A novel glycosidation of glycosyl fluoride using a designed ionic liquid and its effect on the stereoselectivity

The glycosidations of glucopyranosyl fluoride and alcohols using an ionic liquid containing a protic acid effectively proceeded under mild conditions to afford the corresponding glycosides in good to high yields. The stereoselectivity of the glycosidation was significantly affected by the ionic liquid solvent. 1-n-Hexyl-3-methylimidazolium trifluoromethanesulfonate (C₆mim[OTf]), containing a trifluoromethanesulfonate anion, and 1-(3-cyanopropyl)-3-methylimidazolium trifluoromethanesulfonimidide (CNC₃mim[NTf₂]), possessing a cyano group at the side chain of the imidazolium cation, gave the β-stereoselectivity.     

Stereocontrolled glycosidations using a heterogeneous solid acid, sulfated zirconia, for the direct syntheses of α- and β-manno- and 2-deoxyglucopyranosides

Novel α- and β-stereocontrolled glycosidations using a heterogeneous solid acid, sulfated zirconia (SO₄/ZrO₂), as an activator have been developed. The glycosidations of manno- and 2-deoxyglucopyranosyl α-fluorides with several alcohols using SO₄/ZrO₂ in MeCN proceeded α-stereoselectively, while those with the same activator in the presence of MS 5A in Et₂O occurred with β-stereoselectivity. Thus, both the α- and β-manno- and 2-deoxyglucopyranosides were effectively obtained by the present glycosidations.     

Remarkably efficient activation of glycosyl trichloro- and (N-phenyl)trifluoroacetimidates with bismuth(III) triflate

Easily handled and nontoxic Bi(OTf)₃ is a powerful activator for trichloro- and (N-phenyl)trifluoroacetimidate glycosyl donors. This catalyst allows glycosidations to be performed at low temperatures in very short times. Rewarding yields were obtained from a wide range of donors of varying reactivity.     

An approach to the highly stereocontrolled synthesis of α-glycosides. Compatible use of the very acid labile dimethoxytrityl protecting group with Yb(OTf)3-promoted glycosidation

The very acid labile dimethoxytrityl group is demonstrated to survive Yb(OTf)₃-promoted glycosidations with N-phenyl trifluoroacetimidates as the donors. In addition, the installation of this sterically demanding protecting group at the primary position of the donor allows the achievement of a very high selectivity in the synthesis of α-glycosides with a variety of saccharidic acceptors.     

A novel promoter, heteropoly acid, mediated chemo- and stereoselective sulfoxide glycosidation reactions

The chemo- and stereoselective glycosidations of sulfinylglycosides and alcohols using a heteropoly acid, H₃PW₁₂O₄₀, as a new promoter have been developed.     

Effect of dimethoxyethane in Yb(OTf)3-promoted glycosidations

1,2-Dimethoxyethane (DME) is shown to be a suitable co-solvent for sensibly improving the α-selectivity of glycosidations performed with trihaloacetimidate donors. This solvent works equally well by using either moisture stable Yb(OTf)₃ or standard TMSOTf as the promoters.     

Critical and three phase behavior in the carbon dioxide/tridecane system

The PT behavior of the carbon dioxide/normal alkane series exhibits a distinct transition in the CO₂/nC₁₃H₂₈ system. This particular diagram is characterized by two liquid—liquid—vapor (l-l-g) loci, a lower liquid-upper liquid (l-l) critical branch extending from high pressures to the upper critical end point (UCEP) and two liquid—vapor (l-g) critical branches which cross near the lower critical end point (LCEP).An experimental PTx diagram in the vicinity of the CO₂ critical point, LCEP and K point reveals the emergene at the LCEP of a l-l region which increases in size with temperture while the upper liquid—vapor (L₂-g) region diminishes, eventually disappearing at the K point. The l-l-g surface illustrates the compositional changes of each phase with temperture.Detailed Px diagrams at three temperatures between the LCEP and K point are presented and each exhibits two critical points, a l-l-g locus and curves of constant phase volume ratio which show discrete changes in both value and slope at the l-l-g locus. Graphical and numerical methods of determining the phase densities and compositions from three phase volumetric behavior are presented.     

