Solvent‐free one‐pot synthesis of pyrane derivatives

A straightforward and an efficient method for the synthesis of 2H‐pyrans via the one‐pot, reaction of alkyl bromides, carbon disulfide, secondary amines, activated acetylenes and isocyanides under solvent‐free conditions without using any catalyst at room temperature is reported. The method offers several advantages including high yields of products and an easy work‐up procedure. J. Heterocyclic Chem., (2011).     

Solvent‐free synthesis of rotaxanes

Rotaxane‐type (macro)molecules are important materials in various fields of research, with many approaches for their synthesis having been developed over the past 30 years or so. When prepared in solution, the efficiency of interlocking pseudorotaxane complexes into the corresponding rotaxanes relies, to a great extent, on the affinity between the host and guest components; these interactions are not always sufficiently strong to overcome the deleterious effects of high reaction temperatures, competitive solvents, and low concentrations. Upon evaporating the solvent, however, the concentrations of the host and guest species increase significantly and, ultimately, their corresponding pseudorotaxanes can be generated with high efficiency in the solvent‐free residue. Furthermore, in the absence of the solvent, the influence of any disrupting byproducts (generated during the interlocking process) on the complexation equilibrium can also be largely reduced. Therefore, high synthetic efficiency and low consumption of solvents and energy can be expected when synthesizing rotaxanes under solvent‐free conditions. This mini‐review covers the main publications dealing with the solvent‐free syntheses of rotaxanes – those in which the interlocking step involves no solvent (or only a trace of it).     

Solvent‐free synthesis of polyacrylamide by frontal polymerization

Polymerization and characterization of polyacrylamide prepared by frontal polymerization are described. Frontally polymerized polyacrylamide is imidized and crosslinked during polymerization. Imide formation was determined by elemental analysis. The addition of commercial polyacrylamide or barium carbonate to the monomer (acrylamide) and initiator (potassium persulfate) decreased the reaction temperature from 235 °C to < 100 °C, thereby reducing imide formation. The commercial polyacrylamide‐diluted product, frontally polymerized polyacrylamide‐diluted product, and the barium carbonate‐diluted product were characterized by IR, TGA, and elemental analysis. Molecular weights of barium carbonate‐diluted samples were determined by light scattering and found to be on the order of one million. Conversion of the barium carbonate‐diluted product was determined to be 76 ± 6%, independent of the amount of diluent over the range 0.8:1–1.5:1. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1129–1135, 2000     

Solvent‐free one‐pot approach for synthesis of substituted 2‐aminochromenes

A solvent‐free one‐pot approach for the preparation of 2‐aminochromenes in the presence of NaHCO₃ by grinding was described. Its advantages are easy work‐up, mild reaction condition, high yield and environmental compatibility.     

Solvent‐free three‐component synthesis of 7‐aryl‐1,1‐dioxothieno[3,2‐b]pyran derivatives catalyzed by ammonium acetate

An efficient synthesis of 7‐aryl‐1,1‐dioxothieno[3,2‐b]pyran derivatives via the reaction of aryl aldehyde, tetrahydrothiophene‐3‐one‐1,1‐dioxide and malononitrile or ethyl 2‐cyanoacetate was performed at room temperature catalyzed by ammonium acetate under solvent‐free conditions. Compared with the conventional methods, this protocol features mild reaction conditions, high yields, and eco‐friendliness. J. Heterocyclic Chem., (2011).     

Solvent‐free neat synthetic route to tetrahydroacridinones

An environmentally benign approach for the synthesis of acridines using inorganic solid supports and “neat reaction'' technology is described. These methodologies completely eliminate the use of solvent during the course of reaction. Moreover, microwave‐assisted reactions reduce the reaction time from hours to minutes with improved yield. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:138–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20080     

Solvent‐free Synthesis of Hexagonal Iron Sulfide Nanoflowers

Employing green and economic solvent‐free synthesis route, hexagonal iron sulfide (Fe₇S₈) nanoflowers were successfully synthesized for the first time. In the experiment, ferric hexadecylxanthate was used as the precursor, and hexagonal iron sulfide (Fe₇S₈) nanoflowers were obtained by thermal decomposition of the precursor at 260°C without any additional solvent or inert gas protection. The as‐prepared iron sulfide nanoflowers were characterized by means of X‐ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The characterization results indicated that the nanoflowers had uniform size distribution with an average size of about 160 nm. The proposed strategy provides a possible general route for the synthesis of other metal chalcogenide nanostructures.     

