Molecular and electronic structure of several 2,3-dithienylquinoxalines and their 2:1 complexes with silver(I) nitrate

We have synthesized three bis (thienyl) quinoxalinesilver(I) complexes;however, unlike analogous silver(I) complexes of pyridylquinoxaline that utilize (N, N) bidentate behavior from the quinoxaline and pyridyl ring nitrogens, the bis(thienyl) quinoxaline ligands did not utilize the bonding potential of the thienyl rings to give (N, S) bonding modes. PES spectra modeling of these ligands indicates that the preferential metal bonding via only the quinoxaline nitrogen atoms is due to the N-rich, but S-poor, characters of the frontier orbitals.

Combined electronic/atomic level computational, surface(SEM/EDS),chemical and electrochemical studies of the mild steel surface by quinoxalines derivatives anti-corrosion properties in 1 mol·L^(-1) HCl solution

This work is devoted to the study of the inhibition of corrosion of mild steel(MS)in molar hydrochloric acid(1 mol·L-1 HCl)by two named quinoxaline derivatives namely,2-(2,4-dichlorophenyl)-1,4-dihydroquinoxaline(HQ)and 2-(2,4-dichlorophenyl)-6-methyl-1,4-dihydroquinoxaline(CQ).The inhibitory efficacy of HQ and CQ compounds is first evaluated using the gravimetric method and using electrochemical techniques(stationary and transient techniques).The results showed that our compounds are efficient corrosion inhibitors and the inhibition rates(ηEIS%)reached up to 91%and 94.2%at 10-3 mol·L-1 for HQ and CQ,respectively.The mentioned molecules are classified as mixed-type inhibitors.The adsorption of these inhibitors on the surface of steel in hydrochloric HCl 1 mol·L-1 medium obeys the Langmuir adsorption isotherm.The results of the scanning electron microscope(SEM)showed the formation of a protective film on the surface of the steel in the presence of the inhibitors studied.Elementary analysis is obtained by energy dispersive X-ray spectroscopy(EDS).The inhibition property was further elucidated by theoretical approaches such as:Density Functional Theory(DFT),quantum chemical descriptors(QCD),local reactive indices,solvent effect,theoretical complexation,Molecular Dynamic(MD)simulation,effect of temperature on adsorption energy(Eads),Radial Distribution Function(RDF),and Mean Square Displacement(MSD).The results of these approaches support the experimental results.

Ga(ClO_4)_3-catalyzed Reaction of 1,2-Diamines and α-Bromoketones:Synthesis of 2-Substituted Quinoxalines

Ga（ClO4）3-catalyzed reaction of 1,2-aryldiamines and α-bromoketones to afford 2-substituted quinoxalines in good yields is described.The reaction proceeded via grinding process with 10%（molar fraction） catalyst under solvent-free conditions at room temperature.For unsymmetrical o-phenylenediamines bearing electron-withdrawing groups,regio-selective quinoxalines were obtained.

Catalyst-free and solvent-free method for the synthesis of quinoxalines under microwave irradiation

A facile procedure for the synthesis, of quinoxalines is being reported starting from benzil and 1,2-diaminobenzene. The reactions were carried out catalyst-free, solvent-free and under microwave irradiation conditions in high yield （84-98%） with short time （3-6 min） and environmental benign, as well as convenient operation. The structures of all the compounds have been confirmed on the basis of their IR, 1H NMR, and/or 13C NMR, mass spectral data.

Convenient Synthesis of Substituted Quinoxalines and 2H-Benzo[b][1,4]oxazines in Water

A facile and convenient synthesis method has been developed for substituted quinoxalines and 2H-benzo[b][1,4]oxazines from the reactions of a-bromoketones with benzene-1,2-diamine and 2-aminophenol, respectively, which were catalyzed by tetrabutylammonium bromide（TBAB） in aqueous basic media.

Nano-TiO_2:An eco-friendly alternative for the synthesis of quinoxalines

Nano-TiO_2 as an eco-friendly and efficient nanocatalyst was applied for quinoxaline preparation with improved yield.In this protocol,diketones and 1,2-diamines were condensed in the presence of catalyst at room temperature.

Unexpected activated carbon-catalyzed pyrrolo[1,2-a]quinoxalines synthesis in water

An interesting and recyclable activated carbon/water catalytic system for efficient synthesis of pyrrolo[1,2-a]quinoxaline derivatives was developed. The intramolecular C-N and C-C bond can be easily constructed in water under mild condition. This reaction features a broad substrate scope, a good tolerance to water and air, metal-free, additive-free and redox reagent-free.

