This research was supported by the Bill and Linda Frost Fund.

CAUTION: Please review all relevant material safety data sheets (MSDS) before use. Follow all appropriate safety practices when using the microwave reactor including reviewing the microwave reactor protocols and the use of personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes). This procedure is designed to work using an aryl hydrazine and either 3-aminocrotononitrile or an &#945;-cyanoketone. The appropriate microwave vial and stir bar should be used according to the scale of the reaction as specified by the manufacturer.
1. Preparation of reaction mixture
NOTE: The following reaction between 4-fluorophenylhydrazine hydrochloride and 3-aminocrotononitrile on a 2 mmol scale is representative. The procedure is identical when substituting &#945;-cyanoketones in place of 3-aminocrotononitrile14.
<ol>
	<li>Obtain a microwave vial designed for reaction volumes of 2-5 mL that has been dried overnight in a glassware oven and add an appropriate stir bar.</li>
	<li>Add 0.325 g of 4-fluorophenylhydrazine hydrochloride (1 equiv., 2 mmol) and 0.164 g of 3-aminocrotononitrile (1 equiv., 2 mmol) to the microwave vial.</li>
	<li>Add 5 mL of 1 M HCl to make the concentration of starting reagents as 0.4 M. Using a stir plate, ensure that the heterogeneous suspension is stirred. Add additional solvent if reactants have poor solubility and the reaction mixture cannot be stirred properly. Transfer the solution to a larger vial if necessary, to avoid exceeding the recommend solvent volume as specified by the microwave reactor operating manual.</li>
</ol>
2. Heating the reaction in the microwave reactor
<ol>
	<li>Seal the microwave vial with a microwave vial cap using the appropriate crimper tool.</li>
	<li>Place the vial in the microwave reactor. Program the microwave settings for time (10 min), temperature (150 &#176;C), and absorption (Very High). 
	CAUTION: Pay attention to the reactor pressure during the heating phase. A sudden drop in pressure may indicate a leak and/or vessel failure.</li>
	<li>Once the reaction has cooled (&#60; 40 &#176;C), remove the vial from the microwave reactor.</li>
	<li>Remove the cap using an appropriate decapper tool.</li>
</ol>
3. Isolation of the product by vacuum filtration
<ol>
	<li>In a well ventilated fume hood, clamp the microwave vial over a stir plate.</li>
	<li>Add 2 mL of 10% NaOH with stirring to make the solution alkaline and cause immediate precipitation of product. The pH of the solution should be &#62;10 as indicated by pH paper. Sonication and scraping the vial with a spatula can aid with mixing and dislodging product from the vessel walls. 
	NOTE: Some products oil out of the alkaline solution. If this occurs, transfer the solution with the aid of ~20 mL of deionized water to a separatory funnel and extract 3x with dichloromethane or ethyl acetate. Dry the combined organic layers and evaporate to obtain the product.</li>
	<li>Set up a vacuum filtration apparatus to isolate solid product precipitate. Use deionized water to rinse any remaining product from the microwave vial and wash the isolated product.</li>
	<li>Allow the product to dry overnight on the bench top or in a desiccator. Isolated yields are typically in the 70-90% range14.</li>
	<li>Obtain a 1H NMR spectrum in CDCl3 to confirm product identity and purity.</li>
</ol>

