Alkali metals plus silica gel: powerful reducing agents and convenient hydrogen sources

Alkali metals absorbed into silica gel yield three stages of unique loose black powders (M-SG) that are strong reducing agents. All react nearly quantitatively with water to form hydrogen. Liquid Na-K alloys form air-sensitive powders at room temperature that can be converted at 150 degrees C to a form that is sensitive to moisture but not to dry air. Slowly heating sodium and silica gel to 400 degrees C yields a third type that can be handled in ambient air with only slow degradation by atmospheric moisture. These materials eliminate many hazards associated with pure alkali metals and provide easily handled reducing agents and hydrogen sources. They could be used in continuous-flow reactors to reduce and protonate aromatics, dechlorinate alkyl and aryl halides, and desulfurize various compounds.     

Pivaloylpyruvic acid as a new acylating reagent for amines

Pivaloylpyruvic acid is an efficient reagent for preparative acylation of amines. A method for the synthesis of substituted pivaloylpyruvamides with domination of (Z)-β-keto-enol tautomer is proposed. The structure of pivaloylpyruvic acid and its amides, as well as the specific features of the reaction of pivaloylpyruvic acid with amines, are discussed.     

Structures of alkali metals in silica gel nanopores: new materials for chemical reductions and hydrogen production

Alkali metals and their alloys can be protected from spontaneous reaction with dry air by intercalation (with subsequent heating) into the pores of silica gel (SG) at loadings up to 40 wt %. The resulting loose, black powders are convenient materials for chemical reduction of organic compounds and the production of clean hydrogen. The problem addressed in this paper is the nature of the reducing species present in these amorphous materials. The atomic pair distribution function (PDF), which considers both Bragg and diffuse scattering components, was used to examine their structures. Liquid Na-K alloys added to silica gel at room temperature (stage 0) or heated to 150 degrees C (stage I) as well as stage I Na-SG, retain the overall pattern of pure silica gel. Broad oscillations in the PDF show that added alkali metals remain in the pores as nanoscale metal clusters. 23Na MAS NMR studies confirm the presence of Na(0) and demonstrate that Na+ ions are formed as well. The relative amounts of Na(0) and Na(+) depend on both the overall metal loading and the average pore size. The results suggest that ionization occurs near or in the SiO2 walls, with neutral metal present in the larger cavities. The fate of the electrons released by ionization is uncertain, but they may add to the silica gel lattice, or form an "electride-like plasma" near the silica gel walls. A remaining mystery is why the stage I material does not show a melting endotherm of the encapsulated metal and does not react with dry oxygen. Na-SG when heated to 400 degrees C (stage II) yields a dual-phase reaction product that consists of Na(4)Si(4) and Na(2)SiO(3).     

Salen impregnated silica gel as a new sorbent for on-line preconcentration of cadmium(II)

A new sorbent – salen impregnated silica gel – was prepared and characterised for application as a minicolumn packing for flow-injection on-line preconcentration of cadmium(II). The system was coupled with flame atomic absorption spectrometer (FI-FAAS). The optimal pH for Cd(II) sorption was in the range of 7.4–8.8 and nitric acid (1%, v/v) was efficient as eluent. Sorption was most effective within the sample flow rate up to 7?mL?min^?1. Sorption capacity of the sorbent found in a batch procedure was 26.3?µmol?g^?1 (2.95?mg?g^?1). Enrichment factor (EF) and limit of detection (LOD) obtained for 120-second loading time were 113 and 0.26?µg?L^?1, respectively. The sorbent stability in the working conditions was proved for at least 100 preconcentration cycles. The evaluated method was applied to Cd(II) determination in various water samples.     

Dibepin-2: A new color reagent for primary aliphatic amines

3-Chloro-3-[2, 3(CO), 6, 5(CO)dibenzoylene-4-pyridyl]phthalide (Dibepin-2) is an analytical color reagent for primary aliphatic amines and arylalkylamines (with the exception of ethylenediamine and 1, 2-diaminopropane). The reaction is always negative with secondary and tertiary amines.     

