Perfluoroalkylation of aromatics

Several methods for the perfluoroalkylation of aromatics were reported.Both per-fluoroalkanesulfonyl bromide/BPO and perfluoroalkanesulfinate/oxidant systems were efficientreagents for the introduction of a pcrfluoroalkyl group onto various aromatic nuclei.In atwo-phase solvent system with tetraalkylammonium salt as PTC,rcaction of perfluoroalkyliodide and aromatics in the presence of sodium dithionitc gave perfluoroalkyl aromatics and/oraddition-dimerization products.     

ZSM-5沸石结晶度对乙苯叔丁基化对位选择性的影响(英文)

Highly crystalline ZSM-5 zeolites are important for para-selective alkylation of alkyl aromatics, because they carry few external acid sites for isomerization of p-dialkyl products. Such zeolites (Si/Al = 25, 50, and 75) were synthesized in a fluoride medium between pH 4 and 6. Their crystallinities, crystal sizes, and surface areas were higher than those of a commercial ZSM-5 zeolite. Their para selectivities in alkylation were tested for vapor-phase tert-butylation of ethylbenzene between 200 and 400 °C. As expected, all the catalysts showed more than 90% para selectivity. At 300 °C, ethylbenzene conversion decreased in the order ZSM-5(25, commercial) > ZSM-5(25) > ZSM-5(50) > ZSM-5(75). The catalysts had weak, medium, and strong acid sites, but all the acid sites of ZSM-5(75) were weaker than those of ZSM-5(25) and ZSM-5(50). The high activity of commercial ZSM-5 was caused by its strong acid sites being stronger than those of the synthesized zeolites. Although the activity of the commercial catalyst was higher than those of the present catalysts, the selectivity for 4-t-butylethylbenzene (4-t-BEB) was low. The optimum feed ratio (ethylbenzene:t-butyl alcohol) was 2:1 and the feed rate was 1.65 h?1 for high ethylbenzene conversion and 4-t-BEB selectivity. Time-on-stream studies showed slow catalyst deactivation. Highly crystalline ZSM-5 zeolites are therefore better than a commercial zeolite for para-selective alkylation of alkyl aromatics. They do not require much post-modification for high para selectivity. A fluoride medium is therefore better than an alkaline medium for obtaining highly crystalline para-selective ZSM-5 zeolites.     

Transformation of Biomass into Aromatics with Zeolite Catalysts

Biomass is a nature renewable resource which can be used for the production of high value chemicals and bio-fuels. In the present work, the transformation of sawdust into aromat- ics such as benzene, toluene and xylenes was investigated over a series of zeolite catalysts （NaZSM-5, HZSM-5, ReY and HY catalysts）. Among the tested catalysts, the HZSM-5 catalyst shows the highest activity for the production of aromatics. The yield and carbon selectivity of aromatics reached about 26.5% and 62.5C-mo1%, respectively over the HZSM-5 catalyst under the optimal condition of T=450 ℃, f（N2）=300 cm^3/min, and catalyst/lignin ratio of 2. The effects of the reaction conditions including temperature, gas flow rate, and catalyst/sawdust ratio on the production of aromatics were investigated in detail and the formation of aromatics from lignocellulosic biomass was also addressed.     

Formaldehyde intermediate participating in the conversion of methanol to aromatics over zinc modified H-ZSM-5

Metal-modified H-ZSM-5 has a high selectivity of aromatics in methanol to aromatics(MTA)reaction,which is often attributed to the metal promoting the aromatization of intermediate olefins.However,the effect of methanol dehydrogenation on aromatics formation over these catalysts is rarely studied.Here,we report that HCHO,which is formed by methanol dehydrogenation over Zn/H-ZSM-5 prepared by Zn impregnation,can participate in the synthesis of aromatics.Methanol conversion can produce more aromatics than olefins(propylene or ethylene)conversion over Zn/H-ZSM-5,indicating the conventional MTA pathway including methanol-to-olefins and olefins-to-aromatics is not complete.Moreover,an MTA mechanism including the conventional pathway and the methanol and HCHO coupling pathway is systematically proposed.     

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.     

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 ...     

An efficient synthesis of substituted alkyl acrylates using α-keto amides

The addition of α-keto amides as a NH-acid to alkyl propiolates and dialkyl acetylenedicarboxylates in the presence of a catalytic amount of triphenylphosphine gives the corresponding substituted alkyl acrylates.     

