Showing papers on "Lewis acids and bases published in 1981"
TL;DR: The Lewis acids (CH3)3SiOSO2CF3 (3), CH3 5S iOSO2C4F9 (6), and CH3 3SiClO4 (4) are highly selective and efficient Friedel-Crafts catalysts for nucleoside formation form silylated heterocycles and peracylated sugars as discussed by the authors.
Abstract: The novel Lewis acids (CH3)3SiOSO2CF3 (3), (CH3)5SiOSO2C4F9 (6), and (CH3)3SiClO4 (4) are highly selective and efficient Friedel-Crafts catalysts for nucleoside formation form silylated heterocycles and peracylated sugars as well as for rearrangements of persilylated protected nucleosides. With basic silylated heterocycles these new catalysts give much higher yields of the natural N-1-nucleosides than with SnCl4.
772 citations
TL;DR: In this article, the acid strength of SbF 5 -SiO 2 -Al 2 O 3 was analyzed and showed that both Bronsted and Lewis acid sites were present on the surface when SiO 2 −Al 2 -O 3 was treated at low temperatures below 100 °C, but only Lewis acids sites when treated at 300 °C.
109 citations
TL;DR: In this paper, BF4-doped polypyrrole grown on platinum was used as electrodes in a series of reactions, and they were found to be quite stable and nonporous; they generally do not perturb the redox reactions of dissolved species and they display rapid surface-substrate electron transfer kinetics.
Abstract: Films of BF4-doped polypyrrole grown on platinum, hereafter termed [Pt]polypyrrole, were used as electrodes in a series of reactions. These organic electrodes are found to be quite stable and nonporous; they generally do not perturb the redox reactions of dissolved species and they display rapid surface-substrate electron-transfer kinetics. The polypyrrole films are sensitive to the presence of Lewis bases in solution, which apparently act as nucleophiles, leading to degradation of the electrode properties
84 citations
TL;DR: In this paper, Fourier transform infrared spectroscopy was used to identify three forms of adsorbed CO, namely linearly adorbed, diadsorbed and μ-bridge adorbs.
84 citations
81 citations
TL;DR: The use of these reagents for Lewis acid catalyzed ene, Diels-Alder and cycloaddition reactions and Claisen rearrangements is described in this paper.
66 citations
65 citations
65 citations
TL;DR: Methyl 2,3-dihydrofurane-3-carboxylates are synthesized from siloxycyclopropaneesters and ketones in the presence of TiCl 4 with good yields as discussed by the authors.
59 citations
TL;DR: In this paper, the possibilities of using some coordination compounds to prepare III-V thin films by the metalorganic CVD process are examined, and the importance of various parameters, particularly the partial pressure of the starting product, the bond strength of the coordination compounds, the nature of the Lewis base and acid, the type of elimination of the substituents bonded to the III and V elements, are pointed out.
55 citations
TL;DR: The adsorption of H2S, CH3SH and (CH3)2S has been studied by gravimetry and infrared spectroscopy in this paper, showing that 60 µmol g−1 are irreversibly coordinated to stronger sites of this type.
Abstract: The adsorption of H2S, CH3SH and (CH3)2S has been studied by gravimetry and infrared spectroscopy. Some experiments have been carried out with preadsorbed pyridine as a poison. The results show that (CH3)2S is bonded to Lewis acid sites and that 60 µmol g–1 are irreversibly coordinated to stronger sites of this type. Dissociative chemisorption has been observed for H2S and CH3SH. Poisoning experiments lead us to conclude that the first adsorption steps involve either a coordinative adsorption (ca. 30 µmol g–1) or a hydrogen bond between a surface basic oxygen atom and the H atom of the SH bond (ca. 50 µmol g–1). The reversible adsorption of CH3SH is thought to occur by these two processes besides another one in which the S atom is H bonded to a hydroxyl surface group. These results clarify the nature of the adsorption sites of alumina.
TL;DR: Nine 9-beta-D-Ribofuranosylpurine-6-carboxamide compounds showed significant in vitro antiviral activity at nontoxic dosage levels and were tested against several RNA and DNA viruses in cell culture.
Abstract: To examine the structural parameters necessary for antiviral efficacy of certain purine nucleosides, several 9-beta-D-ribofuranosylpurine-6-carboxamides have been synthesized. Glycosylation of the Me3Si derivative of purine--6-carboxamide with protected ribofuranose in the presence of a Lewis acid gave the blocked nucleoside which on deprotection furnished 9-beta-D-ribofuranosyl-6-iodopurine with cyanide ion. Certain 2-amino- and 2-methyl-9-beta-D-ribofuranosylpurine-6-carboxamides have also been prepared. 8-Carbamoylguanosine (16) has been prepared by homolytic acylation of the parent nucleoside. These compounds were tested against several RNA and DNA viruses in cell culture. 9-beta-D-Ribofuranosylpurine-6-carboxamide (6a), the corresponding 6-thiocarboxamide (7b), and 4-amino-8-(beta-D-ribofuranosylamino)pyrimido[5,4-d]pyrimidine (8) showed significant in vitro antiviral activity at nontoxic dosage levels. 6a employed in the treatment of Rift Valley fever virus infected mice at 50 (mg/kg)/day gave a 55% survival rate on day 21 compared to a 30% survival in the controls.
