Quantum-chemical study on the reaction of phenyl isocyanate with linear methanol associates: II. Addition at the C=O bond

Addition of linear methanol associates at the C=O group of phenyl isocyanate involves a concerted cyclic asymmetric late transition state. The reaction is accompanied by formation of pre- and post-reaction complexes. Isomerization of intermediate methyl hydrogen phenylimidocarbonate into methyl phenylcarbamate is characterized by a considerable energy barrier. The reactivity of methanol molecules increases in parallel with the degree of their association, which is related to increase in their electron-donor power. Comparison of the calculated parameters for the addition of methanol associates at the C=N and C=O bonds of phenyl isocyanate clearly indicates that the first path is preferred.     

Quantum-chemical study on reactions of isocyanates with linear methanol associates: VIII. Relative reactivity of linear phenol and methanol associates toward methyl isocyanate

The mechanisms of the reactions of methyl isocyanate with phenol monomer and linear dimer were studied at the B3LYP/6-311++G(df,p) level of theory, and the results were compared with those obtained for the reactions with methanol associates. All the examined reactions involve asymmetric concerted transition states. The addition of phenol is electrophilic, whereas the addition of methanol is nucleophilic. The formation of H-complexes with phenol and methanol molecules increases not only electron-donating power but also gasphase acidity and basicity.     

Quantum-chemical investigation of isocyanate reactions with linear methanol associates: V. Aryl isocyanate reactions with linear methanol associates

The mechanism of addition of linear methanol associates (monomer, dimer, trimer) to aryl isocyanates at their C=N and C=O bonds was investigated applying the quantum-chemical method B3LYP/6-311++G(df,p). Notwithstanding the electronic character of substituents in the aromatic ring of the isocyanates all reactions proceed through concerted asymmetric late transition states. The addition to the C=N bond is considerably more preferable than to the C=O bond. In the transformations under consideration the intermolecular donor-acceptor interactions between the reagents result in the appearance of abnormal selectivity.     

Phase Transitions in Solid Methanol

Neutron powder diffraction patterns were measured for the ordered α-phase and the disordered β-phase of deuterated methanol. The structure of the α-phase at 160 K is in agreement with that found earlier at 15 K. A complete refinement of the structure of the β-phase at 170 K was also carried out. The space groups are α-P2₁2₁2₁ and β-Cmcm. For the disordered phase, the thermal parameters indicate that the molecules are localized rather than being in free rotation. A transformation matrix was found that relates the unit cells of the two phases. The transition involves mainly the large-angle rotation of molecules in a plane. In a second experiment, the α- to β-phase transition in both deuterated and undeuterated solid methanol was examined using Raman spectroscopy and a metastable phase was produced, for the undeutered sample, by rapid quenching through the phase transition. Only two modes of the methyl groups in this metastable phase differ from the internal modes of the stable α-phase.     

贫电子环丙烷衍生物与甲醇的反应

顺-1-呋喃乙酰基-2-对位取代苯基-6,6-二甲基-5,7-二氧-螺-[2,5]-4,8-辛二酮和顺-1-噻吩乙酰基-2-对位取代苯基-6,6-二甲基-5,7-二氧-螺-[2,5]-4,8-辛二酮与甲醇于封管中80℃反应72 h得到β-呋喃甲酰基-γ-甲氧基-γ-对取代苯基-丁酸甲酯及β-噻吩甲酰基-γ-甲氧基-γ-对取代苯基-丁酸甲酯,其结构经1H NMR,13C NMR,IR,MS及APT。讨论了反应机理。     

Carbonylation of Methanol with Carbon Monoxide in the Presence of Sulfur-containing Catalysts

Physicochemical features of methanol carbonylation with carbon monoxide catalyzed with sodium sulfides Na_2Sx (x = 1, 2, 4) were studied. The effect of admixtures of sulfur dioxide in the gas phase on the yield of the target product (methyl formate) was revealed.     

