Oxidation of 2,5-dimethylpyrazine with oxygen in the vapor phase on oxide catalysts and in the liquid phase in the presence of bases

The vapor-phase oxidation of 2,5-dimethylpyrazine with oxygen on vanadium-molybdenum oxide catalysts modified with silver oxide gives 5-methyl-2-formylpyrazine and 2,5-diformylpyrazine in 37% and 35% yields, respectively. Pyrazine-2,5-dicarboxylic acid was obtained in 53% yield by the liquid-phase oxidation of 2,5-dimethylpyrazine with oxygen in the presence of a strong base and an interphase catalyst.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 532–537, April, 1990.     

Regioselective double Boekelheide reaction: first synthesis of 3,6-dialkylpyrazine-2,5-dicarboxaldehydes from dl-alanine

Pyrazine-2,5-dicarboxaldehyde was synthesized on a multi-gram scale by MnO₂ oxidation of 2,5-bis(hydroxymethyl)pyrazine, which in turn was obtained from 2,5-dimethylpyrazine employing double Boekelheide reaction as a key step as reported previously. This reaction was subsequently utilized in a regioselective fashion as a key step to synthesize efficiently, for the first time, 3,6-di(long-chain)alkylpyrazine-2,5-dicarboxaldehydes starting from dl-alanine. These monomers are certain to have importance as electron deficient and chemically versatile components for new materials development.     

Synthesis of pyrazinyl compounds from glycerol and 1,2-propanediamine over Cu-TiO2 catalysts supported on γ-Al2O3

Cu-TiO₂ catalysts supported onγ-Al₂O₃ are prepared and used in glycerol cyclization with 1,2-propanediamine to produce pyrazinyl compounds including 6-hydroxymethyl-2-methylpyrazine,5-hydroxymethyl -2-methyIpyrazine,2,6-dimethylpyrazine and 2,5-dimethylpyrazine in a fixed-bed system.It is found that glycerol cylclization with 1,2-propanediamine gave a high total yield of pyrazinyl compounds（>80%） over Cu-Ti02/γ-Al₂O₃ catalyst,and cyclization was through the reactions between activated 1,2-propanediamine and the intermediates from glycerol dehydration and oxidation.In addition,the regioselectivity of the pyrazinyl compounds was mainly controlled by the steric hindrance of the substrates during the cyclization process.     

Studies on pyrazines. 31 Alkylation of chloropyrazine N-oxides by nickel-catalyzed cross-coupling reaction with dialkylzincs

3-Chloro-2,5-dimethylpyrazine 1-oxide underwent cross-coupling with dialkylzinc reagents forming 3-alkyl-2,5-dimethylpyrazine 1-oxides. The reaction was realized by catalytic 1,3-bis(diphenylphosphino)-propane nickel(II) chloride and the optimum results were examined.     

Anodic oxidation of methyl-substituted nitrogen-containing heterocyclic compounds at the

Methyl derivatives of several nitrogen-containing heterocyclic compounds were converted into the corresponding carboxylic acids by means of electrochemical oxidation at the nickel oxohydroxide anode in alkaline medium, using a nondiaphragm electrolyzer. The oxidation of 2,5-dimethylpyrazine was used to demonstrate the effect of adding chromium (III) and cobalt (II) compounds to the reaction mixture. The composition and electronics state of the anode surface were studied usign x-ray diffraction and XPS methods.     

Stress-Relieving Effects of Sesame Oil Aroma and Identification of the Active Components

(1) Sesame oil aroma has stress-relieving properties, but there is little information on its effective use and active ingredients. (2) Methods: ICR male mice were housed under water-immersion stress for 24 h. Then, the scent of sesame oil or a typical ingredient was inhaled to the stress groups for 30, 60, or 90 min. We investigated the effects of sesame oil aroma on mice behavior and the expression of the dual specificity phosphatase 1 (DUSP1) gene, a candidate stress marker gene in the brain. (3) Results: In an elevated plus-maze test, the rate of entering into the open arm of a maze and the staying time were increased to a maximum after 60 min of inhalation, but these effects decreased 90 min after inhalation. As for the single component, anxiolytic effects were observed in the 2,5-dimethylpyrazine and 2-methoxy phenol group, but the effect was weakened in the furfuryl mercaptan group. The expression levels of DUSP1 in the hippocampus and striatum were significantly decreased in 2,5-dimethylpyrazine and 2-methoxy phenol groups. (4) Conclusions: We clarified the active ingredients and optimal concentrations of sesame oil for its sedative effect. In particular, 2,5-dimethylpyrazine and 2-methoxy phenol significantly suppressed the stress-induced changes in the expression of DUSP1, which are strong anti-stress agents. Our results suggest that these molecules may be powerful anti-stress agents.     

