Synthesis and electrochemical properties of substituted para-benzoquinone derivatives

A facile transformation of pentasubstituted tribromophenol derivatives to the corresponding alkyl-substituted dibromo-p-benzoquinones has been achieved using PbO₂ as oxidizing agent in combination with 60% aq HClO₄ in acetone in 70-72% yields. The electrochemical properties of these quinones were studied by means of cyclic voltammetry and compared with p-benzoquinone (BQ) and 2,3-dichloro-5,6-dicyano-benzoquinone (DDQ) recorded under identical experimental conditions.     

Mixed monolayers of polymethacrylic esters containing aromatic and aliphatic groups

The interfacial properties of mixtures of polymethacrylic polymers containing either aromatic or aliphatic side groups were studied at water-air interface in order to define the role of geometrical orientation on surface compatibility and the effect of aromatic interactions on ordered bidimensional systems. Two binary systems were studied: polyphenylmethacrylate/ polyhexylmethacrylate and polyphenylmethacrylate/polybenzylmethacrylate.Surface pressure and surface potential measurements were performed in the 288–303 K temperature range on the mixtures at different polymer concentrations. Further information was obtained from ellipsometric measurements and scanning electron microscopy of the collapsed material. The experimental results allow for the conclusion that both polymers containing aromatic groups are almost ideally miscible whereas mixtures of aliphatic and aromatic polymers are completely immiscible.     

Thermal and photochemical reactions of allylcobaloximes with para-substituted benzenesulphonyl chloride under aerobic and anaerobic conditions

The compounds p-XC₆H₄SO₂Cl (X = Cl, Br, I, OMe) react regiospecifically with allyl-, 2-methylallyl-, 3-methylallyl- and 3,3-dimethylallyl-cobaloximes under thermal and photochernical conditions. A rearranged organic product is obtained in each case. The yields are much better in photochemical reactions. A chain mechanism is involved in which the organosulphonyl radical and cobaloxime(II) are the chain propagating species. Yields of the sulphones are drastically reduced when the reactions are carried out in the presence of oxygen.     

Straightforward protocol for the efficient synthesis of varied N-acylated (aza)indole 2-/3-alkanoic acids and esters: optimization and scale-up

A library of approximately 40 N¹-acylated (aza)indole alkanoic esters and acids was prepared employing a microwave-assisted approach. The optimized synthetic route allows for parallel synthesis, variation of the indole substitution pattern, and high overall yield. Additionally, the procedure has been scaled up to yield multi-gram amounts of preferred indole compounds, e.g.: 2′-des-methyl indomethacin 2. The reported compounds were designed as biomedical tools for primary and secondary in vitro and in vivo studies at relevant molecular targets.     

Synthesis and self-assembly properties of para-acyl-calix[8]arenes

The synthesis of a series of novel para-acyl-calix[8]arenes is described, while for acyl chain lengths of greater than eight carbon atoms total substitution at the para position occurs, in contrast to the para-acyl-calix[4]arenes, some esterification at the phenolic face may also occur, particularly for shorter acyl chain lengths. Simple saponification with potassium hydroxide in ethanol allows the pure compounds to be obtained in good yields. All the derivatives show amphiphilic behaviour with formation of stable monolayers at the air-water interface and apparent molecular areas between 150 and 275 Å².     

Effect of zinc chloride on thermal decomposition of polymethacrylic and polyacrylic esters

Zinc chloride reduces the rate of thermal and thermooxidative decompositions of polymethacrylic esters and increases the thermal decomposition rate of polyacrylic esters. Mechanisms of the thermal decompositions of polymethacrylates and polyacrylates in the presence of ZnCl₂ have been suggested.For thermal decomposition polymethacrylic esters, the rate of depolymerization decreases due to the formation of cycles in a polymer chain by reaction of Zinc chloride with neighbouring ester groups. For thermooxidative decomposition of polymethacrylates, ZnCl₂ decreases also the rate of initiation of depolymerization and causes decomposition of hydroperoxide groups by a heterolytic mechanism. The increase in thermal decomposition rate of polyacrylic esters results from the high activity of complexes of ester groups and ZnCl₂ in decomposition reactions with formation of alcohol and CO₂ through Cameron mechanism.     

