New oxo-bridged dinuclear peroxotungsten(VI) complexes: Synthesis, stability and activity in bromoperoxidation

Two new dinuclear oxo-bridged peroxo complexes of tungsten with coordinated dipeptides of the type, Na₂[W₂O₃(O₂)₄(glycyl-glycine)₂] · 3H₂O (1) and Na₂[W₂O₃(O₂)₄(glycyl-leucine)₂] · 3H₂O (2) have been synthesized from the reaction of H₂WO₄, 30% H₂O₂ and the respective dipeptide at pH ca. 2.5. Synthesis of the compounds, in addition to pH, is sensitive to reaction temperature and concentrations of the components. The compounds were characterized by elemental analysis, spectral and physico-chemical methods including thermal analysis. In the dimeric complexes the two W(VI) centres with edge bound peroxo groups are bridged by an oxo group. The dipeptides occurring as zwitterions bind the metal centers through O (carboxylate) atoms leading to hepta co-ordination around each W(VI). Thermal stability of the compounds as well as their stability in solution were determined. The compounds are highly stable toward decomposition in solutions of acidic as well as physiological pH. These compounds, besides another similar dimeric compound Na₂[W₂O₃(O₂)₄(cystine)] · 4H₂O (3) efficiently oxidized bromide to a bromination competent intermediate in phosphate buffer at physiological pH, a reaction in which only two of the peroxide groups of the complex species were found to be active. The complexes could also mediate bromination of organic substrate in aqueous-organic media.     

Electrochemical formation of conducting polymer coating on porous p‐ and n‐silicon substrates

Electrochemical synthesis of polyaniline was carried out in aqueous sulfuric acid solutions of aniline on porous p‐ and n‐silicon under galvanostatic, potentiostatic and potential pulse regimes. It is shown that the introduction of catalytic quantities of oxidants, potassium hexachloroiridate, potassium dichromate, potassium permanganate and chloranilic acid, in electrolytes accelerates the formation of polymer films and lowers the overvoltage of electrosynthesis. The resulting polymer coatings are characterized by cyclic voltammetry and IR spectroscopy. It is shown that polyaniline coatings on porous p‐ and n‐silicon electrodes are electroactive and conducting in anodic and cathodic ranges. Copyright © 2000 John Wiley & Sons, Ltd.     

液相氧化碳纳米管的氧化剂选择

研究了在不同氧化剂作用下,碳纳米管引入含氧官能团的情况,提出了利用Boehm滴定法对碳纳米管表面的羧基进行定量分析的方法。结合X-射线光电子能谱对含氧官能团的分析,进一步探讨了碳纳米管氧化的过程和机理。     

NH_4C1·CrO_3对烯丙基醚和苄基醚的选择性氧化成酯的研究

本文报道了NH_4Cl·CrO_3(简称ACC)在无溶剂反应条件下,以较好的产率,将烯丙基醚或苄基醚选择性地氧化成相应的酯。     

Polystyrylsulfonyl-3-nitro-1H-1,2,4-triazolide-resin: a new solid-supported reagent for the esterification of amino acids

We describe the application of the polystyrylsulfonyl-3-nitro-1H-1,2,4-triazolide-resin, readily available from the corresponding commercially available polystyryl sulfonyl chloride resin, to the solution-phase synthesis of esters from protected α-amino acids and alcohols in high yields and purity with a low level of racemisation of the amino acids. All by-products can be removed by filtration and extraction.     

Effect of the nature of acid dopant and oxidizer on the polymerization of aniline in the presence of polycarbonate dispersion

The characteristics of aniline polymerization in the absence and in the presence of a dispersion of polycarbonate powder in dependence on the nature of acid dopant and oxidant has been studied. By monitoring the polymerization in situ by electronic spectroscopy and redoxometry allows the determination of the stages of formation of shell of polyaniline on the surface of polymer particles and the influence of the latter on the rate of these stages and of the process as a whole. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 1, pp. 52–57, January–February, 2008.     

New reaction for the preparation of liquid rubber

The article reports on the noncatalytic transformation of a polybutadiene (number‐average molecular weight = 128,000) into a functionalized liquid rubber via the carboxidation of the polymer C?C bonds by nitrous oxide. The reaction was conducted in a benzene solution at 160–230 °C and a pressure of 3–6 MPa. The carboxidation mechanism was determined. The main route (95%) of the reaction proceeded without cleavage of C?C bonds and led to the formation of ketone groups in the polymer backbone. A minor route (5%) of the reaction proceeded with the cleavage of C?C bonds, yielding two smaller fragments containing aldehyde and vinyl end groups. The availability of the cleavage route could lead to a dramatic decrease in the molecular weight, which, depending on the carboxidation degree, could be 1–2 orders of magnitude less than that of the initial material. Thus, the carboxidation of more than 15% of the polybutadiene C?C bonds transformed it into a C?O‐functionalized liquid rubber with a narrow molecular weight distribution. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2510–2520, 2006     

D-氨基葡萄糖、α-甘氨酸金属混配物的研究

报道了D－氨基葡萄糖，α－甘氨酸与Cu(Ⅱ),Zn(Ⅱ),Fe(Ⅲ），Co(Ⅲ),Ni(Ⅱ)形成的混配物的合成方法，通过元素分析，IR，UV－Vis,1HNMR,13CNMR等手段对配合物进行了表征。采用Pryrogallol-NBT比色法对化合物清除超氧自由基（O2－）的能力进行了测试，结果表明各配位体对超氧自由基（O2－）均有一定的清除作用。     

An internal oxidant-directing strategy enabling transition metal-free C–S bond ligation

Organic sulfur compounds have broad applications in biology, medicine and material sciences and intensive efforts have been devoted to developing mild and general C–S bond-forming methods. However, a mild, transition-metal-free, direct C–H bond functionalization method remains elusive. Here, we report the use of an internal oxidant-directing strategy to achieve this goal. The cascade reactions described here show excellent chemoselectivity and a wide substrate scope for both oxyamines and sulfenylation reagents. This study enlarges the synthesis toolbox for preparing structurally diverse sulfilimines under mild conditions.     

High-loading polyglycerol supported reagents for Mitsunobu- and acylation-reactions and other useful polyglycerol derivatives

Summary In this paper we present soluble dendritic polyglycerol (PG) supported reagents PG-DEAD, PG-PPh₃, and PG-DCC as well as scavengers PG-carbonate, PG-carbazate, and PG-amine, which all have been synthesized in high overall conversions and yields using simple purification techniques. The supported reagents have been used simultaneously in Mitsunobu and acylation reactions. All polymeric reagents and scavengers can be removed by simple precipitation/filtration protocols to give chromatography-free products of high purity. In the course of the syntheses of the polymeric reagents three intermediates turned out to be precious polyglycerol derivatives: a mixed carbonate as an electrophilic derivative, polyglyceryl carbazate as a scavenger for carbonyl compounds, as well as polyglycerylamines as amino analogues of polyglycerol.