<ol>
	<li>Gradler, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fragment-based+discovery+of+focal+adhesion+kinase+inhibitors.">Fragment-based discovery of focal adhesion kinase inhibitors.</a> Bioorganic &amp; Medicinal Chemistry Letters. 23 (19), 5401-5409 (2013).</li><li>Chandak, N., Kumar, S., Kumar, P., Sharma, C., Aneja, K. R., Sharma, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploration+of+antimicrobial+potential+of+pyrazolo[3,4-b]pyridine+scaffold+bearing+benzenesulfonamide+and+trifluoromethyl+moieties.">Exploration of antimicrobial potential of pyrazolo[3,4-b]pyridine scaffold bearing benzenesulfonamide and trifluoromethyl moieties.</a> Medicinal Chemistry Research. 22 (11), 5490-5503 (2013).</li><li>Huo, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+biological+activity+of+novel+N-(3-furan-2-yl-1-phenyl-1H-pyrazol-5-yl)+amides+derivatives.">Synthesis and biological activity of novel N-(3-furan-2-yl-1-phenyl-1H-pyrazol-5-yl) amides derivatives.</a> Chinese Chemical Letters. 27 (9), 1547-1550 (2016).</li><li>Anand, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antileishmanial+activity+of+pyrazolopyridine+derivatives+and+their+potential+as+an+adjunct+therapy+with+miltefosine.">Antileishmanial activity of pyrazolopyridine derivatives and their potential as an adjunct therapy with miltefosine.</a> Journal of Medicinal Chemistry. 60 (3), 1041-1059 (2017).</li><li>Eldehna, W. M., El-Naggar, D. H., Hamed, A. R., Ibrahim, H. S., Ghabbour, H. A., Abdel-Aziz, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-pot+three-component+synthesis+of+novel+spirooxindoles+with+potential+cytotoxic+activity+against+triple-negative+breast+cancer+MDA-MB-231+cells.">One-pot three-component synthesis of novel spirooxindoles with potential cytotoxic activity against triple-negative breast cancer MDA-MB-231 cells.</a> Journal of Enzyme Inhibition and Medicinal Chemistry. 33 (1), 309-318 (2017).</li><li>Briebenow, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+optimization+of+substituted+5-aminopyrazoles+as+potent+and+selective+adenosine+A1+receptor+antagonists.">Identification and optimization of substituted 5-aminopyrazoles as potent and selective adenosine A1 receptor antagonists.</a> Bioorganic &amp; Medicinal Chemistry Letters. 20 (19), 5891-5894 (2010).</li><li>Marinozzi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pyrazole[3,4-e][1,4]thiazepin-7-one+derivatives+as+a+novel+class+of+Farnesoid+X+Receptor+(FXR)+agonists.">Pyrazole[3,4-e][1,4]thiazepin-7-one derivatives as a novel class of Farnesoid X Receptor (FXR) agonists.</a> Bioorganic &amp; Medicinal Chemistry. 20 (11), 3429-3445 (2012).</li><li>Ochiai, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discovery+of+new+orally+available+active+phosphodiesterase+inhibitors.">Discovery of new orally available active phosphodiesterase inhibitors.</a> Chemical and Pharmaceutical Bulletin. 52 (9), 1098-1104 (2004).</li><li>Ganesan, A., Heathcock, C. 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S., Kipling, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave-assisted+synthesis+of+N-pyrazole+ureas+and+the+p38&#945;+inhibitor+BIRB+796+for+study+into+accelerated+cell+ageing.">Microwave-assisted synthesis of N-pyrazole ureas and the p38&#945; inhibitor BIRB 796 for study into accelerated cell ageing.</a> Organic &amp; Biomolecular Chemistry. 4 (22), 4158-4164 (2006).</li><li>Su, W., Lin, T., Cheng, K., Sung, K., Lin, S., Wong, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+efficient+on-pot+synthesis+of+N-(1,3-diphenyl-1H-pyrazol-5-yl)amides.">An efficient on-pot synthesis of N-(1,3-diphenyl-1H-pyrazol-5-yl)amides.</a> Journal of Heterocyclic Chemistry. 47 (4), 831-837 (2010).</li><li>Eagon, S., Anderson, M. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave-assisted+synthesis+of+tetrahydro-&#946;-carbolines+and+&#946;-carbolines.">Microwave-assisted synthesis of tetrahydro-&#946;-carbolines and &#946;-carbolines.</a> European Journal of Organic Chemistry. (8), 1653-1665 (2014).</li><li>Everson, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave+synthesis+of+1-aryl-1H-pyrazole-5-amines.">Microwave synthesis of 1-aryl-1H-pyrazole-5-amines.</a> Tetrahedron Letters. 60 (1), 72-74 (2019).</li></ol>

The authors have nothing to disclose.

A number of 1-aryl-1H-pyrazole-5-amines were prepared by combining an &#945;-cyanoketone or 3-aminocrotonitile with an aryl hydrazine in 1 M HCl and heating the solution to 150 &#176;C in a microwave reactor. Nearly all compounds were synthesized in 10-15 min, with the slowest substrate requiring 35 min of heating14. The use of water as the solvent allows for rapid heating of the solution and minimizes the use of hazardous organic solvents.
Higher temperature a...

