An efficient synthesis of 1-cyanoacetyl-5-halomethyl-4,5-dihydro-1H-pyrazoles in ionic liquid

The synthesis of eleven 1-cyanoacetyl-5-hydroxy-5-halomethyl-4,5-dihydro-1H-pyrazoles from the reaction of 4-alkoxy-3-alken-2-ones f(R ³C(O)C(R ²) = C(R ¹)OR, where R ³ = CF₃, CCl₃, CHCl₂, CO₂ Et; R ²/R ¹ = H/H, H/Me, H/Et, -(CH₂)₄-, Me/H, H/Pr, and R = Me, Et) with cyanoacetohydrazide is reported. The reaction was carried out in the ionic liquid ([bmim][BF₄]) and molecular solvents. The results showed that when the ionic liquid was used as reaction medium, the reaction time was drastically decreased and the yield was improved.     

'Click' cycloaddition catalysts: copper(I) and copper(II) tris(triazolylmethyl)amine complexes

The CuI complex of the 'click' ligand tris(benzyltriazolylmethyl)amine is an unusual dinuclear dication with one triazole unit bridging two metal centers, and is an effective catalyst for the 'click' cycloaddition reaction.     

Debye to non-Debye scaling of the Boson peak dynamics: critical behavior and local disorder in vitreous germania

We report on the observation of a significant softening of the Boson peak (BP) frequency of vitreous GeO(2) above the glass transition temperature. The softening reminds a critical trend, with a transition temperature intermediate between the glass transition temperature, T(g), and the melting point. The softening of the BP frequency corresponds to a transition from a region dominated by Debye scaling to a non-Debye one. Below T(g) the density of vibrational states varies according to the modification of the elastic continuum medium. Above T(g) the relevant softening of the BP modes can be explained by a broadening of the distribution of elastic constants between neighboring atoms, induced by the structural rearrangement. These findings are discussed together with recent experimental and theoretical results on the low frequency vibrations in glasses.     

Crystallization mechanism of glass-ceramics prepared from Ni–Cu–Co mining wastes

The presence of minor elements on the crystallization kinetics of iron-rich glass obtained from a Ni–Cu–Co mining waste has been investigated. Two glasses named WG2 and RG were melted at 1500 °C. WG2 was prepared by using the mining waste, whereas RG contains pure oxides and no minor elements. WG2 and RG glasses presented high tendency toward crystallization with K_H coefficients of 0.21 and 0.29, respectively. Due to the presence of minor elements WG2 crystallizes at lower temperatures than RG glass leading to an increase in the viscosity. Crystallization kinetics analyzed by different models gives activation energy values close to 500 and 400 kJ·mol^? 1 for WG2 and RG, respectively. The Avrami parameter, n, depends on the particle size used for measurement and indicates the high tendency toward surface crystallization for both glasses.     

The unexpected cyclization routes of N,N′-bis(oxotrifluoroalkenyl)-1,3-phenylenediamines in polyphosphoric acid medium

The unexpected results of the cyclization reactions of N,N′-bis(oxotrifluoroalkenyl)-1,3-phenylenediamines [1,3-C₆H₄-(NHCRCHC(O)CF₃)₂], where R = H, Me, and Ph, in a strongly acidic medium (PPA), allowing the synthesis of new trifluoromethylated heterocycles containing the 1,7-phenanthroline nucleus in 32-40% yields and 7-aminoquinolines (38-40% yields), is reported. The bis-enaminoketone intermediates were easily isolated from the reactions of 4-alkoxy-4-alkyl(aryl)-1,1,1-trifluoroalk-3-en-2-ones with 1,3-phenylenediamine in ethanol under mild conditions (68-86% yields).     

General method for dehydration, intramolecular cyclization, and fluorination of trifluoromethyl-1H-pyrazoles using DAST

In this study, the versatile diethylaminosulfur trifluoride (DAST), a well-known fluorinating agent, was applied in the dehydration, intramolecular cyclization, and mono- and difluorination reactions of some 5-trifluoromethyl-1H-pyrazoles and 2-pyrazolines employing a general, mild, and efficient methodology. The azole precursors were synthesized from the reactions of acyclic and cyclic trifluoroacetylated enol ethers with hydrazines [NH₂NHR, where R = C₆H₅, C₆F₅, 2-Furanoyl] and showed a differentiated chemical behavior in the presence of DAST.     

13C NMR Chemical Shifts of β-Alkoxyvinyl Ketones: III✠-Empirical Substituent Effects in 1-Alkylamino-6-Ethoxy-1,5-Hexadien-3,4-Diones and 1,6-bis(Alkylamino)-1,5-Hexadien-3,4-diones

Evaluation by empirically derived equations for the substituent effect (E_Xn and E_Yn, n = 1 to 6) on the ¹³C NMR chemical shifts for C-1, C-2, C-3, C-4, C-5 and C-6 in 1-alkylamino-6-ethoxy-1,5-hexadien-3,4-diones 1a-f and 1,6-bis(alkylamino)-1,5-hexadien-3,4-diones 2a-f [XCH=CHC(O)-C(O)CH=CHY, where X, Y = OEt, NH₂, PhCH₂NH, n-BuNH, i-PrNH, cyclo-C₆H₁₁NH, t-BuNH], taking as reference the 1,6-diethoxy-1,5-hexadien-3,4-dione (3), is reported. From the calculated values for the E_Xn and E_Yn effects for each substituent it was possible to estimate the chemical shift of each carbon of the compounds 1,2 with excellent precision: 100% of the calculated chemical shifts are found to be within ±0.5ppm. The carbon-13 chemical shifts of C-1, C-2 and C-3 of compounds 1a,2a,3 led a good correlation with carbon charge densities (qr).     

Theoretical investigation of electronic and optical properties of andalusite within density functional theory

The electronic and optical properties of andalusite were studied by using quantum-mechanical calculations based on the density functional theory (DFT). The electronic structure shows that andalusite has a direct band gap of 5.01 eV. The complex dielectric function and optical constants, such as extinction coefficient, refractive index, reflectivity and energy-loss spectrum, are calculated. The optical properties of andalusite are discussed based on the band structure calculations. It is shown that the O-2p states and Al-3s states play a major role in optical transitions as initial and final states, respectively.