Solvent‐free polymerization of citric acid and D‐sorbitol

Copolymers of citric acid and D ‐sorbitol were synthesized with a solvent‐free vacuum‐oven synthesis with molar ratios of citric acid to D ‐sorbitol ranging from 1/1 to 6/1. The extent of the reaction was followed by the monitoring of the residual acid content of the system. As expected, the reaction occurred much more rapidly at 150 than at 110 °C. The Fourier transform infrared (FTIR) spectra of the products showed the expected FTIR bands at approximately 1735 and 1188 cm^?1, which were indicative of ester formation. Gel permeation chromatography showed a major product with a molecular weight of approximately 3500 Da. An insoluble material with a water‐absorption index of up to 17 was also synthesized and could lead to possible applications as absorbers, thickeners, and biobased seed coatings. Additionally, the mono‐ and disodium salts of citric acid were also polymerized with D ‐sorbitol in a manner similar to that of the citric acid system. Soluble polymers were synthesized with a residual acid content of 5 mequiv/g of polymer. These materials showed Ca⁺²‐sequestering ability (up to 0.56 mmol of Ca⁺²/g of the product). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4259–4267, 2006     

Solvent‐free Liquid Crystals and Liquids from DNA

As DNA exhibits persistent structures with dimensions that exceed the range of their intermolecular forces, solid‐state DNA undergoes thermal degradation at elevated temperatures. Therefore, the realization of solvent‐free DNA fluids, including liquid crystals and liquids, still remains a significant challenge. To address this intriguing issue, we demonstrate that combining DNA with suitable cationic surfactants, followed by dehydration, can be a simple generic scheme for producing these solvent‐free DNA fluid systems. In the anhydrous smectic liquid crystalline phase, DNA sublayers are intercalated between aliphatic hydrocarbon sublayers. The lengths of the DNA and surfactant are found to be extremely important in tuning the physical properties of the fluids. Stable liquid‐crystalline and liquid phases are obtained in the ?20 °C to 200 °C temperature range without thermal degradation of the DNA. Thus, a new type of DNA‐based soft biomaterial has been achieved, which will promote the study and application of DNA in a much broader context.     

An efficient synthesis of highly substituted pyrrole and bis pyrrole derivatives

An efficient synthesis of highly substituted pyrrole and bis pyrrole derivatives is reported.     

Solvent‐free cyanosilylation of aldehydes catalyzed by SmI2

A novel method to obtain racemic cyanohydrin silylethers by reaction of trimethylsilyl cyanide with a variety of aldehydes promoted by catalysis of SmI₂ is reported. The corresponding cyanosilylethers were obtained in high yields (up to 99%) in solvent‐ free conditions at room temperature within a relatively short time using 0.01–0.5 mol% catalyst loadings. Copyright © 2007 John Wiley & Sons, Ltd.     

Solvent‐free synthesis of 2H‐pyrans: One‐pot reactions of dithiocarbamates,alkyl propiolates,and isocyanides

A novel, convenient, and an efficient approach to the synthesis of 2H‐pyrans has been reported based on the multicomponent reaction. Solvent‐free condition for the reaction of dithiocarbamates, alkyl propiolates and isocyanides lead to the formation of 2H‐pyrans in good yields. In these reactions, synthesis of 2H‐pyrans is possible based on the one‐pot reaction and without using any catalyst. The mild reaction conditions and high yields of the products exhibit the good synthetic advantage of these methods. J. Heterocyclic Chem., lpar;2011).     

Solvent‐free fabrication of proton‐conducting membranes based on commercial elastomers

Five different types of elastomers were examined as the matrix materials in the preparation of non‐fluorinated proton exchange membranes utilizing a solvent‐free route via the in situ reaction of sodium 4‐styrenesulfonate (NaSS). The morphology of the elastomer/NaSS vulcanizates was studied to evaluate the effect of polarity, viscosity and saturation degree of the elastomer matrixes. Much better dispersion of NaSS was found in chlorosulfonated polyethylene rubber (CSM) and hydrogenated nitrile butadiene rubber (HNBR) matrixes than in the other three types of elastomer matrixes. For CSM/NaSS and HNBR/NaSS proton exchange membranes, distinctive membrane properties were observed and correlated with their different structure and morphologies. The CSM/NaSS membranes exhibited the proton conductivity as high as ~0.03 S cm^?1 and the selectivity (the ratio of proton conductivity to methanol permeability) higher than that of Nafion. Copyright © 2015 John Wiley & Sons, Ltd.     

Eco‐friendly synthesis of quinoxaline derivatives by grinding under solvent‐free conditions

An efficient and facile synthesis of quinoxaline derivatives in excellent isolated yields by the condensation of 1,2‐diamines and 1,2‐diketones on grinding under solvent‐free conditions at ambient temperature has been developed. The important features of this method are that it is reasonably fast, very clean, high yielding, simple workup, and environmentally benign. J. Heterocyclic Chem., 00 , 00 (2011).     

An Efficient Three‐component,One‐pot Synthesis of Quinazolines under Solvent‐free and Catalyst‐free Condition

An efficient green protocol for the synthesis of quinazolines in the absence of solvent and catalyst has been developed. 2,4‐Disubstituted quinazolines have been synthesized from three‐component one‐pot reactions of 2‐aminoaryl ketones, orthoesters, and ammonium acetate. The present method has advantages of operational simplicity, substrate generality, clean reaction, high yields (76–94%), and moderate reaction time. The plausible mechanism of the reaction has been proposed based on the spectral characterization and single crystal X‐ray analysis of isolated intermediate.