The authors thank Dr. A. Tejeda-Cruz (X-ray; IIM-UNAM). R.Y. thanks CINVESTAV, Mexico for technical support. M.S.S acknowledges the financial support by Spanish Government, MINECO (MAT2012-31127). I.A.I thanks CONACyT (212318) and PAPIIT UNAM (IN100415), Mexico for financial support. E.G-Z. thanks CONACyT (156801 and 236879), Mexico for financial support. Thanks to U. Winnberg (ITAM and ITESM) for scientific discussions.

CAUTION: The chemicals used in this catalytic procedure are relatively low in toxicity and non-carcinogenic. Please use all appropriate safety precautions when performing this experimental procedure such as safety glasses, gloves, lab coat, full length pants and closed-toe shoes. One part of the following procedures involves standard air-free handling techniques.
1. Activation of the Catalyst (HKUST-1)
<ol>
	<li>Crystallinity Characterization of the Catalyst 
	Note: HKUST-1 is a commercially available porous coordination polymer (catalyst). In order to corroborate the crystallinity of the catalyst, samples of HKUST-1 need to be characterized by powder X-ray diffraction (PXRD).
	<ol>
		<li>Collect a PXRD pattern of a 0.1 g sample of HKUST-1 (on a diffractometer operating at 160 W (40 kV, 40 mA)) for Cu-K&#945;1 radiation (&#955; = 1.5406 &#197;) in Bragg-Brentano geometry. Record a PXRD pattern from 5&#176; to 60&#176; (2&#952;) in 0.02&#176; steps and 1 sec counting time44.</li>
	</ol>
	</li>
	<li>Desolvation of HKUST-1
	<ol>
		<li>Weigh 0.05 g of the catalyst (HKUST-1).</li>
		<li>Clamp a 250 ml two-neck round-bottom flask to a stand and insert a magnetic stirring bar into the round-bottom flask.</li>
		<li>Attach a condenser to the round-bottom flask.</li>
		<li>Use some vacuum grease or Teflon tape between the joints of the flask and condenser in order to generate a perfect seal.</li>
		<li>Connect the condenser, from the top, to a vacuum pump (via a stopcock to a hose).</li>
		<li>Make sure that the vacuum generated by the pump is approximately 10-2 bar. 
		Note: For convenience, this experimental set up (the two-neck round-bottom flask attached to a condenser, which is connected to a vacuum pump) will be referred as the activation system.</li>
		<li>Place the catalyst (0.05 g) inside the 250 ml two-neck round-bottom flask.</li>
		<li>Insert a rubber septum in the second neck of the round bottom flask and make sure that it seals (fits) properly.</li>
		<li>Carefully, place the activation system into a sand bath.</li>
		<li>Start the vacuum pump and carefully turn the stopcock until it is fully open. With a hot plate, heat the activation system up to 100 &#176;C for 1 hr.</li>
		<li>Stir at the lowest speed of the hot plate, in order to distribute homogenously the catalyst at the bottom of the round-bottom flask.</li>
		<li>Turn off the heat (hot plate) after 1 hr of heating, and let the activation system cool to room temperature (under vacuum).</li>
		<li>Once the activation system has cooled down to room temperature, turn the stopcock off (thus, the activation system would be under passive vacuum) and turn the pump off.</li>
		<li>Connect a balloon filled with nitrogen (N2), through the septum, to the two-neck round-bottom flask and wait a few seconds to reach the equilibrium pressure. 
		Note: After the activation of the catalyst, leave it under an inert atmosphere (N2) since the access to the uncoordinated metal sites (or open metal sites) is the key to obtain an active catalyst.</li>
		<li>Remove the balloon filled with N2, when the equilibrium pressure has been achieved. 
		Note: A color change from turquoise (as-received HKUST-1) to dark blue (upon activation) is observed.</li>
	</ol>
	</li>
</ol>
2. Synthesis of Vanillin via Heterogeneous Catalysis
<ol>
	<li>Degassing of the Organic Solvent
	<ol>
		<li>Degas approximately 70 ml of ethanol by bubbling N2 for 5 min.</li>
	</ol>
	</li>
	<li>Preparation of the Catalytic Reaction
	<ol>
		<li>Add 10 ml of degassed ethanol to the two-neck round-bottom flask and gently stir the suspension on a hot plate.</li>
		<li>Add 5 ml of H2O2 (30 % in H2O) to the suspension.</li>
		<li>Add 0.25 ml of acetonitrile to the suspension.</li>
		<li>Weigh 0.50 g of ferulic acid and dissolve it in 20 ml of degassed ethanol in a beaker.</li>
		<li>Add the dissolved ferulic acid to the suspension.</li>
		<li>Wash the beaker with 20 ml of degassed ethanol and add it to the suspension.</li>
	</ol>
	</li>
	<li>Oxidation of Trans-ferulic Acid to Vanillin
	<ol>
		<li>Unplug the hose that connects the condenser to the vacuum pump.</li>
		<li>Turn on the tap water that goes through the condenser. Preferably, use a water pump.</li>
		<li>Heat the suspension up to 100 &#176;C (refluxing) for 1 hr.</li>
		<li>Turn off the heat and stirring. Carefully lift the two-neck round-bottom flask (attached to the condenser) and let it cool to room temperature.</li>
	</ol>
	</li>
	<li>Work-up of the Reaction
	<ol>
		<li>Filter off the reaction mixture (use a Buchner funnel and flask), recover the catalyst (HKUST-1) and wash it with 200 ml of ethyl acetate. 
		Note: In order to speed up the filtration process, use a vacuum (connected to the Buchner flask) to quickly recover and wash the catalyst.</li>
		<li>Corroborate the retention of framework crystallinity of the catalyst by PXRD as in Section 1.</li>
		<li>Concentrate the combined organic phases (under vacuum with a rotary evaporator) and re-dissolve it with 100 ml ethyl acetate.</li>
		<li>Wash the organic phases (use a separation funnel) with a saturated solution of NH4Cl (30 ml).</li>
		<li>Recover the organic phases and mix them with anhydrous Na2SO4 (30 g). Let the suspension stand for 15 min.</li>
		<li>Filter the suspension off and recover the filtrate.</li>
		<li>Concentrate the filtrate (to approximately 20 ml) under vacuum with a rotary evaporator.</li>
	</ol>
	</li>
	<li>Purification of the Residue (Vanillin)
	<ol>
		<li>Purify the residue by flash column chromatography44. The stationary phase is silica gel and the mobile phase is a solvent mixture of ethyl acetate-hexane (5:95).</li>
		<li>Pack the glass column for chromatography (1 cm x 30 cm) with silica gel (1 cm x 6 cm). Saturate the column with acetate-hexane (5:95) solvent mixture.</li>
		<li>Pour carefully the concentrated-filtrate at top of the glass column.</li>
		<li>Slowly add the solvent mixture to the glass column and collect all of the fractions until 1,200 ml are collected.</li>
		<li>Concentrate the organic fractions (1,200 ml) with a rotary evaporator until dryness.</li>
		<li>Recover the final solid powder that is the purified vanillin.</li>
	</ol>
	</li>
</ol>

