Long-range fluorine-proton coupling in 1,2,4-triazole derivatives

Several 1,2,4-triazole derivatives containing a 2-fluorophenyl substituent at either the 3- or 5-position and a methyl group at the 4-position were synthesized. These derivatives exhibit long-range ¹⁹F-¹H and ¹⁹F-¹³C through-space coupling in their ¹H and ¹³C nmr spectra between the fluorine and the 4-methyl group. The close spatial proximity of these nuclei was confirmed by X-ray analysis and by fluorine irradiated proton observe ({¹⁹F}-¹H) NOE difference spectroscopy.     

Electrocatalytic reduction of ROOH by iron porphyrins

Electrocatalytic reduction of a series of chemical oxidants of different power (tert-butyl hydroperoxide, potassium peroxomonosulfate, peracetic acid, and m-chloroperbenzoic acid) at iron-porphyrin-modified graphite electrodes is studied in buffered aqueous solutions by rotating disk and ring-disk voltammetry. Both ferric and ferrous porphyrins are catalytically active. Turnover of ferric catalysts is slower than that of the ferrous analogues and involves competing catalytic reduction and disproportionation. The kinetic data are consistent with reactant binding being the rate-determining step in catalysis by Fe(III). In catalysis by Fe(II), the turnover is controlled by the first electron transfer. The covalently linked proximal imidazole ligand is found to be crucial for achieving the Fe(III) catalysis.     

Synthesis of ferrocenyl-1,2-diketones and related compounds: Crystal and molecular structures of 1,2-diferrocenylethanedione and 1-ferrocenyl-2-(4-biphenylyl) ethanedione

Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C₅H₅)Fe(C₅H₄)] can be prepared by oxidation of acylferrocenes FcCOCH₂R or, more efficiently, by oxidation of the isomeric ketones FcCH₂COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH₂PPh₃)⁺I⁻ via the acylated salts [FcCH(COR)PPh₃]⁺I⁻. The haloacylferocenes FcCOCCl_x H_3−x (x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel—Crafts acylation of ferrocene using CCl_xH_3−xCOCl/AlCl₃, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl_xH_3−x and the other giving the reduced products FcCOCCl_x−1H_4−x. Two diketones FcCOCOFc 3b and FcCOCOC₆H₄Ph 3c have been structurally characterised by single-crystal X-ray diffraction.     

Synthesis of tetrahydropyrido[2,3-b]pyrazine scaffolds from 2,3,5,6-tetrafluoropyridine derivatives

Reactions between N,N′-dimethylethylene diamine and a range of 2,3,5,6-tetrafluoropyridine derivatives provided ready access to the corresponding tetrahydropyrido[2,3-b]pyrazine systems if the substituent located at the 4-position of the pyridine ring was either hydrogen or an electron withdrawing substituent. In contrast, the presence of electron donating substituents at the 4-position made the formation of ring-fused products much more difficult. The two-step sequential nucleophilic substitution procedures from pentafluoropyridine gave convenient and adaptable methodology for the synthesis of polyfunctional tetrahydropyrido[2,3-b]pyrazine scaffolds of interest to the life science discovery arenas.     

Determination of zwitterionic and cationic surfactants by high-performance liquid chromatography with chemiluminescenscent nitrogen detection

The use of chemiluminescent nitrogen specific detection (CLND) combined with an HPLC separation allows for the identification and quantification of cationic and zwitterionic surfactants. The CLND provides equimolar responses, based on the amount of nitrogen within any compound. This allows for the detection of any nitrogen containing surfactant. Reversed-phase separation methods using cyano columns are developed for cationic and zwitterionic (sulfobetaine) surfactant mixtures. The limits of detection for these surfactants are in the single micromolar range (1 ng N). A linear response was obtained (R2=0.9981) between 50 microM and 5 mM. The methodology was then applied to the determination of an industrial zwitterionic surfactant, Rewoteric AM CAS U [coco(amidopropyl)hydroxyldimethylsulfobetaine].     

Three polymorphs of 4‐4′‐diiodobenzalazine,and 4‐chloro‐4′‐iodobenzalazine

Three polymorphs of 4,4′‐diiodobenzalazine (systematic name: 4‐iodobenzaldehyde azine), C₁₄H₁₀I₂N₂, have crystallographically imposed inversion symmetry. 4‐Chloro‐4′‐iodobenzalazine [systematic name: 1‐(4‐chlorobenzylidene)‐2‐(4‐iodobenzylidene)diazane], C₁₄H₁₀ClIN₂, has a partially disordered pseudocentrosymmetric packing and is not isostructural with any of the polymorphs of 4,4′‐diiodobenzalazine. All structures pack utilizing halogen–halogen interactions; some also have weak π (benzene ring) interactions. A comparison with previously published methylphenylketalazines (which differ by substitution of methyl for H at the azine C atoms) shows a fundamentally different geometry for these two classes, namely planar for the alazines and twisted for the ketalazines. Density functional theory calculations confirm that the difference is fundamental and not an artifact of packing forces.     

Heterogeneous oxidation of pyrimidine and alkyl thioethers in ionic liquids over mesoporous Ti or Ti/Ge catalysts

Heterogeneous catalytic oxidation of a series of thioethers (2-thiomethylpyrimidine, 2-thiomethyl-4,6-dimethyl-pyrimidine, 2-thiobenzylpyrimidine, 2-thiobenzyl-4,6-dimethylpyrimidine, thioanisole, and n-heptyl methyl sulfide) was performed in ionic liquids by using MCM-41 and UVM-type mesoporous catalysts containing Ti, or Ti and Ge. A range of triflate, tetrafluoroborate, trifluoroacetate, lactate and bis(trifluoromethanesulfonyl)imide-based ionic liquids were used. The oxidations were carried out by using anhydrous hydrogen peroxide or the urea-hydrogen peroxide adduct and showed that ionic liquids are very effective solvents, achieving greater reactivity and selectivity than reactions performed in dioxane. The effects of halide and acid impurities on the reactions were also investigated. Recycling experiments on catalysts were carried out in order to evaluate Ti leaching and its effect on activity and selectivity.     

Ca(2.5)Sr(0.5)GaMn2O8: diamagnetic Ga in control of the structural and electronic properties of a bilayered manganate

The temperature dependence of the crystal structure and electronic properties of brownmillerite-like Ca(2.5)Sr(0.5)GaMn(2)O(8) has been studied by neutron powder diffraction and muSR spectroscopy. The results show that short-range 2D magnetic order begins to develop within the perovskite-like bilayers of MnO(6) octahedra approximately 50 K above the 3D Néel temperature of approximately 150 K. The bilayers show a structural response to the onset of magnetism throughout this temperature range whereas the GaO(4) layers that separate the bilayers only respond below the 3D ordering temperature. XANES spectroscopy shows that the sample contains Mn(3+) and Mn(4+) cations in a 1:1 ratio, and the behavior in the region of the Néel transition is interpreted as a local charge ordering. Electron diffraction and high-resolution electron microscopy have been used to show that the local microstructure is more complex than the average structure revealed by neutron diffraction, and that microdomains exist in which the GaO(4) tetrahedra show different orientations. It is argued that the bonding requirements of diamagnetic gallium control the electronic behavior within the perovskite-like bilayers.