Steric selectivity in oxidations of diols

Oxidations of 2,2-disubstituted-1,4-butanediols by the combination of nickel(II) bromide and benzoyl peroxide and by trityl tetrafluoroborate produce β,β-disubstituted-γ-butyrolactones with exceptional selectivity.     

Synthesis,Characterization, and Crystal Structure of Thallium(I) Complex containing Monodeprotonated 2,6‐Pyridinedicarboxylic Acid

The reaction of an ethanolic solution 2,6‐pyridinedicarboxylic acid ( 1 , LH₂) with TlNO₃ in the presence of triethylamine led to the coordination polymer [Tl(LH)]_n ( 2 ). The complex was characterized by elemental analysis, IR spectroscopy and single‐crystal X‐ray diffraction. Crystal data for 2 at –80 °C: monoclinic, space group I2/a, a = 696.1(1), b = 1190.6(2), c = 931.0(2) pm, β = 103.28(1)°, Z = 4, R₁ = 0.0256.     

SPECTROSCOPIC STUDIES OF CUTANEOUS PHOTOSENSITIZING AGENTS. XVIII. INDOMETHACIN

Abstract— The photochemistry, photophysics, and photosensitization (Type I and II) of indomethacin (IN) (N-[p-chlorobenzoyl]-5-methoxy-2-methylindole-3-acetic acid) has been studied in a variety of solvents using NMR, high performance liquid chromatography-mass spectroscopy, transient spectroscopy, electron paramagnetic resonance in conjunction with the spin trapping technique, and the direct detection of singlet molecular oxygen (^l O₂) luminescence. Photodecomposition of IN (λ_ex > 330 nm) in degassed or air-saturated benzene proceeds rapidly to yield a major (2; N-[p-chlorobenzoyl]-5-methoxy-2-methyl-3-methylene-indoline) and a minor (3; N-[p-chlorobenzoyl]-5-methoxy-2, 3-dimethyl-indole) decarboxylated product and a minor indoline (5; 1-en-5-methoxy-2-methyl-3-methylene-in-doline), which is formed by loss of the p-chlorobenzoyl moiety. In air-saturated solvents two minor oxidized products 4 (N-[p-chlorobenzoyl]-5-methoxy-2-methylindol-3-aldehyde) and 6 (5-methoxy-2-methyl-indole-3-aldehyde) are also formed. When photolysis was carried out in ¹⁸O₂-saturated benzene, the oxidized products 4 and 6 contained ¹⁸O, indicating that oxidation was mediated by dissolved oxygen in the solvent. In more polar solvents such as acetonitrile or ethanol, photodecomposition is extremely slow and inefficient. Phosphorescence of IN at 77 K shows strong solvent dependence and its emission is greatly reduced as polarity of solvent is increased. Flash excitation of IN in degassed ethanol or acetonitrile produces no transients. A weak transient is observed at 375 nm in degassed benzene, which is not quenched by oxygen. Irradiation of IN (λ_ex > 325 nm) in N₂-gassed C₆H₆ in the presence of 5, 5-dimethyl-1-pyrroline-N-oxide (DMPO) results in the trapping of two carbon-centered radicals by DMPO. One adduct was identified as DMPO/^.COC₆H₄-p-CI, while the other was probably derived from a radical formed during IN decarboxylation. In air-saturated benzene, (hydro) peroxyl and alkoxyl radical adducts of DMPO are observed. A very weak luminescence signal from ¹O₂ at 1268 nm is observed initially upon irradiation (λ_ex= 325 nm) of IN in air-saturated benzene or chloroform. The intensity of this ¹O₂ signal increases as irradiation is continued suggesting that the enhancement in ¹O₂ yield is due to photoproduct(s). Accordingly, when 2 and 3 were tested directly, 2 was found to be a much better sensitizer of ¹O₂ than IN. In air-saturated ethanol or acetonitrile no IN ¹O₂ luminescence is detected even on continuous irradiation. The inability of IN to cause phototoxicity may be related to its photo stability in polar solvents, coupled with the low yield of active oxygen species (¹O₂, O₂^?_-) upon UV irradiation.     

Rh(II)-Catalyzed Isomerizations of Cyclopropenes Evidence for Rh(II)-Complexed Vinylcarbene Intermediates

The thermocatalytic rearrangements of cyclopropenes 1-4 have been investigated in the presence of Rh(IT) perfiuorobutyrate. 1, 2, 3-Triphenylcyclopropene ( 1a ) undergoes rearrangement lo diphenylindene 5a or, with alkoxycyclopropene derivatives, to α, β-unsaturated ketone 6. Furan formation occurs with 2, 3-diphenylcyclo-propenecarboxylate 2, but the diethyl counterpart 3 rearranges to dienoate 8. 2-Alkylcyclopropenecarboxylates 4 afforded (E)-methylidenecyclopentane derivatives 9 as the only isolable product in yields of ca. 35 %. A mechanism involving regio- and stereospecific cyclopropene ring opening to a Rh-complexed vinylcarbene and insertion of the latter into the C? H bond to give 9 is proposed. An analogous mechanism should account for the rearrangement products of 1 to 3 .     

A tetra-coordinate nickel(II) complex as neutral carrier for nitrate-selective PVC membrane electrode

The potentiometric response properties and applications of a tetra-coordinate nickel(II) complex with relatively high selectivity toward nitrate ion are described. The nickel(II) complex of 5,7,12,14-tetramethyl-1,4,8,11-tetraazacyclotetradeca-4,6,11,13-tetraene was used as a neutral carrier into plasticized poly(vinyl chloride) (PVC) membrane. The influence of several variables was investigated in order to optimize the potentiometric response and selectivity of the electrode. The resulting membrane electrode incorporating 31.0% PVC, 61.0% dioctyl phthalate (DOP) as plasticizer, 3% methyltrioctylammonium chloride (MTOAC) as a cationic additive and 5% carrier (all w/w) demonstrates a Nernstian response slope of −59.6 mV per decade over the concentration range of 5×10⁻⁶-1×10⁻¹ M NO₃⁻. The electrode exhibits a fast response time (≤10 s), a detection limit of 2.5×10⁻⁶ M, and can be used over a wide pH range of 4-12. The electrode shows improved selectivity in comparison to most of the previously reported nitrate-selective electrodes. It was successfully applied to the determination of nitrate ion in natural water samples.     

