Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.

Ionic-liquid materials for the electrochemical challenges of the future.

Biomass is an important feedstock for the renewable production of fuels, chemicals, and energy. As of 2005, over 3% of the total energy consumption in the United States was supplied by biomass, and it recently surpassed hydroelectric energy as the largest domestic source of renewable energy. Similarly, the European Union received 66.1% of its renewable energy from biomass, which thus surpassed the total combined contribution from hydropower, wind power, geothermal energy, and solar power. In addition to energy, the production of chemicals from biomass is also essential; indeed, the only renewable source of liquid transportation fuels is currently obtained from biomass.

The Catalytic Valorization of Lignin for the Production of Renewable Chemicals

For economical and ecological reasons, synthetic chemists are confronted with the increasing obligation of optimizing their synthetic methods. Maximizing efficiency and minimizing costs in the production of molecules and macromolecules constitutes, therefore, one of the most exciting challenges of synthetic chemistry.1-3 The ideal synthesis should produce the desired product in 100% yield and selectivity, in a safe and environmentally acceptable process.4 It is now well recognized that organometallic homogeneous catalysis offers one of the most promising approaches for solving this basic problem.2 Indeed, many of these homogeneous processes occur in high yields and selectivities and under mild reaction conditions. Most importantly, the steric and electronic properties of these catalysts can be tuned by varying the metal center and/or the ligands, thus rendering tailor-made molecular and macromolecular structures accessible.5,6 Despite the fact that various efficient methods, based on organometallic homogeneous catalysis, have been developed over the last 30 years on the laboratory scale, the industrial use of homogeneous catalytic processes is relatively limited.7 The separation of the products from the reaction mixture, the recovery of the catalysts, and the need for organic solvents are the major disadvantages in the homogeneous catalytic process. For these reasons, many homogeneous processes are not used on an industrial scale despite their benefits. Among the various approaches to address these problems, liquidliquid biphasic catalysis (“biphasic catalysis”) has emerged as one of the most important alternatives.6-11 The concept of this system implies that the molecular catalyst is soluble in only one phase whereas the substrates/products remain in the other phase. The reaction can take place in one (or both) of the phases or at the interface. In most cases, the catalyst phase can be reused and the products/substrates are simply removed from the reaction mixture by decantation. Moreover, in these biphasic systems it is possible to extract the primary products during the reaction and thus modulate the product selectivity.12 For a detailed discussion about this and other concepts of homogeneous catalyst immobilization, the reader is referred elsewhere.6,7 These biphasic systems might combine the advantages of both homogeneous (greater catalyst efficiency and mild reaction conditions) and heterogeneous (ease of catalyst recycling and separation of the products) catalysis. The advent of water-soluble organometallic complexes, especially those based on sulfonated phosphorus-containing ligands, has enabled various biphasic catalytic reactions to be conducted on an industrial scale.13-15 However, the use of water as a * Corresponding author. Fax: ++ 55 51 3316 73 04. E-mail: dupont@iq.ufrgs.br. 3667 Chem. Rev. 2002, 102, 3667−3692

https://www.chem.ccu.edu.tw/~joyce/referance/gump/IL/Chem.%20Rev.%202002,%20102,%203667.pdf

Ionic liquid (molten salt) phase organometallic catalysis.

2.5. Stabilization of IL Emulsions by Nanoparticles 2623 3. Hydrogenations in ILs 2623 3.1. Hydrogenation on IL-Stabilized Nanoparticles 2623 3.1.1. Hydrogenation of 1,3-Butadiene 2623 3.1.2. Hydrogenation of Alkenes and Arenes 2624 3.1.3. Hydrogenation of Ketones 2624 3.2. Homogeneous Catalytic Hydrogenation in ILs 2624 3.3. Hydrogenation of Functionalized ILs 2625 3.3.1. Selective Hydrogenation of Polymers 2625 3.4. Asymmetric Hydrogenations 2626 3.4.1. Enantioselective Hydrogenation 2626 3.5. Role of the ILs Purity in Hydrogenation Reactions 2628

Catalysis in ionic liquids

Roger Sheldon (1942) received a PhD in organic chemistry from the University of Leicester (UK) in 1967. This was followed by post-doctoral studies with Prof. Jay Kochi in the U.S. From 1969 to 1980 he was with Shell Research in Amsterdam and from 1980 to 1990 he was R&D Director of DSM Andeno. In 1991 he moved to his present position as Professor of organic chemistry and catalysis at the Delft University of Technology (The Netherlands). His primary research interests are in the application of catalytic methodologies—homogeneous, heterogeneous and enzymatic—in organic synthesis, particularly in relation to fine chemicals production. He developed the concepts of E factors and atom utilization for assessing the environmental impact of chemical processes.