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J., Narbad, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vanilin.">Vanilin.</a> Phytochemistry. 63 (5), 505-515 (2003).</li><li>Serra, S., Fuganti, C., Brenna, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biocatalytic+preparation+of+natural+flavours+and+fragrances.">Biocatalytic preparation of natural flavours and fragrances.</a> Trends Biotechnol. 23 (4), 193-198 (2005).</li><li>Longo, M. A., Sanrom&#225;n, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Production+of+Food+Aroma+Compounds:+Microbial+and+Enzymatic+Methodologies.">Production of Food Aroma Compounds: Microbial and Enzymatic Methodologies.</a> Food Technol. Biotechnol. 44 (3), 335-353 (2006).</li><li>Yepez, R., 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=Catalytic+activity+of+HKUST-1+in+the+oxidation+of+trans-ferulic+acid+to+vanillin.">Catalytic activity of HKUST-1 in the oxidation of trans-ferulic acid to vanillin.</a> New. J. Chem. 39 (7), 5112-5115 (2015).</li></ol>

The authors have nothing to disclose.

The fundamental step for the catalytic conversion of trans-ferulic acid to vanillin was the activation of the catalyst (HKUST-1). If the catalyst is not activated in situ (under vacuum and at 100 &#176;C), only partial conversion of trans-ferulic acid to vanillin was observed44. In other words, the accessibility to open metal sites is crucial for the catalytic cycle44, and this can be achieved by the elimination of coordinated water to the Cu(II) metal sites within the por...

