Showing papers on "Methanol published in 1988"

Dynamics of Growth of Silica Particles from Ammonia-Catalyzed Hydrolysis of Tetra-ethyl-orthosilicate

Abstract: The NH3-catalyzed formation of colloidal silica particles from tetra-ethyl-orthosilicate (TEOS) in methanol and ethanol is studied by means of light scattering and Raman spectroscopy. We find that the growth is characterized by an incubation period after which no significant nucleation takes place. The particles have uniform, non-fractal structure and show low polydispersity. In the presence of excess water, the rate-limiting step is the hydrolysis, which is a first-order process in the orthosilicate concentration. © 1988 Academic Press, Inc.

Adsorption and decomposition of aliphatic alcohols on titania

Abstract: Etude, par thermodesorption, de l'adsorption puis de la decomposition chimique du methanol, ethanol, propanol-1 et propanol-2 sur le dioxyde de titane

Enzyme‐caytalyzed oxidation of cholesterol in supercritical carbon dioxide

Abstract: Supercritical carbon dioxide was studied as a solvent for the enzymatic oxidation of cholesterol with molecular oxygen. Enzymes isolated from Streptomyces sp., Norcardia sp., Pseudomonas sp., and Gloeocysticum chrysocreas are active in supercritical carbon dioxide. For the oxidation of cholesterol to cholest-4-ene-3-one (via cholesterol oxidase) from Gloeocysticum chrysocreas, turnovers are almost two orders of magnitude higher than those found in aqueous solutions; initial rates of the reaction catalyzed by Streptomyces sp. in supercritical carbon dioxide are comparable to or greater than those found in aqueous solutions. Cholesterol oxidase from Gloeocysticum chrysocreas is stable in supercritical carbon dioxide at 100 bar and 35°C, while the enzyme from Streptomyces sp. is not. A trace amount of water is necessary for catalysis in carbon dioxide. The rate of oxidation is increased markedly by addition of small amounts of tert-butanol and iso-butanol, moderately by ethanol, slightly by acetone and n-butanol, and not at all by addition of methanol. Solubility data cannot explain these observations. EPR spectroscopy reveals no large conformational changes in the enzyme from Gloeocysticum chrysocreas as a function of carbon dioxide pressure or cosolvent addition. However, EPR spectroscopy indicates that aggregation of cholesterol molecules in supercritical carbon dioxide is strongly affected by changes in pressure or cosolvent content. The degree of cholesterol aggregation correlates well with observed rate enhancements.

Selective conversion of methanol into aromatic hydrocarbons over zinc-exchanged ZSM-5 zeolites

Abstract: The conversion of methanol into hydrocarbons over ZSM-5 zeolites has been studied with a special emphasis on improving the selectivity to aromatic hydrocarbons. The introduction of zinc or gallium cations to ZSM-5 appreciably increased the yield of or selectivity for aromatic hydrocarbons. Thus, under the reaction conditions of 700 K, methanol pressure of 40 kPa and W/F= 9.0 g h mol–1, the yields of aromatic hydrocarbons over H-ZSM-5, Ga-ZSM-5, and Zn-ZSM-5 were 40.3, 48.2 and 67.4%, respectively. Over Zn-ZSM-5 the distribution of aromatic products on a molar basis was as follows; benzene (5.8%), toluene (28.0%), xylenes + ethylbenzene (45.6%) and C9+(20.6%). The reaction conditions were optimized to obtain the highest yield of aromatic hydrocarbons over Zn-ZSM-5. The yield of aromatics increased with temperature up to 700 K, but a further temperature increase led to the decomposition of methanol to carbon oxides. The selectivity for aromatics gave a maximum of 70% at a methanol partial pressure of 22 kPa. The yield of aromatic hydrocarbons increased with the degree of cation-exchange of H-ZSM-5 with Zn-cations, indicating the essential role of zinc species in the enhancement of the selectivity to aromatics. It is concluded that the zinc species has a capability of efficiently converting alkene intermediates to aromatic hydrocarbons.

Direct conversion of methane to methanol in a flow reactor

Abstract: The gas-phase homogeneous partial oxidation of methane with oxygen was studied over a range of operating conditions in a high-pressure tubular reactor. The experimental data indicated that methanol selectivities of 70 - 80% could be achieved at methane conversions of 8 - 10% by operating at suitable reaction conditions. The higher methanol selectivities obtained in this study were probably due to the use of a Pyrex glass liner in the reactor, which may have minimized surface reactions.

