Synthesis and characterization of non-symmetrical liquid crystals containing a cholesteryl ester moiety

In this paper,a series of chiral non-symmetrical liquid crystals(nBA-chol)consisting of a cholesteryl ester moiety as chiral entity and a biphenyl aromatic core with different terminal alkyl chain has been synthesized and investigated for their liquid crystalline properties.Effects of numbers of methylene units in the terminal alkyl chain on the phase transition temperatures and on the temperature-dependent pitch lengths of the chiral liquid crystals have been studied.The long terminal alkyl chain tends ...     

Flow microcalorimetry of adsorption of anionic alkyl surfactants at the solid/liquid interface

Flow microcalorimetry was used to study the adsoption of anionic alkyl surfactants from aque--ous solutions onto silica. It is found that for alkyl sulfate systems the strength of adsorption interactionincreases with increases of the alkyl chain length and decreases as temperature rises. The adsorptiondepends only on monomer concentration of the solution even above the critical micelle concentration(cmc). The assumption is made that the adsorption involves only a transfer of monomers from bulkto surface phase. A different adsorption mechanism is operative for the alkyl carboxylate.     

Chemoselective desulfurization-fluorination/bromination of carbonofluoridothioates for the O-trifluoromethylation and O-bromodifluoromethylation of alcohols

Herein, a method for synthesizing various alkyl trifluoromethyl and alkyl bromodifluoromethyl ethers using carbonofluoridothioates(R–OC(=S)F) as precursors has been described. Carbonofluoridothioates were obtained upon the reaction of an alcohol and S=CF_2 generated via the decomposition of an SCF_3 anion, and then selectively transformed into their corresponding trifluoromethyl and bromodifluoromethyl ethers upon changing the reaction conditions. This transformation has also been extended to the one-pot, two-step conversion of alcohols into alkyl trifluoromethyl ethers. A series of alkyl bromodifluoromethyl ethers has also been synthesized. These compounds open up a new avenue for the synthesis of a wide range of useful fluorinated products. In addition, this method is suitable for the late-stage introduction of trifluoromethyl ethers in complex small molecules.     

A facile and convenient method for synthesis of alkyl thiocyanates under homogeneous phase transfer catalyst conditions

A simple and environmentally friendly method is described for the efficient conversion of alkyl halide to alkyl thiocyanate using tetrabutylammonium bromide （TBAB） as a phase transfer catalyst. The reactions occur in water and furnish the corresponding alkyl thiocyanate in high yields. No evidence for the formation of isothiocyanates as by-product of the reaction was observed and the products were obtained in pure form without further purification.     

Influence of terminal alkyl chain length on helical twisting property of chiral 1,2-propanediol derivatives

In this study,a novel series of chiral 1,2-propanediol derivatives with different terminal alkyl chain length were synthesized and characterized by FT-IR,~1H NMR and DSC.After doped into a nematic liquid crystal host,all the chiral dopants induced chiral nematic liquid crystals exhibiting a helix inversion with temperature variation.The results indicate that terminal alkyl chain length has a prominent influence on helical twisting property of the chiral dopants.With increasing the terminal alkyl chain le...     

SYNTHESES OF HINDERED ALKYL PHOSPHONATES AND PHOSPHONIC & PHOSPHINIC ACIDS

A series of di-n-hexyl alkyl phosphonates with bulky substituent on phosphorus was synthesized by PTC P-alkylation using crown ether.Upon saponification of the resulting di-n-hexyl alkylphosphonates in the presence of crown ether or quaternary ammonium halide, corresponding mono-hexyl esters of alkyl phosphonic acids were prepared.Ultrasonic wave, as we found, can catalyze the reaction between dialkyl phosphite & metallic sodium and hydrolysis of dihexyl alkyl phosphonates.A series of di-t-alkyl phosphinic acids were synthesized by the reaction of Grignard reagent with PCl_3 followed by oxidation with 30% H_2O_2.It was found that the reaction between dibutyl phosphite and Grignard reagent of t-alkyl chloride is a new synthetic method for the preparation of mono-esters of highly hindered alkyl phosphonic acids.     

PHOTOREDUCTION OF ALKYL VIOLOGENS AND POLYVlOLOGENS IN 2-PROPANOL AQUEOUS SOLUTION

In order to study the effect ofalkyl chain length and the polymer effect on the photoreduction behavior of some viologens, a series of alkyl viologen, polyviologen and bisviologen compounds have been synthesized. In the presence of excess 2-propanol, the initial photoreduction of alkyl viologens and polyviologens follow the peudo--seeond--order reaction, the calculated rate constants are related to the alkyl chain length: In addition, the intramoleeular association of radical cations of polyviologens has been found even in dilute solution. However the extent of association is varied with the aikyl chain length. The observed polymer effect of polyviologens in the photoreduetion is significant which can be explained in terms of the nature of second order reaction.     

