Investigation on the thermal degradation of acrylic polymers with fluorinated side-chains

The thermal degradation of poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′,7″-tridecafluoroheptylacrylate and poly-2,2′,3,3′,4,4′,5,5′,6,6′,7,7′-dodecafluoroheptylmethacrylate has been studied in isothermal conditions at 450-750 °C using pyrolysis-gas chromatography. The type and composition of the pyrolysis products give useful information about mechanism of thermal degradation. It was shown that the main thermal degradation process for both polymers is random main-chain scission. The major degradation products for fluorinated polyacrylate are monomer, dimer, saturated diester, trimer, and corresponding methacrylate. The fluorinated polymethacrylate gives monomer as the main product of thermal destruction. As a result of side-chain reaction, the thermal degradation of the fluorinated polyacrylate also produces remarkable amounts of alcohol. On the other hand, the respective alcohol is only a minor component among the pyrolysis products of the fluorinated polymethacrylate. For both polymers, the main nontrivial degradation product coming from the alkyl ester decomposition is the corresponding fluorinated cyclohexane. The formation of the fluorinated cyclohexanes may be accounted for a nucleophilic bimolecular substitution pathway.     

Efficient synthesis of 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl (X: NMe2; OMe) by homocoupling of 1-bromo-3,5-di(p-X-phenylethynyl)benzene or by heterocoupling of 3,3′,5,5′-tetraethynylbiphenyl with p-X-phenylbromobenzene with nickel or palladium complexes, respectively

The conjugated 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl derivatives were efficiently obtained by homocoupling of 1-bromo-3,5-di(p-X-phenylethynyl)benzene mediated by zero-valent nickel complexes.The 1-bromo-3,5-di(p-X-phenylethynyl)benzene was previously prepared by heterocoupling between 1-bromo-3,5-di(ethynyl)benzene and p-X-iodobenzene (X: NMe₂; OMe) catalysed by the palladium/copper system in good yield. The necessary 1-bromo-3,5-di(ethynyl)benzene was obtained by heterocoupling between 1,3,5-tribromobenzene and 2-methyl-3-butyn-2-ol catalysed by palladium and successive treatment with sodium hydroxide in dry toluene, in good yield.The same 3,3′,5,5′-tetra(p-X-phenylethynyl)biphenyl (X: NMe₂; OMe) derivatives were alternatively synthesised in highest yield by heterocoupling between 3,3′,5,5′-tetra(ethynyl)biphenyl and p-X-bromobenzene (X: NMe₂; OMe) catalysed by palladium in excellent yields. Previously, 3,3′,5,5′-tetra(ethynyl)biphenyl was obtained in practically quantitative yield by homocoupling of 1-bromo-3,5-di[4-(2-methyl-3-butyn-2-ol)] benzene mediated by the zero-valent nickel complex to the 3,3′,5,5′-tetra{di[4-(2-methyl-3-butyn-2-ol)]}biphenyl followed the treatment with sodium hydroxide.     

Investigation of 3,3′,5,5′-tetramethylbenzidine as colorimetric substrate for a peroxidatic DNAzyme

In this work, the suitability of 3,3′,5,5′-tetramethylbenzidine sulfate (TMB) as the substrate of a DNAzyme catalytic system composed of a guanine-quadruplex DNA molecule and hemin was investigated. In the presence of H₂O₂, the hemin-DNA complex catalyzes the oxidation of TMB to produce two colored products, much like a peroxidase. The color-generating activity of this system could be influenced by several factors such as buffer type, pH value, DNA sequence, reaction time, and concentrations of both the hemin and H₂O₂. To illustrate the utility of this catalytic system, we designed a colorimetric assay, in which a synthetic oligonucleotide with a sequence complementary to the G-quadruplex DNA was used as the target. A detection limit of 1.86 nM was obtained. Our data have shown that TMB was an excellent colorimetric indicator that reported the peoxidase activities of the widely studied hemin-G-quadruplex DNAzyme system.     

A facile method for the preparation of hexafluoroisopropanol functionalized derivatives using hexafluoroacetone trihydrate via a carbonyl-ene reaction

Hexafluoroacetone trihydrate was shown to undergo an efficient carbonyl-ene reaction with a variety of alkenes in the presence of molecular sieves under microwave heating and conventional heating producing hexafluoroisopropanol functionalized derivatives in high yields.     

