratripyrrin units that are perpendicular to each other, whereas the DFT-optimized structure of meso-cyclopentyl-substituted calix[6]phyrin showed a bird-like structure with two telluratripyrrin units that are almost in the same plane.

Computational insights into selective glucose to 5-hydroxymethylfurfural (HMF) conversion by reducing humins formation in aqueous media under Brønsted acid-catalyzed conditions.

5-Hydroxymethylfurfural (HMF) is known for its potential in biofuel production and as a platform chemical for many commercially important molecules. The cost-effective large-scale production of HMF from glucose is hampered by its poor yield in aqueous media due to the formation of polymeric side products known as humins. Thus, reducing humins formation is a strategy for the efficient conversion of glucose to HMF. However, the origin of humins formation and their structures are elusive. In this regard, we investigated the polymerization mechanism and the structure of humins formed during the Brønsted-acid-catalyzed dehydration of glucose to HMF in an aqueous medium by employing density functional theory-based calculations and microkinetic analyses. Notably, the results of this work indicate that humins formation occurs only after the formation of HMF in the reaction mixture and the major part of the humins structure (about 60%) is composed of furanic rings. Furthermore, based on the knowledge gained from in-depth mechanistic and microkinetic studies, potential strategies to reduce humins formation and thereby enhance HMF selectivity are proposed here.

Synthesis of anthracene-bridged expanded rosarin.

The newly synthesized precursor 1,8-di(1H-pyrrol-2-yl)anthracene was condensed with pentafluorobenzaldehyde under acid-catalyzed conditions to afford the first example of a unique anthracenyl-bridged rosarin. The X-ray structure revealed a coil-like arrangement of three dipyrromethene moieties and three anthracenyl units in the rosarin framework, which exhibits a weak fluorescence at 676 nm.

Equilibrium of esterification in Chinese distilled liquor (Baijiu) during ageing

Different Baijiu varieties are characterised by their specific flavours and ester aromas. These flavours originate from the process of esterification during long-term ageing. Despite their wide popularity and long history, the mechanism of esterification during ageing has not been experimentally demonstrated. This study aimed to elucidate the esterification mechanism experimentally to promote advances in the ageing technology for Baijiu and to help advance the Baijiu brewing industry to transform it into a carbon-neutral industry. In this study, traditional acid-catalysed conditions were applied and esterification during ageing was accelerated. Equilibrium constants were obtained for the major esters via thermodynamic calculations and these constants were corrected using the experimental results. These corrected constants can predict the acid and ester contents of the liquor during ageing. Thus, the results can also help standardise Baijiu brewing technology.

Tough conductive cellulose organohydrogels with antifreezing capability, strain-sensitivity and for multi-functional sensors

The mechanical strength of traditional hydrogels is weak, and it is easy to freeze and harden below zero to lose the characteristics and conductivity of hydrogels, which seriously limits the application of hydrogels in sensors. To solve this problem, an organic hydrogel was prepared using a simple method. After testing, this organic hydrogel not only has good frost resistance but also has excellent mechanical properties. Cellulose-based hydrogels have received increasing attention as good materials for preparing flexible, wearable sensors due to their good biocompatibility, flexibility, and excellent mechanical strength. We polymerized 4-carboxy benzaldehyde (FBA) and polyvinyl alcohol (PVA) into gels under acid-catalyzed conditions, imparted freeze resistance to the hydrogels by introducing dimethyl sulfoxide (DMSO) into the hydrogels, and added water-soluble cellulose acetate (WSCA) to the hydrogels to enhance the mechanical properties of the hydrogels. The organic hydrogel prepared by this method is more stable than conventional hydrogel in low-temperature environments, even below − 80゜C can still maintain the soft state and good mechanical flexibility of the hydrogel, of which WSCA can enhance the mechanical properties, and the stress of the hydrogel can reach 0.85 MPa when the WSCA content is 2%, which is 2.5 times that of the hydrogel without WSCA. In addition, the prepared hydrogel also has good electrochemical performance, under the condition of − 80゜C, connected to the circuit, the small bulb can still maintain a weak brightness. Moreover, the sensor composed of hydrogels can distinguish vigorous movement and weak movement of the human body, which provides a new idea for the application of hydrogels on the sensor.