不同温度焙烧的Au-Pd/SiO2催化剂上甲醇选择性氧化制备甲酸甲酯

以溶胶固定法制备了Au-Pd/SiO₂催化剂,考察了催化剂焙烧温度对甲醇选择氧化制甲酸甲酯反应性能的影响。在200~500℃,400℃焙烧的Au-Pd/SiO₂具有最好的低温催化性能,在室温下就有活性,反应温度为100℃时甲醇转化率为25.3%,甲酸甲酯的选择性为100%。采用BET、XRD、UV-vis DRS、XPS、TEM和DRIFTS技术对催化剂进行表征,结果表明,催化剂中活性组分Au和Pd的高分散性,合适的Au和Pd粒径,Au-Pd合金的形成以及Au和Pd之间的强相互作用力,有利于甲醇氧化为甲酸甲酯反应的进行。初步推测出了甲醇在Au-Pd/SiO₂上氧化为甲酸甲酯的反应机理,甲醇在Au-Pd/SiO₂催化剂上是通过甲氧基中间体得到甲酸甲酯的。     

Determination of Fatty Acid Methyl Esters in Biodiesel Produced from Yellow Horn Oil by LC

A simple and accurate HPLC method with refractive index detection was developed to determine the main fatty acid methyl esters in biodiesel produced from yellow horn oil. Methyl linoleate, methyl linolenate, methyl arachidate, methyl stearate, methyl palmitate and methyl oleate were separated on a HIQ SIL C18W column using methanol as mobile phase. The method has good repeatability and precision, the intraday and interday RSD for both retention time and peak area was less than 3.2%. The LOD (S/N = 3) and LOQ (S/N = 9) were less than 0.004 and 0.015 mg mL⁻¹, respectively.     

钼催化剂上甲醇直接气相羰基化活性与吸附的关系

 制备了一系列非负载的钼催化剂，考察了催化剂上甲醇直接气相\r\n羰化活性与反应物及产物吸附的关系．结果发现，催化剂的制备方法对\r\n甲醇直接气相羰化活性的影响很明显，以纯二硫化钼试剂制备的催化剂\r\n，甲醇转化率与羰化产物乙酸甲酯的选择性最低；以三氧化钼气相还原\r\n硫化制备的催化剂，其羰化活性较低；以钼酸铵溶液经硫化铵溶液或硫\r\n化氢气体硫化制得的催化剂，其性能明显优于前两种，尤以钼酸铵经硫\r\n化铵溶液硫化制得的催化剂的性能最佳．催化剂的羰化活性明显依赖于\r\n催化剂的吸附性能，羰化活性高的催化剂不仅吸附CO的量大，而且对甲\r\n醇和乙酸甲酯的吸附量也明显较大．     

(Liquid + liquid) equilibria of methanol + ethylbenzene + isooctane + methy <Emphasis Type="Italic">tert</Emphasis>-butyl ether quaternary system at <Emphasis Type="Italic">T</Emphasis> = 303.15 K

Tie line data of {methanol + methyl tert-butyl ether + isooctane} ternary systems were obtained at T = 303.15 K, while data for {methanol + ethylbenzene + isooctane} were taken from literature. The ternary system {methanol + methyl tert-butyl ether + ethylbenzene} and {methyl tert-butyl ether + ethylbenzene + isooctane} were completely miscible. A quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether} was also studied at the same temperature. In order to obtain equilibium data of the quaternary system, four quaternary sectional planes with several methyl tert-butyl ether/methanol ratios were studied. The effect of the addition of methyl tert-butyl ether on the liquid-liquid equilibrium data of {methanol + ethylbenzene + isooctane} ternary system has been investigate at the same temperature. The distribution curves for ternary and quaternary system was analysed. For the quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether}, experimental data demonstrated that the distribution coefficient of ethylbenzene between the hydrocarbon and methanol phase on a methyl tert-butyl ether–free basis slightly increases with the increase of methyl tert-butyl ether/methanol ratio. Ternary experimental results were correlated with the UNIQUAC and NRTL equation. The NRTL equation is more accurate than the UNIQUAC equation for the ternary systems studied here. The equilibrium data of three ternary systems were used for determining interactions parameters for the UNIQUAC equation. The UNIQUAC equation fitted to the experimental data appeared to be more accurate than the UNIFAC method for the same quaternary system.     

