9-acetoxyanthracene derivatives. Part VIII. The mechanism of degradation of 9-acetoxy-10-arylanthracenes to anthraquinone

The mechanism of degradation of 9-acetoxy-10-arylanthracenes to anthraquinose with the use of HNO₃ in AcOH has been reported. This was proved by way of example on 9-acetoxy-10-(4′-acetoxyphenyl )anthracene (1) by means of separation and identification of intermediate products $\text{2}$, $\text{3}$ and $\text{4}$.     

Direct measurement of gas solubility and diffusivity in poly(vinylidene fluoride) with a high-pressure microbalance

We present solubility and diffusion data for the gases methane and carbon dioxide in the polymer poly(vinylidene fluoride). The polymer was cut from extruded piping intended for use in offshore oil and gas applications. Measurements were carried out using a purpose-built high-pressure microbalance. These properties were determined in the temperature range 80-120 °C and in the pressure range 50-150 bar for methane and 20-40 bar for carbon dioxide. In general, good agreement was obtained for similar measurements reported in the literature. Solubility follows a Henry’s law (linear) dependence with pressure. Diffusion coefficients for each of the gases in the polymer were also measured using the balance. Activation energies for diffusion and heats of solution for the two gases in the polymer were also determined.     

Suzuki-Miyaura cross-coupling of aryl and alkyl halides using palladium/imidazolium salt protocols

A simple new protocol for the high yielding Suzuki-Miyaura cross-couplings of aryl chlorides with aryl boronic acids using a palladium/imidazolium salt catalytic system is presented. The first examples of a palladium/imidazolium salt protocol for sp³-sp³ Suzuki-Miyaura couplings of alkyl halides are also disclosed.     

Stereoselective E/Z photoisomerization of oxazolidinone functionalized enecarbamates: direct and triplet sensitized irradiation

Oxazolidinone-functionalized enecarbamates undergo diastereoselective E/Z photoisomerization upon direct and triplet sensitized irradiations with chiral/achiral sensitizers, showing that the enhanced product diastereoselectivity depends on the solvent and temperature.     

Synthesis and capsule formation of upper rim substituted tetra-acrylamido calix[4]arenes

Upper rim substituted tetraiodo calix[4]arenes are coupled to a variety of acrylamides using the palladium catalysed Heck reaction. Tetra-acrylamido upper rim substituted calix[4]arenes are obtained in good yields with exceptionally high stereoselectivity, to produce the all-trans isomers. Tetra-acrylamido calix[4]arenes derived from secondary acrylamides are shown to dimerise via eight hydrogen bonds to form dimeric capsules, which are able to include small organic molecules.     

Determination of uranium after its selective extraction as phenylacetate

The method described is based on the extraction of uranium with a chloroform solution of phenylacetic acid from slightly acidic solution containing nitrilotriacetic acid, which masks all interfering metals. After stripping into very dilute hydrochloric acid, uranium is reduced with ascorbic acid and determined complexometrically. The method permits reliable determination of uranium in the presence of all quadri-, ter- and bivalent metals investigated, molybdenum(VI), tungsten(VI), and vanadium(V).     

Electrophilic acetylation and bromination reactions of benzo[b]naphtho[2,3-e][1,4]dioxin

The reactivity of benzo[b]naphtho[2,3-e][1,4]dioxin in the electrophilic aromatic substitution reactions has been studied. Friedel-Crafts acetylation resulted in the formation of three out of the possible five monoacetylated products, with the acetyl group located in positions 8 (major), 7 and 6 (minor) of the heterocycle. In the bromination reaction a higher selectivity was observed with the 6-bromo derivative found as the only monobrominated product and the 6,11-dibromo derivative found as the only polybrominated product. A ratio of unreacted heterocycle:6-bromo:6,11-dibromo derivatives in the bromination reaction has been found to depend strongly on the reaction conditions and on the heterocycle:bromine ratio.     

Determination of cadmium in mixtures with metal ions

A method for the determination of cadmium microamounts in mixtures with metallic ions withE _1/2 near toE _1/2 of cadmium is discussed. For higher selectivity cadmium was extracted in the form of the pyridin-thiocyanate complexes prior to polarography.

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Bestimmung von Cadmium(II) neben anderen Metallionen

Zusammenfassung Es wird eine polarographische Methode zur Bestimmung von Cd(II) neben anderen Metallionen mitE _1/2 naheE _1/2(Cd) diskutiert. Zur Erhöhung der Selektivität und Genauigkeit wird eine Pyridin-Thiocyanat-Extraktion vorgeschalten.

     

Ortho effect in the mass spectrometric behaviour of N(pyrimidin-4-yl)aminobenzoic acids and their methyl esters

Ortho-. meta- and para-isomers of N-(pyrimidin-4-yl)aminobenzoic acid and their methyl esters were investigated by electron impact mass Spectrometry. Their fragmentation was found to be strongly dependent on the position of the substituent in the aminobenzoic moiety. Two different kinds of ortho effect were studied and confirmed with the aid of deuterium-labelled derivatives.     

Synthesis, structure determination, and spectroscopic/computational characterization of a series of Fe(II)-thiolate model complexes: implications for Fe-S bonding in superoxide reductases

A combined synthetic/spectroscopic/computational approach has been employed to prepare and characterize a series of Fe(II)-thiolate complexes that model the square-pyramidal [Fe(II)(N(His))(4)(S(Cys))] structure of the reduced active site of superoxide reductases (SORs), a class of enzymes that detoxify superoxide in air-sensitive organisms. The high-spin (S = 2) Fe(II) complexes [(Me(4)cyclam)Fe(SC(6)H(4)-p-OMe)]OTf (2) and [FeL]PF(6) (3) (where Me(4)cyclam = 1,4,8,11-tetramethylcyclam and L is the pentadentate monoanion of 1-thioethyl-4,8,11-trimethylcyclam) were synthesized and subjected to structural, magnetic, and electrochemical characterization. X-ray crystallographic studies confirm that 2 and 3 possess an N(4)S donor set similar to that found for the SOR active site and reveal molecular geometries intermediate between square pyramidal and trigonal bipyramidal for both complexes. Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature variable-field MCD (VTVH-MCD) spectroscopies were utilized, in conjunction with density functional theory (DFT) and semiemperical INDO/S-CI calculations, to probe the ground and excited states of complexes 2 and 3, as well as the previously reported Fe(II) SOR model [(L(8)py(2))Fe(SC(6)H(4)-p-Me)]BF(4) (1) (where L(8)py(2) is a tetradentate pyridyl-appended diazacyclooctane macrocycle). These studies allow for a detailed interpretation of the S-->Fe(II) charge transfer transitions observed in the absorption and MCD spectra of complexes 1-3 and provide significant insights into the nature of Fe(II)-S bonding in complexes with axial thiolate ligation. Of the three models investigated, complex 3 exhibits an absorption spectrum that is particularly similar to the one reported for the reduced SOR enzyme (SOR(red)), suggesting that this model accurately mimics key elements of the electronic structure of the enzyme active site; namely, highly covalent Fe-S pi- and sigma-interactions. These spectral similarities are shown to arise from the fact that 3 contains an alkyl thiolate tethered to the equatorial cyclam ring, resulting in a thiolate orientation that is very similar to the one adopted by the Cys residue in the SOR(red) active site. Possible implications of our results with respect to the electronic structure and reactivity of SOR(red) are discussed.