Parallel synthesis of 1,2,4-triazole derivatives using microwave and continuous-flow techniques

Abstract  

An efficient and convenient solution-phase synthesis of a 1H-1,2,4-triazole library with potential agrochemical activity is reported employing microwave-assisted organic synthesis (MAOS) and continuous-flow microfluidic synthetic methods starting from commercially available 3,5-dibromo-1H-1,2,4-triazole (1). MAOS was used for the synthesis of 5-amino-3-bromo-1,2,4-triazole analogs 3 and for their 3-aryl derivatives 4 via Suzuki–Miyaura coupling with polymer-supported catalyst. A microfluidic hydrogenation reactor integrated into an automated parallel synthesis platform was built and utilized for the reductive dehalogenation reactions providing 5-aminotriazoles (5).     

Mössbauer spectroscopy monitoring the spin transition of a FeII 1D chain with a fluorinated 4-R-1,2,4-triazole

The spin transition properties of [Fe(fletrz)₃](BF₄)₂?2H₂O are described. Fletrz (4-(2’-fluoroethyl)-4H-1,2,4-triazole) is a novel fluorine substituted 1,2,4-triazole ligand which forms 1D chain upon self-assembly with Fe^II ions. This coordination polymer exhibits reversible abrupt thermochromic spin transition that has been probed by SQUID magnetometry, variable temperature ⁵⁷Fe Mossbauer spectroscopy (77–300 K) and differential scanning calorimetry (100–300 K).     

Cycloaddition of 2′-azidoethyl glycosides to fullerene[C60] under ultrasonic irradiation

The reactions of fullerene[C₆₀] with 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-α-d-mannopyranoside (2a) and 2′-azidoethyl 2,3,4,6-tetra-O-acetyl-β-d-galactopyranoside (2b) under ultrasonic irradiation cause the cycloaddition of 2′-azidoethyl glycosides to fullerene[C₆₀] and lead to d-glycosyl fullerene[C₆₀] derivatives 3a and 3b, respectively. The glycosyl fullerene[C₆₀] derivatives were characterized by ¹H and ¹³C NMR, UV–vis, FAB-MS, FT-IR spectra and were a 1:1 glycoside fullerene [C₆₀]-adduct.     

Understanding the adsorption of 4H-1,2,4-triazole derivatives on mild steel surface in molar hydrochloric acid

This study examines the use of some 4H-triazole derivatives, namely 3,5-diphenyl-4H-1,2,4-triazole (DHT), 3,5-bis(4-pyridyl)-4H-1,2,4-triazole (4-PHT) and 3,5-bis(4-methyltiophenyl)-4H-1,2,4-triazole (4-MTHT) for corrosion and dissolution protection of mild steel in normal hydrochloric acid solution. The inhibiting efficiency of the different additives is evaluated by means of weight loss and electrochemical techniques such as ac impedance measurements and polarisation curves. The experimental results obtained reveal that 4-MTHT is the best effective inhibitor and the inhibition efficiency is found to be in the following order: 4-MTHT > 4-PHT > DHT. The variation in inhibitive efficiency mainly depends on the type and nature of the substituents present in the inhibitor molecule. Polarisation curves show that theses triazoles are mixed-type inhibitors in 1 M HCl. The inhibition efficiency increases with 4H-triazole derivatives concentration and attains the maximum value of 99.6% in the case of 4-MTHT at 5 × 10⁻⁴ M. The results obtained from weight loss electrochemical studies were in reasonable agreement. The adsorption of 4H-triazole derivatives on the steel surface obeys to the Langmuir isotherm model. The thermodynamic data of adsorption and activation are determined and discussed. The fundamental thermodynamic functions were used to glean important information about the 4H-triazoles inhibitory behaviour. Molecular modeling was used to get better insight, about structural and electronic effects in relation to the inhibition efficiencies.     