Extraction of platinum with Astrafloxin FF from aqueous-organic solutions: Separative extraction-spectrophotometric determination of platinum(II) and platinum(IV) species

The optimum conditions of the extraction of the ion associates of platinum with the thiocyanate ions and the polymethine basic dye Astrafloxin FF by aromatic hydrocarbons and acetic acid esters from aqueous and aqueous-organic solutions were studied. The introduction of water-soluble donor-active solvents (hexamethylphosphoric triamide, N,N-diethylacetamide, N,N-dimethylformamide, and N,N-diethylformamide) leads to a considerable increase in the extraction of the ion associates of platinum and the simultaneous suppression of the extraction of the simple dye salt. The molar absorption coefficients of the extracts of ion associates are as high as (8.1?C13.3) × 10⁴. 84?C96% platinum is extracted in the form of ion associates by a single extraction. The conversion of platinum into ion associates makes it possible to separate platinum from many elements, including Cu, Cd, Ni, Co, Cr, Pb, In, Ag, Pd, Ir, Rh, and Ru, by extraction. In this case, platinum(II) is extracted in the form of ion associates under standard conditions, whereas platinum(IV) is extracted only after the preliminary thermal treatment of the test sample. A new procedure was developed for the extraction-spectrophotometric determination of the trace amounts of platinum(II) and platinum(IV), in particular, in their mixtures.     

High Yields of Methanol from Methane by C−H Bond Activation at Low Temperatures

Activation, oxidation, and functionalization are the essential steps in the direct selective conversion of methane into liquid chemicals such as methanol, formaldehyde, higher paraffins, and olefins. In the best process so far for the synthesis of methanol from methane, the reagent is converted with 90% conversion and 81% selectivity into methyl bisulfate in 102% sulfuric acid at 220°C and in the presence of Pt complexes that contain very stable ligands. The desired product can be trapped by esterification and thus be protected from nonselective consecutive reactions.     

Cucurbituryl Associates with Trigonal and Cubane Transition Metal Cluster Aqua Complexes

This paper discusses a new approach to crystallization of cluster aqua anions using an organic macrocyclic cavitand — cucurbituryl. Six water molecules coordinated to the cluster nucleus are geometrically complementary to the six oxygen atoms of the C=O groups of cucurbituryl, forming with them a stable system of hydrogen bonds. The resulting associates have low solubility and good crystallization properties. The crystal structures of 15 compounds of this type have been studied, and the main structural features have been revealed.     

Reaction of methyl acrylate with N,N-dimethylethanolamine in the presence of a titanium alkoxide

The kinetic features were examined for transesterifi cation of methyl acrylate with N,N-dimethylethanolamine in the presence of tetra(N,N-dimethylaminoethyl) titanate at different molar ratios of the reactants and at temperatures within 50?C80°C, as well as for side reactions of Michael addition at 95?C125°C. The major parameters governing the selectivity of the synthesis of N,N-dimethylaminoethyl acrylate were determined.     

Quantum-chemical study on reactions of isocyanates with linear methanol associates: VII. Effect of nonspecific solvation on the reaction of methyl isocyanate with linear methanol associates

The effect of nonspecific solvation on the reactivity of methyl isocyanate toward linear methanol associates and thermodynamic parameters of this reaction was studied at the B3LYP/6-311++G(df,p) level of theory in terms of the polarizable continuum model (PCM). Transformations in the liquid phase are more exothermic than in the gas phase. Change of the solvent nature leads to variation of the geometric parameters and intrinsic free energies of the reactants and transition states. Increase in solvent polarity is accompanied by increase in the degree of asymmetry and polarity of transition states. As the dielectric permittivity rises, the polar constituent of the Gibbs energy of solvation decreases, while its nonpolar constituent increases. Owing to the opposite variations of these constituents of the Gibbs energy of activation, the reaction is weakly sensitive to solvent polarity.     

Alkylation of Ethylbenzene with Methanol on HY,HM and HZSM-5 Zeolite

The alkylation of ethylbenzene with methanol on various zeolites has been studied at atmospheric pressure, 300–500 °C and with ethylbenzene/methanol = 3 mol/mol in a fixed-bed, integral-flow reactor. The catalytic activity decreased in the order HZSM-5 > HY > HM. The optimum conditions for the formation of ethyltoluene were HY zeolite, 400 °C and W/F = 4.1 g-cat h/g-feed. The catalyst decay rate increased in the order HZSM-5 << HY < HM; coking of the zeolite increased the fraction of para-isomer in the ethyltoluenes. On HZSM-5 modified with alkaline earth metal, the conversion of ethylbenzene decreased with concomitantly increased selectivity of para-ethyltoluene especially evident in cases of magnesium and calcium (> 93% para-selectivity). These results are interpreted in terms of diminution of both the strong acid sites and the pore size of zeolites. For the reaction on HY at 400 °C, the reaction paths were determined; the ethylbenzene reacted via alkylation, disproportionation and dealkylation with initial selectivities 84.7%, 13.1% and 2.2%, respectively.     