Isothermal versus non-isothermal calorimetric technique to evaluate thermokinetic parameters and thermal hazard of tert-butyl peroxy-2-ethyl hexanoate

Liquid organic peroxides have been broadly employed in the process industries such as tert-butyl peroxy-2-ethyl hexanoate (TBPO). This study investigated the thermokinetic parameters of TBPO, a typical liquid organic peroxide, by isothermal kinetic algorithms and non-isothermal kinetic algorithms with thermal activity monitor III, and differential scanning calorimetry, respectively. An attempt has been made to determine the thermokinetic parameters by simulation software, such as exothermic onset temperature (T ₀), maximum temperature (T _max), decomposition (?H _d), activation energy (E _a), self-accelerating decomposition temperature, and isothermal time to maximum rate (TMR_iso). A liquid thermal explosion model was established for a reactor containing liquid organic peroxide of interest. From experimental results, liquid organic peroxides?? optimal conditions for avoiding a violent runaway reaction of storage and transportation were created.     

Optical and morphological characterization of polyacrylamide hydrogel and liquid crystal systems

In this work, the thermotropic liquid crystal MBBA (N-(4-methoxybenzilidene)-4-butylaniline), entrapped on hydrogels, based on cross-linked polyacrylamide (PAAm), was studied. The liquid crystalline phases of system were characterized by polarized optical microscopy (POM), refractive index, optical transmittance, scanning electron microscopy (SEM) and water loss. It was verified the presence of birefringence on hydrogel + liquid crystal. The dynamic of formation of such birefringence finished 40 days after the hydrogel synthesis. The effective birefringence Δn, i.e., the difference on refractive index of polyacrylamide hydrogel to refractive index of hydrogel + liquid crystal (Δn₁) and the difference on refractive index of liquid crystal (MBBA) to refractive index of hydrogel + liquid crystal (Δn₂) are dependent of content of acrylamide (AAm) and MBBA on hydrogel. The increase on Δn₁ and Δn₂ with the polyacrylamide content on hydrogel was attributed to decreasing of the mobility liquid crystal inside the hydrogel. Also, an increase on MBBA concentration in the polymeric matrix provides a reduction in the values of optical transmittance in the system. The morphology observed by SEM shows that hydrogel + liquid crystal is more compact that PAAm hydrogels. The presence of MBBA causes an increase in hydrophobicity. The water loss speed is favored by the increase in the amount of MBBA present in the hydrogels.     

Detection of hydrogen peroxide produced at a liquid/liquid interface using scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) was used to monitor in situ hydrogen peroxide (H₂O₂) produced at a polarized water/1,2-dichloroethane (DCE) interface. The water/DCE interface was formed between a DCE droplet containing decamethylferrocene (DMFc) supported on a solid electrode and an acidic aqueous solution. H₂O₂ was generated by reducing oxygen with DMFc at the water/DCE interface, and was detected with a SECM tip positioned in the vicinity of the interface using a substrate generation/tip collection mode. This work shows unambiguously how the H₂O₂ generation depends on the polarization of the liquid/liquid interface, and how proton-coupled electron transfer reactions can be controlled at liquid/liquid interfaces.     

Vibrational coupling in collision-induced raman scattering

The observed splitting of the collision-induced Raman band v₃ in liquid SF₆ is interpreted as vibrational exciton line splitting The bandwidth of the collision-induced Raman bands v₃ and v₆, in liquid SF₆ and v₂ and v₃ in liquid CO₂ and CS₂ can be explained by contributions from reonentational motion and from transition dipole-transition dipole vibrational coupling.     