Experimental evidence of the vibrational coupling of nearest neighbours in 1D spin crossover polymers of rigid bridging ligands

The nuclear inelastic scattering signatures of the low spin centres of the methanosulphonate, tosylate and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole)₃]⁺²) _n have been compared for the pure low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the spectral pattern in the 320–500 cm^?1 region is observed involving the decrease of the intensities of a band at ～320 cm^?1 and those over 400 cm^?1 as the molar fraction of the low-spin centres decreases. On the basis of the DFT calculations (B3LYP/CEP-31G) this effect is interpreted in terms of vibrational coupling of the iron centres of the same spin.     

Synthesis,measurements, and theoretical analysis of carbazole derivatives with high-triplet-energy

In order to obtain the blue light-emitting organic materials with high triplet state energy, two 3,5-diphenyl-4H-1,2,4-triazole (Tz) containing carbazole (Cz) derivatives of 9-(4-(3,5-diphenyl-4H-1,2,4-triazol-4-yl)phenyl)-9H-carbazole (TzCz1) and 3,6-di-tert-butyl-9-(4-(3,5-diphenyl-4H-1,2,4-triazol-4-yl)phenyl)-9H-carbazole (TzCz2) are synthesized using Cz acting as the starting material, as well as characterized by the ¹H NMR spectra, ultraviolet–visible (UV–vis) absorption spectra, and the IR absorption spectra. The luminescence quantum yields (LQYs) of TzCz1 and TzCz2 are measured in CH₂Cl₂ solution to be 32.1% and 47.5%, respectively. The electrochemical analysis and the photophysical measurements suggest that the triplet energy levels and the energy gaps of the highest-occupied orbital and the lowest-unoccupied orbital are 2.83 eV and 3.59 eV for TzCz1, and 2.80 eV and 3.43 eV for TzCz2. At last, the theoretical analyses of their ground state geometries and the simulated UV–vis absorption spectra are carried out at B3LYP1/6-31G? level. The studies mentioned above indicate that both TzCz1 and TzCz2 are suitable for the host materials of blue light-emitting diodes.     

Thermodynamic and quantum chemistry characterization of the adsorption of triazole derivatives during Muntz corrosion in acidic and neutral solutions

Some triazole derivatives (4-amino-5-mercapto-3-methyl 1,2,4-triazole (AMMT), 4-amino-5-mercapto-3-ethyl 1,2,4-triazole (AMET) and 4-amino-5-mercapto-3-propyl 1,2,4-triazole (AMPT)) have been evaluated as new corrosion inhibitors for the corrosion of muntz alloy (60Cu-40Zn) in acidic and neutral solutions. The adsorption of these compounds has been tested thermodynamically which was found to be of a physisorption mode. Furthermore, some activation thermodynamic parameters such as ΔH^*, ΔS^* and ΔG^* of activation have been estimated. In addition, a trial to find a quantitative relationship between the inhibition efficiency and the electronic properties of the inhibitor molecules was carried out.     

Gas-phase quasi-degeneracy of zwitterionic and canonical tautomers of glycine and proline induced by the presence of the MAlF4 (M = Li,Na, K) salts

The ionic MAlF₄ salts (M = Li, Na, K) are postulated to act as effective stabilising agents with respect to glycine and proline zwitterionic tautomers. On the basis of ab-initio MP2/6-311++G(d,p) theoretical calculations, it is demonstrated that strong electrostatic interactions between the polar MAlF₄ moiety and either Gly and Pro zwitterion should allow to suppress the intra-molecular proton transfer in the amino acid and thus render the zwitterion tautomer stable in the gas phase. Among the systems proposed, the K⁺AlF₄^– turned out to be the most efficient stabilising compound as its presence is expected to lead to the energetic quasi-degeneracy of the canonical and zwitterionic tautomers of glycine and proline.     

