Determination of trace metals in aluminium oxide by electrothermal atomic absorption spectrometry with direct injection of aqueous suspensions

Trace amounts (10^-5–10^-6% $\text{w}\text{w}$) of Ca, Cr, Cu, Fe, Na and Pb in aluminium oxide can be determined by graphite-furnace a.a.s. with injection of stirred sample suspensions into the tube. Calibration is possible either with Al₂O₃ standards for peak height and peak area measurements, or with standard solutions containing no aluminium for peak area measurements (except for copper). The analytical signals do not depend on the quantity of applied sample (0.02–1 mg Al₂O₃). Relative standard deviations are 2–6%.     

Simple camphor derivatives as chiral auxiliaries for asymmetric conjugate addition

The chiral enoates, $\text{4}$, readily available in two simple steps from (+)-camphor, Undergo asymmetric conjugate addition with the Gilman reagent LiBu₂Cu. Chemical yields are high (70–90%) and in the case of the naphthyl-substituted enoate $\text{4e}$ excellent diastereoselectivity (95% $\text{d.e.}$) is observed. 3-Methyl-heptan-l-ol of correspondingly high enantiomeric purity is obtained by reduction of the conjugate adduct with lithium aluminium hydride.     

Studies on 1-carbadethiacephems, part II: Reaction of 4-acetoxy-2-azetidinone with aluminium enolates

A procedure for the novel reaction of αβ-unsaturated ketones (as zinc-free aluminium enolates) with 4-acetoxy-2-azetidinone, giving products $\text{2}$, is reported. A 1-carbadethia-2-oxocephem derivative $\text{5}$ has been prepared from compound $\text{2b}$.     

Fluorocyclohexanes Part XIV [1] 1-H-decafluorocyclohexylamine

1-$\text{H}$-Decafluorocyclohexylamine (V) has been prepared from decafluorocyclohexene (I). (I) gave the corresponding epoxide (II) by reaction with alkaline hydrogen peroxide, reaction of (II) with fluoride ion in sulpholane yielded decafluorocyclohexanone (III). This then gave decafluorocyclohexylidene imine (IV), lithium aluminium hydride reduction affording the desired 1-$\text{H}$-decafluorocyclohexylamine (V).     

Complexes of carbonyl compounds with RnAlX3-n compounds: III. The stoichiometry of complexes of ketones with aluminium trichloride

Acetophenone and p-methylacetophenone complex with aluminium trichloride; $\text{1}\text{1}$ and $\text{1}\text{2}$ complexes are formed in equilibrium in benzene solution. A 6-membered ring structure is proposed for the $\text{1}\text{2}$ complex.     

Contributions to the complexometric determination of cation mixtures: Simultaneous titration of iron(iii) and aluminium in the presence of ammonium thiocyanate as indicator

With thiocyanate as indicator iron(III) and aluminium(III) can be titrated simultaneously if [Fe⁺³]/[Al⁺³] ? $\text{1}\text{4}$; iron(III) is titrated directly with EDTA, and aluminium(III) is determined by back-titration of the excess of EDTA with cobalt nitrate solution in an acetone-water medium.     

A convenient synthesis of substituted γ-pyrones

An efficient and general synthetic method for various 2-mono- and 2,6-disubstituted γ-pyrones has been developed. This utilizes the $\text{C}$-acylation (70–85%) of β-methoxy-α,β-enone lithium enolates $\text{4}$ by acid chlorides $\text{3}$ followed by the acid-catalyzed cyclization (>80%) of the resulting enols $\text{5}$ to γ-pyrones $\text{6}$.     

Adamantane rearrangement mechanisms. 1,2-trimethylenenorbornanes

Unexpected differences in the aluminium bromide-catalyzed rearrangement behaviour of 1,2-$\text{endo}$-trimethylenenorbornane ($\text{1}$) and its 1,2-$\text{exo}$-isomer ($\text{2}$) are interpreted. Isotopic labelling studies indicate that reversible abstraction of the tertiary 2-$\text{endo}$ hydride in $\text{2}$ does not occur. Instead, rearrangement to $\text{6}$ is favored. The label scrambling in the final product, adamantane ($\text{8}$), is attributed to degenerate isomerization in the proto-adamantyl precursor, $\text{7}$.     

