Lithium n-benzyltrimethylsilylamide (LSA): a new reagent for conjugate addition - enolate trapping reactions

Lithium N-benzyltrimethylsilyl amide (LSA) adds to crotonates in a 1,4-manner, though the reaction of ordinary lithium amides with α,β-unsaturated carbonyl compounds is accompanied with a 1,2-addition and hydrogen abstraction at the γ-position. The conjugate addition via LSA followed by enolate trapping with electrophiles produces the corresponding α-substituted β-amino esters, which are, in turn, converted into β-lactams and α-substituted α, β-unsaturated esters.     

Triphenyltetrazolium chloride as a new analytical reagent for molybdenum(VI): Application to plant analysis

Solvent extraction of molybdenum(VI) ion associate with triphenyltetrazolium chloride (TTC) has been studied. TTC was proposed as reagent for the spectrophotometric determination of micro amounts of molybdenum(VI) at λ_max 250 nm. The optimum conditions for extraction of molybdenum(VI) as an ionassociation complex with TTC has been determined. Beer’s law is obeyed in the range of 0.5–10 μg/mL molybdenum(VI). The molar absorptivity of the ion-pair is 1 × 10⁶ L/mol cm. The sensitivity of the method is 9.6 × 10⁻⁵ μg/cm². The characteristic values for the extraction equilibrium and the equilibrium in the aqueous phase are: distribution constant K _D = 32.64, extraction constant K _ex = 2.19 × 10¹⁰ association constant β = 6.71 × 10⁸. The interferences of different cations, anions on molybdenum(VI) determination were also investigated. A sensitive and selective method for the determination of microquantities of molybdenum(VI) has been developed. The determination was carried out without preliminary separation of molybdenum. A novel procedure of molybdenum(VI) extraction and spectrophotometric determination in different plant samples was examined.     

Tetrahydroxyazon SCl as a new analytical reagent for determining copper(II)

2,2′,3,4-Tetrahydroxy-3′-sulfo-5-chloroazobenzene was synthesized from pyrogallol and 2-aminophenol-5-chlorobenzenesulfonic acid. The complexation of copper(II) with this reagent was studied. A homoligand compound of the stoichiometry 1: 1 was obtained at pH 2. The optimum conditions for complexation were found and the equilibrium constant of the reaction was calculated. The selectivity of the reaction was studied and the stability constant of the complex was evaluated. Procedures were developed for the photometric determination of copper in alloys and soils.     

Neotetrazolium chloride: a new reagent for spectrophotometric determination of manganese

The interaction of Mn(VII) and the Neotetrazolium chloride has been examined. The ion-associate formed is extracted into 1,2di-chloroethane. The optimum conditions have been established. The molar absorptivity of the complex is (9.1+/-0.08)x10(5) l mol(-1) cm(-1). The sensitivity of the method is 6.04x1010(-5) mug cm(-2). It is possible to extract and determine manganese in the presence of large number of cations and anions. The characteristic values for the extraction and the aqueous phase equilibria were determined: extraction constant K(ex)=3.21x10(9), distribution constant K(D)=33 and association constant beta=9.72x10(7). The method is applicable to analysis of soils and steels.     

Palladium (II) chloride as a reagent for the mild aromatization of piperidine and cyclohexanone

Summary Piperidine may be rapidly converted into pyridine using palladium(II) Chloride or tetrachloropalladate(II) ion in aqueous medium at pH 10-11 and in the absence of oxygen. Cyclohexanone may be aromatized under the same conditions, although more slowly. The products fromo-cyclohexenylcyclohexanone are also described.     

Tin (II) chloride in glycerol as a titrimetric reagent in carbonate media

Tin(II) chloride solutions in glycerol are much more stable to light and atmospheric oxidation than the usual hydrochloric acid solutions, although the general reducing properties of the solutions are similar. In bicarbonate media, ferricyanide and chromate can be readily determined; some possible applications are outlined.     