Hydrodynamic properties and conformation of molecules of para- and meta-isomers of polyoxyphenylbenzoxazoleterephthalamide

Translational diffusion and intrinsic viscosity in 96% H₂SO₄ have been investigated for 20 samples of the para-isomer of polyoxyphenylbenzoxazoleterephthalamide (PpOPhBT) and 17 samples of its meta-isomer (PmOPhBT). The Mark-Kuhn equations have been obtained. The equilibrium rigidity of macromolecules in solution, calculated by using the wormlike chain theory, was characterized for PpOPhBT by the length of the Kuhn segment $\text{A = 320}\text{A}\text{?}$, the number of monomer units in a segment s = 17 and the coefficient of hindrance to intramolecular rotation in the chain σ = 1.5. For PmOPhBT the corresponding values are: $\text{A = 96}\text{A}\text{?}$, s = 5.9 and σ = 1.6. Analysis of flexibility mechanisms was carried out for PpOPhBT and PmOPhBT chains in solution.     

Preparation and properties of carboxyl-functional mixed esters of hydrolyzed starch

Mixed esters of hydrolyzed starch represent a new class of chemically modified natural polymers demonstrating a broad range of properties. Members of this class of polymers have both neutral aliphatic ester side chains and carboxyl-functional half-ester side chains. Use of hydrolyzed starch as the backbone polymer results in products that are considerably lower in molecular weight than whole starch derivatives, but which are still polymeric in character. Synthesis proceeds smoothly in pyridine using anhydrides as acylating agents and the pure solid mixed ester products are isolated by precipitation in water. Measurement of degree of substitution (D.S.) by NMR or hydrolysis characterizes the chemical composition of the polymers. The actual D.S. achieved in the synthesis depends upon the competition between starch and residual water for anhydrides, which can be quantitatively evaluated by monitoring the acid content of the reaction mixture. The T_g and T_s of starch mixed esters vary with both D. S. and length of the aliphatic ester side chain. As the composition changes from acetate—phthalate to butyrate—phthalate a T_g range of greater than 100°C is observed. Hydrolyzed starch mixed esters are hydrophobic and organic-soluble, but may be readily solubilized in aqueous base through the half-ester groups. Solutions show surface activity which varies according to the type and extent of substitution.     

Spectral and photochemical properties of hydroxylated 2-styrylquinoline derivatives

The spectral and photochemical properties of 2-(4-hydroxystyryl)quinoline 1 and 2-(2-hydroxystyryl)quinoline 2 have been studied. The trans-cis photoisomerization quantum yield for 1 and 2 in the neutral form is 0.2–0.5, and it is reduced by a factor of 6–7 by protonation, presumably, owing to the competitive process of hydroxyl group deprotonation in the excited state and the formation of quinoid tautomers. The quantum yield of the back cis-trans photoisomerization in the protonated form varies insignificantly. The neutral, protonated, and deprotonated forms of 1 have been used for to simulate a molecular logic gate, the half-adder with chemical inputs and absorbance as outputs.     

Synthesis of para-substituted styrenes

Using double Stille cross-coupling reaction bromo (or chloro)benzylbromide is easily transformed into substituted styrene monomers bearing a wide range of substituents in para position     

Preparation and properties of pure lithio esters of some carboxylic acids

Lithio esters of carboxylic acids have been prepared in pure state and their properties are described. Interaction between the lithio esters with alkali metals alkoxides has been demonstrated, and some adducts have been isolated. The IR and UV spectra of these compounds are described, and their structures are discussed.     