TL;DR: In this paper, the role of the oxo-or imido-ligand as bridge for binding the Lewis acid and the nature of the active species in meta-thesis are discussed.
Abstract: Three families of molecular complexes for the homogeneous metathesis of olefins are described; the role of the oxo-or imido-ligand as bridge for binding the Lewis acid and the nature of the active species in meta-thesis are discussed.
TL;DR: In this article, the termo-dynamically unfavourable α-anomers are formed predominantly in C-glycopyranosides with enol-silanes.
Abstract: Acetylated glycals undrgo Lewis acid-catalysed condensations with enol silanes in virtually quantitative yields to form C-glycopyranosides in which the termo-dynamically unfavourable α-‘anomers’ are formed predominantly.
TL;DR: In this paper, the stereochemistry of cyclodehydration of meso -2,5-hexanediol was investigated and the previously assumed S N 2 mechanism for acid-catalysed ring-closure was found to hold in most cases.
Patent•
19 Aug 1981TL;DR: In this paper, a tri-halogenated polystyrene flame retardant for synthetic resins is described, in the presence of a catalytic amount of a Lewis acid.
Abstract: There is disclosed a process for producing a tri-halogenated polystyrene flame retardant for synthetic resins, whereby high molecular weight polystyrene is reacted with bromine chloride in a chlorinated hydrocarbon solvent, under substantially anhydrous conditions, in the presence of a catalytic amount of a Lewis acid.
TL;DR: The stereospecific polymerization of diolefins using new catalytic systems based on less conventional transition metal complexes is reviewed in this article, where two families of catalysts based on new complexes of π-allyl type of actinide and lanthanide elements, as well as three component systems formed by rare-earth metal alkoxides, aluminum alkyls, and a Lewis acid are described.
Abstract: The stereospecific polymerization of diolefins using new catalytic systems based on less conventional transition metal complexes is reviewed. In particular, two families of catalysts based on new complexes of π-allyl type of actinide and lanthanide elements, as well as three component systems formed by rare-earth metal alkoxides, aluminum alkyls, and a Lewis acid are described. A peculiarity of both actinide and lanthanide catalysts is their ability to give, at very low concentration, extremely high cis diolefin polymers and copolymers in aliphatic solvents.
TL;DR: In this paper, the reaction of α-methoxyurethanes with trialkyl phosphites in the presence of Lewis acid catalysts was studied on twelve examples. But it was not shown to be a new carbon-phosphorous bond forming reaction.
TL;DR: The tetrahedral pnigogenic clusters E n [Co(CO) 3 ] 4 - n (EP, As; n = 1-3) react with soft Lewis acids and bases to give products of substitution and transformation of the cluster as discussed by the authors.
TL;DR: In this paper, the total synthesis of (±)-modhephene (2 ) and (µ)-epimodhephemide (3 ) were reported.
Patent•
24 Feb 1981
TL;DR: A process for the preparation of electrically conductive hetero-polyphenylenes, having conductivities greater than 10 -2 S/cm, is described in this article.
Abstract: A process for the preparation of electrically conductive hetero-polyphenylenes, having conductivities greater than 10 -2 S/cm, wherein from 0.5 to 35 percent by weight of a strong Lewis acid having a pk a of from -10 to +4, preferably AsF 5 , SbF 5 , UF 6 , HClO 4 , NO + SbF 6 - , NO 2 + SbF 6 - , NO + AsF 6 - , NO + PF 6 - , NO 2 + PF 6 - , NO + BF 4 - , NO 2 +BF 4 - , NO + ClO 4 - , (CF 3 ) 2 SO 4 , 2,4,6-trinitrophenol, 2,4,6-trinitrophenylsulfonic acid or 2,4,6-trinitrobenzoic acid, is added to a hetero-polyphenylene in the absence of moisture and of oxygen.
TL;DR: In this paper, the stability of estertin chlorides with nitrogen donors has been investigated in CH 2 Cl 2 solution at 25 ± 1°C by UV and IR methods, and the following conclusions can be made: (i) Cl 3 SnCH 2 CH 2 CO 2 Me appears as strong a Lewis acid as MeSnCl 3 towards bidentate ligands and a single py molecule (from K 1 values); (ii) Cl 2 SnCl 3 · Me · D (D = monodentate ligand) is a poorer acceptor than MeSn
Patent•
23 Feb 1981
TL;DR: In this article, the authors present a disclosure process for the rearrangement of alpha-haloketals in the presence of a Lewis acid, which is suitable for the preparation of esters of alkanoic acids.
Abstract: OF THE DISCLOSURE Process for preparing esters of alkanoic acids via rearrangement of alpha-haloketals in the presence of a Lewis acid. The reaction is preferably carried out in the presence of catalytic amounts of a Lewis acid and of a diluent at a temperature in the range from about 0° to the reflux temperature of the diluent. The esters thus obtained are useful as inter-mediate products for preparing drugs. The process involves the preparation of new alpha-haloketals.