Self-supported heterogeneous titanium catalysts for enantioselective carbonyl-ene and sulfoxidation reactions

A new strategy for the heterogenization of chiral titanium complexes was developed by the in situ assembly of bridged multitopic BINOL ligands with [Ti(OiPr)4] without using a support. The assembled heterogeneous catalysts (self-supported) showed excellent enantioselectivity in both the carbonyl-ene reaction of alpha-methylstyrene with ethyl glyoxylate (up to 98 % ee) and the oxidation of sulfides (up to >99 % ee). The catalytic performance of these heterogeneous catalytic systems was comparable or even superior to that attained with their homogeneous counterparts. The spacers between the two BINOL units of the ligands in the assembled catalysts had significant impact on the enantioselectivity of the carbonyl-ene reaction. This demonstrates the importance of the supramolecular structures of the assemblies on their catalytic behavior. In the catalysis of sulfoxidation, the self-supported heterogeneous titanium catalysts were highly stable and could be readily recycled and reused for over one month (at least eight cycles) without significant loss of activity and enantioselectivity (up to >99.9 % ee). The features of these self-supported catalysts, such as facile preparation, robust chiral structure of solid-state catalysts, high density of the catalytically active units in the solids, as well as easy recovery and simple recycling, are particularly important in developing methods for the synthesis of optically active compounds in industrial processes.     

Roads less traveled: Nitrogen reduction reaction catalyst design strategies for improved selectivity

Direct electrochemical nitrogen reduction for ammonia production is necessary to reduce the use of fossil fuels from conventional Haber–Bosch methods. Applications of nitrogen reduction electrocatalysts remain inhibited by slow reaction kinetics and low faradaic efficiencies because of competitive H₂ production pathways. Current strategies to address this challenge in selectivity have focused on catalyst design, reactor configuration, and electrolyte conditions. This brief review discusses the thermodynamic and kinetic challenges in the field as well as current underused approaches for selective catalyst development including bimetallic catalysts, transition metal nitrides, and carbon supports.     

SiO2负载的Au-Ni双金属催化剂在乙炔选择加氢反应中的应用

负载型Au催化剂在乙炔选择加氢反应中表现出很高的乙烯选择性,但其转化率相对较低.通过添加第二种金属如Pd,Fe,Ag和Cu等,制备双金属催化剂是提高其在加氢反应中催化活性的一种非常有效的手段.其中Au-Pd双金属催化剂是最受关注的体系之一,Pd的加入可以非常显著地提高其催化乙炔选择加氢反应的活性.据文献报道,与Pd同一主族的Ni也具有较好的加氢活性.尽管与Pd相比,Ni很难与Au形成合金,但目前已有Au-Ni双金属催化剂在多种反应中表现出协同效应的报道,如水气变换、CO氧化以及芳香硝基化合物选择加氢等.因此,向Au催化剂中添加Ni也可能提高催化剂在乙炔选择加氢反应中的催化活性.因此,我们采用两步法制备了一系列SiO2负载的具有不同Ni:Au原子比的Au-Ni双金属催化剂,并将其用于乙炔选择加氢反应,发现Au-Ni双金属催化剂在该反应中表现出了显著的协同效应,其活性明显优于相应单金属催化剂的活性.尽管其乙烯选择性略低于单金属Au催化剂,但明显高于单金属Ni催化剂.通过调节还原温度和/或Ni:Au的比例,对催化剂的性能进行了优化.结果显示,当Ni:Au=0.5时,催化剂表现出最优的综合性能,即兼具较高的乙炔转化率和乙烯选择性.为了研究Au-Ni双金属催化剂中金属纳米粒子的结构、组成以及Au-Ni之间的相互作用,我们对催化剂进行了X射线衍射(XRD)、高分辨透射电镜(HRTEM)、能量散射谱(EDS)以及原位红外光谱(DRIFTS)表征.XRD和TEM结果显示,催化剂中的Au-Ni双金属纳米粒子都具有高分散和粒径均匀的特点.通过EDS分析,发现在Au-Ni双金属催化剂中的单个金属纳米粒子同时含有Au和Ni两种元素,尽管每个纳米粒子中Ni:Au的比例有差异.HRTEM结果发现,Au-Ni双金属纳米粒子的晶格间距介于Au(111)和Ni(111)的晶面间距之间,说明在Au-Ni双金属催化剂中有Au-Ni合金形成.原位DRIFTS结果显示,在Au-Ni双金属催化剂中,Au的存在促进了Ni的还原,说明Au与Ni之间存在紧密的相互作用.综上可见,Au和Ni在乙炔选择加氢反应中所表现出的协同效应主要归功于Au-Ni合金的形成,其中金属态Ni起主要的活性作用,而Au的存在则提高了催化剂的乙烯选择性.     

