Showing papers on "Tetrahydrofuran published in 1988"

Origin of glassy crystalline behavior in the thermal properties of clathrate hydrates: a thermal conductivity study of tetrahydrofuran hydrate

Abstract: The thermal conductivity of tetrahydroruran hydrate was measured from 15 to 100 K. The present data complement earlier measurements at higher temperatures and confirm the speculation on the glassy behavior in the tehermal conductivity of clarathrate hydrates. The experimental results can be interpreted by using a resonant scattering mechanism. The interactions between localized low-frequency vibrations of the guest molecules with the acoustic phonons of the host lattice are responsible for the thermal glassy behavior of the clathrate hydrates, despite their well-defined crystalline structures

Identification of Surface Films Formed on Lithium in Dimethoxyethane and Tetrahydrofuran Solutions

Abstract: Surface films formed on lithium metal in dimethoxyethane (DME) and tetrahydrofuran (THF) solutions of ,, and were analyzed using FTIR, SIMS, and XPS spectroscopies. The films formed in both solvents were found to contain lithium alkoxides. The main reaction products detected with FTIR were in DME, and in THF. SIMS measurements are consistent with this finding. Reaction mechanisms are discussed. When the water concentration in these systems is 0.01M or greater, is formed on the lithium surface and appears to be a major component in the surface films. XPS measurements gave evidence for simultaneous salt reduction on the lithium surface in addition to the solvent reactions.

A convenient synthesis of alkali metal selenides and diselenides in tetrahydrofuran and the reactivity differences exhibited by these salts toward organic bromides. Effect of ultrasound

Abstract: Synthese des composes du titre a partir de Li, Na ou K et de selenium; les composes du titre reagissent avec des hydrocarbures halogenes pour conduire a des seleniures et des diseleniures organiques

Organopalladium and Platinum Compounds with Pentahalophenyl Ligands

Abstract: Publisher Summary This chapter discusses the existing synthetic methods that permit introduction of up to four C 6 X 5 groups in the coordination sphere of palladium or platinum as well as the reactivity of the different complexes obtained. It presents much more numerous compounds with the metals in oxidation state (II), because these provide the gateway for the preparation of other complexes involving oxidation state (I), (III), or (IV), whose chemistry is more reduced in scope. All the complexes show infrared bands characteristic of the presence of the C 6 X 5 groups, most readily observed for C 6 F 5 compounds. Some of these internal absorptions are related to the skeletal symmetry of the molecule and to the oxidation state of the metal center and have therefore been used for structural diagnosis. The information obtained from infrared (IR) data is also discussed. Because the carbanions C 6 X 15 – are not strong nucleophiles, they do not displace neutral Group Vb ligands in the starting compounds MCI 2 L 2 , and bisaryl derivatives M(C 6 X 5 ) 2 L 2 are obtained. A general method that gives the four possible complexes in yields over 85% involves the addition of aqueous HCI to the corresponding tetrakis(pentahalophenyl) compound in methanolic solution (2:1 ratio) albeit half of the pentahalophenyl groups are lost as C 6 X 5 H. The title compounds have interesting possibilities for a variety of syntheses. Platinum(II) complexes cis-Pt(C 6 X 5 ) 2 L 2 undergo redox condensation with Pt(η-C 2 H 4 )(PPh 3 ) 2 in oxygen-free refluxing tetrahydrofuran to give binuclear Pt(I) complexes. The C 5 F 5 groups show strong absorptions in the 1650, 1500, 1300, 1050, 950, and 800 cm –1 regions.

Mechanistic and kinetic studies on the photoinitiated polymerization of tetrahydrofuran

Abstract: Polymerization of tetrahydrofuran (THF) (bulk) promoted by a free radical source, 2,2-dimethoxy-2-phenyl acetophenone (DMPA), in the presence of 4,4′-di-(methylphenyl)iodonium hexafluorophosphate was studied in detail. Rate dependence of the polymerizing system on both DMPA and the iodonium salt was studied dilatometrically. Rate saturation for the iodonium salt was attributed to the formation of iodobenzene, which may react with propagating cations to form an iodonium salt. DMPA was shown to be an efficient transfer agent in the cationic polymerization of THF. A transfer constant for DMPA was estimated to be 2.8 and, whilst the precise details of the overall mechanism cannot be deduced from the present results, it may result in functionalized polytetrahydrofuran chains having photochemically active end groups.

