Dehydration Condensation Research Articles

Preparation of Organic/Inorganic Composite Aerogel through Gelation and Supercritical Fluid Drying of Para-Aramid Fibril/Silicon Alkoxide Dispersion

Organic/inorganic composite aerogels were obtained from poly-paraphenylene terephthalamide (PPTA) micro-fibrils and methyltrimethoxysilane (MTMS). They are prepared using the following four-step process: the gelation of 1.0 wt% PPTA fibril dispersion containing MTMS by cooling, dehydration condensation of MTMS by immersing the wet gel in a catalyst solution, substituting the solvent in the wet gel, and supercritical drying of the wet gel. When the PPTA/MTMS dispersion containing 1.0 wt% MTMS was gelatinized, the PPTA fibrils strongly adhered to each other, and the PPTA/MTMS composite wet gel obtained better morphological stability. Furthermore, the wet gel prevented shrinkage during the catalyst soaking and supercritical fluid drying processes, and the resulting aerogel had a minimum density of < 0.03 g/cm3. It also had a composite network structure with silica spheres of approximately 30 nm attached to the PPTA fibril network. In contrast, when the PPTA/MTMS dispersions containing 5.0 or 10 wt% MTMS were gelatinized, the obtained composite aerogels had an entangled structure of PPTA fibril networks around silica spheres ranging from 500 nm to 700 nm in size. Moreover, aerogels comprising PPTA/MTMS dispersion with 10 wt% MTMS had a specific surface area of 610 m2/g and retained 70 % of their weight after the heat resistance evaluation at 600°C.

Stereodivergent dehydrative allylation of β-keto esters using a Ru/Pd synergistic catalyst

α-Alkylation of a β-keto ester is a frequently used reaction for carbon–carbon bond formation. However, extension to a stereoselective reaction remains a significant challenge, because the product easily racemizes under acidic or basic conditions. Here, we report a hybrid system consisting of Pd and Ru complexes that catalyzes the asymmetric dehydrative condensation between cinnamyl-type allylic alcohols and β-keto esters. α-Non-substituted β-keto ester can be allylated to afford an α-mono-substituted product with high regio-, diastereo-, and enantioselectivity. No epimerization occurs owing to the nearly neutral conditions, which is achieved by a rapid proton transfer from Pd-enolate formation to Ru π-allyl complex formation. Four diastereomers can be synthesized on demand by changing the stereochemistry of the Pd or Ru complex. Eight stereoisomers with three adjacent stereogenic centers can be synthesized by employing diastereoselective reduction of the ketone in the products. The formal synthesis of (+)-pancratistatin demonstrates the utility of the reaction.

Synthesis of highly dispersed TiO2 NPs/GO composites sol and its application in inverted perovskite solar cells

The poor dispersion property and agglomerate of TiO 2 /graphene oxide (GO) composites greatly limit its application in optoelectronic devices. Here, low-temperature processed, high dispersion TiO 2 nanoparticles/GO (TiO 2 NPs/GO) sol was synthesized via modified sol-gel strategy combing by a hydrothermal process. The formation mechanism of TiO 2 NPs/GO sol is investigated and the results show that the TiO 2 NPs can be embedded to GO sheet with Ti–O–C chemical bond via dehydration condensation reaction between the hydroxyl groups on the surfaces of them. In addition, there are charge transportation between TiO 2 NPs and GO is confirmed, which benefits to enhance the charge transport efficiency of TiO 2 NPs. Using TiO 2 NPs/GO composite as cathode interface, the energy barrier of cathode interface is eliminated, and the hysteresis effect is largely suppressed. The highest power conversion efficiency (PCE) of 17.73% is achieved with TiO 2 NPs/GO, and the average PCE is also enhanced by 14.71% comparing to the control devices. This simple strategy light on the preparation high dispersive TiO 2 NPs/GO composites and correspondingly applied in inverted PSCs to enhance the interface contact. • Low-temperature processed, high dispersive TiO 2 NPs/GO composite sol has been synthesized. • The interface energy barrier and hysteresis are eliminated with TiO 2 NPs/GO interface modification. • The highest power conversion efficiency (PCE) of 17.73% is achieved.

