Presence Of N-methylimidazole Research Articles

Dual role of epoxidized soybean oil (ESO) as plasticizer and chain extender for biodegradable polybutylene succinate (PBS) formulations

This work reports the effect of 1–5 wt% epoxidized soybean oil (ESO) addition on the thermal, mechanical, and morphological properties of polybutylene succinate (PBS). ESO acts as a chain extender as well as a mild plasticizer of PBS. N-methylimidazole (NMI) is used as a catalyst to promote the reaction between PBS and ESO, and thermal, rheological, and spectroscopic analyses demonstrate increased viscoelastic properties, compatibility, crystallinity and thermal stability of the melt reacted formulations. In the presence of NMI, storage modulus (G’) values two orders of magnitude higher than that of pure PBS are achieved, confirming the completion of the chain extension reaction. A drastic refinement of the biphasic structure of the blend is observed, with the formation of a homogenous structure where ESO is well incorporated into the matrix. Finally, tensile tests reveal enhanced mechanical performance in the blends reacted in the presence of NMI. These findings pave the way for the development of a versatile family of materials which could find potential application in sustainable biodegradable packaging.

Lewis Acid-Base Adducts of α-Amino Acid-Derived Silaheterocycles and N-Methylimidazole

In chloroform solution, the reaction of bis(tert-butylamino)dimethylsilane ((tBuNH)2SiMe2) and an α-amino acid (α-amino isobutyric acid, H2Aib; D-phenylglycine, H2Phg; L-valine, H2Val) in the presence of N-methylimidazole (NMI) gave rise to the formation of the pentacoordinate silicon complexes (Aib)SiMe2-NMI, (Phg)SiMe2-NMI and (Val)SiMe2-NMI, respectively. Therein, the amino acid building block was a di-anionic bidentate chelator at the silicon atom. In solution, the complexes were involved in rapid coordination–dissociation equilibria between the pentacoordinate Si complex (e.g., (Aib)SiMe2-NMI) and its constituents NMI and a five-membered silaheterocycle (e.g., (Aib)SiMe2), as shown by 29Si NMR spectroscopy. The energetics of the Lewis acid-base adduct formation and the competing solvation of the NMI molecule by chloroform were assessed with the aid of computational methods. In CDCl3 solution, deuteration of the silaheterocycle NH group proceeded rapidly, with more than 50% conversion within two days. Upon cooling to −44 °C, the chloroform solvates of the adducts (Aib)SiMe2-NMI and (Phg)SiMe2-NMI crystallized from their parent solutions and allowed for their single-crystal X-ray diffraction analyses. In both cases, the Si atom was situated in a distorted trigonal bipyramidal coordination sphere with equatorial Si–C bonds and an equatorial Si–N bond (the one of the silaheterocycle). The axial positions were occupied by a carboxylate O atom of the silaheterocycle and the NMI ligand’s donor-N-atom.

Photoredox Cascade Catalyst for Efficient Hydrogen Production with Biomass Photoreforming.

Biomass photoreforming is a promising method to provide both a clean energy resource in the form of hydrogen (H2 ) and valuable chemicals as the results of water reduction and biomass oxidation. To overcome the poor contact between heterogeneous photocatalysts and biomass substrates, we fabricated a new photoredox cascade catalyst by combining a homogeneous catalyst, 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO), and a heterogeneous dual-dye sensitized photocatalyst (DDSP) composed of two Ru(II)-polypyridine photosensitizers (RuP6 and RuCP6 ) and Pt-loaded TiO2 nanoparticles. During blue-light irradiation (λ=460±15 nm; 80 mW), the DDSP photocatalytically reduced aqueous protons to form H2 and simultaneously oxidized TEMPO• radicals to generate catalytically active TEMPO+ . It oxidized biomass substrates (water-soluble glycerol and insoluble cellulose) to regenerate TEMPO• . In the presence of N-methyl imidazole as a proton transfer mediator, the photocatalytic H2 production activities for glycerol and cellulose reforming reached 2670 and 1590 μmol H2 (gTiO2 )-1 h-1 , respectively, which were comparable to those of state-of-the-art heterogeneous photocatalysts.