The impetus to create a streamlined synthesis of 1-aryl-1H-pyrazole-5-amines is due to the myriad of applications of these small molecules. They appear in kinase inhibitors1, antibiotics2, pesticides3, and among many other biologically active compounds4,5. Synthetic schemes for these compounds are abundant, but most involve complex isolation and purification techniques. A common method involves the reflux of aryl hydrazine and 3-aminocrotononitrile in either alcoholic or aqueous solutions followed by a subsequent purification via chromatography and/or recrystallization6,7,8,9,10. A handful of isolated reports have detailed the synthesis of these compounds using microwave radiation, but all required extensive heating time and offered little advantage when compared to other previously reported methods11,12.
Despite their utility, there are a limited number of 1-aryl-1H-pyrazole-5-amines available from commercial vendors. We recently had success preparing nitrogen heterocycles using a microwave reactor13 and decided to investigate a related methodology for pyrazole-5-amine analogs. In this paper, we detail our procedure to prepare 1-aryl-1H-pyrazole-5-amines by reacting an aryl hydrazine with either 3-aminocrotononitrile or an &#945;-cyanoketone in 1 M HCl under microwave radiation. The advantages of this procedure include a short reaction time and the ability to incorporate a variety of functional groups including halides, nitriles, phenols, sulfones and nitro groups14.

<table border="0" cellpadding="0" cellspacing="0" style="width:757px;" width="757">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">2-5mL Microwave vial set</td>
			<td style="width:121px;">Chemglass</td>
			<td style="width:185px;">CG-4920-01&#160;</td>
			<td style="width:167px;">Set includes appropriate stir bars and 20mm aluminum seals</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">Biotage Initiator+ microwave</td>
			<td style="width:121px;">Biotage</td>
			<td style="width:185px;">356007</td>
			<td>Includes crimper and decapper tool.</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">Sonicator</td>
			<td style="width:121px;">Kendal</td>
			<td style="width:185px;">Ultrasonic Cleaner GB-928</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">Glassware oven</td>
			<td style="width:121px;">Quincy Lab</td>
			<td style="width:185px;">20GC</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">4-Fluorophenylhydrazine hydrochloride</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:185px;">AC119590100</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">3-Aminocrotonitrile</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:185px;">AC152451000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">CDCl3</td>
			<td style="width:121px;">Cambridge Labs</td>
			<td style="width:185px;">DLM-7-100</td>
			<td>99.8% D</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">Hydrochloric acid, concentrated</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:185px;">A144SI-212</td>
			<td>Used to prepare 1 M HCl solution</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:284px;">Sodium hydroxide pellets</td>
			<td style="width:121px;">Fisher</td>
			<td style="width:185px;">S318-100</td>
			<td>Used to prepare 10% NaOH solution</td>
		</tr>
	</tbody>
</table>

microwave-assisted preparation of 1-aryl-1h-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it efficient in both time and resources and utilizes water as the solvent. 3-Aminocrotononitrile or an appropriate &#945;-cyanoketone is combined with an aryl hydrazine and dissolved in 1 M HCl. The mixture is then heated in a microwave reactor at 150 &#176;C, typically for 10-15 min. The product can be readily obtained by basifying the solution with 10% NaOH and isolating the desired compound with a simple vacuum filtration. The use of water as a solvent in this reaction lends to its ease and utility in production, and this method is easily reproducible with a variety of functional groups. Typical isolated yields range from 70-90%, and reactions can be performed on the milligram to gram scale with little to no change in observed yields. Some of the applications of these molecules and their derivatives include pesticides, anti-malarials, and chemotherapeutics, among many others.

In this demonstration, 3-aminocrotononitrile and 4-fluorophenylhydrazine hydrochloride were reacted to produce 1-(4-fluorophenyl)-3-methyl-1H-pyrazol-5-amine (Figure 1). The mixture of the starting material in the microwave vial seen in Figure 2a shows the heterogeneous suspension created by combining the starting materials in the 1 M HCl solvent. It is recommended to pre-mix the solution for a few seconds over a stir plate to ensure th...

