Thianaphthenoyltrifluoroacetone as an analytical reagent: The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone

Summary The keto-enol tautomerism of the 2- and 3-isomers of thianaphthenoyltrifluoroacetone has been studied and the results explained by considering the relative negativities of the 2- and 3-position of thianaphthene. The results of the comparison of the keto-enol tautomerism of 3-thianaphthenoyltrifluoroacetone to that of 2-thenoyltrifluoroacetone in 80% benzene-20% ethanol may explain in part the greater sensitivity of the former in trace metal analysis.

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Zusammenfassung Die Keto-Enol-Tautomerie der 2- und 3-Isomeren des Thianaphthenoyltrifluoracetons wurde untersucht und mit der relativen Negativität der 2- und 3-Stellung des Thianaphtens zu erklären versucht. Der Vergleich der Keto-Enol-Tautomerie von II mit der des 2-Thenoyltrifluoracetons in BenzolÄthanol (80+20) könnte eine Erklärung für die größere Sensitivität von II bei der Spurenmetallanalyse bieten.

     

Free radical-mediated vinyl amination: access to N,N-dialkyl enamines and their beta-stannyl and beta-thio derivatives

[reaction: see text] The first examples of free radical-mediated vinyl amination are described by nonconventional vinyl radical addition to azomethine nitrogen. This new vinyl amination protocol is mild and provides convenient synthetic access to nonstabilized N,N-dialkyl enamines and tandem bond-forming processes.     

Development of delta(15)N stratification of NO(3)(-) in soil profiles

New evidence, obtained using a robust method for measuring the delta(15)N of NO(3)(-)-N in soil, is consistent with denitrification being the major determinant in the vertical distribution of NO(3)(-)-delta(15)N in soil profiles. These data also suggest that varying moisture regimes result in different effects of soil NO(3)(-)-N leaching on residual whole soil delta(15)N.     

A systematic study of magnetic order in divalent europium perovskites

The magnetic properties of a series of cubic perovskite materials, Eu(Al_0.5Ta_0.5)O₃, Eu(Mg_0.5W_0.5)O₃, and Eu(Lu_0.5Ta_0.5)O₃ have been investigated using bulk magnetic and Mössbauer techniques. Eu(Al_0.5Ta_0.5)O₃ is a ferromagnet (T_c ～ 5°K, θ_c = + 8°K), Eu(Lu_0.5Ta_0.5)O₃ is an antiferromagnet (T_N = 4.0, θ_c = ?8°K), while Eu(Mg_0.5W_0.5)O₃ is probably antiferromagnetic (T_N = 2.8°K, θ_c = ? 1°K). These data are compared with the known properties of EuLiH₃ and EuTiO₃ and a sharp drop in θ_c as a function of increasing lattice constant is noted. A molecular field theory analysis of the data yields two possible sets of nn (J₁) and nnn (J₂) exchange constants for each compound which are compared with existing theories.     

Reactions and X-ray crystal structure of (3-cyano-2,4-pentanedionato-N)pentaamminecobalt(III) perchlorate chloride dihydrate

The pentaamminecobalt(III) complex with the 3-cyano-2,4-pentanedionate anion coordinated through the nitrile nitrogen has been characterized by X-ray crystallography. The crystals of [(NH₃)₅CoNCacac](Cl)(ClO₄)·2H₂O are triclinic, space group P , a = 10.245(2) Å, b = 14.071(4) Å, c = 6.971(2) Å, = 90.03(3)°, β = 109.86(2)°, γ = 108.91(2)°, V= 887.1 ų, Z = 2, D_c = 1.64 g cm⁻³, F(000) = 456, Mo-K radiation, λ = 0.71069 Å, μ(Mo-K) = 12.7 cm⁻¹. The structure was determined by the heavy-atom method, and refined by block-diagonal least-squares calculations, R = 0.0537, R_w = 0.0607, for 2499 observed reflections. Principal dimensions are: Co---N(NH₃) trans to NCacac⁻ 1.940(5), other Co---N(NH₃) 1.967(2), Co---N(NCacac⁻) 1.911(5) Å. The pendant acac moiety is best described in terms of a delocalized bond network with, for example, C---C distances in the range 1.44–1.52(1) Å. Several reactions involving this free acac group are also described including the preparation and characterization of the dimeric species pentaamminecobalt(III) - μ - (3 - cyano - 2,4 - pentanedionato) - bis(propylenediamine) cobalt(III) perchlorate.     

Bronsted acid-promoted olefin aziridination and formal anti-aminohydroxylation

A straightforward synthesis of aziridines is reported from an electron-rich azide (alkyl or aryl azide), electron-deficient olefin, and triflic acid in cold acetonitrile. The only coproduct of the reaction is dinitrogen (N2). Active ester substrates bearing a nucleophilic carbonyl engage the putative protonated aziridine intermediate to produce the product of olefin aminohydroxylation in which the nitrogen is benzyl protected and the oxygen is acylated. The possibility that a triazoline need not be an intermediate in aziridine production is advanced.     

Synthesis of 17β-hydroxy-1′-H-5α-androst-2-eno[3,2-b]pyrrole and 17β-hydroxy-1′-H-5α-androst-3-eno[3,4-b]pyrrole from O-(2-hydroxyethyl)ketoxime precursors

Pyrrolosteroids such as 17β-hydroxy-1′-H-5α-androst-2-eno[3,2-b]pyrrole ( 1 ) and the novel 17β-hydroxy-1′-H-5α-androst-3-eno[3,4-b]pyrrole ( 12 ) can be synthesized from the corresponding O-(2-hydroxyethyl)ketoxime precursors. In the case of 1 , yields compare favourably with previously reported literature methods.     

Optical barcoding of colloidal suspensions: applications in genomics,proteomics and drug discovery

The enormous amount of information generated through sequencing of the human genome has increased demands for more economical and flexible alternatives in genomics, proteomics and drug discovery. Many companies and institutions have recognised the potential of increasing the size and complexity of chemical libraries by producing large chemical libraries on colloidal support beads. Since colloid-based compounds in a suspension are randomly located, an encoding system such as optical barcoding is required to permit rapid elucidation of the compound structures. We describe in this article innovative methods for optical barcoding of colloids for use as support beads in both combinatorial and non-combinatorial libraries. We focus in particular on the difficult problem of barcoding extremely large libraries, which if solved, will transform the manner in which genomics, proteomics and drug discovery research is currently performed.     

Isolation of ammonium-N as 1-sulfonato-iso-indole for measurement of delta15N

The conversion of ammonium (NH(4) (+)) to 1-sulfonato-iso-indole has been examined as a method for natural abundance measurement of delta(15)N of NH(4) (+). The reaction is complete within 2 h and is based on the derivatisation of NH(4) (+) by o-phthaldialdehyde and sodium sulfite at a high pH, 11.2. The product is readily concentrated from dilute solutions by reverse-phase solid-phase extraction (SPE). The method is compound-specific despite partial derivatisation of potentially interfering amino acids, as their derivatives are not extracted by SPE. delta(15)N values of NH(4) (+) in KCL soil extracts can be measured within 48 h by automated continuous-flow IRMS with a precision of 0.23 per thousand (1 SD). Parallel measurements of NH(4) (+) standards of known delta(15)N are made to allow correction for the isotopic dilution by non-sample NH(4) (+). The practicality of this method is demonstrated by measuring the changes in NH(4) (+) concentration and delta(15)N following the addition of urea as a nitrogen source to inorganic N-depleted soil.