Oxidation of 2,6-di-tert-butylphenol with polymer anchored molybdenyl and vanadyl complexes

The oxidation of 2,6-di-tert-butylphenol with tert-butylhydroperoxide (Bu^tO₂H) has been studied using polymer (XAD₄) anchored salicylaldoxime, 1,3-propylene-bis-salicylaldimine and o-phenylene-bis-salicylaldimine complexes of molybdenum and vanadium in acetonitrile. The predominant products formed in the oxidation reactions were 2,6-di-tert-butylbenzoquinone (BQ) and 3,3′-5,5′-tetra-tert-butyldiphenoquinone (dPQ), whereas with some only 2,6-di-tert-butylbenzoquinone was formed. This is the first reported use of polymer anchored molybdenyl and vanadyl complexes in selective oxidation of 2,6-di-tert-butylphenol. Solvent plays an important role in this reaction. The effects of varying the ligand, metal and the support on the catalytic activity in the oxidation of 2,6-di-tert-butylphenol have been studied. With polymer anchored MoO₂(salpen), 81% of 2,6-di-tert-butylbenzoquinone was formed from 2,6-di-tert-butylphenol.     

Spin-transition behaviour of transition metal complexes with 2,6-bis-(benzimidazol-2′-yl)-pyridine induced by deprotonation of the complex

Summary 2,6-bis-(Benzimidazol-2-yl)-pyridine (bzimpy = H₂ L) acts as a bidentate ligand when combining with transition metal ions. The complexes [M(bzimpy)₂](ClO₄)₂ (M = Fe²⁺, Mn²⁺, Zn²⁺, Co²⁺, and Ni²⁺) were obtained as solids. The protonation constants (logK) for the ligand and the complexes were evaluated in 30:70 (v/v) H₂O:EtOH at 293 K and at constant ionic strength of 0.12M KCl. Coordination of the ligand to the metal ions leads to an increase of acidity of the imino-hydrogen of the benzimidazole group of the ligand as a function of the complex stability. Deprotonation leads to a spin-state transition (intermediate spin-state low-spin) of the iron(II)-complex, followed by a shift of the metal-to-ligandcharge transfer band (MLCT) to lower energies (_max=563 to 580 nm). The d-d absorption bands are found to shift to higher energies and the low-spin isomer is favoured at room temperature. An opposite shift of theMLCT band (_max=563 to 557 nm) is observed when HClO₄ is added to the complex solution, rendering the high-spin state of the complex more favourable.On leave from the Chemistry Department, Jahangirnagar University, Dhaka, Bangladesh     

Determination of TNT and its metabolites in water samples by voltammetric techniques

Square-wave voltammetry with the hanging drop mercury electrode as the working electrode was used for the determination of ultratraces of explosives in aqueous solution. It was shown that the strong pressure dependence of the pneumatically controlled multimode electrode system of a conventional Metrohm apparatus could be compensated by an additional pressure regulation, through which the pressure variations could be decreased when switching from deaeration to the static measurements. By using square-wave voltammetry with this electrode system after this modification the limits of detection for 2,4,6-trinitrotoluene (TNT) and other TNT-metabolites could be decreased down to 0.2 μg L⁻¹ when using a measurement time of 6 min. Also a simultaneous determination of TNT and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) was shown to be possible over a wide linear range and the detection limits then were 2.2 μg L⁻¹ for TNT and 25 μg L⁻¹ for RDX. By applying the highly stable and adjustable pressure as mentioned before, the calibrations could be kept stable over a period of up to 1 week.     

[K2(TNR)(H2O)]n的制备、分子结构和热分解机理

2,4,6-三硝基间苯二酚(斯蒂芬酸)及其盐类,如斯蒂芬酸铅、斯蒂芬酸钡等是常用的含能材料[1],但斯蒂芬酸铅盐及钡盐在爆炸后产生重金属污染,对使用人员的健康及环境都产生危害.     

A Polymeric Iodiplumbate(Ⅱ) Templated by Conjugated Quaternary Ammonium: Synthesis, Band Structure and Optical Properties

A new lead(Ⅱ) iodide coordination polymer [(npq)(PbI3)]n 1 (npq = N-propyl- quinolinium) has been synthesized in the presence of npq as structure-directing reagent (SDA). Compound 1 crystallizes in the orthorhombic system, space group Pbca, with a = 19.158(4), b = 7.9909(16), c = 22.929(5) (A), V = 3510.2(12) (A)3, Z = 8, Dc = 2.877 g/cm3, F(000) = 2672, C12H14I3NPb, Mr = 760.14, μ(MoKα) = 14.872 mm-1, the final R = 0.0431 and wR = 0.1021 for 3678 observed reflections with I＞2σ(I). Structure determination indicates that the [PbI3]-n infinite chains in each unit cell shape the sketch of 1, which could be described as the result of face-sharing distorted PbI6 octahedra running along the b axis. Electrostatic interaction between conjugated organic counter-cations and inorganic moieties presents and contributes to the crystal packing. 1 was further characterized with IR and elemental analysis. Based on the crystal structure data, quantum chemical calculation with DFT method was used to reveal the electronic structure and optical property of 1.     