Hypervalent iodine-mediated gem-difluorination of vinyl halides enabled by exclusive 1,2-halo migration

β-Difluorinated alkyl halides are of significant value in the modular synthesis of gem-difluorinated molecules. An exclusive 1,2-halo migratory gem-difluorination of vinyl halides with in situ-generated PhIF_2·HF is described. This protocol provides a general and practical approach towards a wide variety of β-difluorinated alkyl bromides. Both α-and β-bromoalkyl alkenes are suitable substrates, leading to two distinct types of products. The extension of this protocol to vinyl chloride and iodide are also feasible.The synthetic versatility of this method has been highlighted by the late-stage modification of complex small molecules and further transformations of the β-difluorinated alkyl halides to valuable CF_2-containing compounds.     

Radical Addition and Substitution Reactions of (η6-Arene)-tricarbonylmetal Complexes

We report here the first alkyl radical additions of (η6-arene)tricarbonylmanganese complexes in the presence of alkylmercury chloride and NaI (Eq. 1). The mechanism was postulated to be the alkyl radical addition to ArMn- (CO)+3 cation to form the corresponding 17 valence electron intermediate, which was then reduced by alkylmercury chloride via a single electron transfer process to afford the product and regenerate an alkyl radical. [1]     

Investigation of the Curing Behavior of a Trifunctional Cross- linking Agent by Liquid Chromatography-Mass Spectrometry

TACT is a mixture of tris (alkylcarbamoyl)triazines where the alkyl termini are methyl, butyl or a mix of both groups.One concern regarding the TACT curing process is the selective curing of one terminus over the other, especially when TACT is part of a formulation.     

Practical Synthesis of N‐Alkyl‐N‐alkyloxycarbonylaminomethyl Prodrug Derivatives of Acetaminophen,Theophylline, and 6‐Mercaptopurine

We report a novel synthesis of N‐alkyl‐N‐alkyloxycarbonylaminomethyl (NANAOCAM) prodrugs of acetaminophen, theophylline, and 6‐mercaptopurine by alkylation of the corresponding drug molecule with N‐alkyl‐N‐alkyloxycarbonylaminomethyl chlorides in good yield. Most of the alkylating agents were efficiently synthesized by chloromethylation of N‐alkyl carbamic acid alkyl esters, which in turn were made from alkyl amines and alkyl chloroformates. In cases where the alkyl chloroformates were not available, synthesis of N‐alkyl carbamic acid alkyl esters was accomplished by converting an alcohol to a chloroformate or to an activated acylating agent such as acyl imidazoles or p‐nitrophenylcarbonate esters, followed by their reaction with alkyl amines.     

Synthesis of a wide range of thioethers by indium triiodide catalyzed direct coupling between alkyl acetates and thiosilanes

An indium triiodide-catalyzed substitution of the acetoxy group in alkyl acetates with thiosilanes provides access to a variety of thioethers. The method is efficient for a wide scope of acetates such as primary alkyl, secondary alkyl, tertiary alkyl, allylic, benzylic, and propargylic acetates.     

Iron-Catalyzed Reductive Cross-Coupling of Alkyl Electrophiles with Olefins

In terms of its abundance and its minimal toxicity, iron has advantages relative to other transition metals. Although alkyl–alkyl bond construction is central to organic synthesis, examples of iron-catalyzed alkyl–alkyl couplings of alkyl electrophiles are relatively sparse. Herein we report an iron catalyst that achieves cross-coupling reactions of alkyl electrophiles wherein olefins, in the presence of a hydrosilane, are used in place of alkylmetal reagents. Carbon–carbon bond formation proceeds at room temperature, and the method employs commercially available components (Fe(OAc)₂, Xantphos, and Mg(OEt)₂); interestingly, this set of reagents can be applied directly to a distinct hydrofunctionalization of olefins, hydroboration. Mechanistic studies are consistent with the generation of an alkyl radical from the alkyl electrophile, as well as with reversibility for elementary steps that precede carbon–carbon bond formation (olefin binding to iron and β-migratory insertion).     

Copper‐Catalyzed Reductive Cross‐Coupling of Nonactivated Alkyl Tosylates and Mesylates with Alkyl and Aryl Bromides

A copper‐catalyzed reductive cross‐coupling reaction of nonactivated alkyl tosylates and mesylates with alkyl and aryl bromides was developed. It provides a practical method for efficient and cost‐effective construction of aryl–alkyl and alkyl–alkyl C?C bonds with stereocontrol from readily available substrates. When used in an intramolecular fashion, the reaction enables convenient access to various substituted carbo‐ or heterocycles, such as 2,3‐dihydrobenzofuran and benzochromene derivatives.     

Influence of alkyl chain length on phosphate self-assembled monolayers

A series of alkyl phosphates with alkyl chain lengths ranging from C10 to C18 have been synthesized. Self-assembled monolayers (SAMs) of these molecules were prepared on titanium oxide surfaces by immersion of the substrates in alkyl phosphate solutions of 0.5 mM concentration in n-heptane/isopropanol. The SAMs were characterized by means of dynamic water contact angle (dCA) measurements, variable-angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). A higher degree of order and packing density within the monolayers was found for alkyl phosphates with alkyl chain lengths exceeding 15 carbon atoms. This is reflected in a lower dCA hysteresis, as well as a film thickness measured by VASE and XPS close to the expected values for SAMs with an average alkyl chain tilt angle of 30 degrees to the surface normal. Additionally a shift of the symmetric and antisymmetric C-H stretching modes in the PM-IRRAS spectra to lower wave numbers was observed. These findings imply a higher two-dimensional crystallinity of the films derived from alkyl phosphates with a longer alkyl chain length.     