Hemilabile Amine-Functionalized Efficient Azo-Aromatic Cu-Catalysts Inspired by Galactose Oxidase: Impact of Amine Sidearm on Catalytic Aerobic Oxidation of Alcohols.

A series of azo-aromatic copper(II) complexes, [1a-g] and a Cu(I) complex, [1h], with varying amine-functionalized hemilabile pincer-like [HL1-3] and [L1,2], methyl-substituted azo [L3], and imine [L4] ligands, were synthesized and characterized. These complexes were investigated for aerobic oxidation of a variety of aromatic alcohols in the presence of 2.0 mol % precatalysts [1a-g], cobaltocene (2.0 mol %), N-methyl imidazole (NMI) (8.0 mol %), and TEMPOH (2.0 mol %) at room temperature. The Cu(I) complex (1h) acted as a catalyst in the absence of cobaltocene. To understand the mechanism, detailed experimental and theoretical studies have been performed with the representative complex [1a], which has suggested a new kind of mechanism involving a Cu(II)/Cu(I) redox couple. Cobaltocene acts as a reductant to [1a] to generate a Cu(I) complex, which activates dioxygen in the presence of NMI. TEMPOH transfers a hydrogen atom to the activated dioxygen with the generation of TEMPO•, which further participates in α-C-H bond activation in the Cu(II)-alkoxide intermediate in an intermolecular fashion in the catalytic cycle. The amine sidearm in the ligand backbone of the complexes has a significant role in catalytic activity. Complexes with amine sidearms are more effective than complexes without them. Moreover, the aliphatic secondary amine sidearm is more efficient among the amine sidearm than the aromatic secondary amine and tertiary amines. The amine sidearm that remained coordinated to the Cu(II) center is hemilabile, and it facilitates alcohol coordination in the catalytic process. Alcohol coordination was the rate-limiting step, and it was supported by the isotope effect study on benzyl alcohol, substitution effect on the amine moiety of the ligands, and DFT calculation. The hemilabile amine sidearm of the coordinated ligand also acted as a base in deprotonating the alcoholic O-H proton and acted as an acid in releasing H2O2 during the catalysis.

An efficient synthetic approach toward a sporadic heterocyclic scaffold: 1,3-Oxathiol-2-ylidenes; alkaline phosphatase inhibition and molecular docking studies

We developed a simple and robust method for synthesis of 1,3-oxathiol-2-ylidene benzamides (4a–m) a sporadic class of heterocycles, by reacting freshly prepared aroyl isothiocyanates, with ethyl 2-chloroacetoacetate in presence of N-methylimidazole in dry acetonitrile. The synthesized compounds were explored for their inhibition against alkaline phosphatases and HeLa cancer cell lines. The results suggest that almost all the compounds possess good % inhibition against both enzymes, with compound 4m showing dual inhibition while 4g and 4i as potent and selective inhibitors of TNAP and c-IAP respectively. Structure activity relationship for the active members of series has been carried out based on molecular docking studies. The result of SAR shows the involvement of active inhibitors in H-bonding at various sites with different amino acid residues in addition to secondary metal ion interactions with Zn ions inside the active pocket of the enzyme. The π-π interactions between the 1,3-oxathiole ring and imidazole ring of His321 and His 317 further defines the dual mode of inhibition by compound 4m. These compounds also possess inhibition potential against cervical cell lines in the range of 2.42–69.03% with the maximum inhibition shown by the unsubstituted member 4a compared to the reference drug cisplatin.