Regioselective C3-H Alkylation of Imidazopyridines with Donor-Acceptor Cyclopropanes.

Alkylated imidazopyridines are crucial structures for medicinal chemistry. Here, an efficient method for the C3-H alkylation of imidazopyridines was devised. Under Lewis acid-catalyzed conditions, reactions of imidazopyridines with different donor-acceptor cyclopropanes were carried out. Finally, 1,3-bisfunctionalizaton of donor-acceptor cyclopropanes was performed. In addition, synthesized C3-alkylated imidazopyridines are amenable for diverse synthetic applications.

Gamma-valerolactone biorefinery: Catalyzed birch fractionation and valorization of pulping streams with solvent recovery

In this study, we propose a full gamma-valerolactone (GVL) organosolv biorefinery concept including the utilization of all pulping streams, solvent recovery, and preliminary material and energy balances. GVL is a renewable and non-toxic solvent that fractionates woody biomass. The silver birch chips were pulped (45–65 wt% GVL, 150 °C, 2 h) under a series of acid-catalyzed conditions (5–12 kg H2SO4/t), and the fully bleached pulp was spun into fibers by the IONCELL® process and knitted into the fabric. The dissolved lignin was precipitated by water from spent liquor (1:1) and processed into polyhydroxyurethane. Most of the dissolved hemicelluloses were in the form of xylose, therefore, the crystallization efficiency of xylose from spent liquor in the presence of residual GVL was studied. The GVL recovery rate in the lab column was 66%, however by increasing the number of equilibrium stages, 99% recovery could be achieved.

Synthesis and Studies of Mono-functionalized Telluradithiasapphyrins and Covalently Linked Porphyrin- Telluradithiasapphyrin Dyads.

A series of mono-functionalized aromatic 22π telluradithiasapphyrins containing functional groups such as p-bromophenyl, p-iodophenyl, p-nitrophenyl and p-trimethylsilylethynyl phenyl groups at one of the meso-positions were synthesized by condensing appropriately functionalized unsymmetrical bithiophene diol and 16-telluratripyrrane in CH2 Cl2 under acid-catalyzed conditions. To demonstrate the reactivity of mono-functionalized telluradithiasapphyrins, we synthesized the first examples of covalently linked diphenyl ethyne bridged four novel 18π porphyrin/metalloporphrin-22π telluradithiasapphyrin dyads by coupling meso-ethynyl phenyl porphyrin with telluradithiasapphyrin containing meso-iodophenyl group under Pd(0) coupling conditions followed by metalation of porphyrin unit by treating free base dyad with appropriate metal salts. The dyads were characterized and studied by mass, 1D & 2D NMR, absorption, cyclic voltammetry, fluorescence and DFT techniques. The DFT analysis showed that the porphyrin/metalloporphyrin and sapphyrin units in dyads orient with each other in different angles and Zn(II) porphyrin-sapphyrin dyad (Zn-dyad) showed minimum whereas the free base dyad showed maximum angle of deviation. NMR, absorption, and redox studies indicated that the dyads exhibit the overlapping features of their constituted monomers and maintain their individual characteristic features. The steady-state fluorescence studies revealed that the fluorescence of the porphyrin/metalloporphyrin unit was significantly quenched due to possible energy/electron transfer from the porphyrin/metalloporphyrin unit to non-emissive sapphyrin unit in dyads.

Bent Dithienoporphyrin(2.1.2.1): Synthesis, Structure, Optical and Electronic Properties, and Metal Complexation