The use of porous coordination polymers (PCPs) as heterogeneous catalysts1-4 is a relatively new research field. Due to very interesting properties that PCPs show, e.g., porous regularity, high surface area and metal access, they can offer new alternatives for heterogeneous catalysts5-6. The generation of catalytically active PCPs has been the main focus of many research groups7-10. A porous coordination polymer is constituted by metal ions and organic linkers and thus, the catalytic activity of these materials is provided by any of these parts. Some PCPs contain unsaturated (active) metals that can catalyze a chemical reaction11. However, the generation of unsaturated metal sites (open metal sites) within coordination polymers is not a trivial task and it represents a synthetic challenge that can be summarized in: (i) the generation of vacant coordination by removal of labile ligands7-11; (ii) the generation of bimetallic PCPs by incorporating organometallic ligands (previously synthesized)8,12-13; (iii) the post-synthetic variation of the metal ions9,14-15 or to the organic ligands10, 16-17 within the pores of the PCPs. Since the methodology (i) is the simplest thus, it is the most frequently used. Typically, the generation of open metal sites has been used for enhancing the affinity of PCPs towards H218-19, as well as for designing active heterogeneous catalysts20-27. In order to achieve good catalyst properties, PCPs need to show, additionally to the accessibility of open metal sites, retention of the crystallinity after the catalytic experiment, relatively high thermal stability and chemical stability to the reaction conditions.
HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate)7 is a well-investigated porous coordination polymer constructed with Cu(II) cations, that are coordinated to the carboxylate ligands and water. Interestingly, these water molecules can be eliminated (by heating) and this provides a square planar coordination around the copper ions which exhibit hard Lewis acid properties11. Bordiga and co-workers28 showed that the elimination of these H2O molecules did not affect the crystallinity (retention of the regularity) and the oxidation state of the metal ions (Cu(II)) was not affected. The use of HKUST-1 as a catalyst has been extensively investigated29-33 and in particular (very relevant for the present work) the oxidation with hydrogen peroxide of aromatic molecules34.
Vanilla is one of the most widely used flavoring agents in the cosmetic, pharmaceutical and food industries. It is extracted from the cured beans of the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon. The Mayan and Aztec civilizations (pre-Columbian people) first realized the enormous potential of vanilla as a flavoring agent since it improved the chocolate flavor35-37. Vanilla was first isolated in 185838 and it was not until 187439 that the chemical structure of vanillin was finally determined. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long40, the rest of vanillin is synthesized40. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc. However, these approaches have the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents41-43. Herein, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