Watch this Scientific Journal Video about Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines at JoVE.com

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an &#945;-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it ...

microwave-assisted-preparation-of-1-aryl-1h-pyrazole-5-amines

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6.6K Views.  California Polytechnic State University. 1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an α-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

Video: Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Microwave-assisted Functionalization of Poly(ethylene glycol) and On-resin Peptides for Use in Chain Polymerizations and Hydrogel Formation

One of the main benefits to using poly(ethylene glycol) (PEG) macromers in hydrogel formation is synthetic versatility. The ability to draw from a large variety of PEG molecular weights and configurations (arm number, arm length, and branching pattern) affords researchers tight control over resulting hydrogel structures and properties, including Young&#8217;s modulus and mesh size. This video will illustrate a rapid, efficient, solvent-free, microwave-assisted method to methacrylate PEG precursors into poly(ethylene glycol) dimethacrylate (PEGDM). This synthetic method provides much-needed starting materials for applications in drug delivery and regenerative medicine. The demonstrated method is superior to traditional methacrylation methods as it is significantly faster and simpler, as well as more economical and environmentally friendly, using smaller amounts of reagents and solvents. We will also demonstrate an adaptation of this technique for on-resin methacrylamide functionalization of peptides. This on-resin method allows the N-terminus of peptides to be functionalized with methacrylamide groups prior to deprotection and cleavage from resin. This allows for selective addition of methacrylamide groups to the N-termini of the peptides while amino acids with reactive side groups (e.g.&#160;primary amine of lysine, primary alcohol of serine, secondary alcohols of threonine, and phenol of tyrosine) remain protected, preventing functionalization at multiple sites. This article will detail common analytical methods (proton Nuclear Magnetic Resonance spectroscopy (;H-NMR) and Matrix Assisted Laser Desorption Ionization Time of Flight mass spectrometry (MALDI-ToF)) to assess the efficiency of the functionalizations. Common pitfalls and suggested troubleshooting methods will be addressed, as will modifications of the technique which can be used to further tune macromer functionality and resulting hydrogel physical and chemical properties. Use of synthesized products for the formation of hydrogels for drug delivery and cell-material interaction studies will be demonstrated, with particular attention paid to modifying hydrogel composition to affect mesh size, controlling hydrogel stiffness and drug release.

Microwave-assisted Functionalization of Polyethylene glycol and On-resin Peptides for Use in Chain Polymerizations and Hydrogel Formation

This video will illustrate a rapid, efficient method to methacrylate poly(ethylene glycol), enabling chain polymerizations and hydrogel synthesis. It will demonstrate how to similarly introduce methacrylamide functionalities into peptides, detail common analytical methods to assess functionalization efficiency, provide suggestions for troubleshooting and advanced modifications, and demonstrate typical hydrogel characterization techniques.

One of the main benefits to using poly(ethylene glycol) (PEG) macromers in hydrogel formation is synthetic versatility. The ability to draw from a large ...

Preparation of Silica Nanoparticles Through Microwave-assisted Acid-catalysis

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle diameters ranging from 30-250 nm by varying the reaction conditions. Through the selection of a microwave compatible solvent, silicic acid precursor, catalyst, and microwave irradiation time, these microwave-assisted methods were capable of overcoming the previously reported shortcomings associated with synthesis of silica nanoparticles using microwave reactors. The siloxane precursor was hydrolyzed using the acid catalyst, HCl. Acetone, a low-tan &#948; solvent, mediates the condensation reactions and has minimal interaction with the electromagnetic field. Condensation reactions begin when the silicic acid precursor couples with the microwave radiation, leading to silica nanoparticle sol formation. The silica nanoparticles were characterized by dynamic light scattering data and scanning electron microscopy, which show the materials&#39; morphology and size to be dependent on the reaction conditions. Microwave-assisted reactions produce silica nanoparticles with roughened textured surfaces that are atypical for silica sols produced by St&#246;ber&#39;s methods, which have smooth surfaces.