双马来酰亚胺树脂/SiO_2纳米复合材料的制备及性能

以表面含有胺基官能团的纳米SiO_2为填料,通过一步原位聚合法制备双马来酰亚胺树脂/SiO_2纳米复合材料(BMI/SiO_2).采用热重分析仪(TGA)、红外光谱分析仪(FTIR)、邵氏D硬度计(H)等仪器设备对BMI/SiO_2纳米复合材料进行测试分析,探讨纳米SiO_2对双马来酰亚胺聚酯树脂的热稳定性能、硬度和界面强度的影响.结果表明,所制备的BMI/SiO_2纳米复合材料的硬度随加入的纳米SiO_2含量的增加,呈现逐渐升高趋势.当纳米SiO_2含量为3%时,相对于双马来酰亚胺聚酯,复合材料的硬度提高了80%.通过热稳定性分析可知,纳米SiO_2的加入降低了双马来酰亚胺树脂基体材料的热分解温度,使其从458℃降低到451℃.通过对双马来酰亚胺/SiO_2纳米复合材料的界面分析发现,纳米SiO_2的表面接枝了双马来酰亚胺分子链,说明纳米SiO_2参与了双马来酰亚胺的聚合过程,有利于提高聚合物基体材料与填料间的界面强度,进而提高复合材料的机械性能.     

A vicarious synthesis of unsymmetrical meta- and para- terphenyls from 2H-pyran-2-ones

An innovative synthesis of terphenyls functionalized with electron-withdrawing or -donating substituents is described and illustrated by carbanion-induced ring transformation of 2H-pyran-2-ones with 2-methoxyacetophenone in excellent yields. The existing protocols for the synthesis of terphenyls are generally inter- and intramolecular aryl-aryl cross couplings in the presence of metal complexes. In this letter, we report a potentially useful alternative to conventional metal-catalyzed cross-coupling reactions.     

C/Nd/TiO2催化剂的制备及光催化性能研究

利用溶胶-凝胶法以钛酸四丁酯为钛源、硝酸钕为钕源、葡萄糖为碳源,制备了C和Nd单掺杂及共掺杂TiO_2催化剂。通过XRD、XPS、漫反射、SEM和物理吸附对所制备的催化剂进行表征与评价。结果表明,C和Nd共掺杂TiO_2的晶型仍为锐钛矿型,表面光滑,晶粒大小分散均匀,孔径分布在20~34 nm之间;与其他三种催化剂相比,共掺杂催化剂比表面积较大;通过掺杂C和Nd元素,形成新能带E_(C2p)和E_(Nd3+4f),降低了电子跃迁能,有利于光催化活性增强。C和Nd共掺杂TiO_2对可见光的吸收能力有明显提高,对甲基橙染料降解效果较佳,其脱色率为61.24%。     

Microwave-assisted synthesis of pyridylpyrroles from N-acylated amino acids

A small library of 3- and 4-pyridyl-substituted pyrroles was prepared from N-acylated amino acids. Nicotinoyl or isonicotinoyl chloride was used for the N-acylation of benzyl esters of amino acids. Debenzylation by palladium-catalyzed hydrogenation gave N-acylated amino acids. Dehydration of the acylated amino acids gave cyclic intermediates, münchnones or azlactones, which were treated in situ with alkynes in 1,3-dipolar cycloadditions. The starting materials were prepared in a parallel fashion, and microwave irradiation was used to facilitate the cycloaddition reactions. The regiochemistry of the cycloaddition was studied.     

Preparation and properties of FeAs2 and FeSb2

Single crystals of FeAs₂ and FeSb₂ were prepared by chemical vapor transport using chlorine as the transporting agent. Electrical and magnetic measurements have been made on well-characterized samples. FeAs₂ was found to be a diamagnetic semiconductor with a band gap of 0.22 eV. FeSb₂ has an extremely narrow band gap and shows unusual electrical and magnetic properties. Aproposed band model is used to explain the experimental results.