Vibrational spectroscopic studies of some dimethylpyrazine cadmium (II) tetracyanonickelate benzene clathrates: [Cd(C6H8N2)Ni(CN)4]·C6H6

Two new cadmium dimethylpyrazine (2,3-dimethylpyrazine or 2,5-dimethylpyrazine) tetracyanonickelate benzene clathrates, [Cd(C₆H₈N₂)Ni(CN)₄]·C₆H₆, have been prepared in powder form and characterized by FT-IR spectroscopy, Raman spectroscopy, X-ray diffraction, thermal analyses and elemental analyses. Vibrational assignments are proposed for the bands of the host lattice and guest molecule. It is shown that the spectra are consistent with a proposed crystal structure for these compounds derived from X-ray diffraction measurements. The C, H, N, Cd and Ni analyses were carried out for all the compounds. Thermal behaviors of these compounds are followed using TG and DTA techniques. The FT-IR, Raman spectroscopic, XRD, thermal and elemental analyses results propose that these compounds are similar in structure to the Hofmann-type clathrates. Their structure consists of planar polymeric layers, {M–Ni(CN)₄}_∞, formed from Ni(CN)₄ anions coordinated to the bridging 2,3- or 2,5-dimethylpyrazine molecules bound directly to the cadmium. The cadmium atoms are bound to four N atoms of the CN ions and, the Ni atoms are surrounded by four C atoms of the CN groups in a square-planar layer.     

Structural study of silver(I) sulfonate complexes with pyrazine derivatives

In this Article, 11 silver complexes, namely, [Ag(L1)(2-Pyr)(H2O)] (1), Ag(L1)(2,3-Pyr) (2), [Ag2(L1)2(2Et,3Me-Pyr)2(H2O)] (3), [Ag(2,6-Pyr)](L1).1.5H2O (4), Ag(L1)(2,5-Pyr) (5), [Ag(H2O)2](L2).H2O (6), [Ag(L2)(2-Pyr)] (7), [Ag(L2)(2,3-Pyr)].1.5H2O (8), [Ag(L2)(2Et,3Me-Pyr)].2H2O (9), [Ag2(L2)(2,6-Pyr)(H2O)2](L2).H2O (10) and [Ag(L2)(2,5-Pyr)].H2O (11) (2-Pyr=2-methylpyrazine; 2,3-Pyr=2,3-dimethylpyrazine; 2Et,3Me-Pyr=2-ethyl-3-methylpyrazine; 2,6-Pyr=2,6-dimethylpyrazine; 2,5-Pyr=2,5-dimethylpyrazine; L1=p-aminobenzenesulfonate anion and L2=6-amino-1-naphthalenesulfonate anion), have been synthesized and characterized by elemental analyses, IR spectroscopy, and X-ray crystallography. In 1, 3, and 4, Ag(I) centers are linked by bridging pyrazine ligands to form one-dimensional chains, whereas compound 2 shows a double-chain structure through weak Ag-C interactions. The structure analyses show that both 5 and 11 form two-dimensional networks composed of 26-membered metallocycles. Unexpectedly, compounds 6 and 10 show discrete structures. In compound 7, silver(I) centers are bridged by sulfonate anions to form a polymeric helical structure, and the 2-Pyr molecule acts as a monodentate ligand. Compounds 8 and 9 show hinged chain structures containing 14-membered rings, and these chains interlace with each other to generate unique three-dimensional structures. These results indicate that the substituting groups and the substituting sites of pyrazine derivatives play an important role in the framework formation of silver complexes. Additionally, the luminescent properties of these compounds are also discussed.     