Silica nanoparticles were prepared using acid-catalysis of a siloxane precursor and microwave-assisted synthetic techniques resulting in the controlled growth of nanomaterials ranging from 30-250 nm in diameter. The growth dynamics can be controlled by varying the initial silicic acid concentration, time of the reaction, and temperature of reaction.

Microwave-assisted synthetic techniques were used to quickly and reproducibly produce silica nanoparticle sols using an acid catalyst with nanoparticle ...

Preparation of Carbon Nanosheets at Room Temperature

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into defined aggregates in aqueous media and at the air-water interface. In the aggregated state, the oligoynes can then be carbonized under mild conditions while preserving the morphology and the embedded chemical functionalization. This novel approach provides direct access to functionalized carbon nanomaterials. In this article, we present a synthetic approach that allows us to prepare hexayne carboxylate amphiphiles as carbon-rich siblings of typical fatty acid esters through a series of repeated bromination and Negishi-type cross-coupling reactions. The obtained compounds are designed to self-assemble into monolayers at the air-water interface, and we show how this can be achieved in a Langmuir trough. Thus, compression of the molecules at the air-water interface triggers the film formation and leads to a densely packed layer of the molecules. The complete carbonization of the films at the air-water interface is then accomplished by cross-linking of the hexayne layer at room temperature, using UV irradiation as a mild external stimulus. The changes in the layer during this process can be monitored with the help of infrared reflection-absorption spectroscopy and Brewster angle microscopy. Moreover, a transfer of the carbonized films onto solid substrates by the Langmuir-Blodgett technique has enabled us to prove that they were carbon nanosheets with lateral dimensions on the order of centimeters.

We present the synthesis of an amphiphilic hexayne and its use in the preparation of carbon nanosheets at the air-water interface from a self-assembled monolayer of these reactive, carbon-rich molecular precursors.

Amphiphilic molecules equipped with a reactive, carbon-rich "oligoyne" segment consisting of conjugated carbon-carbon triple bonds self-assemble into ...

Preparation of Biopolymer Aerogels Using Green Solvents

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers (gelatin, agar, cellulose), only recently have biomasses been recognized as an abundant source of chemically diverse macromolecules for functional aerogel materials. Biopolymer aerogels (pectin, alginate, chitosan, cellulose, etc.) exhibit both specific inheritable functions of starting biopolymers and distinctive features of aerogels (80-99% porosity and specific surface up to 800 m2/g). This synergy of properties makes biopolymer aerogels promising candidates for a wide gamut of applications such as thermal insulation, tissue engineering and regenerative medicine, drug delivery systems, functional foods, catalysts, adsorbents and sensors. This work demonstrates the use of pressurized carbon dioxide (5 MPa) for the ionic cross linking of amidated pectin into hydrogels. Initially a biopolymer/salt dispersion is prepared in water. Under pressurized CO2 conditions, the pH of the biopolymer solution is lowered to 3 which releases the crosslinking cations from the salt to bind with the biopolymer yielding hydrogels. Solvent exchange to ethanol and further supercritical CO2 drying (10 - 12 MPa) yield aerogels. Obtained aerogels are ultra-porous with low density (as low as 0.02 g/cm3), high specific surface area (350 - 500 m2/g) and pore volume (3 - 7 cm3/g for pore sizes less than 150 nm).

A new way for the production of biopolymer-based aerogels by carbon dioxide (CO2) induced gelation is shown. The technique utilizes pressurized carbon dioxide (5 MPa) for the production of biopolymer hydrogels and supercritical CO2 (12 MPa) to convert gels into aerogels. The only solvents needed besides CO2 are water and ethanol.

Although the first reports on aerogels made by Kistler1 in the 1930s dealt with aerogels from both inorganic oxides (silica and others) and biopolymers ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Microfluidic Preparation of Liquid Crystalline Elastomer Actuators

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation usually consists in the formation of droplets containing low molar mass liquid crystals at elevated temperatures. Subsequently, these particle precursors are oriented in the flow field of the capillary and solidified by a crosslinking polymerization, which produces the final actuating particles. The optimization of the process is necessary to obtain the actuating particles and the proper variation of the process parameters (temperature and flow rate) and allows variations of size and shape (from oblate to strongly prolate morphologies) as well as the magnitude of actuation. In addition, it is possible to vary the type of actuation from elongation to contraction depending on the director profile induced to the droplets during the flow in the capillary, which again depends on the microfluidic process and its parameters. Furthermore, particles of more complex shapes, like core-shell structures or Janus particles, can be prepared by adjusting the setup. By the variation of the chemical structure and the mode of crosslinking (solidification) of the liquid crystalline elastomer, it is also possible to prepare actuating particles triggered by heat or UV-vis irradiation.