Four kinds of isomeric dithienoporphyrins(2.1.2.1) were prepared using two di(1H-pyrrolo-2-yl)thiophenes as building blocks and two arylaldehydes under mild acid-catalyzed conditions. The molecular conformation and optical and electronic properties of dithienoporphyrins(2.1.2.1) were investigated by NMR spectroscopy, X-ray diffraction, UV–vis absorption spectroscopy, electrochemical measurements, and theoretical calculations. The crystal structure of [2,3]F5TP has the largest angle between the two planes of the dipyrrin units among dibenzo-/dinaphthoporphyrins(2.1.2.1). This result indicates that the incorporation of thiophene subunits into a porphyrin(2.1.2.1) macrocycle results in the alteration of the molecular geometry to a more planarized structure. Dithienoporphyrin(2.1.2.1) is found to act as a ligand that can form metal complexes with nickel(II), copper(II), and palladium(II) ions. The molecular structures of the dithienoporphyrin(2.1.2.1) metal complexes exhibited bent molecular conformations. The red-shifted absorption, reversible redox processes, and theoretical calculations indicated that the electronic properties of the dithienoporphyrin(2.1.2.1) metal complexes are controlled by the inserted metal ions.

Sustainable continuous flow synthesis of β-aminocarbonyls via acid-catalyzed hydration of N-Boc-2-azetines

In this work we report a waste-minimized continuous flow process for the synthesis of β-aminocarbonyls through hydration of N-Boc-2-azetines promoted under acid-catalysed conditions.

Structural isomers of di-p-benzidithiaoctaphyrins.

The cis and trans structural isomers of di-p-benzidithiaoctaphyrins were synthesized by adopting two different synthetic routes using readily available precursors under acid-catalyzed conditions, and the isomers were separated using basic alumina column chromatography. 1D and 2D NMR spectroscopy were used to deduce the molecular structures of the macrocycles, which also helps to differentiate the cis isomer from the trans isomer. DFT studies revealed that both the cis and trans isomers adopt figure of eight conformations but exhibit clear differences in their structural features, and the trans isomer is more distorted than the cis isomer. Experimental and theoretical studies revealed that both the cis and trans isomers are nonaromatic stable macrocycles and show subtle differences in their structure, spectral and redox properties. The cis and trans isomers of di-p-benzidithiaoctaphyrin exhibit nonaromatic absorption features in the visible-NIR region, and electrochemical studies revealed their electron-rich nature. TD-DFT studies are in agreement with the experimental observations.

Effect of hydrochar from acid hydrolysis on anaerobic digestion of chicken manure

Acid hydrolysis is a key process for the production of platform chemicals from biomass, however solid residues by-products can amount to 50 wt% of the starting biomass material. In this study, solid residues from the production of biofuel precursor levulinic acid were generated via microwave-assisted acid hydrolysis of Miscanthus x Giganteus and investigated for the supplementation of anaerobic reactors digesting Chicken Manure. The addition of the solid residues increased the methane yields by up to 14.1%, depending on the additive concentration levels, 2–10 g/L. A mild ammonium related inhibition was observed during the fermentation trials, which was mitigated by the solid residue additive. An experimental optimum of concentration 6 g/L residue was found which corresponded with a 20% decrease in ammonium concentrations and increased microbial diversity, where phyla Bacteroidetes and Firmicutes were the most prevalent, whilst the relative abundance of Archaea (Euryarchaeota) decreased without negative effects on methane production. The effects of acid catalysis conditions on solid residue properties and methane yields from chicken manure were evaluated. All solids residue investigated exhibited ammonium absorption and improved microbial diversity during anaerobic digestion. The integration of anaerobic digestion downstream second generation biorefineries is a promising green waste disposal method for solid by-products from thermo-catalytic processes.

Dual Roles of Azide: Dearomative Dimerization of Furfuryl Azides

A dearomative dimerization of furfuryl azides for the construction of furfuryl triazoles is developed. As a rare leaving group, azide is capable of initiating the generation of a furfuryl cation under the Lewis acid-catalyzed conditions, followed by reacting with the other azide to realize an intermolecular [3 + 2] cycloaddition/furan ring-opening cascade. By extending the reaction time, a fragmentation reaction of resulting furfuryl triazoles occurs to afford 1H-triazoles in high yield. Control studies demonstrated that key furfuryl cations also can be obtained from furfuryl triazoles. Furthermore, a chemoselective cross-cycloaddition can be achieved between furfuryl azides and a benzyl azide.