Substituent effects of pyrazine on construction of crystal structures of Zn(II)-benzoate complexes and their catalytic activities (dinuclear,trinuclear, and pentanuclear to 1-D and 2-D)

Several substituted pyrazine ligands (2,3-dimethylpyrazine, 2,6-dimethylpyrazine, 2,5-dimethylpyrazine, quinoxaline) as well as simple pyrazine have been employed to investigate how the bridging pyrazine ligand influences on construction of Zn-benzoate complexes. Simple pyrazine and 2,5-dimethlpyrazine are used as bridging ligands to form two-dimensional and one-dimensional polymeric compounds, respectively. The other quinoxaline and two dimethyl-substituted pyrazine ligands are used only as terminal ligands to form dinuclear, trinuclear, and pentanuclear complexes. This result indicates that the substituents of pyrazine are very important roles for construction of Zn-benzoate complexes. Interestingly, the compounds 1–5 catalyzed efficiently the transesterification of a variety of esters, and among them, the pentanuclear complex 3 showed the most efficient reactivity. The substrates with the electron-withdrawing substituents have undergone faster transesterification, while those with the electron-donating ones have shown slow reaction. In addition, p-nitrophenyl acetate and p-nitrophenyl benzoate, known to be problematic substrates for the transesterification reaction, were also converted quantitatively to the corresponding products. Selectivity test of primary over secondary alcohol protection in the presence of 3 has provided, exclusively, the primary acetate, propyl acetate, suggesting that this catalytic system can be potentially useful in selecting for primary alcohols.     

Synthesis of pyrazine acetals by the biased reaction of symmetric 2,5-bis(chloromethyl) or 2,3,5,6-tetrakis(chloromethyl) substituents on pyrazine ring with sodium alkoxides

2,5-Bis(chloromethyl)pyrazine reacted with sodium alkoxide to give unexpected 2-dialkoxymethyl-5-methylpyrazine along with normal substitution product, 2,5-bis(alkoxymethyl)pyrazine. The reaction of 2,3,5,6-tetrakis(chloromethyl)pyrazine with sodium alkoxide afforded similar results to yield 2,6-bis(dialkoxymethyl)-3,5-dimethylpyrazine along with other alkoxymethylpyrazines. The ratio of products depended on the solvent and alkoxide used. A general discussion of the mechanism of such a pyrazine acetal synthesis in the basic conditions is given.     

Total chemical synthesis of 2-ethenyl-3,5-dimethylpyrazine and 3-ethenyl-2,5-dimethylpyrazine

The aroma compounds 2-ethenyl-3,5-dimethylpyrazine 1 and 3-ethenyl-2,5-dimethylpyrazine 2 were synthesized via a new chemical route. The key steps of the synthesis involve cyclocondenzation of 1-[bicyclo[2.2.1]5-hepten-2-yl]-1,2-propanedione and 1,2-propanediamine, aromatization of the resulting 5,6-dihydropyrazines, and subsequent Retro-Diels-Alder reaction to generate pyrazines 1 and 2. Pyrazine 1, a powerful odorant, was obtained in large excess (8:2) when endo-1-[bicyclo[2.2.1]5-hepten-2-yl]-1,2-propanedione was used as intermediate substrate.     

Construction of polyoxometalates-based coordination polymers through direct incorporation between polyoxometalates and the voids in a 2D network

A series of polyoxometalates (POMs)-based coordination polymers, namely, {[Cu(2,3-Me2pz)(2,5-Me2pz)0.5]4(SiW12O40)(2,5-Me2pz)}n (2,3-Me2pz = 2,3-dimethylpyrazine; 2,5-Me2pz = 2,5-dimethylpyrazine; 1), {[Cu2(4,4'-bipy)4(H2O)4](SiW12O40)(H2O)18}n (4,4'-bipy = 4,4'-bipyridine; 2), {[Cu(2-Mepz)1.5]3(PMo12O40)(H2O)3.5}n (2-Mepz = 2-methylpyrazine; 3), {[Ag(2,3-Me2pz)1.5]4(SiW12O40}n (4), {[Cu(pz)1.5]4(SiW12O40)(H2O)3}n (pz = pyrazine; 5), {[Cu(2,3-Me2pz)1.5]4(SiW12O40)}n (6), {[Cu(4,4'-bipy)1.75]4(SiW12O40)(H2O)2}n (7), and {[Cu2(4,4'-bipy)4(H2O)4](SiW12O40)(4,4'-bipy)2(H2O)4}n (8), were synthesized through direct incorporation between POMs and the voids of the 2D network. Crystal structural analysis reveals that the relationship between the size of the void of the 2D network and that of POMs is of key importance for successful synthesis of POMs-based open metal-organic frameworks. Guest replacement shows that the pore size of the framework constructed through direct incorporation between POMs and the voids of the 2D network is very sensitive to guest molecules.     

