Electrolyte Anion Affinity and Its Effect on Oxyanion Adsorption on Goethite

The influence of various types of background electrolytes (NaCl, NaNO(3), and NaClO(4)) on the proton adsorption and on the adsorption of sulfate and phosphate on goethite have been studied. Below the PZC the proton adsorption on goethite decreases in the order Cl>NO(3)>ClO(4). The decreasing proton adsorption affects the adsorption of oxyanions on goethite. Anion adsorption of strongly binding polyvalent anions is lower in the studied electrolytes in the order Cl相似文献   

Fluoride Adsorption on Goethite in Relation to Different Types of Surface Sites

Metal (hydr)oxides have different types of surface groups. Fluoride ions have been used as a probe to assess the number of surface sites. We have studied the F(-) adsorption on goethite by measuring the F(-) and H(+) interaction and F(-) adsorption isotherms. Fluoride ions exchange against singly coordinated surface hydroxyls at low F(-) concentrations. At higher concentrations also the doubly coordinated OH groups are involved. The replacement of a surface OH(-) by F(-) suggests that all F charge (-1) is located at the surface in contrast to oxyanions which have a charge distribution in the interface due to the binding structure in which the anion only partially coordinates with the surface. Analysis of our F(-) data with the CD-MUSIC approach shows that the formation of the fluoride surface complex is accompanied by a redistribution of charge. This is supposed to be due to a net switch in the H bonding as a result of the change of the type of surface complex from donating (FeOH, FeOH(2)) to proton accepting (FeF). The modeled redistribution of charge is approximately equivalent with the change of a donating H bond into an accepting H bond. At high F(-) concentrations precipitation of F(-), as for instance FeF(3)(s), may occur. The rate of formation is catalyzed by the presence of high electrolyte concentrations. Copyright 2000 Academic Press.     

ARC-length method for differential equations

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｏｒｄｉｎａｒｙａｎｄｐａｒｔｉａｌｄｉｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓｏｆｃｏｎｔｉｎｕｕｍｐｒｏｂｌｅｍａｒｅｏｆｔｅｎｗｉｔｈｃｅｒｔａｉｎｔｙｐｅｓｏｆｓｉｎｇｕｌａｒｉｔｙａｓｓｔｉｆｐｒｏｐｅｒｔｙ,ｏｒ...     

Limitations,mechanism and understanding of the origins of stereocontrol in (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide-mediated epoxidation reactions

The reaction of the (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide with aldehydes gave α,β-epoxy sulfoxides with high enantioselectivity and diastereoselectivity dependent on the aldehyde. The mechanism of the ‘model’ reactions [ylide substituted with Me S(O) or Ph S(O) with MeCHO or PhCHO] has been studied in detail using density functional theory.     

Synthesis and Reactivity of some Aromatic Sulfides Substituted by an Ortho-Phosphonyl Group

Abstract

As phosphorus-based members of the biologically relevant thiosalicylic acid, monoesters of ortho-sulfinylated phenylphosphonic acids such as 3 and 4 (series a, R¹=Me; b, R²2-C₆H₄C0₂H) are of special interest. They might act both as potential sources of new anionic bidentate ligands for the synthesis of cisplatin analogues^[1] and as suitable precursors of phosphorus-containing endocyclic sulfoximides and hypervalent organo-sulfur species. We have therefore undertaken the synthesis of these compounds. The starting phenylphosphonic acid diisopropylesters 1 were formed by using a LDA-induced thiophosphate-mercaptophosphonate rearrangement^[2] described earlier and converted into their dimethyl counterpans 2 by means of a trans-silylation procedure followed by alkylation. We have now performed the selective half-hydrolysis of phosphonic acid diesters 1.2 and sulfoxidation of the resulting monoesters.     

Asymmetric Cyclopropanation of Optically Active Vinyl Sulfoxides: A New Synthetic Approach to Biologically Active Compounds

Abstract

The influence of adjacent substituents on stereochemical course of cyclopropanation of vinyl sulfoxides with stabilized and nonstabilized ylides, as well as dependence on reaction conditions, was investigated. Application of optically active cyclopropanes obtained in the synthesis of conformationally constrained analogs of L-glutamic acid, the useful pharmacological tools in investigation of excitatory amino acid receptors, is presented.     

Hydrogenation of

The course of the hydrogenation of [5]- and [6]metacyclophane (1b and 1c) and their thermochemistry is described. Both compounds are hydrogenated rapidly (within 10 s) to furnish the bridgehead olefins 13b and 12c. The accompanying hydrogenation enthalpies are -220 and -141 kJmol(-1), respectively. Strain energies (SE) and olefinic strains (OS) of a number of bridgehead olefins have been evaluated by DFT calculations; it was concluded that 13b belongs to the class of hyperstable olefins which correlates nicely with its reluctance to undergo hydrogenation. By combining experimental hydrogenation enthalpies and DFT calculations, SE of 187 and 121 kJmol(-1) were derived for 1b and 1c.