Acetylation of bacterial cellulose using N-methyl-imidazole as a catalyst under solvent-free and N,N-dimethylacetamide/lithium chloride solvent systems

Bacterial cellulose acetate (BCA) at a low degree of substitution (DS) was prepared using acetic anhydride in the presence of N-methylimidazole (NMIM) as a catalyst. The acetylated reaction was studied in both solvent-free (heterogeneous) and N,N-dimethylacetamide/lithium chloride (DMAc/LiCl; homogeneous) systems, where the DS ranges of BCA obtained from heterogeneous (BCA-HE) and homogeneous (BCA-HO) systems were recorded as 0.31 to 0.95 and 0.4 to 1.5, respectively. The DS values could be effectively controlled by adjusting the reaction conditions. Compared to the heterogeneous reaction, the homogeneous reaction could be processed under a mild condition within a short time. The BCA-HE and BCA-HO displayed good water solubility at a DS value less than 0.95 and 1.09, respectively. The structural and the characteristic changes were confirmed by scanning electron microscopy, Fourier transform infrared, X-ray diffraction, 13C cross-polarization magic angle spinning nuclear magnetic resonance, and thermogravimetric analyses. The present study may offer a convenient, mild, and green catalyzed-processing to tailor low DS of cellulose acetate.

The dramatic effect of N-methylimidazole on trans axial ligand binding to ferric heme: experiment and theory.

The binding energy of CO, O2 and NO to isolated ferric heme, [FeIIIP]+, was studied in the presence and absence of a σ donor (N-methylimidazole and histidine) as the trans axial ligand. This study combines the experimental determination of binding enthalpies by equilibrium measurements in a low temperature ion trap using the van't Hoff equation and high level DFT calculations. It was found that the presence of N-methylimidazole as the axial ligand on the [FeIIIP]+ porphyrin dramatically weakens the [FeIIIP-ligand]+ bond with an up to sevenfold decrease in binding energy owing to the σ donation by N-methylimidazole to the FeIII(3d) orbitals. This trans σ donor effect is characteristic of ligation to iron in hemes in both ferrous and ferric redox forms; however, to date, this has not been observed for ferric heme.

Synthesis of 2-substituted 4,5-dihydro-4-oxo-3-furancarboxylates using acylative intramolecular cyclization of sulfonium salts

A simple and efficient synthesis of 4,5-dihydro-4-oxo-3-furancarboxylates using an acylative intramolecular cyclization of sulfonium salts is described. The reaction involved the efficient formation of a mixed anhydride between a linear carboxylic acid and trifluoroacetic anhydride in the presence of N-methylimidazole, followed by the sequential conversion into a highly reactive acylammonium species in situ. This procedure is easily handled, uses readily available inexpensive reagents, and provides a variety of 2-substituted 4,5-dihydro-4-oxo-3-furancarboxylates.

Synthesis of 4-selenylidene-4H,5H-chromeno[3,4-e][1,3]oxazin-5-one

A green and efficient synthesis of [1,3]oxazines has been achieved via a three-component, one-pot condensation of 4-hydroxycoumarin, potassium selenocyanate and acyl chlorides in the presence of N-methylimidazole under solvent-free conditions at ambient temperature.

Sequential Introduction of Cations Deriving Large-Grain Csx FA1-x PbI3 Thin Film for Planar Hybrid Solar Cells: Insight into Phase-Segregation and Thermal-Healing Behavior.

Composition engineering of perovskite materials has been demonstrated to be important for high-performance solar cells. Recently, the energy favorable hybridization of formamidinium (FA) and cesium (Cs) in three dimension lead halide perovskites has been attracting increasing attention due to its potential benefit on durability. Herein, we reported a simple and effective method to produce phase-pure CsxFA1-xPbI3 thin film via sequential introduction of cations, in which the FA cation was introduced by interdiffusion annealing in the presence of N-methylimidazole (NMI). NMI was employed as an additive to slow down the crystallization and thus drive the formation of CsxFA1-xPbI3 with micrometer grain size, which probably facilitate the charge dissociation and transportation in photovoltaic devices. More importantly, composition dependent phase-segregation has been revealed and investigated for the first time during the phase-pure mixed-cation perovskites CsxFA1-xPbI3. The present findings demonstrated that suppressing phase-segregation of mixed-cation perovskites by meticulous composition engineering is significant for further development of efficient photovoltaics. It also suggested that phase-pure Cs0.15FA0.85PbI3 may be a promising candidate with superior phase-durability, which performed an efficiency over 16% in planar perovskite solar cells.