Selective extraction and release using (EDTA-Ni)-layered double hydroxide coupled with catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine for sensitive detection of copper ion

Copper is an important heavy metal in various biological processes. Many methods have been developed for detecting of copper ions (Cu²⁺) in aqueous samples. However, an easy, cheap, selective and sensitive method is still desired. In this study, a selective extraction-release-catalysis approach has been developed for sensitive detection of copper ion. Ethylenediaminetetraacetic acid (EDTA) chelated with nickel ion (Ni²⁺) were intercalated in a layered double hydroxide via a co-precipitation reaction. The product was subsequently applied as sorbent in dispersive solid-phase extraction for the enrichment of Cu²⁺ at pH 6. Since Cu²⁺ has a stronger complex formation constant with EDTA, Ni²⁺ exchanged with Cu²⁺ selectively. The resulting sorbent containing Cu²⁺ was transferred to catalyze the 3,3′,5,5′-tetramethylbenzidine oxidation reaction, since Cu²⁺ could be released by the sorbent effectively and has high catalytic ability for the reaction. Blue light emitted from the oxidation product was measured by ultraviolet–visible spectrophotometry for the determination of Cu²⁺. The extraction temperature, extraction time, and catalysis time were optimized. The results showed that this method provided a low limit of detection of 10 nM, a wide linear range (0.05–100 μM) and good linearity (r² = 0.9977). The optimized conditions were applied to environmental water samples. Using Cu²⁺ as an example, this work provided a new and interesting approach for the convenient and efficient detection of metal cations in aqueous samples.     

Colorimetric detection of sulfide based on target-induced shielding against the peroxidase-like activity of gold nanoparticles

Colorimetric recognition and sensing of sulfide with high sensitivity was proposed based on target-induced shielding against the peroxidase-like activity of bare gold nanoparticles. Significant features of the new assay system are its simplicity and cost-effectiveness. The recognition of sulfide by bare gold nanoparticles can be fulfilled in a few seconds and the assay can be accomplished in about 10 min. Furthermore, the new assay system does not require surface modification of GNPs to obtain the specificity for sulfide, and a salt-induced aggregation step is not needed. The detection limit of this method for sulfide was 80 nM. These features make this sensor a potentially powerful tool for the quantitative determination of sulfide in water samples.     

One-pot synthesis of 5,5′-dibromo-2,2′-dipyridylacetylene and its boronic acid derivative

5,5′-Dibromo-2,2′-dipyridylacetylene was prepared from 2,5-dibromopyridine and (trimethylsilyl)acetylene via the new one-pot synthesis approach using a regioselective palladium-catalyzed coupling reaction with a 60% yield. Several protocols of lithium-halogen exchange were then attempted to synthesize 6,6′-(1,2-ethynediyl)bis[3-pyridylboronic acid] from 5,5′-dibromo-2,2′-dipyridylacetylene. The former was successfully obtained with a 54% yield by a reverse addition method using toluene and THF and it showed potential as a useful building block for cross-coupling reactions in the formation of carbon-carbon bonds.     

The first approach to optically active 2,2′-bipyridine alkyl sulfoxides

The synthesis of 6,6′-bis(alkylsulfanyl)-2,2′-bipyridines and their asymmetric oxidation to non-racemic 2,2′-bipyridine alkyl sulfoxides using either (+)-(8,8-dichlorocamphorylsulfonyl)oxaziridine or a modified Sharpless reagent is reported.     

