Synthesis and reactions of perfluoro-n-octylmagnesium bromide

Perfluoro-n-octylmagnesium bromide has been conveniently synthesized through the metal-halogen exchange reaction between perfluoro-n-octyl iodide and ethyl- or phenyl-magnesium bromide. The thermal stability of the Grignard reagent and the products of the thermal decomposition have been estimated in diethyl ether and tetrahydrofuran. Reactions of the Grignard reagent with various substrates such as water, acetone, hexafluoroacetone, trimethylchlorosilane and carbon dioxide indicate the synthetic utility of n-octylmagnesium bromide.     

丙基格林试剂的合成及其在丁基锡衍生反应中的应用

格林试剂衍生方法是气相色谱与元素选择性检测器分离和测定有机锡化合物样品前处理的一个重要环节。研究了丙基格林试剂的实验室合成及其在丁基锡化合物衍生反应中的应用,为这类化合物监测标准方法的建立提供了基础条件。     

NBO‐based CI/MP through‐space/bond interaction analysis and its application to stereoelectronic effects in SN2 reactions

NBO‐based CI/MP through‐space/bond interaction analysis was developed to analyze specific orbital interactions under consideration of the effects of electron correlation. This treatment was applied to the analysis of stereoelectronic effects in S_N2 reactions of allyl bromide in which the effects of electron correlation play an important role (ammonia was used as the nucleophilic reagent). The S_N2 activation energy in allyl bromide is lower than that in propyl bromide, because both the σ–π* and π–σ* interactions in allyl bromide contribute equally to the stabilization of the transition state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

4-(4'-Methyltetrafluorophenyl)-2,3,5,6-tetrafluorobenzyl bromide: a new electrophoric derivatizing reagent

Commercially-available 4,4'-dimethyloctafluorobiphenyl was converted in a single step to 4-(4'-methyltetrafluorophenyl)-2,3,5,6-tetrafluorobenzyl bromide (MTFP-TFBBr) for the purpose of providing a new electrophoric derivatizing reagent. When reacted with this reagent, 2-fluoro-O6-(2'-hydroxyethyl)hypoxanthine, a model analyte, gave a mixture of isomeric products (apparently substituted at N7 and N9, analogous to its known reaction with pentafluorobenzyl bromide), and 53 femtograms of the mixture was detected at S/N = 10 by gas chromatography electron capture mass spectrometry (GC-EC-MS). As intended, the volatility of the MTFB-TFBBr derivative was much less (two-fold) than that of the corresponding pentafluorobenzyl derivative. It is anticipated that MTFB-TFBBr sometimes will be useful in providing an electrophoric derivative that encounters less background noise in analysis by electrophore derivatization/GC-EC-MS.     

Applications of Allylsamarium Bromide as a Grignard Reagent and a Single‐Electron Transfer Reagent in the One‐Pot Synthesis of Dienes and Trienes

The utility of allylsamarium bromide, both as a nucleophilic reagent and a single‐electron transfer (SET) reagent in the reaction of α‐halo, γ‐halo‐α,β‐unsaturated ketones and esters with allylsamarium bromide is reported for the first time in this paper. From a synthetic point of view, a general, efficient and experimentally simple one‐pot method for the preparation of 1,4‐dienes and trienes is developed. A possible mechanism of the transformation is proposed.     

Spectrophotometric study of bromide interference in a cholesterol reaction

A spectrophotometric study of the interference of bromide in the ferric chloride reaction for cholesterol has been described. The interference has been shown to be primarily an enhancement of the color reaction and secondarily an additive color owing to a change in the spectrum of the reagent blank. Tested methods of eliminating the interference included removal of bromide by ion exchange, metathetical exchange using AgIO₃, addition of bromide to a reaction plateau and a change in the solvent character of the reaction medium. It was determined that the use of an ion-exchange resin and the substitution of ethanol for acetic acid along with a modified iron reagent were the simplest choices for eliminating bromide interference in this determination. Iodate was shown to depress color formation and it appears to be a detrimental solution to the problem. Further work on the mechanism of the iodate interference is presently in progress.     

Improved procedure for the synthesis of thiazolium-type peptide coupling reagents: BMTB as a new efficient reagent

An efficient scalable synthesis of 2-halothiazolium-type peptide coupling reagents has been developed. The key step is the formation of the 2-bromothiazole scaffold through cyclization of α-thiocyanato ketones with hydrogen bromide. Using this method, the new coupling reagent 2-bromo-N-methylthiazolium bromide (BMTB) was synthesized. BMTB was tested in a difficult model coupling reaction of two sterically hindered N-methylated amino acids and showed higher activity than the well-established peptide coupling reagent HATU.     