FT-IR spectra of 90 K films of simple, mixed, and double clathrate hydrates of trimethylene oxide, methyl chloride, carbon dioxide, tetrahydrofuran, and ethylene oxide containing decoupled water-d2

Abstract: The spectroscopic investigation of clathrate hydrates prepared by using low-temperature thin-film techniques has been extended to several new gases. These gases have included a highly polar gas (trimethylene oxide or TMO) the simple hydrate of which grows readily from a vapor beam at 120 K, a slightly less polar gas (methyl chloride) the simple hydrate of which grows if the vapor beam is incident onto a crystalline clathrate hydrate base at 125 K, and a nonpolar gas (carbon dioxide) which apparently can only be enclathrated as the mixed hydrate by using a highly polar help gas (e.g., ethylene oxide (EtO)). These structure I hydrates as well as the structure II hydrate of tetrahydrofuran have been prepared under conditions of temperature/base-doping such that no mobile protons exist during the deposit. As a result, it has been possible to isolate intact D/sub 2/O molecules in the water network of the crystalline hydrates. The guest-molecule spectra, all obtained at 90 K, show (a) the apparent generality of the rule that guest-molecule stretching-mode frequencies decrease with an increase in cage size and (b) that the effective size of the structure I small cage increases as the size of the molecule occupying the large cagemore » increases.« less

Structure and reactivity of lithium diphenylamide. Role of aggregates, mixed aggregates, monomers, and free ions on the rates and selectivities of N-alkylation and E2 elimination

Abstract: Rate studies of the N-alkylation of lithium diphenylamide with n-butyl bromide in THF/hydrocarbon mixtures (THF = tetrahydrofuran) are described. Dramatic induction periods observed for the N-alkylation at low THF concentrations are ascribed to the intervention of reactive mixed dimers of lithium diphenylamide and lithium bromide. In the presence of 1 .O equiv of added lithium bromide, the alkylation rate exhibits a first-order dependence on both the mixed aggregate and n-butyl bromide concentrations, supporting a pathway involving direct mixed aggregate alkylation. Incremental changes in the THF concentration uncovered contributions from several additional species. Regions of first or higher order followed by zero-order dependence on the THF concentration are interpreted as an equilibrium shift to a more reactive, highly solvated species assigned as a monomer (or ion pair). At elevated THF concentrations, the alkylation rate increases sharply as a function of the THF concentration, indicating the contribution of an additional, highly solvent dependent alkylation pathway. This latter pathway exhibits fractional-order dependence on the amide concentration, approximate first order dependence on the n-butyl bromide concentration, and a seventh-order dependence on the THF concentration. Common ion rate inhibitions by lithium perchlorate and lithium tetraphenylborate, a significant dependence on dielectric effects, and the observed reaction orders implicate a mechanism involving predissociation of free lithium ions. The appearance of competitive eliminations of the n-alkyl bromides to form 1-alkenes coincides with the appearance of the free ion alkylation pathway.

Synthesis, Characterization, and Application of Poly[Substituted Methylene]S

Abstract: Radical polymerization of fumaric acid derivatives, such as dialkyl fumarates, gave polymers consisting of a less-or nonflexible substituted polymethylene structure. The yield and molecular weight of the polymers produced increased as the bulkiness of the ester substituents increased. For example, when di-t-butyl fumarate was polymerized in bulk with azocyclohexanecarbonitrile (20 mmol/L) at 80°C for 6 h, polymer with M n of more than 100 000 was produced in more than 80% yield. The polymers obtained were colorless powders and did not melt before degradation at ∼250°C, but they were soluble in such organic solvents as benzene, carbon tetrachloride, tetrahydrofuran, and dioxane. A transparent brittle film or fiber was obtained from toluene solution. Some properties and possibilities for application of these polymers are described and discussed.

Structure and reactivity of lithium amides. Lithium-6, carbon-13, and nitrogen-15 NMR spectroscopic studies and colligative measurements of lithium diphenylamide and lithium diphenylamide-lithium bromide complex solvated by tetrahydrofuran

Abstract: /sup 6/Li, /sup 13/C, and /sup 15/N NMR spectroscopic studies of lithium diphenylamide in THF/hydrocarbon solutions (THF = tetrahydrofuran) detected two different species. /sup 6/Li and /sup 15/N NMR spectroscopic studies of (/sup 6/Li, /sup 15/N)lithium diphenylamide showed the species observed at low THF concentrations to be a cyclic oligomer. Structural analogies provided strong support for a dimer while colligative measurements at 0/degrees/C indicated the dimer to be di- or trisolvated. On the basis of the observed mass action effects, the species appearing at intermediate THF concentrations is assigned as a contact or solvent-separated ion-paired monomer. Lithium diphenylamide forms a 1:1 adduct with lithium bromide at low THF concentrations. A combination of /sup 6/Li-/sup 15/N double labeling studies and colligative measurements supports a trisolvated cyclic mixed dimer structure. Although detailed spectroscopic studies at elevated THF concentrations were precluded by high fluctionality, the similarity of the /sup 13/C chemical shifts of lithium diphenylamide in the presence and absence of lithium bromide provide indirect evidence that the mixed dimer undergoes a THF concentration dependent dissociation to the monomeric amide and free lithium bromide. 24 references, 9 figures, 2 tables.