Fischer—Tropsch synthesis in ionic liquids

A comparative evaluation of the activity of different catalysts in the Fischer—Tropsch synthesis was performed. The reaction was conducted under batch conditions (autoclave) with the catalysts suspended in nonpolar and polar media, viz., n-decane or ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate. The fused Fe—K system, cobalt carbonyl, and pivalate complex [Co(Piv)_2–x OH] _n were used as catalysts. In the most cases, the use of the non-acidic ionic liquid decreases the activity of these catalytic systems. The formation of liquid hydrocarbons С₅—С₁₄ is observed only with the combination ionic liquid—Сo₂(CO)₈. When the Fe—К catalyst is modified with a cocatalyst in the form of the ionic liquid supported on the silica gel surface ([BMIM][BF₄](30%)/SiO₂), the conversion of carbon monoxide somewhat increases (by 5—7%). The ratio paraffins/olefins/iso-paraffins/aromatics in the reaction products was shown to change in a wide range.     

Synthesis and liquid crystal properties of a novel family of oligothiophene derivatives

In order to develop novel oligothiophene-based liquid crystals capable of hydrogen bonding, new terthiophene derivatives containing an alkylamide group, N,N′-dialkyl-5,5″-dichloro-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDCl3T, n=8, 18), N,N′-dialkyl-5,5″-dibromo-2,2′:5′,2″-terthiophene-4,4″-dicarboxamide (DNC_nDBr3T, n=5, 8, 16, 18), or N,N′-dialkyl-5,5″-diiodo-2,2′:5′,2″-terthiophene-4,4″-dica-rboxamide (DNC_nDI3T, n=8, 18), were designed and synthesized, and their thermal behaviour was examined. It was found that DNC₁₈DCl3T, DNC₁₈DI3T and DNC_nDBr3T (n=8, 16, 18) form a smectic A phase and that the alkyl chain length greatly affects liquid crystal phase formation. The absence of liquid crystallinity in the corresponding ester derivatives suggests that intermolecular hydrogen bonding also plays a role in the formation of a liquid crystal phases in the DNC_nDBr3T system.     

Phase equilibria in the water-alkali metal or ammonium sulfate-synthanol systems

Solubility was studied for the first time in ternary aqueous phase-separating systems containing synthanol DS-10 or ALM-10 (polyethylene glycol monoalkyl ethers based on primary fatty alcohols, C _n H_{2n ? 1}O(C₂H₄O) _m H, where m = 8–10 and n = 10–18 (synthanol DS-10) or 12–14 (synthanol ALM-10)) and inorganic salt (NH₄)₂SO₄, Na₂SO₄, or Li₂SO₄ at 25°C. The boundaries of two-phase liquid equilibrium regions were determined. It was proposed to use the studied phase-separating systems for liquid extraction of metal ions.     

Phase diagram for the hexane-acetonitrile-tri-<Emphasis Type="Italic">n</Emphasis>-butyl phosphate-solvated thorium(IV) nitrate ternary liquid system

Phase diagrams of the hexane-acetonitrile-[Th(NO₃)₄(TBP)₂] liquid ternary system were studied at various temperatures. The system consists of two pairs of incompletely miscible liquids: hexane-acetonitrile and [Th(NO₃)₄(TBP)₂]-hexane. The two-liquid field in the [Th(NO₃)₄(TBP)₂]-hexane system decreases with increasing temperature; the upper critical solution temperature T _cr = 337.85 ± 0.25 K. The temperature effect on the immiscibility field in the hexane-acetonitrile system is insignificant. The title ternary liquid system is characterized by two homogeneous liquid fields and one two-phase liquid field at T < 338 K. One phase is depleted of acetonitrile and contains variable proportions of [Th(NO₃)₄(TBP)₂] and hexane; the other contains variable proportions of acetonitrile and [Th(NO₃)₄(TBP)₂] and a small proportion of hexane. With rising temperature, the two-phase field narrows and deforms, whereas the homogeneous liquid fields expand. At T > 338 K, the system transforms into a ternary liquid system with one pair of incompletely miscible liquids (hexane-acetonitrile).     