Successive Cleavage and Reconstruction of Lignin β‐O‐4 Models and Polymer to Access Quinoxalines

The construction of N-heterocyclic compounds from lignin remains a great challenge due to the complex lignin structure and the involvement of multiple steps, including the cleavage of lignin C-O linkages and the formation of heterocyclic aromatic rings. Herein, the first example of KOH mediated sustainable synthesis of quinoxaline derivatives from lignin β-O-4 model compounds in a one-pot fashion under transition-metal-free conditions has been achieved. Mechanistic studies suggested that this transformation includes highly coupled cascade steps of cleavage of C-O bonds, dehydrative condensation, sp3 C-H bond oxidative activation, and intramolecular dehydrative coupling reaction. With this protocol, a wide range of functionalized quinoxalines, including an important drug compound AG1295, were synthesized from lignin β-O-4 model compounds and β-O-4 polymer, showcasing the application potential of lignin in pharmaceutical synthesis.

Polydopamine and Mercapto Functionalized 3D Carbon Nano-Material Hybrids Synergistically Modifying Aramid Fibers for Adhesion Improvement.

In order to solve the problem of poor interfacial adhesion between aramid fibers and a rubber matrix, an efficient and mild modification method was proposed via polydopamine and mercapto functionalized graphene oxide (GO) and carbon nanotube (CNTs) hybrids synergistically modifying aramid fibers. GO and CNTs were firstly stacked and assembled into unique 3D GO-CNTs hybrids through π-π conjugation. Then, the mercapto functionalization of the assembled 3D GO-CNTs hybrids was realized via the dehydration condensation reaction between the hydroxyls of GO and the silanol groups of coupling agent. Finally, the mercapto functionalized 3D GO-CNTs hybrids were grafted onto the aramid fibers, which were pre-modified by polydopamine through the Michael addition reaction mechanism. The surface morphology and chemical structures of GO-CNTs hybrids and fibers and the interfacial adhesion strength between fibers and rubber matrix were investigated. The results showed that the modification method had brought about great changes in the surface structure of fibers but not generated any damage traces. More importantly, this modification method could improve the interfacial strength by 110.95%, and the reason was not only the reactivity of functional groups but also that the 3D GO-CNTs hybrids with excellent mechanical properties could effectively share interfacial stress. The method proposed in this paper was universal and had the potential to be applied to other high-performance fiber-reinforced composites.

Boosting the alkali metal ions storage performance of layered Nb2C with a molecular welding strategy

MXenes are promising 2D-layered anode materials for rechargeable batteries. However, MXenes suffer from severe volume expansion and sluggish ion diffusion kinetics during ions insertion/extraction, leading to inferior battery performance. Herein, we developed a molecular welding strategy to stabilize layered structure and enlarge interlayer spacing of Nb2C through a dehydration condensation reaction between the -COOH groups in 1,3,5-benzenetricarboxylic acid (BTC) molecules and -NH2 groups on the surface of the amino-functionalized Nb2C, which enable the BTC to chemically weld into interlayers of Nb2C (named as Nb2C/BTC). The intercalation of BTC into Nb2C contributes both pillar and strain effects to the 2D-layered Nb2C, rendering its maximum utilization. Such Nb2C/BTC with enlarged interlayer spacing and inhibited volume variation could remarkably promote the rate capability and cycling stability of Nb2C when used as the electrodes of alkali metal ions batteries. A decent Li+/Na+ ions storage capacity-retention of 86.6% (0.1 A g−1)/93.5% (1.0 A g−1) can be presented. A much reduced ion diffusion barrier of 0.88 eV is also delivered in Nb2C/BTC through DFT theoretical calculations. This work provides a new strategy for broadening the interlayer spacing and inhibiting the severe volume variation of MXenes for enhanced alkali metal ions storage.

