MW Irradiation (mw + irradiation)

Distribution by Scientific Domains

Selected Abstracts

1,3-Dihydro-2H -imidazo[4,5- c]pyridin-2-one

Jarle Holt
A facile acid catalysed cyclisation method for the preparation of the cyclic urea 2H -imidazo[4,5- c]pyridin-2-one (2) in > 95 % yield is reported. The biologically active compound 2 can be obtained by heating (3-amino-4-pyridinyl)-carbamic acid methyl, ethyl or tert -butyl esters (1a-c) in sulfuric acid (0.1 %) or in aqueous HBF4 (3.5 equivalents) for 10 min. - 3 hrs at 90 C. The corresponding microwave-promoted (MW) reactions afforded the pure product 2 within few minutes. The 6-butylamino-substituted analogue (2a) was correspondingly obtained by MW irradiation in 99 % yield by cyclisation of 2-(butylamino)-5-amino-4-pyridylcarbamic acid isopropyl ester (1d). Quantitative precipitation of product 2 was obtained by pH adjustment. The process represents a solvent-free, "green" method for the preparation of 2. [source]

Microwave-assisted TFA cleavage of peptides from Merrifield resin

Alicja Kluczyk
Abstract Microwave-assisted (MW) reactions are of special interest to the chemical community due to faster reaction times, cleaner reactions and higher product yields. The adaptation of MW to solid phase peptide synthesis resulted in spectacular syntheses of difficult peptides. In the case of Merrifield support, used frequently in synthesis of special peptides, the conditions used in product cleavage are not compatible with off-resin monitoring of the reaction progress. The application of MW irradiation in product removal from Merrifield resin using trifluoroacetic acid (TFA) was investigated using model tetrapeptides and the effects were compared with standard trifluoromethanesulphonic acid (TFMSA) cleavage using elemental analysis as well as chromatographic (HPLC) and spectroscopic (IR) methods. The deprotection of benzyloxycarbonyl and benzyl groups in synthetic bioactive peptides was analyzed using LC-MS and MS/MS experiments. In a 5 min microwave-assisted TFA reaction at low temperature, the majority of product is released from the resin, making the analytical scale MW-assisted procedure a method of choice in monitoring the reactions carried out on Merrifield resin due to the short reaction time and compatibility with HPLC and ESI-MS conditions. Copyright 2009 European Peptide Society and John Wiley & Sons, Ltd. [source]

Microwave-assisted derivatization of cellulose in an ionic liquid: An efficient, expedient synthesis of simple and mixed carboxylic esters

Shirley Possidonio
Abstract Microwave (MW)-assisted cellulose dissolution in ionic liquids (ILs) has routinely led either to incomplete biopolymer solubilization, or its degradation. We show that these problems can be avoided by use of low-energy MW heating, coupled with efficient stirring. Dissolution of microcrystalline cellulose in the IL 1-allyl-3-methylimidazolium chloride has been achieved without changing its degree of polymerization; regenerated cellulose showed pronounced changes in its index of crystallinity, surface area, and morphology. MW-assisted functionalization of MCC by ethanoic, propanoic, butanoic, pentanoic, and hexanoic anhydrides has been studied. Compared with conventional heating, MW irradiation has resulted in considerable decrease in dissolution and reaction times. The value of the degree of substitution (DS) was found to be DSethanoate > DSpropanoate > DSbutanoate. The values of DSpentanoate and DShexanoate were found to be slightly higher than DSethanoate. This surprising dependence on the chain length of the acylating agent has been reported before, but not rationalized. On the basis of the rate constants and activation parameters of the hydrolysis of ethanoic, butanoic, and hexanoic anhydrides in aqueous acetonitrile (a model acyl transfer reaction), we suggest that this result may be attributed to the balance between two opposing effects, namely, steric crowding and (cooperative) hydrophobic interactions between the anhydride and the cellulosic surface, whose lipophilicity has increased, due to its partial acylation. Four ethanoate-based mixed esters were synthesized by the reaction with a mixture of the two anhydrides; the ethanoate moiety predominated in all products. The DS is reproducible and the IL is easily recycled. 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 48: 134,143, 2010 [source]

Noble Metal Decoration and Alignment of Carbon Nanotubes in Carboxymethyl Cellulose

Mallikarjuna N. Nadagouda
Abstract A facile microwave method (MW) is described that accomplishes alignment and decoration of noble metals on carbon nanotubes (CNT) wrapped with carboxymethyl cellulose (CMC). Carbon nanotubes such as single- and multi-walled, and Buckminsterfullerene (C-60) are well dispersed using the sodium salt of CMC under sonication. Addition of respective noble metal salts then generates noble metal-decorated CNT composites at room temperature. However, aligned nanocomposites of CNTs could only be generated by exposing the above nanocomposites to MW irradiation. The CNT composites are characterized using scanning electron microscopy, energy dispersive X-ray analysis, X-ray mapping, transmission electron microscopy, and UV-visible spectroscopy. The general preparative procedure is versatile and provides a simple route to manufacturing useful metal-coated CNT nanocomposites. [source]

Influence of Microwave Irradiation on the Lipase-Catalyzed Ring-Opening Polymerization of , -Caprolactone

Patrick Kerep
Abstract Summary: The microwave (MW)-assisted lipase-catalyzed ring-opening polymerization of , -caprolactone in boiling solvents was investigated for the first time. In case of boiling toluene or benzene the MW-assisted reaction proceeded significantly slower compared to oil bath heating. On the other hand, using boiling diethyl ether as solvent, an increase of the polymerization rate due to MW irradiation was found. Yield, molecular weight measurements, and MALDI-TOF analysis supported the results. Reactivity of the MW-assisted ring-opening polymerization of , -caprolactone compared with conventional thermal heating in different solvents. [source]

Microwave-Assisted Functionalization of Carbon Nanostructures in Ionic Liquids

Ivan Guryanov Dr.
Abstract The effect of microwave (MW) irradiation and ionic liquids (IL) on the cycloaddition of azomethine ylides to [60]fullerene has been investigated by screening the reaction protocol with regard to the IL medium composition, the applied MW power, and the simultaneous cooling of the system. [60]Fullerene conversion up to 98,% is achieved in 2,10,min, by using a 1:3 mixture of the IL 1-methyl-3- n -octyl imidazolium tetrafluoroborate ([omim]BF4) and o -dichlorobenzene, and an applied power as low as 12,W. The mono- versus poly-addition selectivity to [60]fullerene can be tuned as a function of fullerene concentration. The reaction scope includes aliphatic, aromatic, and fluorous-tagged (FT) derivatives. MW irradiation of IL-structured bucky gels is instrumental for the functionalization of single-walled carbon nanotubes (SWNTs), yielding group coverages of up to one functional group per 60 carbon atoms of the SWNT network. An improved performance is obtained in low viscosity bucky gels, in the order [bmim]BF4> [omim]BF4> [hvim]TF2N (bmim=1-methyl-3- n -butyl imidazolium; hvim=1-vinyl-3- n -hexadecyl imidazolium). With this protocol, the introduction of fluorous-tagged pyrrolidine moieties onto the SWNT surface (1/108 functional coverage) yields novel FT-CNS (carbon nanostructures) with high affinity for fluorinated phases. [source]