<table><tbody><tr><td>HKUST-1</td><td>Sigma-Aldrich</td><td>MFCD10567003</td><td></td></tr><tr><td>Ferulic Acid (trans-4-Hydroxy-3-methoxycinnamic acid)</td><td>Sigma-Aldrich</td><td>537-98-4</td><td></td></tr><tr><td>Ethanol</td><td>Sigma-Aldrich</td><td>64-17-5</td><td></td></tr><tr><td>Hydrogen peroxide solution</td><td>Sigma-Aldrich</td><td>7722-84-1</td><td></td></tr><tr><td>Acetonitrile</td><td>Sigma-Aldrich</td><td>75-05-8</td><td></td></tr><tr><td>Ethyl acetate</td><td>Sigma-Aldrich</td><td>141-78-6</td><td></td></tr><tr><td>Ammonium chloride</td><td>Sigma-Aldrich</td><td>12125-02-9</td><td></td></tr><tr><td>Sodium sulfate anhydrous</td><td>Sigma-Aldrich</td><td>7757-82-6</td><td></td></tr><tr><td>Ethyl acetate</td><td>Sigma-Aldrich</td><td>141-78-6</td><td></td></tr><tr><td>n-Hexane</td><td>Sigma-Aldrich</td><td>110-54-3</td><td></td></tr><tr><td>Silica Gel</td><td>Sigma-Aldrich</td><td>112926-00-8</td><td>Size 70/230</td></tr><tr><td>250 ml two-neck round-bottom flask</td><td>Sigma-Aldrich</td><td>Z516872-1EA</td><td>250 ml capacity</td></tr><tr><td>Magnetic stirring bar</td><td>Bel-Art products</td><td>371100002</td><td>Teflon, octagon</td></tr><tr><td>Condenser</td><td>Cole-Parmer</td><td>JZ-34706-00</td><td>200 mm Jacket length</td></tr><tr><td>Vacuum pump (Approx. 10&lt;sup&gt;-2&lt;/sup&gt; bar)</td><td>Cole-Parmer</td><td>JZ-78162-00</td><td>Vacuum/Pressure Diaphragm Pump</td></tr><tr><td>Stopcock</td><td>Cole-Parmer</td><td>EW-30600-00</td><td>with a male Luer slip</td></tr><tr><td>Hose</td><td>Cole-Parmer</td><td>JZ-06602-04</td><td>16.0 mm ID and 23.2&amp;nbsp;mm ED</td></tr><tr><td>Rubber septums</td><td>Cole-Parmer</td><td>JZ-08918-34</td><td>Silicone with PTFE coating</td></tr><tr><td>Hot plate</td><td>Cole-Parmer</td><td>JZ-04660-15</td><td>10.2 cm x 10.2 cm, 5 to 540 &amp;deg;C</td></tr><tr><td>Sand bath</td><td>Cole-Parmer</td><td>GH-01184-00</td><td>Fluidized Sand Bath SBS-4, 50 to 600 &amp;deg;C</td></tr><tr><td>N&lt;sub&gt;2&lt;/sub&gt; gas</td><td>INFRA</td><td>Cod. 103</td><td>Cylinder 9&amp;nbsp;m&lt;sup&gt;3&lt;/sup&gt;</td></tr><tr><td>Ballons (filled with N&lt;sub&gt;2&lt;/sub&gt; gas)</td><td>Sigma-Aldrich</td><td>Z154989-100EA</td><td>Thick-wall, natural latex rubber</td></tr><tr><td>Syringes with removable needles</td><td>Sigma-Aldrich</td><td>Z116912-100EA</td><td>10 ml capacity</td></tr><tr><td>Filter paper</td><td>Cole-Parmer</td><td>JZ-81050-24</td><td>Grade No. 235 qualitative filter paper (90 mm diameter disc)</td></tr><tr><td>Buchner funnel</td><td>Cole-Parmer</td><td>JZ-17815-04</td><td>320 ml capacity which accept standard paper filter sizes</td></tr><tr><td>Buchner flask</td><td>Cole-Parmer</td><td>JZ-34557-02</td><td>250 ml capacity</td></tr><tr><td>Rotary Evaporator</td><td>Cole-Parmer</td><td>JZ-28710-02</td><td></td></tr><tr><td>Beakers</td><td>Cole-Parmer</td><td>JZ-34502-(02,04,05)</td><td>Pyrex Brand 1000 Griffin; 20, 50 and 100 ml</td></tr><tr><td>Separation funnel&amp;nbsp;</td><td>Cole-Parmer</td><td>JZ-34505-44</td><td>Capacity for 125 ml with steam length of 60 mm</td></tr><tr><td>Glass column for chromatography</td><td>Cole-Parmer</td><td>JZ-34695-42</td><td>Column with fritted disk, 10.5 mm ID x 250 mm L</td></tr><tr><td>PXRD diffractometer</td><td>Bruker</td><td></td><td>AXS D8 Advance XRD</td></tr><tr><td>FTIR spectrophotometer</td><td>Thermo scientific</td><td>FT-IR (JZ-83008-02); ATR (JZ-83008-26)</td><td>Nicolet iS5 FT-IR Spectrometer, with KBr Windows and iD5 Diamond ATR</td></tr></tbody></table>

hkust-1 as a heterogeneous catalyst for the synthesis of vanillin

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately 200 different odorant compounds in addition to vanillin. The natural extraction of vanillin (from the orchid Vanilla planifolia, Vanilla tahitiensis and Vanilla pompon) represents only 1% of the worldwide production and since this process is expensive and very long, the rest of the production of vanillin is synthesized. Many biotechnological approaches can be used for the synthesis of vanillin from lignin, phenolic stilbenes, isoeugenol, eugenol, guaicol, etc., with the disadvantage of harming the environment since these processes use strong oxidizing agents and toxic solvents. Thus, eco-friendly alternatives on the production of vanillin are very desirable and thus, under current investigation. Porous coordination polymers (PCPs) are a new class of highly crystalline materials that recently have been used for catalysis. HKUST-1 (Cu3(BTC)2(H2O)3, BTC = 1,3,5-benzene-tricarboxylate) is a very well known PCP which has been extensively studied as a heterogeneous catalyst. Here, we report a synthetic strategy for the production of vanillin by the oxidation of trans-ferulic acid using HKUST-1 as a catalyst.

