PREPARATION AND X-RAY CRYSTAL STRUCTURES OF TWO ALIPHATIC SELENENYL BROMIDES STABILIZED BY N─SE COORDINATION

(1R)-2-endo-(Dimethylamino)methyl-2-exo-methoxy-3-endo-camphor- ylselenenyl bromide and its 2-endo-(pyrrolidenyl)methyl analogue were prepared from (1R)-2-endo-acetamidomethyl-2-exo-hydroxy-3-endo-camphoryl diselenide. Both compounds showed an unusual lack of reactivity in electrophilic oxyselenenylation and cyclization reactions that are typical of other selenenyl bromides. X-ray crystallography indicated that both compounds have strong N─Se interactions, with N─Se interatomic distances of ca. 2.1 Å, which diminish the electrophilic character of the selenium atom.     

醋酸烯丙酯选择性地合成烯丙基硒醚

醋酸烯丙酯被Pd(PPh3)4-SmI2还原，并发生中间体π-烯丙基钯络合物的极性 反转，而后与芳基硒溴化物作用，生成烯丙基硒醚．     

New chiral auxiliaries for highly stereoselective asymmetric methoxyselenenylations

Replacement of the 2-keto group of readily available di(endo-3-camphoryl) diselenide with oxime or O-benzoyloxime substituents, followed by conversion into the corresponding selenenyl triflates, produced highly effective chiral selenium electrophiles for the asymmetric oxyselenenylation of alkenes in the presence of methanol.     

A new route to the improved synthesis of 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils

A new route to C-6-selenenyl analogs of compound 1a from 5-alkyl-6-chlorouracils 6a-b has been described. A mild and highly efficient synthesis of 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils 8a-e has been accomplished from 6a-b in good yields using a two step procedure. Silylation of 5-alkyl-6-chlorouracils 6a-b using N,O-bis(trimethylsilyl)acetamide followed by regioselective alkylation of the silylated intermediate with ethyl or benzyl chloromethyl ether in dichloromethane afforded the desired 1-(alkoxymethyl)-5-alkyl-6-chlorouracils 7a-d in 88–94% yields. Compounds 7a-d readily underwent addition-elimination reaction with an appropriate arylselenol in the presence of ethanolic sodium hyroxide to produce the corresponding 1-(alkoxymethyl)-5-alkyl-6-(arylselenenyl)uracils 8a-e in excellent yields (94–99%).     

Reactions involving selenium metal as an electrophile: Scope and limitations of the enolate-selenolate transformation

When lithium enolates are allowed to react with selenium metal, selenolate (selenide) ions are formed. Alkylation of these selenolate ions produces the corresponding α-alkylselenenyl carbonyl derivatives. These derivatives can then be converted to their unsaturated counterparts using the same type of protocols that are employed with arylselenenyl derivatives.     

Efficient one-pot conversion of carbonyl compounds to their alpha,beta-unsaturated derivatives using a recoverable, minimally fluorous organoselenium reagent

A protocol for the preparation of a fluorous arylselenenyl chloride is described. This selenenyl chloride may be used for the direct alpha-selenation of ketones and, following oxidation and syn-elimination, formation of alpha,beta-unsaturated carbonyl compounds. Treatment of the crude reaction mixtures with sodium metabisulfite reduces the various selenium species to the diaryl diselenide, which is then recovered in high yield by continuous fluorous extraction.     

Enantioselective oxysulfenylation and oxyselenenylation of olefins catalyzed by chiral Brønsted acids

This paper describes Brønsted acid catalyzed enantioselective oxysulfenylation and oxyselenenylation of olefins. Enantiomerically enriched tetrahydrofurans are formed with up to 63% ee with dibenzoyl-d-tartaric acid and its derivatives as catalyst. Chiral β-carboxyl sulfides and selenides have also been obtained with up to 50% and 84% ee, respectively, via enantioselective desymmetrization of thiiranium and seleniranium ions in the presence of catalytic amounts of chiral binaphthol derived N-triflyl phosphoramide.     