This article describes the microfluidic process and parameters to prepare actuating particles from liquid crystalline elastomers. This process allows the preparation of actuating particles and the variation of their size and shape (from oblate to strongly prolate, core-shell, and Janus morphologies) as well as the magnitude of actuation.

This paper focuses on the microfluidic process (and its parameters) to prepare actuating particles from liquid crystalline elastomers. The preparation ...

Reducing Willow Wood Fuel Emission by Low Temperature Microwave Assisted Hydrothermal Carbonization

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative environmental impact and slag formation. The selected short rotation coppice (SRC) willow wood has a high ash content (<img alt="Equation 1" src="/files/ftp_upload/58970/58970eq1.jpg" /> = 1.96%) and, therefore, a high content of emission and slag precursors. Therefore, the reduction of minerals from SRC willow wood by low temperature microwave assisted hydrothermal carbonization (MAHC) at 150 &#176;C, 170 &#176;C, and 185 &#176;C is investigated. An advantage of MAHC over conventional reactors is an even temperature conductance in the reaction medium, as microwaves penetrate the whole reactor volume. This allows a better temperature control and a faster cooldown. Therefore, a succession of depolymerization, transformation and repolymerization reactions can be analyzed effectively. In this study, the analysis of the mass loss, ash content and composition, heating values and molar O/C and H/C ratios of the treated and untreated SCR willow wood showed that the mineral content of the MAHC coal was reduced and the heating value increased. The process water showed a decreasing pH and contained furfural and 5-methylfurfural. A process temperature of 170 &#176;C showed the best combination of energy input and ash component reduction. The MAHC allows a better understanding of the hydrothermal carbonization process, while a large-scale industrial application is unlikely because of the high investment costs.

A protocol for the emission precursor depletion from low quality biomass by low temperature microwave assisted hydrothermal carbonization treatment is presented. This protocol includes the microwave parameters and the analysis of the biocoal product and process water.

Biomass is a sustainable fuel, as its CO2 emissions are reintegrated in biomass growth. However, the inorganic precursors in the biomass cause a negative ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...

Microwave Synthesis and Characterization of Nickel Hydroxide Nanosheets

Effect of Microwave Synthesis Conditions on the Structure of Nickel Hydroxide Nanosheets

A protocol for rapid, microwave-assisted hydrothermal synthesis of nickel hydroxide nanosheets under mildly acidic conditions is presented, and the effect of reaction temperature and time on the material&#39;s structure is examined. All reaction conditions studied result in aggregates of layered &#945;-Ni(OH)2 nanosheets. The reaction temperature and time strongly influence the structure of the material and product yield. Synthesizing &#945;-Ni(OH)2 at higher temperatures increases the reaction yield, lowers the interlayer spacing, increases crystalline domain size, shifts the frequencies of interlayer anion vibrational modes, and lowers the pore diameter. Longer reaction times increase reaction yields and result in similar crystalline domain sizes. Monitoring the reaction pressure in situ shows that higher pressures are obtained at higher reaction temperatures. This microwave-assisted synthesis route provides a rapid, high-throughput, scalable process that can be applied to the synthesis and production of a variety of transition metal hydroxides used for numerous energy storage, catalysis, sensor, and other applications.

Author Spotlight: A Rapid, Microwave-Assisted Hydrothermal Synthesis Of Nickel Hydroxide Nanosheets 

Nickel hydroxide nanosheets are synthesized by a microwave-assisted hydrothermal reaction. This protocol demonstrates that the reaction temperature and time used for microwave synthesis affects the reaction yield, crystal structure, and local coordination environment.

A protocol for rapid, microwave-assisted hydrothermal synthesis of nickel hydroxide nanosheets under mildly acidic conditions is presented, and the effect ...