Temperature-Responsive Ionic Liquids: Fundamental Behaviors and Catalytic Applications

Temperature-Responsive Ionic Liquids: Fundamental Behaviors and Catalytic Applications

Qiao, Y.; Ma, W.; Theyssen, N.; Chen, C.; Hou, Z.

Max-Planck-Institut fur Kohlenforschung &
East China University of Science and Technology

Chem. Rev. ASAP
http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00652

Abstract:

Temperature-responsive ionic liquids (ILs), their fundanmental behaviors, and
catalytic applications were introduced, especially the concepts of upper critical solution
temperature (UCST) and lower critical solution temperature (LCST). It is described that,
during a catalytic reaction, they form a homogeneous mixture with the reactants and products
at reaction temperature but separate from them afterward at ambient conditions. It is shown
that this behavior offers an effective alternative approach to overcome gas/liquid−solid
interface mass transfer limitations in many catalytic transformations. It should be noted that
IL-based thermomorphic systems are rarely elaborated until now, especially in the field of
catalytic applications. The aim of this article is to provide a comprehensive review about
thermomorphic mixtures of an IL with H2O and/or organic compounds. Special focus is laid
on their temperature dependence concerning UCST and LCST behavior, including systems
with conventional ILs, metal-containing ILs, polymerized ILs, as well as the thermomorphic
behavior induced via host−guest complexation. A wide range of applications using
thermoregulated IL systems in chemical catalytic reactions as well as enzymatic catalysis
were also demonstrated in detail. The conclusion is drawn that, due to their highly attractive behavior, thermoregulated ILs have already and will find more applications, not only in catalysis but also in other areas.

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A decarboxylative approach for the regioselective hydroarylation of alkynes

A decarboxylative approach for the regioselective hydroarylation of alkynes 

Zhang, J.; Shrestha, R.; Hartwig, J. F.; Zhao, P. Nature Chem. 2016, 94, 1144-1151.

–North Dakota State University, UC Berkeley

Abstract: 
Regioselective activation of aromatic C–H bonds is a long-standing challenge for arene functionalization reactions such as the hydroarylation of alkynes. One possible solution is to employ a removable directing group that activates one of several aromatic C–H bonds. Here we report a new catalytic method for regioselective alkyne hydroarylation with benzoic acid derivatives during which the carboxylate functionality directs the alkyne to the ortho-C–H bond with elimination in situ to form a vinylarene product. The decarboxylation stage of this tandem sequence is envisioned to proceed with the assistance of an ortho-alkenyl moiety, which is formed by the initial alkyne coupling. This ruthenium-catalysed decarboxylative alkyne hydroarylation eliminates the common need for pre-existing ortho-substitution on benzoic acids for substrate activation, proceeds under redox-neutral and relatively mild conditions, and tolerates a broad range of synthetically useful aromatic functionality. Thus, it significantly increases the synthetic utility of benzoic acids as easily accessible aromatic building blocks.

Remote site-selective C–H activation directed by a catalytic bifunctional template

Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USAZhipeng Zhang, Keita Tanaka & Jin-Quan Yu
Nature (2017) doi:10.1038/nature21418

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature21418.html

Abstract

In chemical syntheses, the activation of carbon–hydrogen (C–H) bonds converts them directly into carbon–carbon or carbon–heteroatom bonds without requiring any prior functionalization. C–H activation can thus substantially reduce the number of steps involved in a synthesis. A single specific C–H bond in a substrate can be activated by using a ‘directing’ (usually a functional) group to obtain the desired product selectively1–5. The applicability of such a C–H activation reaction can be severely curtailed by the distance of the C–H bond in question from the directing group, and by the shape of the substrate, but several approaches have been developed to overcome these limitations6–12. In one such approach, an understanding of the distal and geometric relationships between the functional groups and C–H bonds of a substrate has been exploited to achieve meta-selective C–H activation by using a covalently attached, U-shaped template13–17. However, stoichiometric installation of this template has not been feasible in the absence of an appropriate functional group on which to attach it. Here we report the design of a catalytic, bifunctional nitrile template that binds a heterocyclic substrate via a reversible coordination instead of a covalent linkage. The two metal centres coordinated to this template have different roles: one reversibly anchors substrates near the catalyst, and the other cleaves remote C–H bonds. Using this strategy, we demonstrate remote, site-selective C–H olefination of heterocyclic substrates that do not have the necessary functional groups for covalently attaching templates.