A new reagent for the spectrophotometric determination of magnesium (II): Khimduchlorophosphonazo-I

Summary The colour reaction of magnesium(II) with Khimduchlorophosphonazo-I (KCPA-I) has been studied spectrophotometrically with a view to develop a procedure for the determination of exchangeable magnesium in acidic soils.The optimum acidities are pH 8.78–9.90. The absorption maximum and molar absorptivity of the coloured complex are 580 nm and 1.85 · 10⁴ l · mol^–1 · cm^–1, respectively. The colour intensity is stable for 4 h and is found to obey Beer's law within the concentration range of 0–20 g per 25 ml. The method is simple and reliable (standard deviation 0.8–1.2%). It has been applied to the determination of exchangeable magnesium.

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Neues Reagens für die spektralphotometrische Bestimmung von Magnesium (II): Khimduchlorophosphonazo-I

Zusammenfassung Die Farbreaktion von Magnesium mit Khimduchlorophosphonazo-I wurde im Hinblick auf die Entwicklung eines entsprechenden Analysenverfahrens untersucht. Der optimale pH-Wert liegt im Bereich von 8,78–9,90. Das Absorptionsmaximum liegt bei 580 nm, der molare Extinktionskoeffizient beträgt 1,85 · 10⁴l · mol^–1 · cm^–1. Die Färbung bleibt 4 h lang stabil und befolgt das Beersche Gesetz von 0 bis 20 g/25 ml. Das Verfahren ist einfach und zuverlässig (Standardabweichung 0,8–1,2%) und wurde zur Bestimmung von austauschbarem Magnesium in sauren Böden angewendet.

     

Triethylsilane-indium(III) chloride system as a radical reagent

[reaction: see text] A novel generation method of indium hydride (Cl2InH) was found by the transmetalation of InCl3 with Et3SiH. In the intramolecular cyclization of enynes, the previously reported system (NaBH4-InCl3) has a problem of side reactions with the coexistent borane. In contrast, the problem was solved by the presented system, which affords effective hydroindation of alkynes.     

Chromium (II) Silylamides

Novel, generally highly oxygen sensitive (?hemi”?) Cl? Cr? N(SiMe₃)₂(L)_n, I , and Cr[N(SiMe₃)₂]₂LL′, II , were prepared with L, L′ = (a) aliphatic and cyclic ethers (including polyfunctional ligands) (b) alkyl cyanides, (c) aromatic tertiary amines or (d) mixtures of a and c. The products are characterized by elemental analysis and chemical reactions. Representative reflectance spectra are presented. Chemical and physical properties are strongly dependent on the nature of L, L′ and oxygen sensitivity, thermal stability, solubility and reactivity of the Cr? N linkage (in reactions with surface ) could be regulated by varying the coordinated ligands. Empirical reactivity series for various LL′ combinations and ligand lability interrelationships were established. Behavior of some complexes in Cr(II) alkoxide synthesis, ring opening polymerizations, and in pyrolysis reactions is discussed.     

Chromium (II) Alkoxides

Novel extremely oxygen sensitive (many pyrophoric) alkoxides of Cr(II) were prepared by alcoholysis of Cr[N(SiMe₃)₂]₂LL′, where L, L′ = ether, THF, or Py. They were characterized by elemental analyses, reflectance spectroscoppy, solubility, and chemical behavior. Solubility of the alkoxides is influenced most by drying conditions. Thoroughly dried aliphatic products are quite insoluble and exhibit coordinations polymer characteristics. Sterically hindered alkoxides are less associated, more soluble in general, and tend to form crystalline adducts with donor ligands. Primary alcohols (except MeOH) gave yellow/brown, secondary alcohols purple/violet and tertiary alcohols (as well as many phenols) blue derivatives. Some chemical reactions of selected alkoxides are discussed.     