A molecular route to fluoro-perovskite materials: synthesis of CsCaF3 films through a sol–gel/spin-coating process

Fluoride perovskites have recently attracted great attention due to their unique optical properties. The present study reports for the first time the fabrication of fluoride-based perovskite, CsCaF3, in form of thin films through a combined sol–gel/spin-coating approach using β-diketonate fluorinated precursors. The entire sol–gel process has been carried out in ethanol solution under acid-catalyzed conditions starting from the β-diketonate complexes, Cs(hfa) and Ca(hfa)2•diglyme•H2O (Hhfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione; diglyme = 2–Methoxyethylether), which act as single sources for metal ions and fluorine. A careful optimization of the process parameters, such as molar ratio of the starting mixture, aging time and annealing temperature, has allowed to produce for the first time, selectively and reproducibly, transparent and pure CsCaF3 films. Field-emission scanning electron microscopy and energy dispersive X-ray analyses highlight the formation of films with compact morphologies having a 1:1 stoichiometric ratio of Cs:Ca, uniform throughout the film and compatible with the CsCaF3 phase identified through X-ray diffraction analysis.

Synthesis of meso-Triaryl 22-Oxanorroles.

Norroles are isomers of corroles containing a direct pyrrole N-pyrrole C link instead of a pyrrole C-pyrrole C link of corroles. 22-Oxanorroles are core-modified norroles in which one of the pyrroles is replaced with a furan ring. A straightforward route is adopted to synthesize the first examples of aromatic meso-triaryl-22-oxanorroles containing a pyrrole N-pyrrole α-C direct bond in 4-7% yields by condensing 16-oxatripyrrane and (1H-pyrrol-3-yl)(p-tolyl)methanol in CH2Cl2 under mild acid-catalyzed conditions followed by oxidation with DDQ.

Synthesis and Action of N-acylphenylacetamides and N-acyl-β-ketoamides on the Central Nervous System

Introduction. One of the most promising directions in the search for biologically active compounds is the molecular design of biologically active compounds containing a known pharmacoform fragment. In this article, phenylacetic acid derivatives are considered as a scaffold for the search for biologically active compounds. However, the phenylacetamide derivative is of particular interest, its fragment is included in the structure of the atenolol drug. Optimization of methods for the synthesis of N-acylphenylacetamides and N-acyl-β-ketoamides will expand the boundaries of molecular design and targeted synthesis of biologically active substances containing a phenylacetic acid fragment as a centroid.Aim. Obtain N-acylphenylacetamides and N-acyl-β-ketoamides, optimize the synthesis and isolation methods, and establish the degree of manifestation of the psychotropic activity of the compounds.Materials and methods. Obtaining the target N-acylphenylacetamides was carried out by the interaction of 2-phenylacetamide with carboxylic acid anhydrides under conditions of acid catalysis. The next stage of the synthesis was the preparation of N-acyl-β-ketoamides by the interaction of the synthesized N-acylphenylacetamides with carboxylic acid anhydrides in the proposed catalyst for boron trifluoride diacetate. The structure of the compounds was confirmed by IR, 1H NMR spectrometry. The individuality and purity of the obtained compounds were monitored by thin layer chromatography. The study of the synthesized compounds on the central nervous system was carried out in the tests "Conditioned reflex of passive avoidance – CPAR", "Extrapolation escape (ETI)", "Morris water maze" and "Beam Walking".Results and discussion. As a result of the research, N-acylphenylacetamides and N-acyl-β-ketoamides were synthesized. The essence of the optimization of the procedure for the synthesis of N-acylphenylacetamides is to replace chloric 65 % with concentrated sulfuric acid. The 1H NMR spectra confirming the structures of the synthesized compounds revealed important characteristic features for N-acetyl-3-oxo-2- phenylpentanamide (VI) and N-acetyl-3-oxo-2-phenylhexanamide (VIII) containing a chiral center. The resulting substances have a pronounced effect on the central nervous system, their nootropic activity is to reduce the severity of sensorimotor disorders in animals. As a result of the study, the leading compounds were identified, superior to the effect of the reference drug piracetam.Conclusion. The carried out research confirms the expediency of searching for highly effective and safe nootropic agents in the series of acylated derivatives of phenylacetic acid amide.