Phenomena Affecting the Equilibrium of Al(III) and Zn(II) Extraction with Winsor II Microemulsions

The extraction of Al(III) and Zn(II) from an aqueous solution with two water-in-oil microemulsions, one containing di(2-ethylhexyl)phosphoric acid (DEHPA), was investigated to aid the understanding of the role of the extractant and the metal specific characteristics in the mechanism of microemulsion extraction. The extraction of Al with the DEHPA microemulsion increased by a factor of about 10 with respect to that in the conventional DEHPA system, whereas the extraction of Zn was lower than that in the single DEHPA system. Extraction with the DEHPA-free microemulsion was very low, showing that metal ion solubilization was not important in the mechanism of microemulsion extraction. It is proposed that the effect of the mixed microemulsion on the metal distribution coefficient is the result of the balance between a decrease in the complexation reaction yield due to the interaction between butanol and DEHPA, and the adsorption of the metal complex at the macro- and microinterfaces. The former leads to a decrease in Zn(II) extraction and the latter to Al(III) extraction synergism. Copyright 2000 Academic Press.     

A sub-stoichiometric tungsten-mediated Pauson-Khand reaction: Scope and limitations

Terminal alkynes do not partake in sequential [2+2+1]/benzoannulation reactions with Fischer carbene complexes and highly reactive and sterically hindered olefins; instead, they undergo a Fischer carbene complex-catalyzed Pauson-Khand reaction (PKR). This result has allowed the development, for the first time, of a tungsten-catalyzed PKR, although of limited scope.     

New cascade processes on group 6 Fischer-type carbene complexes: cyclopropanation and metathesis reactions

Alkynyl Fischer carbene complexes 1, which feature a pendant olefin group, undergo novel cascade processes triggered by [2+2], [3+2], and [4+2] cycloadditions. Competition between cyclopropanation and olefin metathesis is controlled by the substitution at the double bond. The method described can be used to obtain different kind of polycarbo- and -heterocycles. A mechanistic explanation by means of DFT computational modeling is provided.     

Photohemolysis sensitized by the furocoumarin imperatorin and its oxyfunctionalized derivatives

The dark and photosensitized (366 nm) hemolytic effects of imperatorin and its photooxidation products, the hydroperoxides I and II as well as the corresponding alcohol of the hydroperoxide I (imperatorin alcohol), were studied on human erythrocytes. Imperatorin was shown to photosensitize hemolysis, its fluence (D) dependence of the rate of photohemolysis (V) followed the equation V = V0 + aD2 + bD1/2, in which V0 is the dark hemolysis rate and a and b are constants. At fluences below 200 kJ/m2, the main hemolytic contribution derives from the bD1/2 component, which is due to the in situ formation of the imperatorin hydroperoxides, while at fluences higher than 200 kJ/m2, the main contribution corresponds to the aD2 component due to the two-photon damage of cell membranes. Hydroperoxides I and II induce oxyhemoglobin cross-linking, as well as its conversion to methemoglobin and hemichrome. These reactions involve hydroxyl and alkoxy radicals, as the hemolysis and oxyhemoglobin conversion could be inhibited by t-butanol and butylated hydrotoluene. For comparison, the dark hemolytic effect of the imperatorin alcohol was approximately 10-fold less than of the hydroperoxides.     

Fluoride-promoted oxidation of Fischer alkoxy carbene complexes: stoichiometric and catalytic conditions

The utility of fluoride anion as promoter of the oxidation of Fischer carbene complexes is presented. Two different and complementary methods that allow the fast and convenient preparation of carbene-derived esters in good yields have been developed using stoichiometric or catalytic quantities of fluoride ion.     

Unprecedented reactivity pattern of chromium fischer carbene complexes. Direct application to one-pot synthesis of 4-aryl-3,4-dihydrocoumarins on a multigram scale

[reaction: see text] Reaction of alkenyl carbene chromium(0) complexes and ketene acetals triggers the formation of 4-aryl-3,4-dihydrocoumarins. The reaction can be carried out as a simple one-pot protocol in air atmosphere. The huge interest of dihydrocoumarins has prompted us to optimize a multigram-scale process.     

机械泵驱动两相回路的实时动态模型分析

在航空航天领域,为了加速系统设计及测试进度,通常需要进行半实物实时仿真,即控制器用实物,受控对象采用数学模型。本文开发出了基于Matlab/Simulink的两相传热模块,并用其搭建了某机械泵驱动两相回路的实时动态模型。通过与实验的对比,验证了模型的可靠性,表明该模型满足实时要求,可以在下一步用于半实物仿真。     

A novel [2 + 2 + 1]/[2 + 1] tandem cycloaddition reaction of Fischer alkynyl carbenes with strained bicyclic olefins

The reaction of strained bicyclic olefins with alkynyl carbenes and terminal olefins involves the creation of five new sigma C-C bonds with the concomitant formation of two new rings, thus creating a complex and densely functionalized structure in a single operation.     

Synthesis of Spiroheterocyclic Oxygen-Containing Tryptanthrin Derivatives

6-Spiro derivatives of tryptanthrin were synthesized in high yields by reaction of indolo[2,1-b]quinazoline- 6,12-dione with alkanediols. The structure of the spiro dioxolane derivatives was studied in detail by X-ray analysis.