Name: retropinacol/cross-pinacol coupling reactions - a catalytic access to 1,2-unsymmetrical diols
Uploaded: 2014-04-04T13:00:00
Description: Watch this Scientific Journal Video about Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols at JoVE.com

The authors thank Deutsche Forschungsgemeinschaft, Bayer Pharma AG, Chemtura Organometallics GmbH Bergkamen, Bayer Services GmbH, BASF AG, and Sasol GmbH for financial support.

1. Preparation of Titanium(IV) tert-butoxide/Triethylchlorosilane Solution
<ol>
	<li>Dissolve 400 mg (400 &#956;l) titanium(IV) tert-butoxide (1&#160;mmol) in 10&#160;ml&#160;of dry dichloromethane. Add 150 mg (170 &#956;l) triethylchlorosilane (1&#160;mmol) to this solution at RT. 1&#160;ml&#160;of this dichloromethane-solution contains 0.1 mmol titanium(IV) tert-butoxide and 0.1 mmol triethylchlorosilane.</li>
</ol>
2. Pinacol-reaction of Tetraphenyl-1,2-ethanediol (1)...

<ol>
	<li>Hirao, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catalytic+reductive+coupling+of+carbonyl+compounds+-+The+pinacol+coupling+reaction+and.">Catalytic reductive coupling of carbonyl compounds - The pinacol coupling reaction and.</a> 279, 53-75 (2007).</li><li>Chatterjee, A., Joshi, N. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evolution+of+the+stereoselective+pinacol+coupling+reaction.">Evolution of the stereoselective pinacol coupling reaction.</a> Tetrahedron. 62, 12137-12158 (2006).</li><li>Ladipo, F. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-valent+titanium-mediated+reductive+coupling+of+carbonyl+compounds.">Low-valent titanium-mediated reductive coupling of carbonyl compounds.</a> Curr. Org. Chem. 10, 965-980 (2006).</li><li>Gans&#228;uer, A., Bluhm, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reagent-controlled+transition-metal-catalyzed+radical+reactions.">Reagent-controlled transition-metal-catalyzed radical reactions.</a> Chem. Rev. 100, 2771-2788 (2000).</li><li>Duan, X. -. F., Feng, J. X., Zi, G. -. F., Zhang, Z. -. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Convenient+synthesis+of+unsymmetrical+pinacols+by+coupling+of+structurally+similar+aromatic+aldehydes+mediated+by+low-valent+titanium.">A Convenient synthesis of unsymmetrical pinacols by coupling of structurally similar aromatic aldehydes mediated by low-valent titanium.</a> Synthesis. , 277-282 (2009).</li><li>Paquette, L. A., Lai, K. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pinacol+macrocyclization-based+route+to+the+polyfused+medium-sized+CDE+ring+system+of+lancifodilactone.">Pinacol macrocyclization-based route to the polyfused medium-sized CDE ring system of lancifodilactone.</a> G. Org. Lett. 10, 3781-3784 (2008).</li><li>Maekawa, H., Yamamoto, Y., Shimada, H., Yonemura, K., Nishiguchi, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mg-+promoted+mixed+pinacol+coupling.">Mg- promoted mixed pinacol coupling.</a> Tetrahedron Lett. 45, 3869-3872 (2004).</li><li>Kang, M., Park, J., Pedersen, S. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pinacol+cross+coupling+reactions+of+ethyl+2-alkyl-2-formylpropionates.+stereoselective+synthesis+of+2,2,4-+trialkyl-3-hydroxy-&#947;-butyrolactones.">Pinacol cross coupling reactions of ethyl 2-alkyl-2-formylpropionates. stereoselective synthesis of 2,2,4- trialkyl-3-hydroxy-&#947;-butyrolactones.</a> Syn. Lett. , 41-43 (1997).</li><li>Askham, F. R., Carroll, K. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anionic+zirconaoxiranes+as+nucleophilic+aldehyde+equivalents.+application+to+intermolecular+pinacol+cross+coupling.">Anionic zirconaoxiranes as nucleophilic aldehyde equivalents. application to intermolecular pinacol cross coupling.</a> J. Org. Chem. 58, 7328-7329 (1993).</li><li>Hou, Z., Takamine, K., Aoki, O., Shiraishi, H., Fujiwara, Y., Taniguchi, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleophilic+Addition+of+lanthanoid+metal+umpoled+diaryl+ketones+to+electrophiles.">Nucleophilic Addition of lanthanoid metal umpoled diaryl ketones to electrophiles.</a> J. Org. Chem. 53, 6077-6084 (1988).</li><li>Groth, U., Jung, M., Vogel, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intramolecular+chromium(II)-catalyzed+pinacol+cross+coupling+of+2-Mmethylene-&#945;,&#969;-dicarbonyls.">Intramolecular chromium(II)-catalyzed pinacol cross coupling of 2-Mmethylene-&#945;,&#969;-dicarbonyls.</a> Syn. Lett. , 1054-1058 (2004).</li><li>Appendino, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+Modified+Ingenol+Esters.">Synthesis of Modified Ingenol Esters.</a> Eur. J. Org. Chem. , 3413-3420 (1999).</li><li>Spaccini, R., Pastori, N., Clerici, A., Punta, C., Porta, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Key+role+of+Ti(IV)+in+the+selective+radical-radical+cross-coupling+mediated+by+the+Ingold-Fischer+effect.">Key role of Ti(IV) in the selective radical-radical cross-coupling mediated by the Ingold-Fischer effect.</a> J. Am. Chem. Soc. 130, 18018-18024 (2008).</li><li>Leonard, J., Lyfo, B., Procter, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Advanced Practical Organic Chemistry. , (2013).</li><li>Scheffler, U., Stoesser, R., Mahrwald, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Retropinacol+/+cross-pinacol+coupling+reactions+-+a+catalytic+access+to+1,2-unsymmetrical+diols.">Retropinacol / cross-pinacol coupling reactions - a catalytic access to 1,2-unsymmetrical diols.</a> Adv. Synth. Cat. 354, 2648-2652 (2012).</li></ol>