Biocatalysis in ionic liquids

The transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with 1-propanol catalyzed by α-chymotrypsin was examined in the ionic liquids 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]) and 1-octyl-3-methylimidazolium hexafluorophosphate ([omim][PF6]), and in combination with supercritical carbon dioxide (SC-CO2). The activity of α-chymotrypsin was studied to determine whether trends in solvent polarity, water activity, and enzyme support properties, observed with this enzyme in conventional organic solvents, hold for the novel environment provided by ionic liquids. α-Chymotrypsin freeze-dried with K2HPO4, KCl, or poly(ethylene glycol) demonstrated no activity in [bmim][PF6] or [omim][PF6] at very low water concentrations, but moderate transesterification rates were observed with the ionic liquids containing 0.25% water (v/v) and higher. However, the physical complexation of the enzyme with poly(ethylene glycol) or KCl did not substantially stimulate activity in the ionic liquids, unlike that observed in hexane or isooctane. Activities were considerably higher in [omim][PF6] than [bmim][PF6]. Added water was not necessary for enzyme activity when ionic liquids were combined with SC-CO2. These results indicate that [bmim][PF6] and [omim][PF6] provide a relatively polar environment, which can be modified with nonpolar SC-CO2 to optimize enzyme activity. © 2001 John Wiley & Sons, Inc. Biotechnol Bioeng 75: 181–186, 2001.

α‐Chymotrypsin catalysis in imidazolium‐based ionic liquids

Screening heterogeneous catalysts for the pyrolysis of lignin

The ability of Fe(III)protoporphyrin(IX) chloride (hemin), microperoxidase-11 (MP-11), and cytochrome c (cyt-c) to oxidize 2-methoxyphenol (guaiacol) was examined in the room-temperature ionic liquids (IL) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) and the hexafluorophosphates of 1-butyl- and 1-octyl-3-methylimidazolium, ([bmim][PF6] and [omim][PF6]), respectively. All three biocatalysts displayed peroxidase activity when activated by an electron acceptor, tert-butyl hydroperoxide for hemin and hydrogen peroxide for MP-11 and cyt-c. Hemin required the addition of a coordinating base, pyridine or N-methylimidazole (NMI), to produce an active complex. Cyt-c did not require exogenous ligands for activity in IL, although their addition increased peroxidase activity. MP-11 could not be solubilized without an exogenous ligand, therefore, whether MP-11 was active in the absence of such ligands was not determined. Pyridine provided higher activities than NMI for the three catalysts. Hemin and MP-11 peroxidase activities were markedly higher in IL compared to molecular solvents of similar polarity, as characterized by probe solvatochromic behavior, while cyt-c activity was comparable between both types of solvents. There was no consistent preference by the catalysts for a particular IL. These observations indicate that IL are suitable media for bioelectrocatalysis.

Comparison of peroxidase activities of hemin, cytochrome c and microperoxidase-11 in molecular solvents and imidazolium-based ionic liquids

Four commercially available esterases were screened for their ability to esterify ferulic acid (4-hydroxy-3-methoxy cinnamate). Novozym® 435 was found to be the only one of those screened to convert ferulic acid to ethyl and octyl ferulate at 20 and 14% yields, respectively. The highest percentage conversion was obtained using a 1∶1 mole ratio of alcohol to ferulic acid in stirred batch reactions in anhydrous 2-methyl-2-propanol at 60°C using one equivalent (wt/wt based on ferulic acid) of Novozym 435. Increased water content and a higher alcohol/ethyl ferulate ratio had adverse effects on the lipase-catalyzed esterification. The Novozym 435 activity was tested in less polar solvents (anhydrous toluene and hexane) by monitoring the alcoholysis of ethyl ferulate with 1-octanol, which resulted in a 50% yield of octyl ferulate. The alcoholysis was improved to 83% by applying a 16 mm Hg vacuum for 5 min every 24 h to remove the ethanol co-product. The optimal alcoholysis parameters were applied to the alcoholysis of ethyl ferulate with monoolein and the transesterification with triolein. The transesterification of ethyl ferulate with triolein in anhydrous toluene produced a combined 44% yield of ferulyl monoolein and ferulyl diolein, a 20% greater yield than that obtained for alcoholysis using monoolein. The highest yield, 77%, of ferulyl monoolein and ferulyl diolein was achieved using a threefold excess of neat triolein. The lipase-catalyzed transesterification of ethyl ferulate with triolein appears to be a technically feasible route to ferulyl-substituted acylglycerols, which are potentially useful sunscreen ingredients.

/pdf/lipase-catalyzed-synthesis-of-ferulate-esters-4es5m0uoww.pdf

Lipase-catalyzed synthesis of ferulate esters

https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=3321&content=PDF

David L. Compton

Papers

α‐Chymotrypsin catalysis in imidazolium‐based ionic liquids

Screening heterogeneous catalysts for the pyrolysis of lignin

Comparison of peroxidase activities of hemin, cytochrome c and microperoxidase-11 in molecular solvents and imidazolium-based ionic liquids

Lipase-catalyzed synthesis of ferulate esters

Direct electrochemical reduction of hemin in imidazolium-based ionic liquids