Light‐induced cationic polymerization

Abstract: Mechanistic studies concerning the initiation of cationic chain reactions with the aid of diaryliodonium and triarylsulphonium salts are reviewed and recent results are presented. Laser flash photolysis in combination with pulse radiolysis experiments revealed evidence for a triplet path occurring parallel to the singlet deactivation route of electronically excited diphenyliodonium ions. The radical cations PhI+− and Ph2S+− were found to react selectively with nucleophiles, the former being more reactive than the latter. Moreover, various aspects of the photo-initiated free radical-promoted cationic polymerization of typical monomers such as tetrahydrofuran and butyl vinyl ether with the aid of acylphosphine oxides and other free radical initiators are discussed.

Facile preparation of π-arene complexes of ruthenium [(η5-C5Me5)Ru(arene)]X including a π-pyridine and the first π-furan derivatives

Abstract: Zinc reduction of (Cp*RuCl2)n(Cp*=η5-C5Me5) in tetrahydrofuran or acetone affords ‘(Cp*RuCl)n’ which reacts smoothly with arenes with or without KPF6, even at –50 °C, to give the π-complexes [Cp*Ru(arene)]X (arene = benzene, 3-methylthiophene, pyridine, 2,6-lutidine, 3,5-lutidine, or furan) including the first detected π-furan complex in solution and a rare example of a π-pyridine complex; the latter is proposed as a model for pyridine co-ordination in hydrodenitrogenation reactions, however, the mode of pyridine co-ordination is highly dependent on the polarity of the solvent

Electrochemical Stability of LiMF6 ( M = P , As , Sb ) in Tetrahydrofuran and Sulfolane

Abstract: The electrochemical stability of LiSbF6 and LiPF6 in aprotic organic solvents has been investigated. Electrochemical studies, conductivity measurements, and open-circuit stability tests were conducted on LiSbF6 in tetrahydrofuran and sulfolane. Cyclic voltammetric studies of SbF6(-) were compared with those of AsF6(-) and PF6(-) anions. Sb(V) was reduced to Sb(III), and then to Sb(0). AsF6(-) was reduced to AsF3, while no reduction of PF6(-) was observed. The reduction products of AsF6(-) and SbF6(-) passivated the glassy carbon electrode, presumably due to LiF precipitation. Peak potentials were observed to shift in the positive direction as a function of concentration. This was accounted for on the basis of a follow-up chemical reaction.

Zur Kenntnis des stabilen Silanimins tBu2SiN ? SitBu3 und seiner Donoraddukte

Abstract: Das blasgelbe, feste, unter Normalbedingungen metastabile, extrem wasserempfindliche Silanimin tBu2SiNSitBu3 (3) entsteht durch Umsetzung von tBu3SiNa mit tBu2SiClN3 in Dibutylether bei ca. −50°C. Es bildet Addukte 3 · D mit Donoren D (Koordination mit dem ungesattigten Siliciumatom in 3); die Lewis-Basizitat der Donoren bezuglich 3 wachst in der Reihenfolge: NEt3, OEt2 (keine Koordination) < Ph2CO < NMe2Et < THF (Tetrahydrofuran). 3 bildet (ahnlich wie 3 · D) mit Wasser, Methanol, Benzol Insertionsprodukte in die OH- bzw. CH-Bindung, mit Propen, Isobuten, Aceton En-Reaktionsprodukte und mit Methylvinylether, Silylaziden Cycloaddukte (vgl. Schema 1, Produkte 7 bzw. 6, 8 bzw. 9, 11). Distickstoffoxid reagiert mit 3 bzw. 3 · THF [wohl auf dem Wege uber ein Cycloaddukt (10, Schema 1) sowie das Silanon tBu2SiO als Reaktionszwischenprodukte] zu einer cyclischen Verbindung (12) bzw. zu tBu2RSiOSitBu2NHSitBu3 (13) (R = Tetrahydro-1-furanyl). Ethyldimethylamin reagiert mit 3 · THF unter Offnung des THF-Rings und Bildung von Me2N[CH2]4OSitBu2NHSitBu3 (14). On the Stable Silanimine tBu2SiNSitBu3 and of Its Donor Adducts Pale yellow, solid silanimine tBu2SiNSitBu3 (3), metastable at normal conditions and extremely sensitive to water, is prepared by reaction of tBu3SiNa and tBu2SiClN3 in dibutyl ether at about −50°C. It forms adducts 3 · D with donors D (coordination with the unsaturated silicon atom in 3), the basicity of which relative to 3 increases in the row NEt3, OEt2 (no coordination) < Ph2CO < NMe2Et < thf (tetrahydrofuran). 3 (similarly to 3 · D) reacts with water, methanol, benzene under formation of insertion products into the OH or CH bond, with propene, isobutene, acetone under formation of ene reaction products, and with methyl vinyl ether, silyl azides under formation of cycloadducts (cf. Scheme 1, products 7 or 6, 8 or 9, 11). Dinitrogen oxide transforms 3 or 3 · thf [obviously by way of a cycloaddukt (10, Scheme 1) and of silanone tBu2SiO as reaction intermediates] under formation of a cyclic compound (12) or tBu2RSiOSitBu2NHSitBu3 (13) (R = tetrahydro-1-furanyl), respectively. Ethyldimethylamine reacts with 3 · thf under opening of the thf ring and formation of Me2N[CH2]4OSitBu2NHSitBu3 (14).