An overall decrease in reaction times and higher yields is observed by deployment of electron-rich carbonyl compounds (compare entry 3 with 17, Table 1 or entry 19 with 13, Table 2). In addition, in reactions of ketones with bulky substituents a decrease in yields is observed under comparable conditions (compare entry 12 with 11, Table 2).

Although a wide range of carbonyl compounds can be applied in this novel pro...

The pinacol coupling reaction is a general and commonly used method for the preparation of symmetrically vicinal diols (1,2-diols, pinacols). For comprehensive reviews in this field see references Hirao1, Chatterjee and&#160;Joshi2, Ladipo3,&#160;and Gans&#228;uer and&#160;Bluhm4. In contrast to that, only a few reports were published to refer an efficient realization of cross-pinacol coupling reactions to yield the corresponding unsymmetrical 1,2-diols (titanium(IV) chloride/manganese5, samarium(II) iodide6, magnesium/trimethylchlorosilane7, vanadium(II)8, zirconium/tin9,&#160;and ytterbium10). Thus, the intermolecular cross-pinacol coupling reaction still remains a big challenge in organic chemistry, especially the catalytic execution of this transformation.
The formation of cross coupling products is kinetically disfavored under conditions of a classical pinacol coupling. To obtain sufficient amounts of the unsymmetrical product delayed addition of one carbonyl compound is possible. There exist a few examples which are developing this concept, but they are based on several specific experimental manipulations and hence cannot be generalized. In addition, the required excess of one carbonyl compound in these transformations resulted in a laborious separation of a complex product mixture11.&#160;An alternative for this purpose is represented by the precomplexation of one reactant rendering equimolar amounts of an additional reagent necessary.
Various examples of a reversible pinacol reaction have been described12.&#160;These lead to the consideration that such conditions might be an optimal starting point for the selective synthesis of cross coupling products. Since a low-valent metal as well as a reactive radical species is formed simultaneously in situ, unsymmetrical diols could be formed exclusively in the presence of a suitable carbonyl reactant. To the best of our knowledge such a method has not been reported before (Porta et al. described a comparable pinacol cleavage and subsequent coupling by the additional deployment of stoichiometric amounts of AIBN (2,2&#8242;-azo-bis-isobutyronitrile) to generate the required radicals)13.
Herein a protocol is visualized which provides a rapid and operationally simple access to unsymmetrical 1,2-diols. The unsymmetrical pinacol products are mostly accessible in excellent yields (&#62;95%). Undesired symmetrically pinacol products are not observed. This new cross-pinacol methodology is based upon a retropinacol/cross-pinacol coupling sequence. It will be demonstrated in the following by representative reactions of benzopinacole (1,1,2,2-tetraphenyl-1,2-ethanediol, 1) with 2-ethylbutyraldehyde (in the aldehyde series) and with diethylketone (in the ketone series).