Reductive cleavage of axially disymmetric tertiary amines and quaternary ammonium salts by lithium aluminium hydride. Synthesis of new 1,1′-binaphthyl substituted amines

Axially disymmetric tertiary amines or quaternary ammonium salts $\text{A}$ are synthesized by double alkylation of primary or secondary amines with racemic or optically pure 2,2′-bis (bromomethyl)-1,1′-binaphthyl. Their reductive cleavage by lithium aluminium hydride in refluxing THF leads to chiral secondary or tertiary amines $\text{B}$, substituted by a binaphthyl unit, with high yields and absence of racemization.     

Comparison of cationic rhodium and iridium complexes in directed homogeneous hydrogenation

The hydrogenation of $\text{endo}$-6-methylenebicyclo[2,2,2]octan-2-ol catalysed by a range of rhodium and iridium complexes has been investigated. Unlike the corresponding $\text{exo}$-alcohol, reduction is highly stereoselective leading to 95 – 99.7% of $\text{endo}$-exo-6-methylbicyclo[2,2,2]octan-2-ol. Selectivity is much less pronounced for the corresponding methyl ether. Rhodium catalysts promote a competitive isomerisation of the double bond to $\text{endo}$-6-methyl-bicyclo[2,2,2]oct-5-en-2-ol, of which an authentic sample was reduced in high yield to pure $\text{exo}$-$\text{endo}$ product. Reduction of both $\text{endo}$-hydroxy substrates by iridium complexes is rapid and highly selective.NMR studies employing europium shift reagents played a central part in defining the stereochemical interrelationships of 2,6-disubstituted bicyclo[2,2,2]octanes.     

Synthesis and 13C nmr characterization of some π-excessive heteropolyaromatic compounds

Several π-excessive heteropolyaromatic compounds, which contain furan and thiophen ring and are possible antifungal agents, have been synthesized in good yields according to two general methods. The first method has been used to prepare compounds possessing thiophens linked by their 2- and 5-positions, such as the ter-aryls $\text{2b}$, $\text{2d}$ and $\text{2a}$. Two precursors of these compounds have been obtained either by the Glaser reaction, or using a novel Pd-mediated reaction. The second method,which consists of the Ni-or Pd-catalyzed heteroarylation of heteroarene halides via cross-coupling with heteroaryl Grignard reagents or zinc halides,has been used to prepare the bi-aryls $\text{1a-e}$, which contain two heteroaromatic units, and the ter-aryl $\text{2c}$. Compound $\text{1e}$ has been also prepared starting from 2-(2-thienyl) furan ($\text{1c}$) by selective lithiation, followed by bromination.The ¹³C NMR signals of $\text{1a-e}$ and $\text{2a-d}$ have been assigned on the basis of the literature data and by relaxation measurements. Relaxation data have been also used to obtain qualitative informations on the conformational equilibria of the bi-aryls $\text{1a}$, $\text{1c}$ and the ter-aryls $\text{2a-d}$.     

Aryl cyclobutyl sulfones by reduction of 1-arylsulfonylbicyclobutanes with lithium aluminium hydride. synthesis of racemic junionone

Cyclobutyl sulfones are obtained by reduction of bicyclobutyl sulfones with lithium aluminium hydride and these may be used in further synthetic transformations, as illustrated by the synthesis of $\text{rac}$-junionone.     

The synthesis of dl-coriolin

The synthesis of dienone $\text{2}$, which has previously been converted into the title compound in one step, is described. The methanoindene $\text{7}$ is transformed into dienone-alcohol $\text{58}$ in eighteen steps (12% overall yield). This was then hyaroxylated at C-8, using the known method, to afford key dienone $\text{2}$.     

Determination of cadmium, copper and lead in natural waters after anion-exchange separtion.