Spectrofluorimetric determination of aliphatic amines using a new fluorigenic reagent: 2,6-dimethylquinoline-4-(N-succinimidyl)-formate

A new amino fluorescence probe, 2,6-dimethylquinoline-4-(N-succinimidyl) formate (DMQF-OSu) has been synthesized. Based on the selective reaction of DMQF-OSu with primary and secondary aliphatic amines to yield strong fluorescence, a new spectrofluorimetric method for the determination of total aliphatic amines has been developed. At λ_ex/λ_em=324.4/416 nm, the linear calibration range was 6×10⁻⁸-6×10⁻⁶ mol l⁻¹ with the detection limit (3σ) of 1.94×10⁻¹⁰ mol l⁻¹ for the determination of aliphatic amines in weak basic media. The proposed method has been applied to the determination of aliphatic amines in tap water and lake water with the recoveries of 99-104%. Compared with the reported methods, the method presented here is rapid, simple, sensitive and feasible.     

Quercetin immobilized on silica gel as a solid phase reagent for tin(IV) determination by using the sorption-spectroscopic method

New chelating sorbents are prepared by 3,3',4',5,7-pentahydroxyflavone adsorption from butanol and acetone-hexane (1:4) solutions, characterized by isotherm of sorption, IR-spectroscopy and studied for pre-concentrating and sorption-spectroscopic determination of Sn(IV). The solid-phase Quercetin with satisfactory analytical characteristics was formed by adsorption from acetone-hexane (1:4) mixture. The quantitative recovery of Sn(IV) from aqueous solution with modified sorbent was observed at pH 1.8-2.2. The tolerance limits of heavy metal ions in the sorption of Sn(IV) are reported. The limit of Sn detection is 0.06 mg l(-1). The linearity of calibration graph has been observed up to 1.2 mg l(-1). The method has been applied to determine Sn in high purity zinc materials.     

Chromium (II) chloride : a new reagent for cross-aldol reactions

The proposed cross aldolization of α-bromoketones with aldehydes in presence of Chromium (II) chloride is an excellent stereospecific reaction. One exception to the stereospecific orientation is reported.     

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.     

A fluorescent dosimeter for formaldehyde determination using the Nash reagent in silica gel beads

Based on the Nash reagent embedded in silica gel beads as a recognition element, a fluorescent dosimeter for formaldehyde determination is established. The system can act as a fluorescent off–on switch for the qualitative detection of formaldehyde. The fluorescence emission of the Nash reagent-loaded silica gel beads is “switches off” (or very low) before exposure to formaldehyde, while fluorescence can be switched on when the beads are contacted with formaldehyde. The slope of fluorescence time scan spectra changes with formaldehyde concentration, which constitutes the basis of quantitative determination of formaldehyde concentration. The formaldehyde can also be semi-quantitatively measured in a naked-eye-detectable fashion. No response of this dosimeter to primary alcohols, ketones and other common substances was observed. The dosimeter is sensitive, inexpensive, a disposable, and simple in operation.     

Anthracene silica gel,a new polycyclic-aromatic-bonded stationary phase for HPLC

Summary N(9-methylanthracene)aminopropyl silica gel is introduced as a new reversed-phase packing material. It has specific selectivity for some aromatic compounds. In this paper the anthracene phase is compared with commercial octadecyl-, phenyl- and aminopropyl-bonded silica gels.     

Fluoroboric acid adsorbed on silica gel as a new and efficient catalyst for acylation of phenols, thiols, alcohols, and amines

Fluoroboric acid supported on silica gel efficiently catalyzes acylation of structurally diverse phenols, alcohols, thiols, and amines under solvent free conditions. Acid-sensitive alcohols are smoothly acylated without competitive side reactions.     

The (1-methyl)cyclopropyloxycarbonyl (MPoc) carbamate: a new protecting group for amines

The (1-methyl)cyclopropyl carbamate (MPoc) group represents a new and useful protecting group for amines. It adds relatively little molecular weight and has a simple ¹H NMR spectrum. It is orthogonal to the commonly used BOC, Cbz, Alloc, and FMOC groups. MPoc protected amines are resistant to extremes of pH, amines, halogens, many oxidizing agents, and to hydrogenation at ambient temperature. The MPoc group is cleaved by exposure to hypobromous acid or upon hydrogenolysis over palladium at 80 °C.     