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:363px;">1.2-Dichloromethane</td>
			<td style="width:179px;">Sigma-Aldrich</td>
			<td style="width:137px;">319929</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Titanium(IV)tert-butoxide</td>
			<td>VWR International</td>
			<td>200014-852</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">2-Ethylbutyraldehyde</td>
			<td>Sigma-Aldrich</td>
			<td>110094</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Benzopinacol</td>
			<td>Aldrich</td>
			<td>B9807</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Triethylchlorosilane</td>
			<td>Aldrich</td>
			<td>&#160;235067</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">hexane, certified ACS</td>
			<td>Fisher scientific</td>
			<td>H29220</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">acetone, certified ACS</td>
			<td>ACROS</td>
			<td>42324</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Ammonium chloride</td>
			<td>ACROS</td>
			<td>19997</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Sodium hydrogen carbonate</td>
			<td>ACROS</td>
			<td>12336</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Magnesium sulphate</td>
			<td>ACROS</td>
			<td>41348</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">silica gel 60 F254 TLC plates</td>
			<td>VWR International</td>
			<td>1,057,140,001</td>
			<td style="width:79px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">&#160;silica gel, 0.035-0.070 for flash-chromatography</td>
			<td>ACROS</td>
			<td>240360300</td>
			<td style="width:79px;"></td>
		</tr>
	</tbody>
</table>

retropinacol/cross-pinacol coupling reactions - a catalytic access to 1,2-unsymmetrical diols

Unsymmetrical 1,2-diols are hardly accessible by reductive pinacol coupling processes. A successful execution of such a transformation is bound to a clear recognition and strict differentiation of two similar carbonyl compounds (aldehydes &#8594; secondary 1,2-diols or ketones &#8594; tertiary 1,2-diols). This fine-tuning is still a challenge and an unsolved problem for an organic chemist. There exist several reports on successful execution of this transformation but they cannot be generalized. Herein we describe a catalytic direct pinacol coupling process which proceeds via a retropinacol/cross-pinacol coupling sequence. Thus, unsymmetrical substituted 1,2-diols can be accessed with almost quantitative yields by means of an&#160;operationally simple performance under very mild conditions. Artificial techniques, such as syringe-pump techniques or delayed additions of reactants are not necessary. The procedure we describe provides a very rapid access to cross-pinacol products (1,2-diols, vicinal diols). A further extension of this new process, e.g. an enantioselective performance could provide a very useful tool for the synthesis of unsymmetrical chiral 1,2-diols.

In reactions of tetraphenyl-1,2-ethanediol 1 and acetone in the presence of catalytic amounts of titanium(IV)-alkoxides we observed the formation of 1,1-diphenyl-1,2-diol 4a and at the same time the formation of benzophenone 3 (Scheme 1). The corresponding symmetrical 1,2-diol formed by a competitive pinacol coupling of acetone was not detected. However, to obtain quantitative conversions extremely long and unacceptable reaction times were required under...

Watch this Scientific Journal Video about Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols at JoVE.com

Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols

A novel account for the synthesis of unsymmetrical 1,2-diols based on a retropinacol/cross-pinacol coupling mechanism is described. Due to the catalytic execution of this reaction a considerable improvement compared to conventional cross-pinacol couplings is achieved.

Unsymmetrical 1,2-diols are hardly accessible by reductive pinacol coupling processes. A successful execution of such a transformation is bound to a clear ...

retropinacolcross-pinacol-coupling-reactions-catalytic-access-to-12

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Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family of easy accessible, very cheap, and air stable, but highly active and universally applicable C-C cross-coupling catalysts with an excellent functional group tolerance. Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1), the least stable complex within this series towards protons; e.g. in the form of water, allows an eased nanoparticle formation and hence, proved to be the most active Heck catalyst within this series at 100 &#176;C and is a very rare example of an effective and versatile catalyst system that efficiently operates under mild reaction conditions. Rapid and complete catalyst degradation under work-up conditions into phosphonates, piperidinium salts and other, palladium-containing decomposition products assure an easy separation of the coupling products from catalyst and ligands. The facile, cheap, and rapid synthesis of 1,1',1"-(phosphinetriyl)tripiperidine and 1 respectively, the simple and convenient use as well as its excellent catalytic performance in the Heck reaction at 100 &#176;C make 1 to one of the most attractive and greenest Heck catalysts available.
We provide here the visualized protocols for the ligand and catalyst syntheses as well as the reaction protocol for Heck reactions performed at 10 mmol scale at 100 &#176;C and show that this catalyst is suitable for its use in organic syntheses.

Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1&#039;,1&#039;&#039;-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions

Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1) is an easy accessible, cheap, and air stable, but highly active Heck catalyst with an excellent functional group tolerance that efficiently operates under mild reaction conditions to give the coupling products in very high yields.

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family ...