Ligand-Controlled Nickel-Catalyzed Regiodivergent Cross-Electrophile Alkyl-Alkyl Couplings of Alkyl Halides

Functionalizing specific positions on a saturated alkyl molecule is a key challenge in synthetic chemistry. Herein, a ligand-controlled regiodivergent alkylations of alkyl bromides at different positions by Ni-catalyzed alkyl-alkyl cross-electrophile coupling with the second alkyl bromides has been developed. The reaction undergoes site-selective isomerization on one alkyl bromides in a controlled manner, providing switchable access to diverse alkylated structures at different sites of alkyl bromides. The reaction occurs at three similar positions with excellent chemo- and regioselectivity, representing a remarkable ligand tuned reactivity between alkyl-alkyl cross-coupling and nickel migration along the hydrocarbon side chain. This reaction offers a catalytic platform to diverse saturated architectures by alkyl-alkyl bond-formation from identical starting materials.     

Dipole moments of some alkyl vinyl and alkyl propenyl ethers

Dipole moments of several alkyl vinyl and alkyl propenyl ethers have been determined by the Halverstadt-Kumler method in benzene solution at 293 K. The μ values depend on the bulkiness of the alkyl group present. In the alkyl vinyl ether series, a part of the varying μ values may be ascribed to changes in molecular geometry with varying bulkiness of the alkyl group. Other factors are clearly involved, since even in the alkyl (Z)-propenyl ether series μ values depend significantly on the alkyl group, although the geometry of the molecules remains essentially constant throughout the series. In the latter series, the total dipole moment is linearly related to the Taft's σ^*-values of the alkyl groups:μ/D=?(1.17±0.15)σ^*+(1.29±0.03). This suggests that the variation of μ with the alkyl radical follows from the changing polar character of the alkyl groups, which leads to changes in the value of the group moment μro.     

Synthesis and mycobacterial growth inhibition activities of bivalent and monovalent arabinofuranoside containing alkyl glycosides

Arabinofuranosides constitute one of the important components of cell wall structures of mycobacteria. With this importance of arabinofuranosides in mind, alkyl glycosides bearing arabinofuranoside trisaccharides were prepared, wherein the sugars were presented either in the monovalent or bivalent forms. Following the synthesis, the monovalent and bivalent alkyl glycosides were tested for their activities in a mycobacterial growth assay. The growth of the mycobacterial strain M. smegmatis was assessed in the presence of the alkyl glycosides and it was realized that the alkyl glycosides acted as inhibitors of the mycobacterial growth. The inhibition of the growth, caused by the above alkyl glycosides, was not observed for the arabinofuranose trisaccharide alone, without the alkyl groups, and for an alkyl glycoside bearing maltose as the sugar component.     

Mesogenic ketohexose and aldopentose derivatives: anomalous behaviour of the alkyl D-fructopyranosides

The thermotropic and lyotropic behaviour of a number of alkyl ketopyranosides, alkyl ketofuranosides, an alkyl pentopyranoside and an alkyl pentofuranoside were studied. With the exception of the alkyl beta-D-fructopyranosides, all the compounds display the expected smectic A* phases. The three alkyl fructopyranoside homologues studied (octyl, decyl and dodecyl) display a novel, rather viscous mesophase (monotropic), the nature of which is as yet unclear. The unknown phase is not a smectic A phase, because a phase transition from smectic A* to phase X is observed for both the decyl and the dodecyl derivative. The lyotropic behaviour of all the compounds in this study is quite similar to that reported earlier for other monoalkylated monosaccharide derivatives, except that the unknown phase X is again observed for the fructopyranoside derivatives.     

Characterization of alkyl polyglycosides by both reversed-phase and normal-phase modes of high-performance liquid chromatography

Alkyl polyglycosides today represent the most important sugar surfactant. Nonionic sugar surfactants produced via different synthetic routes are mixtures of alkyl homologues, oligomers, anomers and isomers. Alkyl homologues and oligomers of alkyl mono- and diglucosides were separated by reversed-phase high-performance liquid chromatography (HPLC) with methanol-water as the mobile phase using a gradient elution. The gradient was optimized in respect to a simultaneous separation of alkyl glycosides according to their alkyl chain length and alkyl polyoxyethylene glucosides with regard to their length of the polyoxyethylene spacer. The separation of alkyl glycosides into alpha- and beta-anomers was carried out by normal-phase HPLC with isooctane-ethyl acetate (60:40, v/v)-2-propanol in the gradient mode. Light scattering detection was used. Matrix-assisted laser desorption ionization time-of-flight mass spectra of alkyl glucosides and dodecyl glucosides with oxyethylene spacer groups are presented.