Zinc Methoxide Research Articles

Decomposition of N,O-dimethylcarbamate to methyl isocyanate: A DFT study

The non-catalytic and catalyzed by phenol and zinc methoxide decomposition of N,O-dimethylcarbamate to methyl isocyanate and methanol was studied by B3LYP/6–311++G(df,p) and PBE0/6–311++G(df,p) methods. Non-catalytic transformation has a large activation barrier and is therefore not feasible. Catalysis with phenol slightly reduces the activation barrier. The non-catalytic and phenol-catalyzed reactions are single-step. Zinc methoxide-catalyzed reaction proceeds through two stages. The greatest decrease in the activation barrier is observed in the case of zinc methoxide-catalyzed reaction.

Superficial visible-light-responsive Pt@ZnO nanorods photocatalysts for effective remediation of ciprofloxacin in water

Fabrication of mesoporous ZnO nanorods photocatalysts exploiting a facile one-pot regime of zinc methoxide and F127 triblock copolymer as a surfactant was conducted. The impact of decoration with platinum on the photocatalytic efficacy, crystallinity, morphology, and physical aspects of mesoporous Pt@ZnO nanorods accommodating various proportions of Pt was interrogated. TEM micrographs affirmed that the fabricated mesoporous ZnO nanorods displayed nanorods architecture and platinum was doped on the surface of mesoporous ZnO nanorods as dots. The measured lattice spacing of the (002) plane of ZnO was found to be about 0.270 nm, affirming the development of the ZnO lattice architecture. On the other hand, the consistent lattice spacing of the (111) plane of Pt was 0.220 nm, endorsing the progression of the metallic platinum lattice architecture. Evidently, the surface area possessed by the fabricated mesoporous ZnO nanorods was 200 m2/g; up to our knowledge, this large surface area wasn’t attained previously. Furthermore, the average pore diameter and the total pore volume possessed by the fabricated mesoporous ZnO nanorods photocatalyst were 6.90 nm and 0.140 cm3/g, respectively. Ciprofloxacin (CIP) was photocatalytically degraded adopting mesoporous ZnO nanorods photocatalyst with a performance of 10%, whereas the photocatalytic performance toward CIP destruction was enhanced up to 100% upon doping ZnO nanorods photocatalyst with 0.6 wt.% Pt. Also, doping of the mesoporous ZnO nanorods photocatalyst with 0.6 wt.% Pt enhanced the photocatalytic degradation rate by 14 times compared with that of mesoporous ZnO nanorods photocatalyst. This conclusion could be attributed to the development of a high concentration of hydroxyl radicals, the accelerated dissipation of ciprofloxacin molecules to the active centers of the developed photocatalyst in addition to the reduced light scattering owing to the large surface area and high pore volume of the photocatalyst.

Copolymerization of CO2and Cyclohexene Oxide: β-Diketiminate-Supported Zn(II)OMe and Zn(II)Et Complexes as Initiators

β-Diketiminate ligands with varying degrees of steric bulkiness and having −CN and −NO2 groups on N-aryl substituents were synthesized. The catalytic activity of some of their [LZnEt] and [LZnOMe]2 complexes (L = β-diketiminato) toward the copolymerization of carbon dioxide and cyclohexene oxide was explored. All the catalysts were found to be highly active and showed very good turnover frequency, and the polycarbonates produced have a very high percentage of carbonate linkages. The complex [LiPr,Me-CNZnEt] showed very high activity and selectivity on par with its zinc methoxide analogue. The polymers produced by [LZnEt] complexes displayed a bimodal molecular weight distribution.

Expanding the synthesis of Stöber spheres: towards the synthesis of nano-magnesium oxide and nano-zinc oxide

In order to synthesise Stober spheres of different diameters, fixed amounts of ethanol, ammonia and water were used with varying amounts of tetraethyl orthosilicate. This simple method was further applied to the synthesis of nano-ZnO and nano-MgO from their respective precursors, zinc methoxide and magnesium ethoxide. The spherical nano-SiO2, nano-ZnO and nano-MgO synthesised in this way were characterised by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. Preliminary investigations found that nano-ZnO and nano-MgO showed good catalytic activity in the trans-esterification reaction that converts vegetable oil to biodiesel.