Some sterically hindered lithium alkylbromo- and alkylchloro-magnesates, -cadmates, and -manganates. Crystal and molecular structures of [Li(thf)2(µ-Br)2Mg{C(SiMe3)3}(thf)], [Li(thf)4][{Cd[C(SiMe3)3]}3(µ-Br)3(µ3-Br)]·0.5C6H12, [{Li(thf)}3(µ3-Br)3(µ3-OSiMe3)Cd{C(SiMe3)3}], and [Li(thf)4][{Mn[C(SiMe3)3]}3(µ-Cl)4(thf)](thf = tetrahydrofuran)

Abstract: Tris(trimethylsilyl)methyl-lithium reacts with anhydrous magnesium(II) bromide to give the magnesate [Li(thf)2(µ-Br)2Mg{C(SiMe3)3}(thf)](1), which has been shown by an X-ray study to have a structure with two bridging bromine atoms between lithium and magnesium. With cadmium(II) bromide, Li{C(SiMe3)3} gives the tricadmate [Li(thf)4][{Cd[C(SiMe3)3]}3(µ-Br)3(µ3-Br)]·0.5C6H12(2)(C6H12= cyclohexane), in which the anion has a structure based on a Cd3Br4 cube with one corner missing. In the presence of traces of moisture, the neutral compound [{Li(thf)}3(µ3-Br)3(µ3-OSiMe3)Cd{C(SiMe3)3}](3), also with a cage structure, is obtained. Both (2) and (3) can be converted into CdBr{C(SiMe3)3}, and Cd(OH){C(SiMe3)3}. The chloride CdCl{C(SiMe3)3} is dimeric in the gas phase. The reaction between tris(dimethylphenylsilyl)methyl-lithium and cadmium(II) bromide yields the cadmate Li(thf)2CdBr2{C(SiMe2Ph)3} which can be converted into Cd(OH){C(SiMe2Ph)3}, CdBr{C(SiMe2Ph)3}, or Cd(OMe){C(SiMe2Ph)3}. The reaction between Li{C(SiMe3)3} and anhydrous manganese(II) chloride gives the trimanganate [Li(thf)4][{Mn[C(SiMe3)3]}3(µ-Cl)4(thf)], in which the anion has been shown by X-ray diffraction to have a cage structure related to that of the anion in (2). In each C(SiMe3)3 group the three SiMe3 fragments are twisted from fully staggered positions so the group as a whole is chiral. In some tris(trimethylsilyl)methylmetal compounds left- and right-handed C(SiMe3)3 groups alternate in the crystal lattice; in other chiralities are arranged randomly.

Metal vapour synthesis of bis{1,3-bis(trimethylsilyl)cyclopentadienyl}-calcium, -strontium, and -barium compounds; X-ray structures of [M{η-C5H3-1,3-(SiMe3)2}2(thf)](M = Ca, Sr; thf = tetrahydrofuran)

Abstract: Cocondensation of C5H4(SiMe3)2, hexane, and metal vapour at –196 °C yields M{C5H3-1,3-(SiMe3)2}2[M = Ca (1), Sr (2), and Ba (3)] which reversibly bind tetrahydrofuran (thf); X-ray structure determinations on the adducts [M{η-C5H3-1,3-(SiMe3)2}2(thf)], [M = Ca (4) Sr, (5)] show they are monomeric bent metallocenes, M–C, M–O 2.662(10)–2.718(9), 2.310(9), (4), 2.78(4)–2.84(5), 2.49(3)A, (5); Centroid–M–Centroid, 139.1, (4), 134°, (5).