Polyazaacene and Cyclazaacene Precursors Synthesized by Dehydration Condensation from a Versatile Bis‐α‐diketone Unit Having an Anthracene Skeleton

AbstractAzaacenes are acene analogs containing nitrogen atoms in their carbon‐based molecular skeletons and are attracting significant attention because of their potential application in organic electronics. However, polyazaacenes have solubility and stability issues. In this study, we report a modular approach employing 8,11‐dihydro‐1,4 : 8,11‐diethanopentacene‐2,3,9,10(1H,4H)‐tetraone (1) as a key compound for π‐extension with commercially available materials to synthesize a series of polytetraazaacene thermal precursors. Exploiting this strategy, tetraazaheptacene, tetraazanonacene, and tetraazaundecacene precursors were successfully synthesized. Thermogravimetric analysis revealed that the tetraazanonacene precursor can be converted to its corresponding tetraazanonacene in a nitrogen atmosphere. To extend the applicability of this method, compound1was also used to synthesize the cyclazaacene precursor at 0.8 % yield. This approach provides a new perspective for exploring the synthesis of polyazaacene and cyclazaacene precursors by using a crucial key compound via dehydration condensation reactions.

Biosensor Based on Covalent Organic Framework Immobilized Acetylcholinesterase for Ratiometric Detection of Carbaryl.

A ratiometric electrochemical biosensor based on a covalent organic framework (COFThi-TFPB) loaded with acetylcholinesterase (AChE) was developed. First, an electroactive COFThi-TFPB with a two-dimensional sheet structure, positive charge and a pair of inert redox peaks was synthesized via a dehydration condensation reaction between positively charged thionine (Thi) and 1,3,5-triformylphenylbenzene (TFPB). The immobilization of AChE on the positively charged electrode surface was beneficial for maintaining its bioactivity and achieving the best catalytic effect; therefore, the positively charged COFThi-TFPB was an appropriate support material for AChE. Furthermore, the COFThi-TFPB provided a stable internal reference signal for the constructed AChE inhibition-based electrochemical biosensor to eliminate various effects which were unrelated to the detection of carbaryl. The sensor had a linear range of 2.2–60 μM with a detection limit of 0.22 μM, and exhibited satisfactory reproducibility, stability and anti-interference ability for the detection of carbaryl. This work offers a possibility for the application of COF-based materials in the detection of low-level pesticide residues.

Preparation and properties of hydrophobic and transparent wood

Natural wood (NW) was treated with sodium chlorite to obtain delignified wood (DW) in this study, then epoxy was impregnated to get transparent wood (TW), and finally the TW was coated with perfluorodecyltriethoxysilane (FAS) to acquire hydrophobic and transparent wood (HTW). The hydroxyl group generated by the hydrolysis of the FAS and the hydroxyl group of the epoxy underwent a dehydration condensation reaction to generate a Si–O–C bond, while the FAS molecules were also dehydrated and condensed to form a Si–O–Si bond according to Fourier transform infrared (FT-IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Therefore, the mechanical property and thermal stability of the HTW were better than the TW based on their tensile tests and thermogravimetric analysis (TGA). Due to the large reduction of hydroxyl in epoxy, the hydrophobicity of the HTW was greatly improved compared with the TW, and their contact angles were 113° and 77°, respectively. The results of scanning electron microscopy (SEM) showed that epoxy was filled in the voids of wood. In addition, the coating of the FAS did not obviously reduce the transmittance, and the transmittance of the TW and HTW was 69% and 67% at 750 nm. All in all, the HTW has potential for application in transparent decoration.