Nuclear inelastic scattering study of a dinuclear iron(II) complex showing a direct spin transition

The results of the nuclear inelastic scattering (NIS)/nuclear resonance vibrational spectroscopy (NRVS) for the powder spectra of dimeric [Fe ₂L₅(NCS) ₄] (L = N-salicylidene-4-amino-1,2,4-triazole) complex are presented. This system is spin crossover (SCO) material tagged with a fluorophore that can sense or “feel” the SCO signal ripping through the molecular network and thereby providing an opportunity to register the SCO transition. The spectra have been measured for the low-spin and high-spin phases of the complex. The high-spin isomer reveals one broad band above 200 cm ^?1, while the low-spin one displays two intense bands in the range from 390 to 430 cm ^?1, accompanied by a number of weaker bands below this area and one at ca. 490 cm ^?1. A normal coordinate analysis based on density functional calculations yields the assignment of the spin marker bands to particular molecular modes. In addition the vibrational contribution to the spin transition has been estimated     

Spin Transition Molecular Materials: New Sensors

This short review article concerns a new family of iron(II) spin transition chain compounds containing 4-R-1,2,4-triazole derivatives whose properties have been followed by several physical techniques. A clear evidence of the LIESST effect at 20 K has been found for one of these materials by ⁵⁷Fe Mössbauer spectroscopy. Potential applications in terms of pressure and thermal sensors are discussed.     

Solvation properties of Li+ and CI− in water: molecular dynamics simulation with a non-rigid model

Molecular dynamics (MD) simulations were carried out to investigate the solvation properties of Li⁺ and C1^? ions in water with a relatively accurate but rarely used non-rigid model, RWK2, in this study. A new set of ion-water interaction parameters was evaluated from the experimental data and first principles calculation results of stable clusters, Li⁺(H₂O) _n (n = 1- 6) and CI^?(H₂O) _n (n = 1–4). With the ion-water potential parameters evaluated from the data of the clusters and the water-water potential predetermined from the non-rigid RWK2 model, the structural (radial distribution functions, angular distribution functions, spatial distribution functions, coordination number), dynamical (residence time) and energetic properties of the ionic salvations in bulk water were studied through a comprehensive analysis of our MD simulation outputs. These results not only agree well with experimental data and first principles calculations, but also reveal some new insights into the microscopic ionic salvation processes.     

Neutral and anionic duality of 1,2,4-triazole α-amino acid scaffold in 1D coordination polymers

A tiny supramolecular synthon, 4H-1,2,4-triazol-4-yl acetic acid (HGlytrz) which is bifunctional by design having an electronic asymmetry and conformational flexibility has been introduced to synthesize iron(II) complexes. Having 1,2,4-triazole or carboxylic extremities on the same framework HGlytrz could display dual functionality by acting as a neutral as well as anionic ligand based on the possibility of deprotonation of carboxylic group. Four new iron(II) HGlytrz complexes with ClO $_{4}^{-}$ (1), NO $_{3}^{-}$ (2), BF $_{4}^{-}$ (3) and CF₃SO $_{3}^{-}$ (4) anions were prepared. Formulation of their composition which is complicated due to ligand deprotonation is discussed. Unlike its ester protected counterpart ethyl-4H-1,2,4-triazol-4-yl-acetate (αGlytrz) which show hysteretic room temperature spin crossover, 1–4 remain in the high-spin state as revealed by ⁵⁷M?ssbauer spectroscopy. Prospects of such 1D coordination polymers with dangling unbounded carboxylic entities in the realm of self-assembled monolayer (SAM) are discussed.     

Proton conducting composite membranes based on poly(1-vinyl-1,2,4-triazole) and nitrilotri (methyl triphosphonic acid)

Polymer electrolyte composite membranes based on poly(1-vinyl-1,2,4-triazole) (PVTRI) and nitrilotri(methyl triphosphonic acid) (TPA) were investigated. PVTRI was produced by free radical polymerization of 1-vinyl-1,2,4-triazole. The polymer PVTRI was doped with TPA at various molar ratios x=0.125, x=0.25, and x=0.5. The proton transfer from TPA to the triazole rings was proved with Fourier-transform infrared spectroscopy (FT-IR). Thermogravimetry (TG) analysis showed that the samples are thermally stable up to approximately 250 °C. DSC results illustrated the homogeneity of the materials as well as the softening effect of the dopant. Cyclic voltammetry results illustrated that the electrochemical stability domain of the dopant extends over 1.5 V. The maximum proton conductivity has been measured for PVTRITPA-0.25 as 8.5×10⁻⁴ S cm⁻¹ at 150 °C.     