Influence of the Chelate Ligand Structure on the Amide Methanolysis Reactivity of Mononuclear Zinc Complexes

Zinc complexes of three new amide-appended ligands have been prepared and isolated. These complexes, [(dpppa)Zn](ClO4)2 (4(ClO4)2; dpppa = N-((N,N-diethylamino)ethyl)-N-((6-pivaloylamido-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), [(bdppa)Zn](ClO4)2 (6(ClO4)2; bdppa = N,N-bis((N,N-diethylamino)ethyl)-N-((6-pivaloylamido-2-pyridyl)methyl)amine), and [(epppa)Zn](ClO4)2 (8(ClO4)2; epppa = N-((2-ethylthio)ethyl)-N-((6-pivaloylamido-2-pyridyl)methyl)-N-((2-pyridyl)methyl)amine), have been characterized by X-ray crystallography (4(ClO4)2 and 8(ClO4)2), 1H and 13C NMR, IR, and elemental analysis. Treatment of 4(ClO4)2 or 8(ClO4)2 with 1 equiv of Me4NOH.5H2O in methanol-acetonitrile (5:3) results in amide methanolysis, as determined by the recovery of primary amine-appended forms of the chelate ligand following removal of the zinc ion. These reactions proceed via the initial formation of a deprotonated amide intermediate ([(dpppa-)Zn]ClO4 (5) and [(epppa-)Zn]ClO4 (9)) which in each case has been isolated and characterized (1H and 13C NMR, IR, elemental analysis). Treatment of 6(ClO4)2 with Me4NOH.5H2O in methanol-acetonitrile results in the formation of a deprotonated amide complex, [(bdppa-)Zn]ClO4 (7), which was isolated and characterized. This complex does not undergo amide methanolysis after prolonged heating in a methanol-acetonitrile mixture. Kinetic studies and construction of Eyring plots for the amide methanolysis reactions of 4(ClO4)2 and 8(ClO4)2 yielded thermodynamic parameters that provide a rationale for the relative rates of the amide methanolysis reactions. Overall, we propose that the mechanistic pathway for these amide methanolysis reactions involves reaction of the deprotonated amide complex with methanol to produce a zinc methoxide species, the reactivity of which depends, at least in part, on the steric hindrance imparted by the supporting chelate ligand. Amide methanolysis involving a zinc complex supported by a N2S2 donor chelate ligand (3(ClO4)2) is more complicated, as in addition to the formation of a deprotonated amide intermediate free chelate ligand is present in the reaction mixture.

Solvent Effects on the Structural and Formyl Substrate Reactivity Properties of a Nitrogen/Sulfur-Ligated Zinc Hydroxide Complex

The solution structural and formyl substrate reactivity properties of a nitrogen/sulfur-ligated zinc hydroxide complex, [(bmnpaZn)2(mu-OH)2](ClO4)2 (1, bmnpa = N,N-bis-2-(methylthio)ethyl-N-((6-neopentylamino-2-pyridyl)methyl)amine), in acetonitrile and methanol are reported. In CH3CN, 1 has a binuclear cation [(bmnpaZn)2(mu-OH)2]2+ that is stabilized by secondary hydrogen bonding and CH/pi interactions involving the bmnpa chelate ligand. In CH3OH, 1 undergoes reaction with solvent to yield a zinc methoxide species, as determined by 1H NMR and electrospray mass spectral analysis. Treatment of 1 with methyl formate in CH3CN results in stoichiometric hydrolysis of the formyl ester to produce [(bmnpa)Zn(O2CH)]ClO4 (2) and methanol. The formate complex was identified via independent synthesis and characterization (X-ray crystallography, 1H and 13C NMR, FTIR, LRFAB-MS, conductance, and elemental analysis). In the solid state, 2n has a formate-bridged coordination polymer-type structure. However, in CH3CN, 2 behaves as 1:1 electrolyte, indicating cleavage of the polymer structure into mononuclear [(bmnpa)Zn(O2CH)]ClO4 species. Treatment of 1 with a stoichiometric amount of formanilide in CH3CN for 48 h at 45 degrees C results in decomposition of the zinc hydroxide complex to yield the free bmnpa ligand and an inorganic solid, presumably a zinc hydroxide or oxide species. Treatment of 1 with a stoichiometric amount of ethyl formate in CD3OD results in rapid, quantitative transesterification of the formyl carboxylate ester. A control reaction indicates that this transesterification reaction does not occur on the same time scale in the absence of the catalyst. Treatment of 1 with an excess of ethyl formate in CD3OD results in catalytic formyl carboxylate ester transesterification, with approximately 1000 turnovers in 60 min at 22(1) degrees C. Treatment of a CD3OD solution of 1 (0.5 equiv) with formanilide (1 equiv) results in the formation of aniline, d3-methyl formate, and the zinc formate complex 2. While aniline is produced stoichiometrically, the yield of d3-methyl formate varied from 30 to 50%, and the yield of 2 varied from 50 to 70% in repetitive experiments. Formation of both d3-methyl formate and 2 indicates that both methanolysis and hydrolysis reactions take place.