Peptization mechanism of aluminum phosphate sol

Aluminum phosphate sol attracts more and more attention due to its excellent particle size and bonding properties. The structure, morphology and Zeta potential of aluminum phosphate sol during the peptizing process were investigated with NMR, FTIR, Raman, TEM and DLS. The results show that the pseudo boehmite particles were fragmentated, dissolved, and then peptized under the electrostatic repulsion of H+. The peptization process presents three stages: the fragmentation-polymerization stage, the reaction stage, and the stabilization stage. The particle diameter of the stable aluminum phosphate sol ranged from 30 to 50 nm, and the particles with varying sizes were interconnected to form a “hand-in-hand” cyclic system. Meanwhile, the dehydration condensation reaction between H3PO4 and pseudo boehmite was occurring continuously. When 2.1 ≤ n(P)/n(Al) < 3, the proportion of QP01, QP10 and QP11 polymers in the system increased to 25–27 %, the degree of polymerization was deepened, and some cyclic oligomers and polymers appeared. Additionally, the crystal water concentration was increased and the peptization solubility was enhanced.

Linear Nonalternant Isomers of Acenes Fusing Multiple Azulene Units.

A modular approach to azulene building blocks was developed starting from readily available aryl-substituted cyclopentadiene and ortho-haloaryl aldehyde by dehydration condensation followed by palladium-catalyzed C-H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzo[e,g]azulene, benzo[1,2-f : 5,4-f']diazulene, benzo[1,2-f : 4,5-f']diazulene, and naphtho[2,3-f : 6,7-f']diazulene, which exhibit narrow band gaps with high stability in addition to protonation-caused enhanced near-infrared fluorescence. We discovered that in these isomers, i) constitutional isomerism influences significantly their photoelectric properties and ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the band gap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene-fused aromatics.

Linear Nonalternant Isomers of Acenes Fusing Multiple Azulene Units

AbstractA modular approach to azulene building blocks was developed starting from readily available aryl‐substituted cyclopentadiene and ortho‐haloaryl aldehyde by dehydration condensation followed by palladium‐catalyzed C−H coupling. It facilitates the synthesis of four nonalternant isomers of pentacene and hexacene, namely, dibenzo[e,g]azulene, benzo[1,2‐f : 5,4‐f′]diazulene, benzo[1,2‐f : 4,5‐f′]diazulene, and naphtho[2,3‐f : 6,7‐f′]diazulene, which exhibit narrow band gaps with high stability in addition to protonation‐caused enhanced near‐infrared fluorescence. We discovered that in these isomers, i) constitutional isomerism influences significantly their photoelectric properties and ii) the elongation of the conjugation system does not necessarily lead to a narrowing in the band gap. Due to the easy modifiability of the nonazulene building blocks, this strategy can be extended to modularly prepare numerous multiazulene‐fused aromatics.

Modulation of Solid-State Chemical Stability of Gabapentin by Pyridinecarboxylic Acid.

Gabapentin (GBP) is an anticonvulsant drug with poor chemical stability that is particularly sensitive to heat and mechanical stress, which can lead to intramolecular lactamization. The purpose of this study was to enhance the chemical stability of GBP by cocrystallization with organic acids. Two novel multicomponent crystals, GBP-2,6-pyridinedicarboxylic acid salt (GBP-2,6PDA salt) and GBP-2,5-pyridinedicarboxylic acid cocrystal (GBP-2,5PDA cocrystal) were synthesized and characterized by various solid-state analytical techniques. The degradation behavior of GBP, GBP-2,6PDA salt and GBP-2,5PDA cocrystals were evaluated under thermal and mechanical stresses. Under thermal and mechanical stresses, GBP-2,5PDA cocrystals were found to undergo severer degradation than GBP-2,6PDA salt and neat GBP. GBP-2,6PDA salt exhibited superior chemical stability compared to the others. Furthermore, the crystal structure revealed that the order of atomic distance between the carboxyl group (C7) and amino group (N12) of GBP is as follows: GBP-2,5PDA cocrystal < GBP < GBP-2,6PDA salt, which is consistent with the chemical stability of GBP in different solid forms. Therefore, we believe that the distance between C7 and N12, the reaction active sites leading to dehydrative condensation of GBP, is a key factor determining the chemical stability of GBP in the solid state. These results provide a potential method to improve the chemical stability of GBP during the manufacturing process and storage.

