Efficient and continuous monoacylation with superior selectivity of symmetrical diamines in microreactors

Efficient and continuous monoacylation of symmetrical diamines performed in microreactors yielded superior selectivity to that predicted by statistical considerations. It is highly valuable that the kinetically controlled product in high yields was achieved without any special catalyst at ambient temperature.     

Oligosaccharide synthesis in microreactors

Described is the combination of microreactors and fluorous phase chemistry to assemble oligosaccharides. The synthesis of a beta-(1-->6) linked D-glucopyranoside homotetramer serves to illustrate this approach. Glycosylations employing a Fmoc-protected glucosyl phosphate building block were performed in a silicon-based micro-structured device to optimize reaction conditions and for reaction scale-up. A perfluorinated linker at the reducing end of the oligosaccharides allowed for purification by fluorous solid-phase extraction (FSPE) and further functionalization.     

PMAA microgel surface-supported phase transfer catalyst as reusable microreactors for ultra-deep desulfurization

The reusable microreactors, poly(methacrylic acid) (PMAA) microgels surfacely covered with 3-(trimethoxysilyl)-propyldimethyloctadecyl ammonium chloride (AEM) and K₂{W(=O)(O₂)₂(H₂O)}₂ (W2) complexes, have been synthesized by using an ion exchange reaction between AEM located on PMAA microgels and W2 in aqueous solution. The final composite microspheres and intermediate products are characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, energy dispersive X-ray spectrophotometer, and thermogravimetric analysis, respectively. The results indicated the PMAA/AEM/W2 composite microspheres with surface-wrinkling morphology and core-shell structure. The feasibility of the composite microspheres used as reusable microreactors in catalytic oxidation of dibenzothiophene (DBT) was investigated. Additionally, the effects of some factors, including the amount of the microreactors, temperature, H₂O₂/DBT molar ratio, the loaded amount of AEM, DBT concentration, and recycling times, on the catalytic oxidation were examined. The results demonstrated that the prepared composite microspheres possess high catalytic performance and reusability in the catalytic oxidation of DBT.     

Fluorination reactions in microreactors

The DAST-mediated conversion of a range of alcohols to the corresponding fluorides in a microstructured device is described. This safe, practical fluorination method will facilitate reactions currently challenging on large scale.     

Efficient photosensitized degradation of 4-chlorophenol over immobilized aluminum tetrasulfophthalocyanine in the presence of hydrogen peroxide

The photosensitized degradation of 4-chlorophenol (4-CP) under visible light (lambda > or = 450 nm) irradiation in an aerated aqueous medium at pH 12 was studied using an immobilized photosensitizer, aluminum tetrasulfophthalocyanine, on a commercial resin Amberlite IRA 400. The catalyst exhibited strong adsorption toward 4-CP, but the adsorption led to an exponential decrease in both the initial rate and the apparent first-order rate constant, as measured by 4-CP loss in the bulk solution. Several intermediates were formed from 4-CP oxidation, including fumaric acid, benzoquinone, and hydroquinone, which were adsorbed strongly on the catalyst and lowered the photosensitized reaction. Addition of H2O2 was found to be an efficient way to eliminate the colored intermediates and consequently recover the catalyst activity. The immobilized sensitizer was stable and could be used repeatedly in the presence of H2O2. The optimal loading of the photosensitizer in the catalyst was about 1.0 wt %.     

Perspectives of heterogeneous process intensification in microreactors

Recent developments in microreactor technology basing on different types of heterogeneous reaction systems: phase transfer catalysis, biocatalysis, and synthesis of nanoparticles are reviewed. Special attention is focused on the intensification of processes in microreactors compared with traditional approaches, which makes microtechnique of great interest for industry.     