Electrophilic addition of lead tetraacetate to 2-carene in an acidic medium

Oxidation of 2-carene by lead tetraacetate in acetic acid afforded p-menth-1(10),2-dien-7-ol, 2-acetyl-6,6-dimethylbicyclo[3.1.0]hexane, p-menth-2-ene-1,7-diol, p-menth-1-ene-3,7-diol, and 2-(m-tolyl)propanol-2.Deceased.A. M. Butlerov Scientific Research Chemical Institute, V. I. Ul'yanov-Lenin Kazan' State University, 420008 Kazan. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 147–150, January, 1992.     

Design of Supramolecular Cyclodextrin Complex Sensors for Ion and Molecule Recognition in Water

The design and function of novel supramolecular fluoroionophore/cyclodextrin (CyD) complex sensors for ion and molecule recognition in water are reviewed. For the crown ether fluoroionophore/-CyD complex, the dimerization of the fluoroionophore inside the -CyD is found to be selectively promoted by alkali metal ion binding, thereby resulting in metal-ion-selective pyrene dimer emission in water. This supramolecular function is successfully utilized in the design of a podand fluoroionophore/-CyD complex for sensing toxic lead ion in water. The boronic acid fluoroionophore/-CyD complex binds sugars and produces increased fluorescence emission in water. The response mechanism appears to be due to the suppression of the photoinduced electron transfer (PET) from pyrene donor to trigonal phenylboronic acid acceptor. This is a novel emission function provided by the boronic acid fluoroionophore/-CyD complex sensors in water.     

Trisubstituted 1,3,5-Triazines. 6. Synthesis of 2,4,6-Tris(acetonyl)-1,3,5-triazine

Acylation of 2,4,6-tris(tert-butoxycarbonylmethyl)-1,3,5-triazine with acetic anhydride in the presence of lithium hydride with subsequent removal of the tert-butoxycarbonyl groups with trifluoroacetic acid leads to 2,4,6-tris(acetonyl)-1,3,5-triazine, the cyclic analog of -cyanoacetone. The special spectral features of this compound compared with triazines obtained previously are discussed.     

Cesium lead halide perovskite nanocrystals for ultraviolet and blue light blocking

Using cesium lead halide perovskite nanocrystals, CsPb(Cl/Br)_3, as a light absorber, we report a highly effective UV and blue light blocking film. The CsPb(Cl/Br)_3 nanocrystals are well dispersed in the ethyl cellulose(EC) matrix to compose a UV and blue light shielding film, and the absorption edge of the film is tunable by adjusting Cl to Br ratio using anion exchange. The CsPbCl_2 Br-EC film exhibits a transmittance of 5% at 459 nm, 90% at 478 nm and 95% in the range of 500–800 nm, which makes it excellent for UV and blue light shielding. In addition, the as-prepared EC-CsPb(Cl/Br)_3 film shows excellent photostability under UV irradiation. Results demonstrate that this EC-CsPb(Cl/Br)_3 based materials with sharp absorbance edges, tunable blocking wavelength, and high photostability can be useful for the applications in UV and blue light blocking and optical filters     

The MNDO-PM3 study of the mechanism of nucleophilic substitution of the phenoxide anion for the nitro group in 1,3,5-trinitrobenzene and 2,4,6-trinitrotoluene in the gas phase and in polar solvents

The semi-empirical quantum chemical MNDO-PM3 calculations of the enthalpies of formation of Meisenheimerortho- andipso--complexes of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) with the phenoxide anion in the gas phase and in water are performed within the framework of the point dipole model. Based on the calculated heats and activation barriers to substitution of the nitro group by the phenoxyl group in TNB and TNT, the possibility of the reactions of TNB and TNT with the phenoxide anion in water is shown. These reactions in water occurvia the S_NAr mechanism involving the correspondingipso--complex as an intermediate. In the gas phase, the S_NAr mechanism is impossible, because the reaction is strongly endothermic. In the case of TNT, the exothermic reaction of elimination of a proton from the methyl group by the phenoxide anion competes with nucleophilic substitution in a polar solvent. The activation energy calculated for this exothermic reaction is 8 kcal mol^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 624–628, April, 1995.