Efficient Copper-Catalyzed Annulation of 2-Formylazoles with 2-Haloanilines for the Synthesis of Pyrrole-and Imidazole-Fused Quinoxalines

Promoted by CuI/2-hydroxybenzohydrazide catalytic system,a variety of pyrrole-and imidazole-fused quinoxalines have been efficiently one-pot synthesized from pyrrole-/imidazole-2-carboxaldehyde and 2-haloanilines in moderate to excellent yields.

Catalytic activity of manganese oxide supported on alumina in the synthesis of quinoxalines

Two catalysts, alumina and manganese oxide supported on alumina, have been prepared by calcination and precipitation-impregnation methods, respectively. The catalysts are characterised by the following techniques： Brunner-Emmett-Teller-N2 adsorption-desorption for sur- face area, temperature programmed desorption of NH3 and n-butyl amine back titration methods for surface acidity, powder X-ray diffraction for textural properties, and Fourier transform infrared spectroscopy for the anionic radicals. The catalytic activity has been determined under heterogeneous conditions in the condensation reaction between o-phenylenediamine and benzil. The product purity is checked by thin-layer chromatography and melting point. The products are also analysed by LC-MS and 1H-NMR techniques. The yields of the products have been found to be good and catalysts exhibited excellent recyclability. The effect of changing the reaction para- meters such as temperature, reaction time, amount of the catalyst, nature of solvent and molar ratio of reactants on the yield of the product has been studied. The surface acidity of the catalysts plays an important role in activating the reaction.

One-pot aqueous-phase synthesis of quinoxalines through oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines catalyzed by a zwtterionic Cu(Ⅱ)/calix[4]arene complex

A green protocol for the synthesis of quinoxalines has been developed from catalytic oxidative cyclization of deoxybenzoins with 1,2-phenylenediamines in water.The optimal conditions are involved in the use of a water-soluble mononuclear copper（Ⅱ） complex of a zwitterionic calix[4]arene[Cu（Ⅱ）LCH2O）]I2（1,H4L=[5,ll,17,23-tetrakis（trimethylammonium）-25,26,27,28-tetrahydroxycalix[4]arene]） as a catalyst in alkali solution after refluxing for 15 h in O2.The target quinoxaline and its derivatives were obtained in good yields（up to 88%）.The procedure described in this paper is simple,practical and environmentally benign.

Visible light-induced synthesis of biomass-derived quinoxaline by using Co phthalocyanine immobilized on pyridine-doped g-C_(3)N_(4)

Visible light-driven valorization of biomass has recently been a pioneering field for nitrogen-containing heterocyclics syntheses due to its sustainable features.Herein,various aromatic ring-doped g-C_(3)N_(4) nanosheets(Ar-g-C_(3)N_(4);Ar=Py,Pm,Ph)were precisely designed to modulate their intrinsic electronic and band structure,which involves pyridine(Py),pyrimidine(Pm),and benzene(Ph)-doped g-C_(3)N_(4).Photocatalysts(CoPc/Ar-g-C_(3)N_(4)) of cobalt(II)phthalocyanine(CoPc)-fabricated Ar-g-C_(3)N_(4) were then developed for oxidative cyclization of furoin with 1,2-phenylenediamines for syntheses of various biomass-derived quinoxalines under visible-light irradiation.The catalytic activity(in terms of TOFs)of serial CoPc/Ar-g-C_(3)N_(4) samples increased with their transient photocurrents with CoPc/Py-g-C_(3)N_(4) as the most active one.For CoPc/Py-g-C_(3)N_(4),CoPc species functioned as both sensitizer and catalytic sites;while,doped Py led to a narrowed bandgap energy.Mechanism research further demonstrated that O_(2) was activated to superoxide radical(·O_(2)^(-)) by photoexcited high-level-energy electron(HLEE)transfer from Py-g-C_(3)N_(4) to CoPc for the subsequent aerobic oxidation.