Reactions in surface microreactors: Computer simulation

Chemical transformations of surface-active substrate in the presence of surface-active catalyst are studied by the methods of computer simulation. Reactions occur in emulsion, at whose interfaces reactants are concentrated. It is established that there is an optimal size of emulsion droplets at which the reaction rate is the highest. It is shown that the kinetics of reactions substantially depends on the surface activity of reactants and the potential barrier of reaction. Under specific conditions, the rate of reaction notably increases during the initial time interval.     

The synthesis of fluorinated materials in microreactors

Synthetic utilities of microreactor for the synthesis of fluorinated materials are described. In particular, synthesis of silylenol ether of 4,4,4-trifluorobutan-2-one and its synthetic application at room temperature. Further, nitroaldol reactions and Michael addition reaction in microreactor are convenient ways for the syntheses of difluoromethylated materials.     

Direct synthesis of hydrogen peroxide in microreactors

Several studies concerning direct synthesis of hydrogen peroxide in microreactors are reviewed. Several types of microreactors have been applied. Their high surface area-to-volume ratio and small internal volume improve safety, which is required when operating with explosive gases. The tested microreactors represent capillary reactors and more sophisticated reactors with a special plate structure on which reaction channels have been machined. Both single- and multi-channel arrangements have been applied. The catalysts have been installed in the reactor in the form of powder or washcoat layer on the channel wall. Palladium and platinum on various support material, such as SiO₂, Al₂O₃ and C, have been tested. Water was the most common solvent, but also methanol, ethanol, and isopropanol have been used because of their better gas dissolving properties. In addition to solvents, chemicals, often called promoters, have been utilised to improve productivity. The most typical promoters were halide ions, such as Br^? and Cl^? and inorganic acids. Hydrogen peroxide has been produced successfully by several research groups. The highest reported mass fraction of hydrogen peroxide was 5 wt %.     

Efficient barrier properties of mechanically enhanced agro-extracted cellulosic biocomposites

The objective of this work was to prepare the mechanically stable hydrophobic biocomposites by incorporating the cellulose fibers into the polymer matrices for their applications in biomedical and food packaging. Herein, two different types of biocomposites were prepared by mixing polylactic acid (PLA) and polyhydroxybutyrate (PHB) with the agro-extracted cellulose, separately at 170 °C. The influence of the cellulose fibers on the thermal, mechanical, and barrier properties of polymer matrices (PLA and PHB) was observed. With an increase in the cellulose content in PLA and PHB, the tensile strength of the biocomposite materials significantly improved with the enhancement of 24.45% and 32.08%, respectively, compared with the pure PLA and PHB. Furthermore, a decrease of 74.16% and 73.49% in the water vapor transmission rate and oxygen transmission rate, respectively, was observed for cellulose/PHB biocomposites. This study highlights that adding cellulose fibers significantly improves the mechanical and the barrier properties of PLA and PHB, suggesting their biocomposites for use in biodegradable polymer industries.     

Role of sulfide radical cations in electron transfer promoted molecular oxygenations at sulfur

The methylene blue, N-methylquinolinium tetrafluoroborate, and pyrylium-cation-sensitized photooxygenations of 5H, 7H-dibenzo[b,g] [1,5]dithiocin, 1, and 1,5-dithiacyclooctane, 2, have been investigated. The methylene blue sensitized reactions exhibit all of the characteristics of a singlet oxygen reaction including isotope effects for the formation of a hydroperoxysulfonium ylide and the ability of 1 and 2 to quench the time-resolved emission of singlet oxygen at 1270 nm. The product compositions in the N-methylquinolinium tetrafluoroborate and pyrylium-cation-sensitized reactions are dramatically different and are both different from that anticipated for the participation of singlet oxygen. This argues for different reaction mechanisms for all three sensitizers. However, both the quinolinium and pyrylium-cation-sensitized reactions display all of the characteristics of electron-transfer-initiated photooxygenations. Both sensitizers were quenched at nearly diffusion-limited rates by 1 and 2. Laser flash photolysis of mixtures of either sensitizer and 1 or 2 resulted in direct observation of the reduced sensitizer and the sulfide radical cation. In addition, electron-transfer reactions involving both sensitizers were shown to be exergonic. These results are consistent with the previously proposed outer sphere electron-transfer mechanism for N-methylquinolinium tetrafluoroborate and were used to argue for a new inner sphere mechanism for the pyrylium cation reactions.     