One flask synthesis of 2′,3′-cyclic nucleoside monophosphates from unprotected nucleosides using activated cyclic trimetaphosphate

The 2′,3′-cyclic nucleoside monophosphates (2′,3′-cNMPs) of adenosine, guanosine, cytidine, and uridine were prepared in good yield in a one pot reaction from unprotected ribonucleosides and activated trimetaphosphate in the presence of N-methylimidazole, 4-nitroimidazole and MgCl2.

ChemInform Abstract: Synthesis of Pyrroles and Thiazolanes Promoted by N‐Methylimidazole in Water.

A convenient and efficient approach to the synthesis of substituted pyrroles is reported based on three-component reaction of primary amines and alkyl propiolates in the presence of N-methyl­imidazole in water. A water-accelerated synthesis of thiazolane derivatives has also been established by employing the three-component reaction of primary amines, alkyl propiolates, and isothiocyanates in the presence of N-methylimidazole.

ChemInform Abstract: One‐Pot Three‐Component Reaction Between 8‐Hydroxyquinoline, Ammonium Thiocyanate and Aroyl Chlorides in the Presence of N‐Methylimidazole under Solvent‐Free Conditions.

Good yields of five 2-aryl-4H-[1,3]oxazino[5,6- h]quinoline-4-thiones were obtained via the reaction of ammonium thiocyanate and aroyl chlorides with 8-hydroxyquinoline in the presence of N-methylimidazole under solvent-free conditions. The important features of this new procedure are cleaner reaction profiles with simple experimental and work-up procedures.

Rapid and mild silylation of β-amino alcohols at room temperature mediated by N-methylimidazole for enhanced detectability by gas chromatography/electron ionization mass spectrometry.

In this work, we expand the use of in situ activation of chloro(dimethyl)phenylsilane using N-methylimidazole (NMI) for the effective derivatization of β-aminoethyl alcohols. Due to its enhanced nucleophilic character, NMI is expected to act as an efficient activator in these reactions. The derivatization of a panel of β-aminoethyl alcohols was accomplished by reacting the analyte with chloro(dimethyl)phenylsilane in the presence of either NMI or pyridine. After the addition of chloro(dimethyl)phenylsilane, the vials were gently tumbled for 1 h at ambient temperature. The phenyldimethylsilyl derivatives were identified using gas chromatography/electron ionization mass spectrometry (GC/EI-MS). A total of ten β-aminoethyl alcohols were successfully derivatized via in situ activation of chloro(dimethyl)-phenylsilane with NMI. Derivatization with NMI was significantly more efficient than with pyridine by a factor of 3-6 for the studied alcohols. The derivatizations in the presence of NMI were found to occur in just 1 h and were conveniently executed at ambient temperature. The use of the nitrogenous base NMI in order to activate chloro(dimethyl)phenylsilane for the efficient silylation of a panel of β-aminoethyl alcohols has been demonstrated. The present work shows that NMI is an efficient base for the smooth derivatization of these types of alcohols. Furthermore, the installation of the bulky PDMS group onto these alcohols adds to the certainty that this is a viable approach for the installation of the more commonly employed, trimethylsilyl group. Published in 2014. This article is a U.S. Government work and is in the public domain in the USA.