Vibrational spectrum and internal rotation in 2,5-dimethylpyrazine

The infrared and Raman spectra of 2,5-dimethylpyrazine have been recorded and assigned on the basis of a C_2h molecular geometry previously determined by MINDO/3. The potential energy function corresponding to the internal rotation of both methyl groups has been used to solve the Schrödinger equation, and to obtain the energy levels of that motion on the basis of a molecular symmetry G₃₆. The rotation of each substituent is found to be almost independent of the other.     

Low-dimensional quantum magnetic systems: Synthesis,structure and magnetic behavior of (2,5-dimethylpyrazine)copper(II) chloride and synthesis and magnetic behavior of bis(2,6-dimethylpyrazine)copper(II) chloride

The synthesis, X-ray structure and magnetic susceptibility of (2,5-dimethylpyrazine)copper(II) chloride (1), and the synthesis and magnetic susceptibility of (2,6-dimethylpyrazine)₂copper(II) chloride (2), are reported. Compound 1 crystallizes in the space group P2₁/c as a coordination polymer of Cu(II) ions bridged by 2,5-methylpyrazine. The resulting chains are magnetically linked via short chloride–chloride contacts. The magnetic susceptibility responds as a uniform Heisenberg chain (2J/k = −20(5) K) with a phase transition to three dimensional order near 5 K. Susceptibility data for compound 2 show that the compound is a linear chain coordination polymer with the copper ions linked by bihalide bridges. A fit to the model for a uniform Heisenberg chain yields 2J = −22.7(2) K.     

Influence of steric hindrance of organic ligand on the structure of Keggin-based coordination polymer

Five Keggin-based 3D coordination polymers, namely, [Cu3(pz)3(PW12O40)] (pz = pyrazine) (1), [Cu3(2,3-Me2pz)3(PW12O40)] (2,3-Me2pz = 2,3-dimethylpyrazine) (2), [Cu2(2,5-Me2pz)(1.5)(2,5-HMe2pz)(PW12O40)] (2,5-Me2pz = 2,5-dimethylpyrazine) (3), [Cu3(2,3-Me2pz)3(PMo12O40)] (4), and [Ag3(pz)3(PW12O40)].0.5H2O (5), were synthesized and structurally characterized. Crystal data are as follows: trigonal, space group R3c, a = 18.4070(14) angstroms, c = 22.544(3) angstroms, gamma = 120 degrees, and Z = 6 for 1; orthorhombic, space group Pccn, a = 16.599(2) angstroms, b = 20.470(3) angstroms, c = 14.3757(18) angstroms, and Z = 4 for 2; triclinic, space group P1, a = 10.667(2) angstroms, b = 11.147(2) angstroms, c = 20.207(4) angstroms, alpha = 90.983(4) degrees, beta = 108.128(3) degrees, gamma = 92.150(4) degrees, and Z = 2 for 3; orthorhombic, space group Pccn, a = 16.450(3) angstroms, b = 20.170(4) angstroms, c = 14.244(3) angstroms, and Z = 4 for 4; and rhombohedral, space group R32, a = 18.2047(13) angstroms, c = 23.637(3) angstroms, gamma = 120 degrees, and Z = 6 for 5. Their structural differences were investigated using crystal structure analysis, revealing that the influence of steric hindrance of organic ligand on the structures of Keggin-based coordination polymers is realized through changing the number of metal-organic units surrounding the POM anion.     

Thermochemical study of three dimethylpyrazine derivatives

The standard (p ⁰=0.1 MPa) molar enthalpies of formation, in the gaseous phase, at T-298.15 K, for 2,5-dimethylpyrazine (2,5-DMePz) and for the two dimethylpyrazine-N,N′-dioxide derivatives, 2,3-dimethylpyrazine-1,4-dioxide (2,3-DMePzDO) and 2,5-dimethylpyrazine-1,4-dioxide (2,5-DMePzDO), were derived from the measurements of standard massic energies of combustion, using a static bomb calorimeter, and from the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry. The mean values for the molar dissociation enthalpy of the nitrogen-oxygen bonds, 〈DH _m⁰〉(N-O), were derived for both N,N′-dioxide compounds. These values are discussed in terms of the molecular structure of the two N,N′-dioxide derivatives and compared with 〈DH _m⁰〉(N-O) values previously obtained for other N-oxide derivatives.     