Three representative samples of HKUST-1 were analyzed by infrared spectroscopy: non-activated, activated at 100 &#176;C for 1 hr in an oven (exposed to air), and activated under vacuum (10-2 bar) at 100 &#176;C for 1 hr. Thus, Fourier transform infrared (FTIR) spectra were recorded using a spectrometer with a single reflection diamond ATR accessory (Figure 1). For all spectra, 64 scans in the 4,000 to 400 cm-1 range were recorded with a spectral reso...

Watch this Scientific Journal Video about HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin at JoVE.com

HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained.

Vanillin (4-hydoxy-3-methoxybenzaldehyde) is the main component of the extract of vanilla bean. The natural vanilla scent is a mixture of approximately ...

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10.1K Views.  Autonomous Metropolitan University-Azcapotzalco. The conversion of trans-ferulic acid to vanillin was achieved by heterogeneous catalysis. HKUST-1 was employed in this synthesis and the essential step in the catalytic process was the generation of unsaturated metal sites. Thus, when the catalyst was activated under vacuum, full vanillin conversion (yield of 95%) was obtained. 

Video: HKUST-1 as a Heterogeneous Catalyst for the Synthesis of Vanillin

Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form catalytically active N-Heterocyclic Carbenes (NHCs). Here we have used ILs as precatalysts in the addition of &#945;,&#946;-unsaturated aldehydes to chalcones to form 1,6-ketoesters, incorporating an anti-diphenyl moiety in a highly stereoselective fashion. The reaction has a broad substrate scope and several functional groups and heteroaromatics can be integrated into the ketoester backbone in generally good yields with maintained stereoselectivity. The reaction protocol is robust and scalable. The starting materials are inexpensive and the products can be obtained after simple filtration, avoiding solvent-demanding chromatography. Furthermore, the IL can be recycled up to 5 times without any loss of reactivity. Moreover, the 1,6-ketoester end product is a potent gelator in several hydrocarbon based solvents. The method enables rapid access to and evaluation of a new class of low molecular weight gelators (LMWGs) from recyclable and inexpensive starting materials.

Ionic liquids (ILs) mediate fast, simple and cheap access to 1,6-ketoesters in high diastereoselectivities and good yields. The reaction protocol is robust and the 1,6-ketoesters can be obtained in gram scale after a simple filtration protocol. Moreover, the 1,6-ketoesters are potent gelators in hydrocarbon solvents.

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form ...

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

Synthesis and Testing of Supported Pt-Cu Solid Solution Nanoparticle Catalysts for Propane Dehydrogenation

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are demonstrated here. The catalyst forms a substitutional solid solution structure, with a small and uniform particle size around 2 nm. This is realized by careful control over the impregnation, calcination, and reduction steps during catalyst preparation and is identified by advanced in situ synchrotron techniques. The catalyst propane dehydrogenation performance continuously improves with increasing Cu:Pt atomic ratio.

A convenient method for the synthesis of 2 nm supported bimetallic nanoparticle Pt-Cu catalysts for propane dehydrogenation is reported here. In situ synchrotron X-ray techniques allow for the determination of the catalyst structure, which is typically unobtainable using laboratory instruments.

A convenient method for the synthesis of bimetallic Pt-Cu catalysts and performance tests for propane dehydrogenation and characterization are ...