Electrochemical determination of dopamine and uric acid with covalent organic frameworks and Ox-MWCNT co-modified glassy carbon electrode

Covalent organic frameworks (COFs) have received tremendous interest due to their structural diversity and versatility. These unique physicochemical properties make them exhibit great application potential in the field of electrochemical sensor. In this study, an imine bond-linked COF with porosity and large specific surface area was fabricated by a dehydration condensation reaction between 1, 3, 5-tris(4-formylphenyl)benzene (TFPB) and 1, 3, 5-tris(4-aminophenyl) benzene (TAPB) and combined with high electrical conductivity of oxidized multi-walled carbon nanotube (Ox-MWCNT). The structure of the COF and the resulted composite material were confirmed through a series of characterization techniques, including Fourier-transform infrared spectroscopy, powder X-ray diffraction, scanning electron microscopy and thermogravimetric analysis, then a co-modified glassy carbon electrode was constructed for simple, sensitive and selective electrochemical recognition of dopamine (DA) and uric acid (UA). The fabricated electrochemical sensor displayed a strong current response to both DA and UA in the phosphate buffer solution (PBS) at pH = 6.5. The synergistic effect between COFs and Ox-MWCNT effectively improved the analytical sensitivity for the target analytes. Under optimized experimental conditions, the method showed good performance for DA and UA in the concentration range of 0.6–250.0 μM with low detection limits of 0.073 μM and 0.063 μM (S/N = 3), respectively. Moreover, the proposed sensor exhibited high selectivity, longtime stability, desirable repeatability and acceptable reproducibility and can be used to analyze simultaneously DA and UA in biological and medicine samples with satisfactory results. Our work not only provides a simple way to detect DA and UA quantitatively in real samples, but also offers a new platform for COF-based composite application in electrochemical sensing . • TFPB-TAPB-COF is prepared via a simple solvothermal method. • TFPB-TAPB-COF/Ox-MWCNT/GCE is fabricated for sensing of dopamine (DA) and uric acid (UA). • The sensor has low detection limits and wide linear ranges for detection DA and UA. • The sensor is successfully applied to the determination of DA and UA in real samples.

Silibinin Schiff Base Derivatives Counteract CCl4-Induced Acute Liver Injury by Enhancing Anti-Inflammatory and Antiapoptotic Bioactivities

BackgroundSilibinin (Sil), a flavonoid lignan-like natural compound derived from milk thistle seeds, has been used to treat hepatic diseases, including early-phase hepatocirrhosis and fatty liver, for many years. However, its poor water solubility limits its gastrointestinal absorption and bioavailability. It clinical use has been limited due to its slow onset of action. Faced with this problem, research on the derivatives of silibinin has been receiving much attention.PurposeA series of silibinin derivatives with good biosafety and higher hepatoprotective activity were obtained by a safe, efficient and green chemical synthesis method.Patients and MethodsFirst, the carbonyl group in the structure of silibinin was used to obtain silibinin Schiff base derivatives by dehydration condensation with the carboxyl group in the sulfur-containing amino acid. Next, relevant experiments were performed to characterize the structure, physical form and solubility of the derivatives. Then, toxicity tests of the derivatives were performed in LO-2 cells and SD rats to evaluate their biosafety. Finally, the anti-inflammatory and antiapoptotic activities were observed using a carbon tetrachloride (CCl4)-induced acute liver injury model in C57BL/6J mice using silibinin as a control.ResultsThe studies showed that SS and ST behaved as amorphous substances and showed a significant increase in solubility compared to silibinin. These two derivatives showed low toxicity in biosafety tests and higher bioactivity (anti-inflammatory and anti-apoptotic) than silibinin against acute liver injury induced by CCl4.ConclusionTwo silibinin derivatives (SS and ST) obtained by the Schiff base reaction improved the solubility of the silibinin parent nucleus in biological media with the help of the hydrophilic and amorphous morphology of the ligand. The low toxicity in vivo and in vitro ensures the biosafety of the derivatives. The hepatoprotective activity (anti-inflammatory and anti-apoptotic) was significantly improved compared to silibinin.