A Heterogeneous Catalyst for the Transformation of Fatty Acids to α-Olefins

Anamitra Chatterjee and Vidar R. Jensen^*

Department of Chemistry, University of Bergen, Allégaten 41, N-5007 Bergen, Norway

ACS Catal., 2017, 7, pp 2543–2547

DOI: 10.1021/acscatal.6b03460

Publication Date (Web): February 28, 2017

http://pubs.acs.org/doi/abs/10.1021/acscatal.6b03460

Abstract

Heterogeneous catalysts have so far not been very efficient [turnover frequency (TOF) < 19 h^–1] or very selective (≤60%) for α-olefin formation in deoxygenation of fatty acids. Here we report more than 20-fold higher activity (TOF = 420 h^–1) and high selectivity (>95%) for one such deoxygenation, decarbonylative dehydration, by using a heterogeneous Pd/C catalyst in the presence of phosphine ligands. The process is solvent free, allows for catalyst recycling, and does not require in situ distillation of the product to maintain high selectivity.

A detailed spectroscopic analysis of the growth of oxy-carbon species on the surface of Pt/Al2O3 during propane oxidation

• Casey P. O'Brien, 
• Ivan C. Lee^, 

• U.S. Army Research Laboratory, Sensors and Electron Devices Directorate, 2800 Powder Mill Road, Adelphi, MD 20783, USA

Received 3 March 2016, Revised 2 November 2016, Accepted 28 December 2016, Available online 21 January 2017

http://dx.doi.org/10.1016/j.jcat.2016.12.021

Keywords

• Propane oxidation; 
• Platinum; 
• Carbon; 
• Spectroscopy

Highlights

•

Many different oxy-carbon species are formed on Pt and spill over onto Al₂O₃.

•

Enolate, ester, and acetone species are more reactive than acetate species.

•

The concentration of oxy-carbon species does not correlate with the CO₂ production rate.

•

Oxy-carbon surface species are inert spectators in the propane oxidation mechanism.

Abstract

The growth of oxygenated carbonaceous (oxy-carbon) species on the surface of Pt/Al₂O₃ during total oxidation of propane is analyzed in detail—including their composition, their location on the catalyst surface, their reactivity, and their role in the propane oxidation mechanism—by in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS). Platinum nanoparticles catalyze the transformation of propane into many different oxy-carbon surface species, including acetate, enolate, aliphatic ester, and acetone, which spillover and grow on the Al₂O₃ support. There is no correlation between the concentration of oxy-carbon surface species and the rate of CO₂production in the gas-phase, which indicates that these species are inert spectators in the propane oxidation mechanism. Temperature-programmed oxidation of the oxy-carbon surface species reveals that enolate, aliphatic ester, and acetone species are removed from the surface by combustion at similar temperatures with an activation barrier of 112 kJ/mol, whereas acetate species are removed at higher temperatures with an activation barrier of 147 kJ/mol. Both the formation and combustion of oxy-carbon surface species occur in pathways that are parallel to, and orders-of-magnitude slower than, the main pathway to CO₂ production.