Aspects on the Mechanism of the 1-Phenyl-1<i>H</i>-pyrazolo[3,4-<i>b</i>]quinoxaline Formation

Condensation of D-glucose, o-phenylenediamine and N,N-benzylphenylhydrazine hydrochloride (NNBPHH) in a one-pot reaction, or condensation of 2-(D-arabino-tetritol-1-yl) quinoxaline and NNBPHH, gave 3-(D-erythro-glycerol-1- yl)-1-phenyl-1H-pyrazolo[3,4-b]quinoxaline. The structure of the latter was determined by 1H NMR spectroscopy and by synthesis using phenylhydrazine hydrochloride instead of NNBPHH. Condensation of D-glucose and 4,5-dichloro-o-phenylenediamine gave 6,7-dichloro-2-(D-arabino-tetritol-1-yl)quinoxaline, which upon condensation with NNBPHH gave the corresponding 6,7-dichloro-3-(D-erythro-glycerol-1-yl)-1-phenyl-1H-pyrazolo[3,4-b]quinoxaline. The structure and mechanism of formation of these compounds are discussed.

Keggin type heteropolyacids-catalyzed synthesis of quinoxaline derivatives in water

Keggin type heteropolyacids was found to be an efficient and reusable catalyst for the synthesis of biologically active quinoxaline derivatives from the condensation of 1,2-diamine with 1,2-dicarbonyl compounds in excellent yields in water. This method provides a new and efficient protocol in terms of small quantity of catalyst, a wide scope of substrates, and simple work-up procedure.

Synthesis of quinoxaline derivatives catalyzed by PEG-400

Polyethylene glycol(PEG) was found to be an effective catalyst for the condensation of 1,2-diamines with 1,2-dicarbonyl compounds to afford the corresponding quinoxaline derivatives in excellent yields under mild reaction conditions.

Hydrothermal Reaction, Structure and Magnetic Properties of a Binuclear Cobalt Complex with N-donor Ligand:2-Methyldipyrido[3,2-f:2ˊ3ˊ-h]quinoxaline

One complex [Co1.5（C6H5CHCHCOO）3（Medpq）]·H2O（C6H5CHCHCOO = cinnamic acid, Medpq = 2-methyldipyrido[3,2-f：2,3-h]quinoxaline） 1 has been hydrothermally synthesized and structurally characterized by elemental analysis, IR spectrum, TG, single-crystal X-ray diffraction and magnetic susceptibility measurements. Complex 1 crystallizes in the triclinic system, space group P1, with a = 10.224（5）, b = 14.572（5）, c = 15.139（5）A, α = 112.704（5）, β = 97.168（5）, γ = 109.749（5）, V = 1871.8（13） 3 and Z = 2（at 293（2） K）. In the crystal structure, the Co（1） ion is hexa-coordinated with six atoms from three different cinnamic acid ligands and the symmetric three different cinnamic acid ligands; the Co（2） center adopts a coordination environment with two nitrogen atoms from Medpq ligand and four oxygen atoms from two different cinnamic ligands, assuming a slightly distorted octahedral geometry, respectively. The negative value of the Weiss constant indicates antiferromagnetic exchange interactions between the Co ions.

Hydrothermal Syntheses and Crystal Structures of Two Metal-organic Complexes with 2,3-Pyridinedicarboxylic Acid and 2-Methyl-dipyrido[3,2-f:2',3'-h]quinoxaline Ligands

Two unusual one-dimensional（1-D） compounds,viz.[Co（Medpq）（QUI）·H2O]2n· 2.4nH2O 1 and [Cd（Medpq）（QUI）·H2O]n·nH2O 2,were synthesized by the combination of two different metallic salts and organic ligands,namely 2,3-pyridinedicarboxylic acid（H2QUI） and 2-methyldipyrido[3,2-f：2＇,3＇-h]quinoxaline（Medpq） ligand.The compounds were characterized by elemental analyses,TG,fluorescent emission and single-crystal X-ray diffraction analyses.

Potential benefits of quinoxaline 1, 4-dioxides in aldosterone dysmetabolism disease—A medical hypothesis

Quinoxaline 1, 4-dioxides (QdNOs) are quinox-aline derivatives which have been used as an-timicrobial agents and growth promoters in animals widely. They are also assumed to cure human disease such as anticancer, antitubercular and inhibiting parasite. QdNOs such as carbadox and their major metabolites induced a special decline of aldosterone production from the swine adrenal in vivo and in vitro, and thus cause hypovolemia, hyponatremia and hyperkalemia. This can also be expected to be the case for human. As a mainly physiological hormone and a novel steroid with potent mineralocorticoid activity, aldosterone plays an important role in the pathophysiological process of brain, renal and heart disease progression and may be a renal and vascular risk factor. Here, we provide evidence to support the hypothesis that QdNOs may lead potential benefits in aldosterone dysmetabolism disease via the synthesis deficiency of aldosterone in adrenal and/or the cardiovascular tissues. If the hypothesis is true, it may provide a new option into the therapy for aldosterone dysmetabolism disease, especially in cardiovascular system, and thus assume a broader application of QdNOs.