Asymmetric flow catalysis: Mix-and-go solid-phase Nd/Na catalyst for expeditious enantioselective access to a key intermediate of AZD7594

An anti-selective catalytic asymmetric nitroaldol reaction was implemented in a continuous-flow reaction platform for the synthesis of a key intermediate of a drug candidate. The requisite solid-phase catalyst was readily prepared by mixing an amide-based chiral ligand and inexpensive inorganic salts, NdCl₃?6H₂O and NaO^tBu, without covalent bond linkages. The flow system was operated with 2-Me-THF as the eluent for ca. 400 h to provide a crude nitroaldol adduct in a highly stereoselective manner with no work-up procedure, reaching turnover number over 1600. Facile reduction of the nitro group of the product afforded a key intermediate of AZD7594, a therapeutic candidate for asthma and chronic obstructive pulmonary disease.     

Facile acid-catalyzed condensation of 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone with phenols, methoxyaromatic systems and enols

Various phenols, methoxy aromatic compounds, 3- and 4-hydroxycoumarins and enols smoothly condense with 2-hydroxy-2,2′-biindan-1,1′,3,3′-tetrone 1 in an acid medium producing 2-aryl/alkyl-2,2′-biindan-1,1′,3,3′-tetrones in high yields. The adducts of resorcinol, 1,3,5-trihydroxybenzene and α- and β-naphthols of 1 preferably remain in the intramolecular hemi-ketal form, confirmed by X-ray diffraction studies. On the other hand para and meta substituted phenols condense with 1 in an acid medium to produce 6 or 7 substituted 2′,4-spiro(1′,3′-indanedion)-indeno[3,2-b]chromenes in good yields.     

用于吖内酯合成的二氧化钛纳米晶体材料PriyankaAnandgaonker,GaneshKulkarni,SureshGaikwad,AnjaliRajbhoj简

Titanium dioxide nanoparticles were prepared by a electrochemical reduction method using parameters such as current density, solvent polarity, distance between electrodes, and concentration of stabilizers to control the size of the nanoparticles. The nanoparticles were characterized by UV-Vis spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy, and their catalytic performance was tested for the synthesis of a series of 4-aryldiene-2-phenyl-5(4)-oxazolones from the cyclodehydration and condensation of the respective aldehyde, hippuric acid and acetic anhydride. Easy availability, reusability and eco-friendliness were some prominent features of the nanocrystalline titanium dioxide catalyst.     

A complicated path of salicylaldehyde through the Biginelli reaction: a case of unexpected spiroketalization

Cyclocondensation of salicylaldehydes with alkyl acetoacetates and 2-aminobenzothiazoles or 2-amino-5-methylthiazole under classical Biginelli reaction conditions gives rare hetarylamino substituted 2,2′-spirobischromanecarboxylate derivatives. The mechanism and observed stereoselectivity of the unexpected pseudo-four-component process are discussed.     

Difluorocarbene chemistry: synthesis of gem-difluorocyclopropenylalkynes and 3,3,3′,3′-tetrafluorobicyclopropyl-1,1′-dienes

A series of gem-difluorocyclopropenylalkynes are easily obtained in good yields by the Sonogashira reaction of 3,3-difluoro-1-iodocyclopropenes with terminal alkynes. Onto these new alkynes addition of difluorocarbene, generated from the decomposition of FSO₂CF₂COOTMS in diglme in the presence of 10 mol% anhydrous NaF at 120 °C, gives 3,3,3′,3′-tetrafluorobicyclopropyl-1,1′-dienes. Acid hydrolysis of gem-difluorocyclopropenylalkynes in refluxing CH₃OH affords the corresponding methoxycarbonylenynes.     

Sequential homo-coupling Diels-Alder/retro Diels-Alder reaction of 5,5′-bi-1,2,4-triazine-containing thiamacrocycles as a new route to thiacrown ethers incorporating a 2,2′-bipyridine subunit

A new route to thiacrown ethers 5a-d and 6a-d incorporating a 2,2′-bipyridine subunit is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfides 3a-d tethered to poly(ethylene glycol) chains with potassium cyanide and (2) Diels-Alder/retro Diels-Alder reaction with norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps.     

活性钛与芳基丙酮的还原偶合反应

羰基化合物还原偶合是形成碳-碳键的一种重要方法。本文首次发现此类反应的产物不仅与反应物本身的结构和还原试剂体系有关，还与操作次序有很大关系，且在活性钛表面反应。