Halogen-Mediated Conversion of Hydrocarbons to Commodities

Ronghe Lin, Amol P. Amrute, and Javier Pérez-Ramírez^*

Institute for Chemical and Bioengineering, Department of Chemistry and Applied Biosciences, ETH Zurich, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland

Chem. Rev., Article ASAP

DOI: 10.1021/acs.chemrev.6b00551

Publication Date (Web): February 2, 2017

Abstract

Halogen chemistry plays a central role in the industrial manufacture of various important chemicals, pharmaceuticals, and polymers. It involves the reaction of halogens or halides with hydrocarbons, leading to intermediate compounds which are readily converted to valuable commodities. These transformations, predominantly mediated by heterogeneous catalysts, have long been successfully applied in the production of polymers. Recent discoveries of abundant conventional and unconventional natural gas reserves have revitalized strong interest in these processes as the most cost-effective gas-to-liquid technologies. This review provides an in-depth analysis of the fundamental understanding and applied relevance of halogen chemistry in polymer industries (polyvinyl chloride, polyurethanes, and polycarbonates) and in the activation of light hydrocarbons. The reactions of particular interest include halogenation and oxyhalogenation of alkanes and alkenes, dehydrogenation of alkanes, conversion of alkyl halides, and oxidation of hydrogen halides, with emphasis on the catalyst, reactor, and process design. Perspectives on the challenges and directions for future development in this exciting field are provided.

Direct Conversion of Methane to Methanol under Mild Conditions over Cu-Zeolites and beyond

Patrick Tomkins†^‡§, Marco Ranocchiari^§, and Jeroen A. van Bokhoven^*‡§

^‡ ETH Zurich, Institute for Chemistry and Bioengineering, Vladimir-Prelog-Weg 1, 8093 Zurich, Switzerland

^§ Paul Scherrer Institute, 5232 Villigen, Switzerland

Acc. Chem. Res., 2017, 50 (2), pp 418–425

DOI: 10.1021/acs.accounts.6b00534

Publication Date (Web): February 2, 2017

Abstract

Conspectus

In the recent years methane has become increasingly abundant. However, transportation costs are high and methane recovered as side product is often flared rather than valorized. The chemical utilization of methane is highly challenging and currently mainly based on the cost-intensive production of synthesis gas and its conversion. Alternative routes have been discovered in academia, though high temperatures are mostly required. However, the direct conversion of methane to methanol is an exception. It can already be carried out at comparably low temperatures. It is challenging that methanol is more prone to oxidation than methane, which makes high selectivities at moderate conversions difficult to reach. Decades of research for the direct reaction of methane and oxygen did not yield a satisfactory solution for the direct partial oxidation toward methanol. When changing the oxidant from oxygen to hydrogen peroxide, high selectivities can be reached at rather low conversions, but the cost of hydrogen peroxide is comparably high. However, major advancements in the field were introduced by converting methane to a more stable methanol precursor. Most notable is the conversion of methane to methyl bisulfate in the presence of a platinum catalyst. The reaction is carried out in 102% sulfuric acid using SO₃ as the oxidant. This allows for oxidation of the platinum catalyst and prevents the in situ hydrolysis of methyl bisulfate toward the less stable methanol. With a slightly different motif, the stepped conversion of methane to methanol over copper-zeolites was developed a decade ago. The copper-zeolite is first activated in oxygen at 450 °C, and then cooled to 200 °C and reacts with methane in the absence of oxygen, thus protecting a methanol precursor from overoxidation. Subsequently methanol can be extracted with water. Several active copper-zeolites were found, and the active sites were identified and discussed. For a long time, the process was almost unchanged. Lately, we implemented online steam extraction rather than off-line extraction with liquid water, which enables execution of successive cycles. While recently we reported the isothermal conversion by employing higher methane pressures, carrying out the process according to prior art only yielded neglectable amounts of methane. Using a pressure <40 bar methane gave higher yields under isothermal conditions at 200 °C than most yields in prior reports. The yield, both after high temperature activation and under isothermal conditions at 200 °C, increased monotonously with the pressure. With this account we show that the trend can be represented by a Langmuir model. Thus, the pressure dependence is governed by methane adsorption. We show that the isothermal and the high temperature activated processes have different properties and should be treated independently, from both an experimental and a mechanistic point of view.