Spectrophotometric determination of Chromium(VI) using cyclam as a reagent

A simple, rapid, sensitive, and inexpensive method for spectrophotometric determination of chromium(VI), based on the absorbance of its complex with 1,4,8,11-tetraazacyclotetradecane (cyclam) is presented. The complex showed a molar absorbtivity of 1.5?×?10⁴?L?mol^?1?cm^?1 at 379?nm. Under optimum experimental conditions, a pH of 4.5 and 1.960?×?10³?mg?L^?1 cyclam were selected, and all measurements were performed 10?min after mixing. Major cations and anions did not show any interference; Beer's law was applicable in the concentration range 0.2–20?mg?L^?1 with a detection limit of 0.001?mg?L^?1. The standard deviation in the determination is ±0.5?mg?L^?1 for a 15.0?mg?L^?1 solution (n?=?7). The described method provides a simple and reliable means for determination of Cr(VI) in real samples.     

Orthometalation reactions of substituted benzylideneamines by palladium(II) chloride

Carbonmetal σ-bonded complexes have been synthesized by reaction of various substituted benzylideneamines with PdCl₂. The chloro-bridged complexes formed have been studied by spectroscopic methods and by thermogravimetric analyses.     

Di-2-Pyridylketoxime,a new reagent for the spectrophotometric determination of iron(II)

Di-2-pyridylketoxime is proposed for the spectrophotometric determination of iron(II). The complex is stable and exhibits an absorption maximum at 534 nm in an alkaline citrate medium. Beer's law is obeyed and the molar absorptivity is 1.5·10³. Large amounts of copper and nickel can be tolerated. The method is simple, convenient and reproducible.     

Pivaloyl chloride/DMF: a new reagent for conversion of alcohols to chlorides

An efficient procedure for conversion of alcohols into the corresponding chlorides is described. Pivaloyl chloride/DMF complex is employed as a mild and inexpensive reagent. A possible reaction mechanism is proposed.     

Chromium(II) chloride as a highly selective (C(5)-dechlorinating agent for functionalized 2,3,5-trichlorocyclopent-2-en-1-ones

(±)-2,3,5-Trichloro-4,4-ethylenedioxy- and (±)-5-allyl(allenyl)-2,3,5-trichloro-4,4-dimethoxycyclopent-2-en-1-ones undergo regioselective reductive C(5)-dechlorination under the action of CrCl₂ to give the corresponding 2,3-dichlorocyclopentenones. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1699–1701, September, 1997.     

N-Acetylacetone-anthranilic acid as a gravimetric reagent for copper(II)

N-Acetylacetone-anthranilic acid has been employed as a reagent for the gravimetric determination of copper(II). The solid copper(II) chelate formed possesses 1:1 metal-ligand stoichiometry and is found to exist as an unsolvated dimer. The complex has a magnetic moment of 1.88 B.M. at 298 K. A non-planar dimeric structure is suggested to explain the observed facts.     

The crystal structure of (phenylazophenyl-C,N')mercury(II) chloride: a dimeric rans-metallation reagent

An X-ray diffraction study of (phenylazophenyl-C,N')mercury(II) chloride has shown it to be dimeric via long HgCl bridging interactions of 3.367 Å.     

(2-Naphthoxy)acetyl chloride,a simple fluorescent reagent

In continuing the search for fluorescent reagents for analytical derivatization in chromatography, we found a simple chemical, (2-naphthoxy)acetyl chloride, with potential fluorophore/chromophore characteristics for the highly sensitive detection of analytes with an amino function. The reagent has an auxochrome (a substituted alkoxy moiety) attached to the fluorophoric/chromophoric naphthalene system, resulting in favorable spectrophotometric properties. The reagent can be easily prepared from (2-naphthoxy)acetic acid and has been used in organic synthesis; it is initially introduced as a fluorescent reagent to derivatise amantadine and memantine (amino pharmaceuticals) as model analytes. The resulting naphthoxy derivatives of the drugs can be analyzed at sub-microM levels by HPLC with fluorimetric detection (excitation wavelength 227 nm, emission wavelength 348 nm). Application of the reagent to the fluorimetric derivatization of important biological amines for sensitive detection can be expected.     

Preparation of (Cyanomethylene)tributylphosphorane: a new mitsunobu-type reagent

(Cyanomethylene)tributylphosphorane (CMBP), which promoted the alkylation of various nucleophiles (HA) with alcohols (ROH) to give RA (Mitsunobu-type reaction), was prepared in two steps starting from chloroacetonitrile.