Anion-receptor molecules: Macrocyclic and macrobicyclic effects on anion binding by polyammonium receptor molecules

The stability constants for anion binding by the acyclic hexaamine 1 , its macrocyclic analogue 2 , and the bicyclic compound 3 in their protonated forms are reported. Compound 3 forms stable and selective complexes with halide ions, the stability sequence being I^? > Br^? > Cl^?. Compound 2 forms more stable complexes with sulfate, oxalate, and malonate dianions than its acyclic analogue 1 and shows a better selectivity pattern. Compound 3 forms stronger complexes with oxalate^2? than 2 and shows a remarkably high binding selectivity between oxalate^2? and malonate^2?. The comparison of the ability of 1–3 to complex anions demonstrates the macrocyclic and macrobicyclic effects on anion binding stability and selectivity.     

Mutual Separation and Determination of Th(IV) and U(VI) Using Arsenazo III as a Dye Collector Reagent by Flotation‐Spectrophotometric Method

This paper reports a simple and highly selective method for the separation, preconcentration, and determination of trace amounts of thorium and uranium in some complex samples via staircase flotation. The method is based on the initial flotation of the Th(IV)‐arsenazo III complex in the presence of U(VI) from a solution of 5 mol dm^?3 HCl, then reduction of U(VI) to U(IV) and repetition of the flotation step. In both steps, the floated complex was dissolved in a 5‐mL portion of methanol and its absorbance was measured at 655 nm, spectrophotometrically. For a 30‐mL portion of the sample, Beer's law was obeyed over the concentration ranges of 3.40 × 10^?7to 3.06 × 10^?6 mol dm^?3 for Th(IV) and3.40 × 10^?7 to 3.40 × 10^?6 mol dm^?3 for U(IV) with the apparent molar absorptivity of 4.20 × 10⁵ dm³ mol^?1 cm^?1 and 3.59 × 10⁵ dm³ mol^?1 cm^?1, respectively. The RSDs (n = 7) corresponding to 1.7 × 10^?6 mol dm^?3 of Th(IV) and U(IV) were obtained as 1.7% and 1.87%. The detection limits (7 blanks) for both the metal ions were found to be 1.7 × 10^?7 mol dm^?3. The important benefit of the method is that the determinations are free from the interference of almost all cations and anions found in the complex matrixes, such as seawater samples. The proposed method was also applied to reference materials, and the determinations were shown to have good agreement with the certified values.     

Lead ion selective PVC membrane electrode based on 5,5'-dithiobis-(2-nitrobenzoic acid)

A PVC membrane electrode for lead ions based on 5,5′-dithiobis-(2-nitrobenzoic acid) as membrane carrier was prepared. The electrode exhibits a Nernstian response for Pb²⁺ over a wide concentration range (1.0×10⁻²–4.0×10⁻⁶ M). It has a relatively fast response time and can be used for at least 3 months without any divergence in potentials. The proposed electrode revealed good selectivities for Pb²⁺ over a wide variety of other metal ions and could be used in a pH range of 2.0–7.0. It was used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.     

Synthesis,Characterization and Crystal Structures of new Coordination Polymers of Cerium(III) and Samarium(III) Containing 2,6‐Pyridinedicarboxylic Acid

The reaction of 2,6‐pyridinedicarboxylic acid ( 1 , LH₂) with CeCl₃·7H₂O and Sm(NO₃)₃·6H₂O in the presence of triethylamine led to the coordination polymer complexes [M(L)(LH)(H₂O)₂]·4H₂O [M = Ce ( 2 ) and Sm ( 3 )]. Both complexes were characterized by elemental analyses, IR spectroscopy and the crystal structures of 2 and 3 . Crystal data for 2 at ?80 °C: monoclinic, space group P2₁/c, a = 1404.6(1), b = 1122.1(1), c = 1296.1(1) pm, β = 102.09(1)°, Z = 4, R₁ = 0.0217 and for 3 at ?80 °C: monoclinic, space group P2₁/c, a = 1395.1(1), b = 1120.1(1), c = 1282.8(1) pm, β = 102.71(1)°, Z = 4, R₁ = 0.019.     

Acetylenchemie 12. Mitt.: Weitere studien über die phasentransfer-katalysierte umsetzung des 9(10H)-acridinons mil alkinylhalogeniden

By the phase transfer catalyzed reaction of 9(10H)-acridinone with 1-bromo-2-propyne, 10-(2-propynyl)-9(10H)-acridinone is synthesized. As prototropic rearrangement products of this 10-(1,2-propadienyl)-9(10H)-acridinone and 10-(1-propynyl)-9(10H)-acridinone are obtained, Under the given conditins 1-bromo-2butyne leads to 10-(2-butynyl)-9(10H)-acridinone and 2-chloro-3-butyne leads to 10-(1-methyl-1,2-propddienyl)-9(10H)-acridinone, 10-(1-methyl-2-propynyl)-9(10H)-acridinone, 9-(1-methyl-2-propynyloxy)acridine and 10-[1-methyl-3-(3,4-dimethylphenyl-2-propynyl)]-9(10H)-acridinone. The formation of the products is experimentally confirmed and with published work compared.