A facile stereoselective synthesis of (E)‐1,2‐disubstituted vinylic selenides via hydromagnesiation of alkylarylacetylenes

Hydromagnesiation of alkylarylacetylenes 1 in diethyl ether gave (E)‐α‐arylvinyl Grignard reagents 2 , which reacted with arylselenenyl bromides 3 in THF to afford stereoselectively (E)‐1,2‐disubstituted vinylic selenides 4 in good yields. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:65–68, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20066     

Highly selective spectrophotometric flow-injection determination of trace amounts of bromide by catalytic effect on the oxidation of m-cresolsulfonephthalein by periodate

A new flow-injection method is reported for the determination of bromide. The method is based on catalytic effect of bromide on the oxidation of m-cresolsulfonephthalein by periodate in acidic media. The reaction was followed spectrophotometrically by measuring the decrease in absorbance at 528 nm. The influence of pH, reagent concentration and manifold variables on the sensitivity was studied. Under optimum conditions, a calibration graph was obtained in the range of 0.160-20.00 microg ml(-1) bromides with a limit of detection of 0.150 microg ml(-1) bromide. The relative standard deviation for ten replicate measurement of 1.0 microg ml(-1) bromide was 2.1%. The influence of potential interfering ions on the selectivity was studied. The method successes to measure bromide in the presence of other halide ions. The method was used to measure bromide in river water and tap water.     

Determination of low levels of bromide in fresh water after chromatographic enrichment

A method has been developed for the determination of bromide in fresh water. The analyte is enriched on the anion-exehanger Dowex 1 x 8, which exhibits a considerably greater affinity for bromide than for the major anions in fresh water. Sodium perchlorate is used as eluent and an enrichment factor of ~100 can be achieved. The eluted bromide is oxidized with peroxodisulphate to bromate, which is determined iodometrically by a previously published spectrophotometric method. The enrichment in the presence of the major components of fresh water has been studied. Only bicarbonate has been found to interfere, but this interference can be avoided by acidifying the sample with hydrochloric acid. The recovery from synthetic fresh water with ionic concentrations corresponding to 0.005 equivalent/l. and spiked with bromide was 100% at bromide concentrations larger than 50 nM (4 mug l. ) and about 90% at 10 nM. The detection limit is 1.5nM and the limit of determination 5nM for 1-litre samples.     

Enthalpies of solution of some tetraalkylammonium bromides in binary mixtures of water and some amides

Enthalpies of solution of tetraethylammonium bromide in mixtures of N,N-dimethylformamide (DMF) and water and of tetramethylammonium bromide in mixtures of DMF and water, N-methylformamide (NMF) and water, formamide (F) and water, and of NMF and F have been measured calorimetrically at 25°C in the whole mole-fraction range. The enthalpies of solution of tetraethylammonium bromide in DMF-water reach a maximum value while the enthalpies of solution of tetraethylammonium bromide in this mixture show a flat, broad maximum and a minimum. A similar behavior is found in NMF-water and F-water mixtures. In the NMF-F system the enthalpies of solution display a nearly ideal behavior. The results are compared with those of tetra-n-butylammonium bromide and of tetra-n-propylammonium bromide.     

有机膨润土的吸附性能研究

有机膨润土处理水中有机物的研究已有报道［1－4］，但尚无就改性所用的表面活性剂对有机膨润土吸附性能的影响及规律的系统研究，对有机膨润土与不同有机物间作用机理的报道也甚少［1］．本文用3种不同的阳离子表面活性剂改性膨润土，并从等温吸附线的特征和有机物的辛醇－水分配系数较系统地研究了有机膨润上对几种有机物的吸附性能和作用机理．1实验部分1．1材料原士为钠基膨润土，经测定其阳离子交换容量为7464meg／100g土；澳化十六烷基王甲铰（CTMAB）为分析纯，溪化十二烷基三甲铰（DTMAB，95％），演化十八烷基三甲按（OTMAB…     