Nanosponge Tunability in Size and Crosslinking Density

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with controlled dimensions. This approach begins with synthesis of a functionalized lactone which is key to the pendant functionalization of the resulting polymer. Valerolactone (VL) and allyl-valerolactone (AVL) are then copolymerized using ring-opening polymerization. Post-polymerization modification is then used to install an epoxide moiety on some or all of the pendant allyl groups. Epoxy-amine chemistry is employed to form nanoparticles in a dilute solution of both polymer and small molecule diamine crosslinker based on the desired nanosponge size and crosslinking density. Nanosponge sizes can be characterized by transmission electron microscopy (TEM) imaging to determine the dimension and distribution. This method provides a pathway by which highly tunable polyesters can create tunable nanoparticles, which can be used for small molecule drug encapsulation. Due to the nature of the backbone, these particles are hydrolytically and enzymatically degradable for a controlled release of a wide range of hydrophobic small molecules.

This article describes a process for tuning the size and crosslinking density of covalently crosslinked nanoparticles from linear polyesters containing pendant functionality. By tailoring synthesis parameters (polymer molecular weight, pendant functionality incorporation, and crosslinker equivalents), a desired nanoparticle size and crosslinking density can be achieved for drug delivery applications.

We describe a protocol for the synthesis of linear polyesters containing pendant epoxide functionality and their incorporation into a nanosponge with ...

Heterogeneous Removal of Water-Soluble Ruthenium Olefin Metathesis Catalyst from Aqueous Media Via Host-Guest Interaction

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst removal via host-guest interactions. The new NHC ligand possesses an adamantyl (guest) tethered linear ethylene glycol units for hydrophobic inclusion into the cavity of a &#946;-cyclodextrin (&#946;-CD) host compound. The new NHC ligand was applied to a Ru-based olefin metathesis catalyst. The Ru catalyst demonstrated excellent activity in representative ring-closing metathesis (RCM) and ring-opening metathesis polymerization (ROMP) reactions in aqueous media as well as organic solvent, CH2Cl2. After the reaction was complete, the lingering Ru residue was removed from the aqueous solution with the efficiency of more than 99% (53 ppm of Ru residue) by simple filtration utilizing a host-guest interaction between insoluble silica-grafted &#946;-CD (host) and the adamantyl moiety (guest) on the catalyst. The new Ru catalyst also demonstrated high removal efficiency via extraction when the reaction is run in organic solvent by partitioning the crude reaction mixture between layers of diethyl ether and water. In this way, the catalyst stays in aqueous layer only. In organic layer, the residual Ru amount was only 0.14 ppm in the RCM reactions of diallyl compounds.

A removable water-soluble N-heterocyclic carbene (NHC) ligand in aqueous media via host-guest interaction has been developed. We demonstrated representative olefin metathesis reactions in water as well as in dichloromethane. Via either host-guest interaction or extraction, the residual ruthenium (Ru) catalyst was as low as 0.14 ppm after the reaction.

A highly efficient transition metal catalyst removal method is developed. The water-soluble catalyst contains a newly-designed NHC ligand for the catalyst ...

Tuning the Acidity of Pt/ CNTs Catalysts for Hydrodeoxygenation of Diphenyl Ether

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid nanosheets, a series of Pt/xHMNO6/CNTs with different solid acid compositions (x = 5, 20 wt%; M = Nb, Ta; N = Mo, W) have been prepared by carbon nanotube pretreatment, protonic exchange, solid acid exfoliation, aggregation and finally Pt particles impregnation. The Pt/xHMNO6/CNTs are characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and NH3-temperature programmed desorption. The study revealed that HNbWO6 nanosheets were attached on CNTs, with some edges of the nanosheets being bent in shape. The acid strength of the supported Pt catalysts increases in the following order: Pt/CNTs &#60; Pt/5HNbWO6/CNTs &#60; Pt/20HNbMoO6/CNTs &#60; Pt/20HNbWO6/CNTs &#60; Pt/20HTaWO6/CNTs. In addition, the catalytic hydroconversion of lignin-derived model compound: diphenyl ether using the synthesized Pt/20HNbWO6 catalyst has been investigated.

A protocol for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs is presented.

We herein present a method for the synthesis of HNbWO6, HNbMoO6, HTaWO6 solid acid nanosheet modified Pt/CNTs. By varying the weight of various solid acid ...