Hot Biological Catalysis: Isothermal Titration Calorimetry to Characterize Enzymatic Reactions

Isothermal titration calorimetry (ITC) is a well-described technique that measures the heat released or absorbed during a chemical reaction, using it as an intrinsic probe to characterize virtually every chemical process. Nowadays, this technique is extensively applied to determine thermodynamic parameters of biomolecular binding equilibria. In addition, ITC has been demonstrated to be able of directly measuring kinetics and thermodynamic parameters (kcat, KM, &#916;H) of enzymatic reactions, even though this application is still underexploited. As heat changes spontaneously occur during enzymatic catalysis, ITC does not require any modification or labeling of the system under analysis and can be performed in solution. Moreover, the method needs little amount of material. These properties make ITC an invaluable, powerful and unique tool to study enzyme kinetics in several applications, such as, for example, drug discovery.
In this work an experimental ITC-based method to quantify kinetics and thermodynamics of enzymatic reactions is thoroughly described. This method is applied to determine kcat and KM of the enzymatic hydrolysis of urea by Canavalia ensiformis (jack bean) urease. Calculation of intrinsic molar enthalpy (&#916;Hint) of the reaction is performed. The values thus obtained are consistent with previous data reported in literature, demonstrating the reliability of the methodology.

Isothermal titration calorimetry measures heat flow released or absorbed in chemical reactions. This method can be used to quantify enzyme-catalysis. In this paper, the protocol for instrumental setup, experiment running, and data analysis is generally described, and applied to the characterization of enzymatic urea hydrolysis by jack bean urease.

Isothermal titration calorimetry (ITC) is a well-described technique that measures the heat released or absorbed during a chemical reaction, using it as ...

Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

Real-time Monitoring of Reactions Performed Using Continuous-flow Processing: The Preparation of 3-Acetylcoumarin as an Example

By using inline monitoring, it is possible to optimize reactions performed using continuous-flow processing in a simple and rapid way. It is also possible to ensure consistent product quality over time using this technique. We here show how to interface a commercially available flow unit with a Raman spectrometer. The Raman flow cell is placed after the back-pressure regulator, meaning that it can be operated at atmospheric pressure. In addition, the fact that the product stream passes through a length of tubing before entering the flow cell means that the material is at RT. It is important that the spectra are acquired under isothermal conditions since Raman signal intensity is temperature dependent. Having assembled the apparatus, we then show how to monitor a chemical reaction, the piperidine-catalyzed synthesis of 3-acetylcoumarin from salicylaldehyde and ethyl acetoacetate being used as an example. The reaction can be performed over a range of flow rates and temperatures, the in-situ monitoring tool being used to optimize conditions simply and easily.

Real-time monitoring allows for fast optimization of reactions performed using continuous-flow processing. Here the preparation of 3-acetylcoumarin is used as an example. The apparatus for performing in-situ Raman monitoring is described, as are the steps required to optimize the reaction.

By using inline monitoring, it is possible to optimize reactions performed using continuous-flow processing in a simple and rapid way. It is also possible ...

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 ...

A Simple, Low-cost, and Robust System to Measure the Volume of Hydrogen Evolved by Chemical Reactions with Aqueous Solutions

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) hydrogen fuel cells. Researchers seeking to develop such systems require a method of measuring the generated hydrogen. Herein, we describe a simple, low-cost, and robust method to measure the hydrogen generated from the reaction of solids with aqueous solutions. The reactions are conducted in a conventional one-necked round-bottomed flask placed in a temperature controlled water bath. The hydrogen generated from the reaction in the flask is channeled through tubing into a water-filled inverted measuring cylinder. The water displaced from the measuring cylinder by the incoming gas is diverted into a beaker on a balance. The balance is connected to a computer, and the change in the mass reading of the balance over time is recorded using data collection and spreadsheet software programs. The data can then be approximately corrected for water vapor using the method described herein, and parameters such as the total hydrogen yield, the hydrogen generation rate, and the induction period can also be deduced. The size of the measuring cylinder and the resolution of the balance can be changed to adapt the setup to different hydrogen volumes and flow rates.

The study of methods to generate on-demand hydrogen for fuel cells continues to grow in importance. However, systems to measure hydrogen evolution from the reaction of chemicals with water can be complicated and expensive. This article details a simple, low-cost, and robust method to measure the evolution of hydrogen gas.

There is a growing research interest in the development of portable systems which can deliver hydrogen on-demand to proton exchange membrane (PEM) ...