Determination of iodide and bromide by ion chromatography with post-column reaction detection

During an investigation into the mechanism of the biosynthesis of thyroid hormones, it became necessary to determine traces of iodide and bromide in biological matrices as well as in food. A vydac 302-IC anion-exchange column with methanesulphonic acid as the mobile phase was used for the ion chromatographic separation of iodide and bromide. A post-column reaction detector was developed based on the reaction between iodide or bromide, chloramine-T and 4,4'-bis(dimethylamino)diphenylmethane. Methods with minimal sample preparation are described for determination of iodide or bromide in serum, milk, salt and water. The detection limit is ca. 20 pg iodide and 15 ng bromide injected.     

Determination of trace quaternary ammonium surfactants in water by combining solid-phase extraction with surface-assisted laser desorption/ionization mass spectrometry.

This study demonstrates the feasibility of combining solid-phase extraction (SPE) with surface-assisted laser desorption/ionization (SALDI) mass spectrometry to determine trace quaternary ammonium surfactants in water. The trace surfactants in water were directly concentrated on the surface of activated carbon sorbent in SPE. The activated carbon sorbent was then mixed with the SALDI liquid for SALDI analysis. No SPE elution procedure was necessary. Experimental results indicate that the surfactants with longer chain alkyl groups exhibit higher sensitivities than those with shorter chain alkyl groups in SPE-SALDI analysis. The detection limit for hexadecyltrimethylammonium bromide is around 10 ppt in SPE-SALDI analysis by sampling 100 mL of aqueous solution, while that of tetradecyltrimethylammonium bromide is about 100 ppt. The detection limit for decyltrimethylammonium bromide and dodecyltrimethylammonium bromide is in the low-ppb range.     

Adsorption of Alkyltrimethylammonium Bromides at the Various Interfaces

The adsorption of alkyltrimethylammonium bromide homologues has been studied at oil/water and air/water interfaces. Dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and hexadecyltrimethylammomium bromide were used. As an oil phase the aliphatic hydrocarbons of the same chain length as that of surfactants molecules were used. The interfacial tension was measured by the drop volume method and the equilibrium values were received. The surface tension was measured by the drop weight method. The values of surface excess Gamma were calculated from the Gibbs equation. The experimental results were tested by the Langmuir isotherm as well as by the isotherm developed by E. Blomgren and J. O'M. Bockris (J. Phys. Chem. 63, 1475 (1959)). Copyright 2000 Academic Press.     

Effect of adsorbed layer surface roughness on the QCM-D response: focus on trapped water

The effect of surface roughness on the quartz crystal microbalance with dissipation monitoring (QCM-D) response was investigated with emphasis on determining the amount of trapped water. Surfaces with different nanoroughnesses were prepared on silica by self-assembly of cationic surfactants with different packing parameters. We used surfactants with quaternary ammonium bromide headgroups: the double-chained didodecyltrimethylammonium bromide (C12)2DAB (DDAB), the single-chained hexadecyltrimethylammonium bromide C16TAB (CTAB), and dodecyltrimethyl-ammonium bromide C12TAB (DTAB). The amount of trapped water was obtained from the difference between the mass sensed by QCM-D and the adsorbed amount detected by optical reflectometry. The amount of water, which is sensed by QCM-D, was found to increase with the nanoroughness of the adsorbed layer. The water sensed by QCM-D cannot be assigned primarily to hydration water, because it differs substantially for adsorbed surfactant layers with similar headgroups but with different nanoscale topographies.     

Reactions in microemulsion media. Nucleophilic displacement reaction of benzyl chloride with bromide ion

A kinetic and synthetic study of the reaction of benzyl chloride with bromide ion has been performed in microemulsions composed of cetyltrimethylammonium bromide, 1-butanol, water, potassium bromide, and hexane; rates and yields of benzyl bromide formation decreased with increasing hexane content.     