Green Synthesis of Novel Triazolothiadiazine‐Coumarins Catalyzed by Agro Waste Extract: An Approach towards In‐Silico and In‐Vitro Anti‐Fungal Activity

AbstractA green, commodious, immensely versatile synthetic route for agro waste extract WELPSA catalyzed cyclocondensation of biologically active triazolothiadiazine‐coumarin hybrid derivatives has been studied. A proficient synthesis offused heterocycles 9 i–wvia dehydrative condensation with cyclization of4‐((4‐amino‐5‐mercapto‐4H‐1,2,4‐triazol‐3‐yl)methyl)‐2‐aryl‐2,4‐dihydro‐3H‐1,2,4‐triazol‐3‐one (5 a‐‐c) and substituted bromoacyl coumarins (8 d‐‐h)has been incorporated in presence of different catalysts including WELPSA, a green catalyst. The in silico docking studies of these previously unknown compounds revealed favorable C score and Chemscore values and the in vitro antifungal assay against three fungal strains showed excellent to good activity.

Synthesis of diaryl phosphates using orthophosphoric acid as a phosphorus source

This paper presents a new synthetic route for diaryl phosphate esters, which are traditionally synthesized from phosphorus oxychloride. Specifically, we report the synthesis of diaryl phosphates by the dehydrative condensation of orthophosphoric acid, a phosphorus source, with aromatic alcohols.

Facile Synthesis of Quinoxaline-2-thiol and Quinoxaline from α-Oxosulfines and o-Arylenediamines

AbstractA series of quinoxaline-2-thiols and quinoxalines were prepared in moderate to good yields from various phenacyl sulfoxides bearing 1-methyl-1H-tetrazole and o-arylenediamines. The proposed reaction mechanism involves generation of sulfines from the phenacyl sulfoxides bearing 1-methyl-1H-tetrazole through thermolysis elimination. Then, site-selective carbophilic addition of sulfines by o-arylenediamines, followed by elimination, intramolecular nucleophilic addition, and dehydration condensation. The current method provides a direct and simple strategy for the preparation of quinoxaline-2-thiols and quinoxalines.

Novel 1, 3, 5‐triazine derivative is a highly efficient inhibitor of corrosion of Q235 carbon steel in an acidic medium

AbstractA novel triazine derivative, 2, 4‐diamino‐6‐dodecamido‐1, 3, 5‐triazine (DT), is synthesized by the dehydration condensation of melamine and lauric acid, and its inhibitive performances for the corrosion of Q235 carbon steel in 1 mol/L HCl solution is investigated by electrochemical polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and atomic force microscope. The results reveal that its best inhibition efficiency reaches 96.98% at a concentration of 2.5 g/L. The calculation results of kinetic and thermodynamic parameters indicate that the adsorption of DT on carbon steel surface obeys Langmuir adsorption isotherm with both physical and chemical adsorption. It is demonstrated that long‐chain amide (&gt;8C) substituted 1, 3, 5‐triazine derivative has the synergistic corrosion inhibition effect of the surface fixation on metal iron and the hydrophobic adsorption layer.

En Route to CO2-Based (a)Cyclic Carbonates and Polycarbonates from Alcohols Substrates by Direct and Indirect Approaches

This review is dedicated to the state-of-the art routes used for the synthesis of CO2-based (a)cyclic carbonates and polycarbonates from alcohol substrates, with an emphasis on their respective main advantages and limitations. The first section reviews the synthesis of organic carbonates such as dialkyl carbonates or cyclic carbonates from the carbonation of alcohols. Many different synthetic strategies have been reported (dehydrative condensation, the alkylation route, the “leaving group” strategy, the carbodiimide route, the protected alcohols route, etc.) with various substrates (mono-alcohols, diols, allyl alcohols, halohydrins, propargylic alcohols, etc.). The second section reviews the formation of polycarbonates via the direct copolymerization of CO2 with diols, as well as the ring-opening polymerization route. Finally, polycondensation processes involving CO2-based dimethyl and diphenyl carbonates with aliphatic and aromatic diols are described.