Thermal Rearrangements of 3<Emphasis Type="Italic">H</Emphasis>- and 4<Emphasis Type="Italic">H</Emphasis>-Pyrazoles Prepared by Reactions of 9-Diazofluoren with Methyl Tetrolate and Methyl 3-Phenylpropiolate

9-Diazofluoren adds in Et₂O at 20°C to methyltetrolate in keeping with Auwers rule and nonregioselectively adds to methyl-3-phenylpropiolate with the formation of spirocyclic 3H-pyrazoles. The methyltetrolate adduct at boiling in toluene converts into methyl 3a-methyl-3aH-dibenzo[e,g]indazole-3-carboxylate, at 190°C in benzene, into methyl 3-methyl-2H-dibenzo[e,g]indazole-2-carboxylate, and at 160°C in methanol, into 3-methyl-2H-dibenzo[e,g]indazole. Auwers adduct of methyl 3-phenylpropiolate at boiling in benzene gives cyclopropene derivative and at boiling in methanol isomerizes into methyl 3a-phenyl-3aHdibenzo[e,g]indazole-3-carboxylate. Anti-Auwers adduct at boiling in benzene isomerizes into methyl 2-phenylpyrazolo[1,5-f]phenanthridine-3-carboxylate.     

Methane Conversion to Methanol in Condensed Phase

The subject of our investigations was the oxidation process of methane to organic oxygenates. The catalytic system proposed by us in which palladium occurs in the form of palladium powder dissolved in oleum has not been described up to now. Methanol was obtained by the transformation of methane into methyl bisulfate. Subsequently, methanol was formed as a result of ester hydrolysis. The reaction temperature was varied in the range of 70–190°C; the time was changed from 1 to 20 h. The reaction products were carbon dioxide, methanol, and traces of formaldehyde. We found that the rate of ester formation depends on the partial pressure of methane, the concentration of free sulfur trioxide in sulfuric acid, and the concentration of ester itself in the reaction mixture. An equation for the rate of formation of the methyl bisulfate was proposed. The rate constants were determined by Marquardt's method.     

Special Mixing Behavior of Chelate-based Ionic Liquid with Methanol

Compared to the general ionic liquids (ILs), a significant deviation of the binary mixtures of 1-decyl-3-methylimidazolium tri(hexafluoroacetylaceto)-copper(II) ([C₁₀mim][Cu(hfacac)₃]) with methanol was found, indicating the way methanol interacts with ILs might be governed by the special structure of the chelating anion. IR results showed that the (C2-H) of 1-decyl-3-methylimidazolium hexafluoroacetylacetonate ([C₁₀mim][hfacac]) blue-shifted more significantly than that of [C₁₀mim][Cu(hfacac)₃], meanwhile the (C=O) red-shifted in [C₁₀mim][Cu(hfacac)₃], which is contrast with that in [C₁₀mim][hfacac]. Two-dimensional correlation analysis of the FTIR spectra indicated that the chelating cavity has little effect on the sequence of the ILs sites that interact with methanol. Combined with small angle X-ray scattering (SAXS) results, the picture of mixing processes in these two systems were proposed. Methanol interacts directly with the anion followed by the cation in [C₁₀mim][hfacac], while methanol preferentially enters the chelating cavity and enhances the packing effect in the [C₁₀mim][Cu(hfacac)₃] system.     

Intra- vs. intermolecular hydrogen bonding: dimers of alpha-hydroxyesters with methanol

Intermolecular hydrogen bonding competes with an intramolecular hydrogen bond when methanol binds to an alpha-hydroxyester. Disruption of the intramolecular OH...O=C contact in favour of a cooperative OH...OH...O=C sequence is evidenced by FTIR spectroscopy for the addition of methanol to the esters methyl glycolate, methyl lactate and methyl alpha-hydroxyisobutyrate in seeded supersonic jet expansions. Comparison of the OH stretching modes with quantum-chemical harmonic frequency calculations and 18O labelling of methanol unambiguously prove the insertion of methanol into the intramolecular hydrogen bond. This is in marked contrast to UV/IR hole burning studies of the homologous system methyl lactate: (+/-)-2-naphthyl-1-ethanol, where only addition complexes were found and the intramolecular hydrogen bond was conserved. This switch in hydrogen bond pattern from aliphatic to aromatic heterodimers is thought to reflect not only a kinetic propensity but also a thermodynamic preference for addition complexes when dispersion forces become more important in aromatic systems.