Laboratory Production of Biofuels and Biochemicals from a Rapeseed Oil through Catalytic Cracking Conversion

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil (HGO) for production of transportation fuels through a fluid catalytic cracking (FCC) route. Cracking experiments are performed with a fully automated reaction unit at a fixed weight hourly space velocity (WHSV) of 8 hr-1, 490-530 &#176;C, and catalyst/oil ratios of 4-12 g/g. When a feed is in contact with catalyst in the fluid-bed reactor, cracking takes place generating gaseous, liquid, and solid products. The vapor produced is condensed and collected in a liquid receiver at -15 &#176;C. The non-condensable effluent is first directed to a vessel and is sent, after homogenization, to an on-line gas chromatograph (GC) for refinery gas analysis. The coke deposited on the catalyst is determined in situ by burning the spent catalyst in air at high temperatures. Levels of CO2 are measured quantitatively via an infrared (IR) cell, and are converted to coke yield. Liquid samples in the receivers are analyzed by GC for simulated distillation to determine the amounts in different boiling ranges, i.e., IBP-221 &#176;C (gasoline), 221-343 &#176;C (light cycle oil), and 343 &#176;C+ (heavy cycle oil). Cracking of a feed containing canola oil generates water, which appears at the bottom of a liquid receiver and on its inner wall. Recovery of water on the wall is achieved through washing with methanol followed by Karl Fischer titration for water content. Basic results reported include conversion (the portion of the feed converted to gas and liquid product with a boiling point below 221 &#176;C, coke, and water, if present) and yields of dry gas (H2-C2's, CO, and CO2), liquefied petroleum gas (C3-C4), gasoline, light cycle oil, heavy cycle oil, coke, and water, if present.

This paper presents an experimental method to produce biofuels and biochemicals from canola oil mixed with a fossil-based feed in the presence of a catalyst at mild temperatures. Gaseous, liquid, and solid products from a reaction unit are quantified and characterized. Conversion and individual product yields are calculated and reported.

The work is based on a reported study which investigates the processability of canola oil (bio-feed) in the presence of bitumen-derived heavy gas oil ...

A Simple and Efficient Protocol for the Catalytic Insertion Polymerization of Functional Norbornenes

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic nature of the monomer is conserved. The resulting polymer, polynorbornene, has a very high glass transition temperature, Tg, and interesting optical and electrical properties. However, the polymerization of functional norbornenes by this mechanism is complicated by the fact that the endo substituted norbornene monomer has, in general, a very low reactivity. Furthermore, the separation of the endo substituted monomer from the exo monomer is a tedious task. Here, we present a simple protocol for the polymerization of substituted norbornenes (endo:exo ca. 80:20) bearing either a carboxylic acid or a pendant double bond. The process does not require that both isomers be separated, and proceeds with low catalyst loadings (0.01 to 0.02 mol%). The polymer bearing pendant double bonds can be further transformed in high yield, to afford a polymer bearing pendant epoxy groups. These simple procedures can be applied to prepare polynorbornenes with a variety of functional groups, such as esters, alcohols, imides, double bonds, carboxylic acids, bromo-alkyls, aldehydes and anhydrides.

We describe the catalytic insertion polymerization of 5-norbornene-2-carboxylic acid and 5-vinyl-2-norbornene to form functional polymers with a very high glass transition temperature.

Norbornene can be polymerized by a variety of mechanisms, including insertion polymerization whereby the double bond is polymerized and the bicyclic ...

A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

Organolithium reagents are powerful tools in the synthetic chemist&#39;s toolbox. However, the extreme pyrophoric nature of the most reactive reagents warrants proper technique, thorough training, and proper personal protective equipment. To aid in the training of researchers using organolithium reagents, a thorough, step-by-step protocol for the safe and effective use of tert-butyllithium on an inert gas line or within a glovebox is described. As a model reaction, preparation of lithium tert-butyl amide by the reaction of tert-butyl amine with one equivalent of tert-butyl lithium is presented.

The safe and proper use of organolithium reagents is described.

Organolithium reagents are powerful tools in the synthetic chemist&#39;s toolbox. However, the extreme pyrophoric nature of the most reactive reagents ...

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. Detailed and generalized protocols are also presented for testing the catalytic activity of such complexes in arylation and Suzuki-Miyaura cross-coupling reactions. Representative results are shown for the catalytic activity of the four complexes in arylation and Suzuki-Miyaura type reactions. For each of the reactions investigated, at least one of the four complexes successfully catalyzed the reaction, qualifying them as promising candidates for catalysis of many carbon-carbon bond-forming reactions. The protocols presented are general enough to be adapted for the synthesis, purification and catalytic activity testing of new palladium N-heterocyclic carbene complexes.

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. The complexes were tested for catalytic activity in arylation and Suzuki-Miyaura reactions. For each reaction investigated, at least one of the four complexes successfully catalyzed the reaction.

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from ...