The visible and ultraviolet organic light-emitting diodes with germanium dioxide as facile solution-processed anode buffer layer

Germanium dioxide (GeO₂) aqueous solutions are facilely prepared and the corresponding anode buffer layers (ABLs) with solution process are demonstrated. Atomic force microscopy, X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements show that solution-processed GeO₂ behaves superior film morphology and enhanced work function. Using GeO₂ as ABL of organic light-emitting diodes (OLEDs), the visible device with tris(8-hydroxy-quinolinato)aluminium as emitter gives maximum luminous efficiency of 6.5 cd/A and power efficiency of 3.5 lm/W, the ultraviolet device with 3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole as emitter exhibits short-wavelength emission with peak of 376 nm, full-width at half-maximum of 42 nm, maximum radiance of 3.36 mW/cm² and external quantum efficiency of 1.5%. The performances are almost comparable to the counterparts with poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) as ABL. The current, impedance, phase and capacitance as a function of voltage characteristics elucidate that the GeO₂ ABL formed from appropriate concentration of GeO₂ aqueous solution favors hole injection enhancement and accordingly promoting device performance.     

Structural and ionic conductivity studies of solid polymer electrolytes based on poly (vinylchloride) and poly (methylmethacrylate) blends

Thin film of poly (vinylchloride) and poly (methylmethacrylate) blend polymer electrolytes plasticized with a combination of DBP and Li₂SO₄ salts have been prepared by solution casting technique. The prepared films were subjected to a.c. impedance measurements as a function of temperature ranging from 304–373 K. The maximum conductivity at 304 K was found to be 1.24 × 10⁻⁸ S·cm⁻¹ for PVC-PMMA-Li₂SO₄-DBP (7.5-17.5-5-70 mole-%). Temperature dependence studies on the ionic conductivity in the PVC-PMMA-Li₂SO₄-DBP system suggest that the ion conduction follows the Williams-Landel-Ferry (WLF) mechanism, which is further confirmed by Vogel-Tamman-Fulcher (VTF) plots. XRD, FTIR, SEM and thermal studies revealed complex formation in.     

Sonochemical synthesis and characterization of new one-dimensional manganese(II) coordination polymer nanostructures

A new Mn(II) coordination polymer, [Mn (L₁)₂(NCS)₂]_n (1) [L₁ = 3,4-bis(4-pyridyl)-5-(2-pyridyl)-1,2,4-triazole] was synthesized by the reaction of ligand L₁ and mixtures of manganese(II) acetate and potassium thiocyanate using the heat gradient method. Compound 1 has been characterized by IR spectroscopy, elemental analyses and X-ray crystallography. The crystal structure of compound 1 was determined by single-crystal X-ray diffraction and shows a new interesting one-dimensional coordination polymer. Nanostructures of compound 1 have been synthesized by sonochemical method. The products were characterized by X-ray powder diffraction, scanning electron microscopy (SEM), and IR spectroscopy. The thermal stability of nano particles of compound 1 was studied by thermal gravimetric and differential thermal analyses.     