Mild cleavage of methoxymethyl (MOM) ethers with trimethylsilyl bromide

Trimethylsilyl bromide is an effective reagent for the deprotection of methoxymethyl ethers under mild conditions.     

Methyl triphenylphosphonium peroxydisulfate (MTPPP): A mild and inexpensive reagent for the cleavage of oximes,penylhydrazones and 2,4-dinitro phenylhydrazones to the corresponding carbonyl compounds under non-aqueous conditions

Methyltriphenylphosphonium peroxydisulfate (MTPPP) was synthesized by treating methyltriphenylphosphonium bromide with potassium peroxydisulfate in aqueous solution. This reagent was used as a suitable and efficient reagent for the cleavage of oximes, phenylhydrazones and 2,4-dinitro phenylhydrazones to their corresponding carbonyl compounds under non-aqueous condition.     

1-(5-萘酚-7-磺酸)-3-[4-(苯基偶氮)苯基]-三氮烯的合成及与阳离子表面活性剂的显色反应

报道了1-（5-萘酚-7-磺酸）-3-[4-（苯基偶氮）苯基]-三氮烯（NASAPAPT）的合成，研究了该试剂与阳离子表面活性剂溴化十二烷基二甲基苄铵（DDMBAB），溴化十六烷基三甲铵（CTMAB）、溴化十六烷基吡啶（CPB）、溴化十四烷基吡啶（TPB）显色反应的条件。测定了显色反应的灵敏度，符合比尔定律的范围。建立了光度法测定微量阳离子表面活性剂的新方法。     

Interaction between thallium(III) bromide and dicyclohexano-18-crown-6 immobilized on silica

The adsorption of cis-syn-cis-dicyclohexano-18-crown-6 on silica gel from organic solvents was studied. In the adsorption from chloroform solutions, the immobilization of the reagent molecules at the surface was coplanar. Hydrogen bonds between surface silanol groups and oxygen atoms of the polyether ring of the crown ether play an important role in the immobilization of the reagent. The reaction between thallium(III) bromide and the immobilized reagent was studied. The composition of complex compounds formed at the surface of the modified adsorbent was found. A procedure was proposed for the sorption-spectrophotometric determination of thallium(III) (≥0.05 mg/L) in the presence of heavy metal ions.     

The phenyldimethylsilyllithium reagent

The phenyldimethylsilyllithium reagent can be titrated using the double titration for organolithium reagents, in spite of the formation of silyl bromide on adding dibromoethane; the reagent is different from alkyllithiums in maintaining its titre over a long period even as traces of water seep in.     

Cyclic flow-injection determination of copper with hexadecyltrimethylammonium bromide micelle-enhanced,fluorescein-sensitized chemiluminescence detection

In the flow-injection system reported, the reagent stream is continuously cycled. The circulating chemiluminescence reagents (β-nitrostyrene/NaOH/hexadecyltrimethylammonium bromide sensitized with fluorescein) allowed 0.1–10 ng of copper(II) to be determined in hundreds of successive injections, even with samples of sea water or a solution of zinc dust.     

A novel organozinc reagent 4-coumarinylzinc bromide; preparation and application in the synthesis of 4-substituted coumarin derivatives

A novel organozinc reagent, 4-coumarinylzinc bromide, was prepared by the direct oxidative addition of active zinc to 4-bromocoumarin. The resulting organozinc bromide underwent the palladium-catalyzed cross-coupling reactions with a variety of aryl halides and acid chlorides affording the corresponding coupling products in good yields under mild conditions.     

Flow-injection determination of phosphate with a cadmium ion-selective electrode

A flow-injection method is described, in which phosphate standards are introduced into a reagent stream containing Cd(2+) ,resulting in the formation of Cd(3)(PO(4))(2). The associated reduction in free metal concentration is sensed by a cadmium-selective electrode. With the exception of major interference from iodide and moderate interference from bromide and thiocyanate, the system exhibits excellent response to phosphate and selectivity over several common anions in solutions buffered at pH 8.4. A maximum sampling rate of 160/hr is possible for phosphate standards in the concentration range 10(-1)-10(-1)M with a 10(-4)M Cd(2+) reagent stream at a total flow-rate (carrier and reagent stream combined) of 8.4 ml/min.     