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products and notably to generate chiral carbon centers. The crucial first step consists in the selective double hydroboration of CO2 catalyzed by an iron hydride complex. The product obtained with this 4 e- reduction is a rare bis(boryl)acetal, compound 1, which is subjected in situ to three different reactions in a second step. The first reaction concerns a condensation reaction with (diisopropyl)phenylamine affording the corresponding imine 2. In the second and third reaction, intermediate 1 reacts with triazol-5-ylidene (Enders&#39; carbene) to afford compounds 3 or 4, depending on the reaction conditions. In both compounds, C-C bonds are formed, and chiral centers are generated from CO2 as the only source of carbon. Compound 4 exhibits two chiral centers obtained in a diastereoselective manner in a formose-type mechanism. We proved that the remaining boryl fragment plays a key role in this unprecedented stereocontrol. The interest of the method stands on the reactive and versatile nature of 1, giving rise to various complex molecules from a single intermediate. The complexity of a two-step method is compensated by the overall short reaction time (2 h for the larger reaction time), and mild reaction conditions (25 &#176;C to 80 &#176;C and 1 to 3 atm of CO2).

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

Catalytic Reactions at Amine-Stabilized and Ligand-Free Platinum Nanoparticles Supported on Titania During Hydrogenation of Alkenes and Aldehydes

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands like amines are removed by diverse pre-treatment procedures before use in heterogeneous catalysis as amines are considered as a catalyst poison. However, a possible beneficial influence of these surface modifiers on hydrogenation reactions, which is known from spectator species on metal surfaces, is often neglected.
Therefore, amine-stabilized Pt nanoparticles supported by titania (P25) were used without any pre-treatment in order to elucidate a possible influence of the ligand in liquid phase hydrogenation reactions. The catalytic activity of amine-stabilized Pt nanoparticles of two different sizes was investigated in a double-walled stirring tank reactor at 69 &#176;C to 130 &#176;C and 1 atm hydrogen pressure. The conversion of cyclohexene to cyclohexane was determined by gas chromatography (GC) and was compared to ligand-free Pt particles. All catalysts were checked before and after reaction by transmission electron spectroscopy (TEM) and X-ray photoelectron spectroscopy (XPS) for possible changes in size, shape, and ligand shell. The hydrogenation of cyclohexene in liquid phase revealed a higher conversion for amine-stabilized Pt nanoparticles on titania than the ligand-free particles. The hydrogenation of 5-methylfurfural (5-MF) was chosen for a further test reaction, since the hydrogenation of &#945;, &#946;-unsaturated aldehydes is more complex and exhibits various reaction paths. However, XPS and infrared spectroscopy (IR) proved that 5-MF acts as catalyst poison at the given reaction conditions.

This protocol shows a convenient method for comparing the catalytic properties of supported platinum catalysts, synthesized by deposition of nanosized colloids or by impregnation. The hydrogenation of cyclohexene serves as a model reaction to determine the catalytic activity of the catalysts.

Ligands like amines are used in the colloidal synthesis approach to protect platinum nanoparticles (Pt NP&#39;s) from agglomeration. Normally, ligands ...

Synthesis of Single-Crystalline Core-Shell Metal-Organic Frameworks

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. However, the synthesis of single-crystalline core-shell MOFs is very challenging, and thus a limited number of examples have been reported. Here, we suggest a method of synthesizing single-crystalline HKUST-1@MOF-5 core-shells, which is HKUST-1 at the center of MOF-5. Through the computational algorithm, this pair of MOFs was predicted to have the matched lattice parameters and chemical connection points at the interface. To construct the core-shell structure, we prepared the octahedral- and cubic-shaped HKUST-1 crystals as a core MOF, in which the (111) and (001) facets were mainly exposed, respectively. Via the sequential reaction, the MOF-5 shell was well-grown on the exposed surface, showing a seamless connect interface, which resulted in the successful synthesis of single-crystalline HKUST-1@MOF-5. Their pure phase formation was proved by optical microscopic images and powder X-ray diffraction (PXRD) patterns. This method presents the potential of and insights into the single-crystalline core-shell synthesis with different kinds of MOFs.

Here, we demonstrate a protocol for the two-step synthesis of single-crystalline core-shells using a non-isostructural metal-organic framework (MOF) pair, HKUST-1 and MOF-5, which have well-matched crystal lattices.

Because of their designability and unprecedented synergistic effects, core-shell metal-organic frameworks (MOFs) have been actively examined recently. ...