弱碱作用下从叔醇简便地合成烯烃

用甲磺酸酐和三乙胺作为脱水剂, 发展了一种从叔醇合成烯烃的简便方法, 反应时间短, 温和的条件和高产率使该方法可以快速地从叔醇合成烯烃.     

甲基乙烯基亚砜的合成

含亚砜基功能高分子可用作高分子药物载体,高分子螯合剂,高分子催化剂及气体分离膜材料等,近年来已引起各国学者的兴     

Acidic properties of fiberglass materials

Acidic properties of fiberglass materials were investigated using the adsorption of NH₃ and the rate of isopropanol dehydration. It is shown that the specific catalytic activity of such materials and amount of the Br?nsted acid sites per their surface unit (100 ?²) exceed considerably those in zeolite HZSM-5.     

High-performance membranes for pervaporation II. Crosslinked poly(vinyl alcohol)–poly(acrylic acid) blends

Dense membranes made by crosslinking of poly(vinyl alcohol) (PVA) with poly(acrylic acid) (PAA) were prepared and tested in pervaporation and differential permeation of water–alcohol mixtures. Instead of a decrease of permeation flux as generally observed with most crosslinking agents, an increase in the permeability was observed with PAA crosslinked membranes at low PAA contents. The permeation flux increases with PAA contents in the polymer with no selectivity reduction for membranes containing less than 15 wt. % PAA. The membranes show good performances to water–2-propanol and water–ethanol mixtures, i.e. high fluxes and high selectivities to pure water. The membranes were stable and highly permeable to water. The enhancement of the permeability of PVA can be explained by a reduced crystallinity and an improved diffusivity due to the presence of PAA.     

Regioselective dehydration of axial and equatorial tertiary alcohols with α-methyl group in the cyclohexane ring by Swern’s reagent

Swern’s reagent (a complex of oxalyl chloride with DMSO) was shown to dehydrate tertiary alcohols containing an α-methyl group in the cyclohexane ring. Dehydration of equatorial alcohols affords mixtures of isomeric compounds where isomers with an exocyclic double bond dominate, whereas isomers with an endocyclic double bond prevail in the products of dehydration of axial tertiary alcohols. Thus, Swern’s reagent can serve as a chemical test to determine the configuration of tertiary alcohols containing an α-methyl group in cyclohexane ring. The composition of the products of dehydration of these alcohols with Swern’s reagent is similar to that obtained by their dehydration with POCl₃ in pyridine. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 800–803, April, 1997.     

Theoretical investigation of the formic acid decomposition kinetics

Decomposition of formic acid (HCO₂H) proceeds via three unimolecular channels: dehydration, decarboxylation, and dissociation, the latter expected to be of minor contribution to the overall kinetics. In addition, despite the similar values reported for the individual activation energies for the dehydration and decarboxylation reactions, experimental works have shown that the former is dominant in the reaction mechanism. These reactions show pressure-dependent rate coefficients, and the high-pressure condition is not yet verified at atmospheric pressure. This work aims to investigate the influence of temperature and pressure on the rate coefficients. Hence, theoretical calculations at the CCSD(T)/CBS level have been performed to accurately describe the unimolecular reaction and Rice-Ramsperger-Kassel-Marcus (RRKM) rate coefficients have been calculated and integrated for the prediction of k(T,P) rate coefficients, adopting both strong and weak collision models, over the intervals 0.5-10 atm and 298-2200 K. Our results suggest that the isomerization path is important and explains the preference for the (CO + H₂O) channel. Rate coefficients for the (CO₂ + H₂) and (CO + H₂O) formations are given, in s⁻¹, as exp(−34404/T) and exp(−33785/T), respectively. The dissociation limit of 107.29 kcal mol^–1, with respect the Z-HCO₂H conformer, leading to OH + HCO, via a barrierless potential curve, with rate coefficients, in s⁻¹, expressed as k_HCO+OH(T) = 1.68 × 10¹⁷ exp(−56018/T). Temperature and pressure dependence for the HCO + OH → CO₂ + H₂ and HCO + OH → CO + H₂O reactions have also been estimated.     

Synthesis and characterization of SnOx/Al2O3 derived gel catalysts

SnO_x/Al₂O₃ catalysts were prepared by the sol-gel method using as starting reactants aluminium-tri-s-butoxide and (i) tetrabutyltin, (ii) tin tetrachloride and (iii) tin tetra-t-amyloxide. The gel derived catalysts show acidities of 0.72, 1.08 and 1.05 mol NH₃/m² and BET areas of 91, 112 and 189 m²/g. The activity and selectivity pattern for isopropanol decomposition were found to depend strongly on the tin precursor used.     

On the structures of X- and Y-type zeolites. Structural changes within the cavities of Na-X during dehydration

Samples of partially dehydrated and dehydrated Na-X were examined structurally by X-ray diffraction methods, revealing the progressive structural changes which occur as water is removed. In general, the total number of Na atoms in the small pore region remains unchanged by dehydration (ca. 18 per unit cell), as does the total number (non-mobile) in the 12-ring and site III regions (ca. 39). The site II population, however, is more than doubled by dehydration, from about 12 to about 25 Na, accounting for most of the loss from the mobile phase. The 12-ring sites, which in hydrated samples appear to comprise pairs of centrosymmetrically related [Na(H₂O)₂]⁺ units, rearrange during dehydration, with site III becoming an important location of Na atoms. At intermediate levels of dehydration, the remaining localized water molecules in the 12-ring region are found in a variety of associations with Na atoms, including perhaps as [Na(H₂O)₅]⁺ units whose Na atom occupies site III. In a sample containing H₃O⁺ ions as well as Na⁺ as counter ions, site II was found to have a very low occupancy.     

Mechanism for binding to the flexible cavity of permethylatedα-cyclodextrin

The cavity of -cyclodextrin (-CDx) is too small to includeo-toluic acid (o-TA) while it is filled byp-toluic acid (p-TA) to form a relatively stable inclusion complex. Such strict selectivity is ascribed to a rigid structure of the -CDx cavity which is stabilized by intramolecular hydrogen bonds between the O(2) hydroxyl groups and the O(3) hydroxyl groups of adjacent glucopyranose units. Meanwhile, the substrate selectivity of hexakis (2,3,6-tri-O-methyl)--CDx (TMe--CDx) remains somewhat obscure because of the flexible nature of its cavity. The absence of the intramolecular hydrogen bonds seems to cause the flexible nature of the TMe--CDx cavity leading to an induced-fit type inclusion. The structures of the inclusion complexes have been presented on the basis of the¹H NMR data. The thermodynamic parameters indicate that the complexation of TMe--CDx witho-TA orp-TA is the entropically favorable process. The entropically favorable complexation of TA with TMe--CDx seems to occur through dehydration from the CO₂H group of TA which is situated at the hydrophobic CDx cavity. The dipole-dipole interaction has been regarded as the force which dominates the orientation of the polar guest molecule in the CDx cavity.