Dibromomalononitrile-potassium bromide complex as a mild bromination and oxidation reagent for the synthesis of mono-, di- and trimethoxyphenyl bromopyridines

The synthesis of mono-, di- and trimethoxyphenyl bromopyridines using the dibromomalononitrile-potassium bromide complex as a mild bromination and oxidation reagent is described.     

Use of competition kinetics with fast reactions of grignard reagents

Competition kinetics are useful for estimation of the reactivities of Grignard reagents if the reaction rates do not differ widely and if exact rates are not needed. If the rate of mixing is slower than the rate of reaction, the ratios between the rates of fast and slow reagents are found to be too small. This is concluded from experiments in which results obtained by competition kinetics are compared with results obtained directly by flow stream procedures. A clearer picture of the reactivity ratios is obtained when the highly reactive reagent is highly diluted with its competitor. A fast reagent may account for almost all the product even when present as only 1 part in 100 parts of the competing agent. In this way allylmagnesium bromide is estimated to react with acetone, benzophenone, benzaldehyde, and diethylacetaldehyde ca. 1.5 x 10(5) times faster than does butylmagnesium bromide. The rates found for the four substrates do not differ significantly, and it seems possible that there is a ceiling over the rate of reaction of this reagent, for example, caused by diffusion control. This may explain that competition kinetics using allylmagnesium bromide have failed to show kinetic isotope effects or effects of polar substituents with isotopically or otherwise substituted benzophenones. A recently reported alpha-deuterium secondary kinetic isotope effect for the reaction of benzaldehyde with allylmagnesium bromide was observed at -78 degrees C, but was absent at room temperature. It is suggested that the reaction of benzophenone and benzaldehyde with allylmagnesium bromide has a radical-concerted mechanism since no radical-type products are produced and since no color from an intermediate ketyl is observed even at -78 degrees C.     

Role of the Polymer Backbone in the Oxidative Properties of Polymer-Supported Dichromate

Crosslinked co/poly(styrene-4-vinylpyridine)/ (1) was converted with hydrogen bromide or alkyl bromide to a pyridinium salt (2) which was further converted in water medium to various immobilized dichromates (3) with CrO₃. The insoluble reagent containing 0.6–1.0 mmol of dichromate on a gram of resin (depending on the structure of the polymer backbone) oxidized several secondary alcohols to ketones. The rate of conversion of alcohols to ketones depended on the structure of the polymer backbone, the structure of the alcohol, and the amount of water (5% or 20%) occluded in the reagent 3.     

(PhCH2PPh3)+Br3 −: A Versatile Reagent for the Chemoselective Oxidation of Sulfides to Sulfoxides

Benzyltriphenylphosphonium tribromide (BTPTB), as a stable solid reagent, is easily prepared by the reaction of benzyltriphenylphosphonium bromide with Br₂. This reagent can be used as an efficient reagent for the chemoselective oxidation of dialkyl and aryl-alkyl sulfides to their corresponding sulfoxides in the presence of diaryl sulfides and primary alcohols. All reactions were performed in a refluxing mixture of methanol and water in very short reaction times.     

New Synthetic Bromination Procedures for Use in Radiolabelling-Chemistry: Reaction of C-Metallated Derivatives of Carbohydrates with Bromide,in the Presence of Mild Oxidizing Agents

In the presence of 2 mol-equiv. of AcONa, both triglycosylborane 1 and dicyclohexylglycosylborane 2 readily react with bromine chloride generated in situ from bromide and N-chlorosuccinimide (NCS) to give the bromo-sugar 3 (75 and 60%, resp.). The use of the BH₃-THF/bromide/NCS/2 AcONa procedure permits the rapid, face-specific synthesis of 6 (58% uptake of bromine) and face-selective synthesis of 8/9 (71% uptake of bromine), from vinyl ether derivatives 5 and 7 , respectively. The dicyclohexylborane/bromide/NCS/2 AcONa procedure leads to the fast and quantitative conversion of 11 to the bromosugar 12 (91%). Hydroboration-transmetallation sequences give access to C-mercuriated carbohydrates 13 (71%) and 14 (78%). The bis(glycosyl)mercury derivative 13 is spontaneously cleaved by reaction with one equivalent of bromide/chloramine-T/aqueous HCl-solution to give 3 (87%) and 14 (76%). Hydrostannylation of acetylenic sugar 15 gave the (E)-stannylvinyl derivative 16 as the major product. This latter precursor 16 is spontaneously cleaved by the bromide/chloramine-T/aqueous HCl-solution reagent to give the bromovinyl-sugar 17 (96%).