Samarium(II) di-iodide induced reductive coupling of α,β-unsaturated esters with carbonyl compounds leading to a facile synthesis of γ-lactone

Abstract: Samarium(II) di-iodide, which is a strong one-electron transfer reducing agent, is effective for the reductive coupling of α,β-unsaturated esters with carbonyl compounds, whereby substituted γ-lactones can easily be prepared in good to excellent yields under very mild conditions. Two mole equiv. of samarium(II) di-iodide to each mole equiv. of starting substrate always give reasonable yields. The presence of an alcohol is essential in the reaction, complex unidentified products being formed in the absence of an alcohol; t-butyl alcohol gave more satisfactory results than methanol and ethanol. The alcohol acts as a proton donor, the use of MeOD leading to a deuteriated γ-lactone. The reaction is applicable to both aliphatic and aromatic ketones or aldehydes, whereas the electrochemical method is limited to aliphatic substrates. The diastereoselectivity is examined in the reaction of 4-t-butylcyclohexanone with ethyl acrylate; an anti-isomer is produced predominantly (syn :anti= 1 : 9) as the result of selective axial attack. The reaction may proceed by a radical mechanism, and reaction may not involve a samarium ester homoenolate. The reaction is extended to the intramolecular reaction of an α,β-unsaturated keto ester (8-oxonon-2-enoate) leading to the ready synthesis of a bicyclic γ-lactone.

Intermediates and Products of Ethanol Oxidation on Platinum in Acid Solution

Abstract: The adsorbate formed during ethanol oxidation in acidic solutions is studied by Fourier transform infrared reflection-absorption spectroscopy (FTIR) at constant potential, on-line (DEMS) and thermal desorption mass spectroscopy (ECTDMS). – As in the case of methanol adsorbate COad was identified by FTIR and in addition COHad by ECTDMS. On-line MS experiments showed the formation of methane during the cathodic sweep of the voltammogram. Main products of ethanol oxidation from the bulk are carbon dioxide and acetaldehyde.

Ruthenium catalyzed N-methylation of aminoarenes using methanol

Abstract: Methanol reacts with aminoarenes in the presence of a catalytic amount of ruthenium trichloride hydrate combined with tributylphosphite at 180 °C to give the corresponding N-methylaminoarenes in high yields.

Electron-transport-driven sodium extrusion during methanogenesis from formaldehyde and molecular hydrogen by Methanosarcina barkeri

Abstract: Methanogenesis from formaldehyde or formaldehyde + H2, as carried out by Methanosarcina barkeri, was strictly dependent on sodium ions whereas methane formation from methanol + H2 or methanol + formaldehyde was Na+-independent. This indicates that the reduction of formaldehyde to the formal redox level of methanol exhibits a Na+ requirement. During methanogenesis from formaldehyde, a ΔpNa in the range of -62 mV to -80 mV was generated by means of a primary, electron-transport-driven sodium pump. This could be concluded from the following results obtained on cell suspensions of M. barkeri. 1 The addition of proton conductors or inhibitors of the Na+/H+ antiporter had no effect on sodium extrusion. 2 During methanogenesis from formaldehyde + H2 a ΔΨ of -60 mV to -70 mV was generated even in the presence of proton conductors. 3 ATPase inhibitors, applied in the presence of proton conductors, had no effect on primary sodium extrusion or generation of a ΔΨ. Evidence for a Na+-translocating ATPase could not be obtained.

Formation of two-carbon acids from carbon dioxide by photoreduction on cadmium sulphide

Abstract: Aqueous solutions of CO2 containing tetramethylammonium chloride were photolysed with visible light in the presence of colloidal CdS to yield glyoxylic acid as well as formic and acetic acids and CH2O.

Methanol and Formate Kinetics in Late Diagnosed Methanol Intoxication

Abstract: In a 21-year-old subject, methanol intoxication was undiagnosed for 12 hours after admission. Only bicarbonate treatment was given during this period, although treatment later included ethanol and haemodialysis. The maximal blood methanol and formate levels were 143 (44.7) and 54.3 mg/dl (11.8 mmol/L), respectively. The delayed diagnosis uniquely allowed for an estimate of methanol elimination kinetics. Before specific treatment, methanol elimination was of zero-order, with a rate of 8.5 mg/dl/h. After admission, the formate levels remained relatively constant until blood pH was normalised by bicarbonate treatment. From this point the formate levels declined, despite an unchanged methanol elimination, indicating that the formate was eliminated faster than it was formed from methanol. Thus, formate elimination may be pH-dependent and aggressive treatment of the acidosis may increase this elimination.