Preparation of ultradispersed transition metals in immobilized microreactors

Preparation of ultradispersed transition metals (20–100 nm) by reduction of metal complexes in molecular microreactors (cavities of immobilized calixarenes, polyelectrolytes) was studied.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1914–1916.Original Russian Text Copyright © 2004 by Altshuler, Sapozhnikova.     

Efficient photosensitized splitting of the thymine dimer/oxetane unit on its modifying beta-cyclodextrin by a binding electron donor

Two modified beta-cyclodextrins (beta-CDs) with a thymine dimer and a thymine oxetane adduct respectively, TD-CD and Ox-CD, have been prepared, and utilized to bind an electron-rich chromophore, indole or N,N-dimethylaniline (DMA), to form a supramolecular complex. We have examined the photosensitized splitting of the dimer/oxetane unit in TD-CD/Ox-CD by indole or DMA via an electron-transfer pathway, and observed high splitting efficiencies of the dimer/oxetane unit. On the basis of measurements of fluorescence spectra and splitting quantum yields, it is suggested that the splitting reaction occurs in a supramolecular complex by an inclusion interaction between the modified beta-CDs and DMA or indole. The back electron transfer, which leads low splitting efficiencies for the covalently-linked chromophore-dimer/oxetane compounds, is suppressed in the non-covalently-bound complex, and the mechanism has been discussed.     

Microwave‐enhanced Efficient Synthesis of Some Polyfunctional Pyridazines

Microwave‐enhanced highly efficient protocol for the synthesis of polyfunctional pyridazines beginning from 3,6‐dichloropyridazine in environmentally benign ionic liquids have been developed. The products obtained were 3‐amino‐6‐chloropyridazine, 3,6‐diaminopyridazine, and 3‐chloro‐6‐methoxypyridazine. These derivatives were then be converted to a variety of polyfunctional pyridazine derivatives. The ionic liquids used were 1‐n‐butyl‐3‐methylimidazolium hydroxide/tetrafluoroborate/hexafluorophosphate and 1,3‐di‐n‐butylimidazolium hydroxide. This powerful strategy is less time‐consuming green methodology. The ionic liquid employed may be recovered and recycled.     

Efficient disc on pillar substrates for surface enhanced Raman spectroscopy

In this work, geometrical optimizations of Ag disc on pillar (DOP) hybrid plasmonic nanostructures were conducted and allowed us to achieve reproducible average enhancement factors of 1 × 10(9) and greater.     

Recent advances in catalytic, enantioselective alpha aminations and alpha oxygenations of carbonyl compounds

The direct introduction of either a nitrogen or oxygen atom adjacent to a carbonyl group in a catalytic, enantioselective manner using both chiral Lewis acid and Lewis base catalysis has been described recently. The enantiomerically enriched products of these reactions, such as alpha-amino acids, represent fundamental building blocks for the construction of complex natural products and other important bioactive molecules. This Minireview provides a synopsis of this ever-growing field and highlights some of the challenges that still remain.     

Efficient methods to study phase equilibria in multinary aqueous systems

We report the results of developing efficient universal isothermal methods for the determination of compositions of all phases (several solid phases and a liquid) involved in invariant equilibria in multicomponent aqueous systems using chemical analysis (a combination method) or not (an optimized sections method) to determine the composition of an equilibrium liquid phase.     

Efficient solution phase parallel synthesis of norstatine analogs

The reaction of glycidic amides with various functionalized nitriles to afford norstatine analogs in a regio- and diastereoselective fashion (43-99% yield) is described. Utilizing this chemistry, a 20 membered solution phase library was prepared in two steps featuring three points of diversity.