High pressure phase equilibria in the system 1,1,1,2-tetrafluoroethane + heptylbenzene

Vapour–liquid, liquid–liquid and liquid–liquid–vapour equilibria for the system 1,1,1,2-tetrafluoroethane + heptylbenzene were determined in the temperature range from 260 to 400 K and at pressures up to 12 MPa. The system was found to be a type II system according to the classification of Van Konynenburg and Scott. The (l₂=l₁)g critical endpoint was found at T=320.07 K and P=1.155 MPa. The mole fraction of heptylbenzene in the critical liquid phase in the critical endpoint is approximately 0.20.     

Gold-catalyzed glycosidations: synthesis of 1,6-anhydro saccharides

Various 1,6-anhydro sugars are synthesized utilizing salient features of gold-catalyzed glycosidations. All the reactions occurred under mild conditions in the presence of 7 mol % of AuBr₃ enabling easy synthesis of 1,6-anhydro sugars from corresponding 6-hydroxy propargyl/methyl monosaccharides, disaccharides, and trisaccharides in good yields.     

Reaction products of dichlorodiorganostannanes with sodium in liquid ammonia: In-situ investigations with Sn NMR spectroscopy and usage as intermediates for the synthesis of tetraorganostannanes

Dichlorodibutylstannane, dichlorodioctylstannane and dichlorodiphenylstannane were reacted with different amounts of sodium in liquid ammonia. At a molar ratio of R₂SnCl₂/Na of 1:2, polystannanes precipitated, in some cases accompanied by cyclic oligostannanes. The products resulting from mixtures with R₂SnCl₂/Na ratios of 1:3 to 1:10 were soluble and, hence, could be studied in-situ in liquid ammonia with ¹¹⁹Sn NMR spectroscopy. The compounds obtained, tin hydrides of the type R₂SnH⁻ and in certain cases distannides of the composition R₄Sn₂²⁻, formed essentially independent of the R₂SnCl₂/Na ratio; this, in contrast to views expressed in the literature. Our experiments showed that the chemical structure of the in-situ generated species did not permit to draw conclusions about the composition of the reaction products with bromoethane and vice versa - a practice commonly described. Furthermore, we observed migration of the butyl groups both in-situ during the reaction of dichlorodibutylstannane with sodium in liquid ammonia, as well as in the final reaction product. By contrast in the case of the phenyl substituent, migration was detected not during the chemical event in liquid ammonia, but only in the compounds formed. These observations imply a different mechanism for butyl and phenyl group migration.     

Biphasic ethylene polymerisation using 1-n-alkyl-3-methylimidazolium tetrachloroaluminate ionic liquid as a medium of the Cp2TiCl2 titanocene catalyst

A systematic analysis was performed on a series of 1-n-alkyl-3-methylimidazolium tetrachloroaluminates (where alkyl = ethyl, butyl, hexyl, and octyl), applied as a medium of the Cp₂TiCl₂ titanocene catalyst, to evaluate the influence of the physical properties of the ionic liquids on the polymerisation reaction carried out in the biphasic ionic liquid/hexane mode. Two alkylaluminium compounds, AlEtCl₂ and AlEt₂Cl, were used as activators. The influence of the activator/catalyst molar ratio on the performance of the ethylene polymerisation was determined for each ionic liquid studied. The best results were obtained using 1-n-octyl-3-methylimidazolium tetrachloroaluminate. For the titanocene catalyst immobilised in the ionic liquid, AlEtCl₂ turned out to be a better activator than AlEt₂Cl in our studies. The properties of the polyethylene product have also been presented.     

Thermal behaviour of the system lead(II) dodecanoate/lead acetate

Data are presented for the heats and entropies of phase changes for the system lead(II) dodecanoate/lead acetate. A phase diagram has also been constructed for the system.Optical observation under a polarising microscope suggests that the phase sequence in this system is the same as in pure lead dodecanoate i.e. crystal → G (smectic) → V₂ (cubic isomorphous) → liquid.The entropy of the V₂ → liquid transition in the mixtures is the same as for pure lead dodecanoate which suggests that addition of lead acetate to lead dodecanoate does not affect the state of aggregation of the soap in the liquid phase.