Mononuclear nitrogen/sulfur-ligated zinc methoxide and hydroxide complexes: investigating ligand effects on the hydrolytic stability of zinc alkoxide species.

The synthesis and properties of mononuclear zinc methoxide ([(ebnpa)Zn-OCH3]ClO4) (1) and hydroxide ([(ebnpa)Zn-OH]ClO4) (2) complexes of a new mixed nitrogen/sulfur ligand (ebnpa = N-2-(ethylthio)ethyl-N,N-bis(6-neopentylamino-2-pyridylmethyl)amine) are reported. The structures of 1 and 2 were determined by X-ray diffraction. Each possesses a single zinc-coordinated anion (methoxide or hydroxide) and exhibits an overall trigonal bipyramidal geometry. Structural and spectroscopic studies indicate the presence of two hydrogen-bonding interactions involving the oxygen atom of the zinc-bound anion in each complex. Treatment of [(ebnpa)Zn-OH]ClO4 with CH3OH results in the formation of an equilibrium mixture of 1 and 2. 1H NMR spectroscopic methods were used to examine the equilibrium as a function of temperature, yielding KMe (304 K) = 0.30(8), DeltaHMe = -0.9(1) kcal/mol, and DeltaSMe = -5(1) eu. The negative enthalpy indicates that spontaneous zinc alkoxide formation from a hydroxide precursor occurs in this system at low temperature. Using the experimentally determined DeltaHMe value, we found the homolytic Zn-O bond dissociation energy (BDE) in the Zn-OCH3 unit to be approximately -14 kcal/mol relative to the Zn-O BDE in the Zn-OH unit.

Mechanisms of Methanol Synthesis from Carbon Dioxide and from Carbon Monoxide at Atmospheric Pressure over Cu/ZnO

Methanol synthesis from CO2 and CO was carried out at atmospheric pressure over a Cu/ZnO catalyst (Cu/Zn = 3/7) and the surface species formed were analyzed by diffuse reflectance FT-IR spectroscopy and temperature programmed desorption. It was revealed that CH3OH and CO were produced from CO2-H2 through parallel pathways. Two types of formate species, HCOO-Cu and HCOO-Cu and HCOO-Zn, and zinc methoxide were formed in the course of methanol synthesis from CO2. HCOO-Cu and HCOO-Zn were hydrogenated to methoxide. A comparison of the rates of hydrogenation with that of methanol synthesis from CO2 suggested that methanol synthesis from CO2 occurred via the hydrogenation of HCOO-Cu. The methanol synthesis from CO proceeded at a rate much slower than that from CO2, HCOO-Zn and zinc methoxide were formed in the course of the CO-H2 reaction. No HCOO-Cu was detected. The amount of the zinc methoxide formed in the CO-H2 reaction greatly exceeded that formed in the CO2-H2 reaction. The rate of the formation of methoxide in the CO-H2 reaction was in reasonable agreement with that of the hydrogenation of HCOO-Zn. On the basis of these findings, the difference in the mechanisms of methanol synthesis from CO2 and from CO was discussed.

Remarks on the assignments of temperature programmed desorption peaks for the surface species formed on Cu/ZnO and ZnO in the methanol synthesis from CO

Temperature programmed desorption (TPD), IR spectroscopy and chemical trapping of the surface species with H2O revealed that the TPD peak of CO frequently assigned to zinc formate species, which were formed in the course of the methanol synthesis from CO-H2, arose from zinc methoxide species.

Methanol synthesis from carbon dioxide at atmospheric pressure over Cu/ZnO catalyst. Role of methoxide species formed on ZnO support

Methanol synthesis from CO2 and H2 was carried out over a Cu/ZnO catalyst (Cu/Zn = 3/7) at atmospheric pressure, and the surface species formed were analyzed by diffuse reflectance FT-IR spectroscopy and temperature programmed desorption method. Two types of formate species and zinc methoxide were formed in the course of the reaction. Zinc methoxide was readily hydrolyzed to methanol. H2O formed through the reverse water gas shift reaction was suggested to be involved in the hydrolysis of zinc methoxide.

Aspects of the chemistry of the hexahydroisochromanone from the carvenone–benzaldehyde condensation

A scheme for the mechanism of formation of the title compound is described and supported by deuteriation studies. The various courses of reduction of the title compound are described. Opening of the heterocyclic ring during attempted zinc–methanol reduction is shown to be due to formation of ‘zinc methoxide’ in the reaction. The courses of bromination and reduction of 4,4,7-trimethyl-1,3-diphenyl-5,6,7,8-tetrahydroisochroman-8-one are outlined, and structures are assigned to the products.