三唑和环戊烯苯并菲衍生物盘状液晶分子的电荷传输性质

电荷传输是有机电子材料的重要性质. 根据Marcus理论模型, 电荷传输为电子-电子相互作用和电子-声子相互作用过程, 电子-声子相互作用耦合强度越大, 重组能越大, 不利于电荷传输. 电子-电子相互作用耦合强度越大, 电荷传输矩阵元越大, 有利于电荷传输. 对含1, 2, 4-三唑、1, 2, 3-三唑和1, 2, 3-三氮-2, 3环戊烯边链的苯并菲衍生物分子的电荷传输性质进行理论研究. 结果表明, 含1, 2, 3-三唑的苯并菲衍生物分子的空穴传输速率和电子传输速率相当, 速率常数为2× 10¹²s^-1. 含1, 2, 4-三唑的苯并菲衍生物分子的空穴传输速率常数为5× 10¹²s^-1, 约为电子传输速率常数的10倍. 含1, 2, 3-三氮-2, 3环戊烯的苯并菲衍生物分子的电子传输速率常数为3× 10¹²s^-1, 约为空穴传输速率常数的10倍. 目标分子的空穴传输或电子传输速率主要受传输矩阵元的影响, 即电子-电子相互作用耦合强度的大小决定传输速率的变化.     

Molecular engineering of the electronic,structural, and electrochemical properties of nanostructured 1-methyl-4-phenyl 1,2,4 triazolium-based [PhMTZ][X<Subscript>1–10</Subscript>] ionic liquids through anionic changing

In the present work, molecular engineering of the physicochemical characteristics of ion pairing in 1-methyl-4-phenyl 1,2,4 triazolium-based ionic liquids [PhMTZ][X] (X_1–10 = CH₃CO₂ ^?, Cl^?, NO₃ ^?, CF₃CO₂ ^?, BF₄ ^?, ClO₄ ^?, N(CN)₂ ^?, PF₆ ^?, NTf₂ ^?, and C(CN)₃ ^?) are explored using at M06-2X/6–311++G(d,p) level. The binding Gibbs free energy of ion pairs are reevaluated using ab initio MP2 method and dispersion corrected M06-2X-D3, B2PLYP, B2PLYP-D, and mPW2PLYP-D functionals. Comparison of Gibbs free bottom electrodes (BEs) calculated by B2PLYP and B2PLYP-D functionals reveals that the contribution of dispersion energy to the total BEs vary from 9% for X1 to 17% for X = 10. Besides, the range of the dispersion contribution estimated by M06-2X-D3 functional is found to be 0.6% for X₂ to 5% for X₃. The Gibbs free BEs in solvent media, Gibbs free energy and enthalpy of formation, electrochemical windows, anodic and cathodic stability, volumetric and electron density properties, charge transfer values, and electrostatic maps are evaluated.     

Synthesis and Characterization of New Fluorene-Based Singlet Oxygen Sensitizers

The synthesis, photophysical characterization, and determination of singlet oxygen quantum yields (Φ_Δ) for a class of fluorene derivatives with potential application in two-photon photodynamic therapy (PDT) is reported. It has been demonstrated that these compounds possess the ability to generate singlet oxygen (¹O₂) upon excitation. A photochemical method, using 1,3-diphenylisobenzofuran (DPBF) as ¹O₂ chemical quencher, was employed to determine the singlet oxygen quantum yields (Φ_Δ) of the fluorene-based photosensitizers in ethanol. Φ_Δ values ranged from 0.35 to 0.75. These derivatives may have potential application as two-photon photosensitizers when pumped via two-photon excitation in the near-IR spectral region.     

Study of the luminescence of H2O and D2O ices induced by charged-particle bombardment

We measured the optical emission of H₂O and D₂O ices in visible region (300-500 nm) induced by energetic hydrogen ions (H⁺, H₂⁺, and H₃⁺) irradiation. Our analysis of the data of ion-stimulated luminescence (ISL) shows that all spectra of ISL emission are identical, independent of projectile. We show that all lines in the ISL emission spectrum may be assigned to decays from excited particles and/or fragments of H, H₂, OH, and H₂O. From the independence of emission spectrum on projectile we conclude that the final process causing the emissions may be attributed to the interaction between H⁺ (and/or H) and the water molecules.