Synthesis of Pyrroles and Thiazolanes Promoted by N-Methylimidazole in Water

A convenient and efficient approach to the synthesis of substituted pyrroles is reported based on three-component reaction of primary amines and alkyl propiolates in the presence of N-methyl­imidazole in water. A water-accelerated synthesis of thiazolane derivatives has also been established by employing the three-component reaction of primary amines, alkyl propiolates, and isothiocyanates in the presence of N-methylimidazole.

One-Pot Three-Component Reaction between 8-Hydroxyquinoline, Ammonium Thiocyanate and Aroyl Chlorides in the Presence of N-Methylimidazole Under Solvent-Free Conditions

Good yields of five 2-aryl-4 H-[1,3]oxazino[5,6- h]quinoline-4-thiones were obtained via the reaction of ammonium thiocyanate and aroyl chlorides with 8-hydroxyquinoline in the presence of N-methylimidazole under solvent-free conditions. The important features of this new procedure are cleaner reaction profiles with simple experimental and work-up procedures.

ChemInform Abstract: Synthesis of Highly Functionalized Pyrroles from Primary Amines and Activated Acetylenes in Water.

Abstract Stable derivatives of pyrroles were prepared using multicomponent reactions of dialkyl acetylenedicarboxylate, primary amine and propiolate in the presence of N-methylimidazole in water at room temperature in good yields.

An efficient synthesis of [1,3,4]thiadiazolo[2,3-c][1,2,4] triazin-4-ones

A three-component reaction between 4-amino-6-methyl-3-thioxo-3,4-dihydro-2H-[1,2,4]triazin-5-one, ammonium thiocyanate and aroyl chlorides in the presence of N-methylimidazole to afford the [1,3,4]thiadiazolo[2,3-c][1,2,4]triazin-4-ones in excellent yields is described.

Ligand Contributions to the Electronic Structures of the Oxidized Cobalt(II) salen Complexes

Square planar cobalt(II) complexes of salen ligands N,N'-bis(3-tert-butyl-5R-salicylidene)-1,2-cyclohexanediamine), where R = OMe (1) and tert-butyl (2), were prepared. 1 and 2 were electrochemically reversibly oxidized into cations [1-H(2)O](+) and [2-H(2)O](+) in CH(2)Cl(2). The chemically generated [1-H(2)O](SbF(6))·0.68 H(2)O·0.82CH(2)Cl(2) and [2-H(2)O](SbF(6))·0.3H(2)O·0.85CH(2)Cl(2) were characterized by X-ray diffraction and NIR spectroscopy. Both complexes are paramagnetic species containing a square pyramidal cobalt ion coordinated at the apical position by an exogenous water molecule. They exhibit remarkable NIR bands at 1220 (7370 M(-1) cm(-1)) and 1060 nm (5560 M(-1) cm(-1)), respectively, assigned to a CT transition. DFT calculations and magnetic measurements confirm the paramagnetic (S = 1) ground spin state of the cations. They show that more than 70% of the total spin density in [1-H(2)O](+) and [2-H(2)O](+) is localized on the metal, the remaining spin density being distributed over the aromatic rings (30% phenoxyl character). In the presence of N-methylimidazole 1 and 2 are irreversibly oxidized by air into the genuine octahedral cobalt(III) bis(phenolate) complexes [1-im(2)](+) and [2-im(2)](+), the former being structurally characterized. Neither [1-im(2)](+) nor [2-im(2)](+) exhibits a NIR feature in its electronic spectrum. 1 and 2 were electrochemically two-electron oxidized into [1](2+) and [2](2+). The cations were identified as Co(III)-phenoxyl species by their characteristic absorption band at ca. 400 nm in the UV-vis spectrum. Coordination of the phenoxyl radical to the cobalt(III) metal ion is evidenced by the EPR signal centered at g = 2.00.

Synthesis of highly functionalized pyrroles from primary amines and activated acetylenes in water

Abstract Stable derivatives of pyrroles were prepared using multicomponent reactions of dialkyl acetylenedicarboxylate, primary amine and propiolate in the presence of N-methylimidazole in water at room temperature in good yields.