Kinetics of the thermal decomposition of 1,2-dioxaspiro[2,5]octane

The products and kinetics of the thermolysis of 1,2-dioxaspiro[2,5]octane in cyclohexanone and cyclohexanone-CCl₄ mixtures are studied. 1,2-Dioxaspiro[2,5]octane is consumed via two parallel routes: isomerization to oxepan-2-one and solvent (cyclohexanone) oxidation with the partial escape of radicals from the cage (17% at 25 °C). Under an inert atmosphere, the alkyl radicals formed by solvent oxidation initiate the chain radical decomposition of 1,2-dioxaspiro[2,5]octane. The mechanism of 1,2-dioxaspiro[2,5]octane thermolysis is discussed on the basis of the results obtained. The activation parameters of 1,2-dioxaspiro[2,5]octane isomerization to oxepan-2-one and reactions of dioxaspiro[2,5]octane with cyclohexanone are discussed.     

Tuning the electronic communication and rates of intramolecular electron transfer of dimers of trinuclear ruthenium clusters: bridging and ancillary ligand effects

Ten new bridged dimers of oxo-centered triruthenium clusters with CO and 4-(dimethylamino)pyridine (dmap), pyridine (py), or 4-cyanopyridine (cpy) as terminal ligands and pyrazine-d(4) (d(4)-pz), 2,5-dimethylpyrazine (dmpz), 2-methylpyrazine (mpz), and 2-chloropyrazine (clpz) as bridging ligands were prepared. The carbonyl stretching frequency, nu(CO), was used as a probe for infrared spectroelectrochemical measurements. In the neutral and doubly reduced states, a single band was observed for each of the dimers, with a shift in frequency due to the oxidation state of the triruthenium clusters. In the singly reduced state, a range of nu(CO) line shapes was observed, depending on the nature of the ligands, from two bands centered at the frequencies of the bands of the neutral and doubly reduced species to one broad band at the average of these two frequencies. By synthesizing new combinations of bridging and ancillary ligands, electronic communication between two bridged triruthenium clusters was effectively tuned, and electron-transfer rates were estimated by IR spectral line-shape analysis. In dimers bridged by the asymmetric ligand mpz, it was possible through selective isotope labeling of one CO ligand to observe "mixed-valence isomers," the two alternate charge distributions of a mixed-valence complex.     

Synthesis, a case of isostructural packing, and antimicrobial activity of silver(I)quinoxaline nitrate, silver(I)(2,5-dimethylpyrazine) nitrate and two related silver aminopyridine compounds

The synthesis and low temperature crystal structures of [Ag(quinoxaline)]n(NO3)n, 1, [Ag(2,5-dimethylpyrazine)(NO3)]n, 2 and [Ag4(3-aminopyridine)4(NO3)4]n 3 are presented. The quinoxaline compound forms a 1D coordination polymer with the characteristic linear 2-coordination figure of silver(I), the N-Ag-N angle being 164.2(1) degrees, and only weak silver-nitrate interactions. In addition there is an interaction giving pairs of parallel chains as the main structural theme. The 2,5-dimethylpyrazine compound has approximately trigonal-planar coordination, also binding one nitrate at the relatively short Ag-O distances 2.444(3) angstroms and 2.484(3) angstroms, respectively, for the two crystallographically different silver atoms. This also results in a 1D coordination polymer that, despite the large differences in the Ag(I) coordination environment, is isostructural with 1. [Ag4(3-aminopyridine)4(NO3)4]n 3 forms a 2D coordination polymer by bridging nitrate ions. The antimicrobial activity of 1-3, and also of [Ag3(2-aminopyridine)4](NO3)3, 4 was screened for 13 different pathogens and substantial activity was shown for 1 against Escherichia coli and Pseudomonas aeruginosa (MIC 4 microg cm(-3)) and somewhat lower activity was registered against Sarcina lutea and Salmonella typhi for 1, Bordetella bronchiseptica for 2, Salmonella typhi and Pseudomonas aeruginosa for 3, and Escherichia coli and Shigella sonnie for 3 (MIC 8 microg cm(-3)). Only low activity was shown against the yeast Candida albicans for 1, 2 and 4 whereas no activity against this pathogen was registered for 3.