RbBr/CsBr-CH3OH/C2H5OH-H2O三元体系的溶解度

采用自制的相平衡研究装置, 测定了RbBr-CH3OH/C2H5OH-H2O和CsBr-CH3OH/C2H5OH-H2O四个三元体系在25、35、45 ℃三个温度下的平衡溶解度;同时得到了四个三元体系饱和溶液中不同盐浓度下的折光率数据. 实验结果表明,在所有的体系中, 随着甲醇或乙醇质量分数的增加, RbBr和CsBr 在水中的溶解度逐渐降低; 并且折光率也逐渐减小. 用经验关联方程对溶解度进行了拟合, 同时给出了CH3OH 和C2H5OH 分别对RbBr和CsBr的盐析率曲线.     

RbBr/CsBr-CH3OH/C2H5OH-H2O三元体系的溶解度

采用自制的相平衡研究装置,测定了RbBr-CH_3OH/C_2H_5OH-H_2O和CsBr-CH_3OH/C_2H_5OH-H_2O四个三元体系在25、35、45℃三个温度下的平衡溶解度;同时得到了四个三元体系饱和溶液中不同盐浓度下的折光率数据.实验结果表明,在所有的体系中,随着甲醇或乙醇质量分数的增加,RbBr和CsBr在水中的溶解度逐渐降低;并且折光率也逐渐减小.用经验关联方程对溶解度进行了拟合,同时给出了CH_3OH和C_2H_5OH分别对RbBr和CsBr的盐析率曲线.     

Synthesis of Cyclic Selenenate/Seleninate Esters Stabilized by ortho‐Nitro Coordination: Their Glutathione Peroxidase‐Like Activities

The syntheses of selenenate/seleninate esters and related derivatives by aromatic nucleophilic substitution (S_NAr) reactions of 2‐bromo‐3‐nitrobenzylalcohol ( 13 ) and 2‐bromo‐3‐nitrobenzaldehyde ( 17 ) with Na₂Se₂/nBuSeNa are described. The reaction of 13 with Na₂Se₂ at room temperature afforded 7‐nitro‐1,2‐benzisoselenole(3 H) ( 15 ) instead of the desired diaryl diselenide 14 . Oxidation of selenenate ester 15 with hydrogen peroxide afforded the corresponding selenium(IV) derivative, 7‐nitro‐1,2‐benzisoselenole(3 H) selenium oxide ( 18 ). 2‐(Butylselanyl)‐3‐nitrobenzaldehyde ( 19 ) was synthesized by treating compound 17 with in situ generated nBuSeNa. The bromination reaction of selenide 19 did not afford the expected arylselenenyl bromide 20 , instead, it resulted in the formation of the unexpected 7‐nitro‐1,2‐benzisoselenol(3 H)‐3‐ol ( 21 ) and 3,3′‐oxybis(7‐nitro‐1,2‐benzisoselenole(3 H)) ( 22 ), respectively. The facile formation of heterocycles 21 and 22 is rationalized in terms of the aromatic ring strain in selenenyl bromide 20 . The presence of intramolecular secondary Se⋅⋅⋅O interactions in esters 15 , 18 , 21 , 22 , and selenenic anhydride 29 has been confirmed by single‐crystal X‐ray diffraction studies as well as computational studies. The presence of an intramolecular Se⋅⋅⋅O interaction in esters 4b , 8 , 15 , 18 , 21 , and 22 has been further proved by natural bond orbital (NBO) and atoms in molecules (AIM) calculations. Glutathione peroxidase‐like (GPx) antioxidant activities of 15 , 18 , 21 , 22 , and related heterocycles such as 7‐nitro‐1,2‐benzisoselenol(2 H)‐3‐one selenium oxide ( 4b ), 7‐nitro‐1,2‐benzisoselenol(2 H)‐3‐one ( 8 ), and 29 have been determined by the coupled reductase assay.