Coordination Modes of Polypyridyl Quinoxaline with Hg(Ⅱ),Pb(Ⅱ),Co(Ⅱ)and Mn(Ⅱ)

The interaction of metal ions（Hg^2＋,Pb^2＋,Co^2＋,Mn^2＋） with polypyridyl quinoxaline ligand 2,3,6,7,10,11-hexakis（2-pyridyl）dipyrazino[2,3-f：20,30-h]quinoxaline（HPDQ） was investigated,and four new complexes have been synthesized and characterized.Complex 1 exhibits a 0dimensional dual-core structure,2 is a one-dimensional chain structure based on a dual-core Pb unit,while 3 and 4 show a 0 dimensional single-core structural unit.Complex 1 is of monoclinic system,space group C2/c with a = 19.211（4）,b = 23.896（5）,c = 12.698（3） A°,β= 120.11（3）°,V= 5043.0（17）A°3,Z = 4,S = 1.053,F（000） = 2976,R^a = 0.0637 and wR^b = 0.1068（I 〉 2σ（I））.Complex 2 adopts triclinic system,space group P1 with a = 10.370（2）,b = 12.195（2）,c = 21.033（4） A°,α = 80.87（3）,β= 81.22（3）,γ = 82.38（3）°,V= 2579.3（8） A°3,Z = 2,S = 1.099,F（000） = 1328,R^a = 0.0609 and wR^b =0.1365（I 〉 2σ（I））.Complex 3 is of monoclinic system,space group Cllc with a = 14.166（3）,b =16.621（3）,c = 20.248（4） ？,β = 92.18（3）°,V= 4764.0（16） A°3,Z = 4,S = 1.005,F（000） = 2108,R^a =0.0589 and wR^b = 0.1332（I 〉 2σ（I））.Complex 4 belongs to the monoclinic system,space group C2/c with a = 14.404（3）,b = 16.626（3）,c = 20.346（4） ？,β = 92.43（3）°,V= 4868.2（17） A°3,Z = 4,S= 1.068,F（000） = 2108,R^a = 0.0833 and wR^b = 0.1591（I 〉 2σ（I））.Furthermore,the behavior of HPDQ with Hg^2＋,Pb^2＋,Co^2＋ and Mn^2＋ in the solution was also investigated,and the result shows after the metal ions were added respectively,the emission of all solutions shows fluorescence quenching and has a red shift compared with that of the HPDQ ligand.

SYNTHESIS AND CHARACTERIZATION OF ORGANOSOLUBLE POLYAMIDES FROM QUINOXALINE BASED DIAMINE

Aromatic/aliphatic polyamides were synthesized from a diamine monomer, 2,3-bis-p-aminophenylquinoxaline （IV）, based on quinoxaline and various dicarboxylic acids of aliphatic, aromatic and heterocyclic. The diamine and polyamides were characterized by elemental analysis, FTIR and IH-NMR. The solubility of the polyamides was affected by the quinoxaline and heterocyclic groups in the polymer chain. They were all soluble in common organic solvents such as dimethylsulfoxide （DMSO）, N,N-dimethylformamide （DMF） and N-methylpyrolidone （NMP）. The polyamides showed inherent viscosity in the range of 0.25-0.3 dL/g in DMSO at 25℃ and good thermal stability with the char yields in the range of 65%-82% at 600℃ in nitrogen.

Structures and Spectroscopic Properties of(1)Dipyridine Quinoxaline with Hg(Ⅱ), Cu(Ⅰ) and Ag(Ⅰ)

The interaction of Hg（Ⅱ）, Cu（Ⅰ） and Ag（Ⅰ） with dipyridine quinoxaline ligand 2,3-bis（2-pyridyl）quinoxaline（DPQ） were investigated, and three new complexes have been synthesized and characterized. Complex 1 exhibits a 0D dual-core structure, complex 2 is a 0D tetra nuclear case based on a dual-core Cu unit, and complex 3 shows a one-dimensional pipeline structure. Furthermore, the optical properties of complex and DPQ were also investigated, and the results showed that the fluorescence intensity of complexes was weaker than that of ligand DPQ.