A method is described for the determination of cadmium, copper and lead in samples of natural non-saline waters. After acidification with hydrobromic acid, the water sample is filtered and, following the addition of ascorbic acid, passed through a column of the strongly basic anion-exchange resin Dowex 1-X8 (bromide form). On this exchanger cadmium(II). copper(I) and lead(II) are adsorbed as anionic bromide complexes. After elution of these elements with 1 M nitric acid, the determinations by atomic absorption spectrometry are carried out in a medium consisting of 90% ($\text{v}\text{v}$) methanol and 10% ($\text{v}\text{v}$) 1.5 M hydrobromic acid. The procedure was used for the routine determination of cadmium, copper and lead in water samples collected in Austria.     

Determination of aluminum and silicon in biological materials by inductively coupled plasma atomic emission spectrometry with electrothermal vaporization

An atomic emission spectrometric method is described for the determination of trace elements in microvolume samples especially of biological materials. Based upon the arrangement of a commercial electrothermal vaporizer and a 40-MHz inductively coupled plasma, the direct determination of aluminum and silicon in human body fluids such as urine and serum and aluminum in hemodialysis solution is performed. The instrumental system involves vaporizing the sample from a modified graphite electrode followed by atomization and excitation of the vapors in the ICP discharge. Compromise experimental conditions are reported and calibration functions compared. Limits of detection in 5-μl samples were 8 pg Al and 2.5 ng Si, and after preconcentration of Al with a poly(acrylamidoxime) resin, the detection limit was 1 pg Al. Recovery of 5 μg $\text{Si}\text{ml}$ and 10 ng $\text{Al}\text{ml}$ from aqueous and synthetic standards was 80–85% and 96–103%, respectively.     

The determination of mercury in air samples by flameless atomic absorption

A method is described for the determination of mercury in air by furnace atomic absorption. The porous graphite cups used ordinarily fail to adsorb mercury vapors from the air. When these same porous graphite cups are plated on the inner surface with a thin layer of gold the retention of mercury from an air sample passed through the cup is shown to be quantitative. The sensitivity of the analytical system is 3 × 10^?10 g which is equivalent to 0.6 $\text{μg}\text{m}{}^3$ for a 500 cm³ air sample. Relative S.D. is 11.2%. The method described should also prove useful for other types of flameless devices.     

Measurement of dilute metallic impurity concentration in lead by differential scanning calorimetry

The traditional method for purity determination by analysis of the peak shape of the melting transition has included fitting to a linear relation between sample temperature (T) and the reciprocal fraction molten ($\text{1}\text{7}$). This technique, however, necessitates the use of a series of calibrants to determine the proper choice of limits for $\text{1}\text{7}$ as a function of purity. In this paper, a non-linear relation between T and $\text{1}\text{7}$ is developed and applied to the determination of metallic impurities in Pb in the range of a few to 1000 parts per million. The results are found to be independent of the range of $\text{1}\text{7}$ used. The use of differential scanning calorimety in this determination is discussed, and rate effects are also mentioned.     

NMR determination of absolute site-specific natural isotope ratios of hydrogen in organic molecules. Analytical and mechanistic applications

It has been shown that the “internal” isotope distribution within a given molecular species at the natural abundance level is accessible by a new method, SNIF-NMR, which is based on deuterium NMR. Relative internal factors, R_i/j,have been defined which enable the isotope content of a given site, i, to be compared to that of another molecular site, j, taken as the reference. Several referencing methods intended to provide direct access to relative $\text{externals}$, T_i , and $\text{absolute}$, (D/H)_i , site-specific parameters, are now discussed from both the theoretical and the experimental points of view. In the $\text{intramolecular referencing method}$, which involves a time-consuming chemical transformation of the sample, the risk exists of more or leas systematic errors resulting from discriminating fractionation effects. However this technique offers, conversely, an interesting way of investigating kinetic isotope effects without the need for specific labelling. In spite of its lower spectral precision the $\text{external referencing method}$ has the advantage of being fast and less sensitive to systematic errois and may be used for direct rough routine determinations of the site-specific isotope contents. More precise results can be obtained, at the price of contaminating the sample, when an $\text{intermolecular reference}$ is added and signal heights are used, remembering however that the intensity parameters then have no strict physical meaning in terms of absolute isotope contents. The site-specific parameters, T_i and (D/H)_i thus accessible, provide new information on the mechanisms of the fractionation effects occurring in natural conditions and examples are considered.