Application of 1,10-phenanthroline for preconcentration of selected heavy metals on silica gel

Stripping voltammetry analysis using a hemispheroidal mercury microelectrode has been previously assessed theoretically as a possible candidate ‘primary method’ for amount of substance measurement. It was shown that the measurement methodology can be described completely by a set of measurement equations when a novel quantification process is employed to measure the steady-state diffusion-limited deposition current over an optimum sampling time, instead of employing an analyte stripping step. The corollary is that, for solutions of known composition, the method may be used for highly accurate determination of diffusion coefficients. This investigation uses experimental data from steady-state diffusion-limited current measurements with sampling periods optimised using Allan deviation techniques, together with a full uncertainty analysis to estimate feasibility and likely accuracy of this method.     

N-Phenylselenosaccharin (NPSSac): a new electrophilic selenium-containing reagent

A new reagent N-phenylselenosaccharin (NPSSac) was simply prepared and used as a source of the electrophilic phenylselenyl group. This relatively stable new compound was able to react with a series of electron rich organic molecules like alkenes in the presence of external or internal nucleophiles, activated aromatic substrates, or enolizable carbonyl derivatives, under very mild experimental conditions.     

Chitosan-coated silica gel as a new support in high-performance liquid chromatography

Summary A new stationary phase was prepared by immobilizing the chitosan, a natural hydrophilic polymer, on microparticolate silica gel. The effect of the polarity, pH and ionic strength of the mobile phase has been studied in order to find optimal conditions for the separation of nucleotides and aminoacids. The influence of the properties of the mobile phase on the retention was examined, allowing to employ the chitosan-coated silica gel both to anion exchange and adsorption, depending on the pH and the polarity of the eluent used.     

Complex formation of heavy metals with 4-(2-pyridy-lazo)resorcinol chemically immobilized on silica gel

The complexing properties of modified silica with 4-(2-pyridylazo)resorcinol covalently immobilized by the Mannich reaction are studied with respect to heavy metals. This adsorbent can be used for the preconcentration of heavy metal ions due to its satisfactory kinetic characteristics. The structures of the heavy metal complexes with 4-(2-pyridylazo)resorcinol immobilized on the silica gel surface are studied by ESR and diffuse reflectance spectroscopy.     

由双硅氧烷偶联剂制备硫醚键合液相色谱固定相的研究及评价

将等摩尔的乙烯基三甲氧基硅烷与3-巯丙基三甲氧基硅烷发生加成反应,合成一种双硅氧烷偶联剂,然后在快速搅拌下,将其键合到分散的10 μm硅胶上,并用三甲基氯硅烷封尾,从而制得一种含硫醚桥基的新型色谱固定相.用红外光谱和热分析等表征新固定相的结构,在甲醇-水作为流动相的条件下,以ODS柱做参比相,选用不同的溶质探针评价了新固定相的色谱性能.考察了多环芳烃、极性的取代芳烃、嘌呤类和蒽醌类化合物在该键合相上的色谱行为.结果表明,该固定相具有明显的反相色谱性能,在色谱分离和样品的前处理方面将有较好的应用前景.     

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.     

Sensitive determination of biogenic amines by capillary electrophoresis with a new fluorogenic reagent 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde

An effective approach was proposed to the derivatization of seven biogenic amines using 3-(4-fluorobenzoyl)-2-quinolinecarboxaldehyde (FBQCA) as a fluorogenic reagent. The sensitive determinations of these derivatives were achieved by micellar electrokinetic capillary chromatography (MEKC) with laser-induced fluorescence (LIF) detection. The derivatization and electrophoretic conditions have been optimized. A running buffer was composed of mixtures of 25 mM pH 9.5 boric acid, 25 mM SDS, and 27% ACN. At 25 °C and 22.5 kV, the baseline separation of the derivatives was accomplished in 13 min. The detection limit (S/N = 3) was found as low as 0.4 nM. The proposed method was validated by the linearity of two orders magnitude and correlation coefficient in the range 0.9969–0.9998. Also, the procedure was successfully applied to the determination of biogenic amines in soy sauce, fish and wine samples.