Amberlyst-15 catalyzed synthesis of alkyl/aryl/heterocyclic phosphonates

A novel and efficient procedure for the synthesis of alkyl phosphonates through one pot condensation of alkyl halide and trialkyl /aryl phosphite in the presence of Amberlyst-15 as catalyst under solvent free conditions was applied.It demonstrated several advantages such as good yields of products,simple operation,convenient separation and inexpensive catalyst.     

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.     

Predictable site-selective radical fluorination of tertiary ethers

In this communication,we disclose the first example of metal-free and site-selective radical fluorination of readily available tertiary alkyl ethers,enabled by synergistic photocatalysis and organocatalysis.This catalytic combination allows for exclusive fluorination of tertiary C–O bonds under mild conditions even in the presence of competing reaction sites.The excellent functional group tolerance affords valuable access to sterically hindered alkyl fluorides through late-stage modification of complex molecules.The successful use of tertiary alkyl ethers in radical fluorination enhances the structural diversity of aliphatic fluorides that can be derived from naturally abundant alcohols.     

A STUDY ON THE DEGRADATION MECHANISM OF PHOTOCROSSLINKING PRODUCTS FORMED BY CYCLIZED POLYISOPRENE-DIAZIDE SYSTEM UNDER THE INFLUENCE OF ALKYL BENZENE SULFONIC ACIDS

The degradation mechanism of photocrosslinking products formed by cyclized polyisoprene-diazide system under the influence of the different alkyl benzene sulfonic acids was studied. The effects of alkyl chain length and the concentration of alkyl benzene sulfonic acids on the rate of degradation reaction were discussed. It was found that in the initial stage of degradation, the cyclicity ratio and the average fused ring number did not change considerably, but the percentage of uncyclized parts content varied significantly. The suitable mechanism was supposed.     

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.     

Mechanism study on UV-induced photodegradation of nonylphenol ethoxylates by intermediate products analysis

Photodegradation of nonylphenol ethoxylates(NP10EO)was investigated in laboratory scale under UV irradiation.Theintermediate photodegradation products were analyzed by LC-ESI-MS.Three kinds of intermediate products including aldehydiccompounds,carboxylic compounds and cyclohexanyl compounds were identified.Five main degradation routes involving theoxidation of the alkyl chain and ethoxylate unit,shortening of the alkyl chain and ethoxylate unit,hydrogenation of the benzene ringwere proposed.     

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.     

Phosphine-free conversion of alcohols into alkyl thiocyanates using trichloroisocyanuric acid/NH4SCN

A convenient and efficient phosphine-free procedure for the one-pot conversion of primary,secondary and tertiary alcohols into the corresponding alkyl thiocyanates or alkyl isothiocyanates is described using trichloroisocyanuric acid/NHUSCN.     

CO2 utilization in syngas conversion to dimethyl ether and aromatics:Roles and challenges of zeolites-based catalysts

Several studies have proven a strong correlation between global warming and CO₂ emissions. Annually,38 billion tons of CO₂ are approximately emitted into the atmosphere. Utilizing CO₂ via chemical conversion to clean fuels and value-added aromatics can substantially contribute to controlling the problem. Considering the thermodynamic and environmental limitations of hydrogenation of CO₂alone to value-added aromatics and fuels, CO₂utilization...     

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.     

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.     

Synthesis of polyfluorenes bearing lateral pyreneterminated alkyl chains for dispersion of single-walled carbon nanotubes

Two kinds of polyfluorenes bearing two lateral pyrene terminated alkyl chains and two alkyl chains per repeating unit were synthesized by Suzuki polycondensation and used to disperse single-walled carbon nanotubes(SWCNT) in organic solvents.Stable polymer-SWCNT complex can be formed via the multivalentπ-πstacking interaction of the lateral pyrene functional groups and the polyfluorene backbone with the outer surface of carbon nanotubes;meanwhile the lateral alkyl chains can impart good solubility to the complex.As expected,polyfluorenes bearing lateral pyrene functional groups and octyl chains exhibited much higher carbon nanotube solubility in common organic solvents than the corresponding polyfluorenes bearing only octyl chains.Photophysical studies indicated that the formation of polymer-SWCNT complex can effectively quench the fluorescence of polyfluorenes.     

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]