a Catalysts which have low antimicrobial toxicity and are aprotic, yet which can act as Brønsted acidic catalysts in the presence of protic additives have been developed. The catalysts are recyclable, considerably more active (i.e. can be used at 10-50 times lower loadings) and of broader scope than their antecedent generation.Since Forbes and Davis reported the design of a class of phosphonium-and imidazolium ion-based ionic liquids (e.g. 1, Fig. 1A) equipped with a pendant acidic sulfonic acid moiety, interest in Brønsted acidic ionic liquids (BAILs) has gathered considerable pace.1,2 These materials afford the practitioner the flexibility of a system which combines strong acidity with the traditional advantages 3 associated with the use of nonvolatile ionic liquids. Subsequently two other strategies for the design of acidic imidazolium-ion based ionic liquids (ILs) were reported: the protonated imidazole conjugate acids 3o,4 (i.e. 2) and traditional imidazolium-ion based ILs which incorporate acidic counteranions (i.e. 3). 5 While these systems have found application in a wide-range of acid-catalysed reactions, the potential uncertainties from an environmental standpoint (to the best of our knowledge the toxicity and biodegradation profiles of these materials have yet to be established) and potential storage difficulties associated with the fact that these materials are strongly Brønsted acidic, remain. We therefore became interested in the design of aprotic salts which could serve as acidic catalysts only when used in conjunction with an additive. These materials hold promise as catalysts which can be designed to be readily storable and of minimal toxicity/environmental impact, the catalytically useful acidity of which could be controlled in an 'on-off' fashion. In short, these catalysts would be acidic only when required.Our inspiration for this work came from the serendipitous discovery that N-alkyl pyridinium ions could catalyse the acetalisation of benzaldehyde in the absence of any discernible acidic species in solution. 6,7 It was later demonstrated that this phenomenon also occurred in the case of N-alkyl imidazolium ions, which allowed the design of a suite of demonstrably low antimicrobial toxicity salts (of which 4, Fig. 1A, proved the most active) capable of promoting the acetalisation of aldehydes (inter alia) at low catalyst loadings (e.g. 5-10 mol%, Fig. 1B). 8a Along the same lines, we recently demonstrated that triazolium ion-based species could act in a similar fashion at loadings of 1-2 mol%. 8b It was proposed that the low resonance stabilisation energy of the imidazolium ion would allow
Imidazolium derived ionic liquid catalysts have been developed which are aprotic and of low antimicrobial and antifungal toxicity, yet which can act as efficient Brønsted acidic catalysts in the presence of protic additives. The catalysts can be utilised at low loadings and can be recycled 15 times without any discernible loss of activity.Over the last decade Ionic Liquids (ILs) have been extensively investigated as potential replacements for volatile organic compounds for use as (inter alia) both tunable reaction media and catalytic solvents.
Ethoxy ester functionalized imidazolium and bis(tri fluoromethanesulfonyl)imide based ionic liquids (ILs) are synthesized and considered as electrolyte for lithium ion batteries. The series of ethoxy ester functionalized ionic liquids were chosen with increase in ethoxy unit from one to three, followed by polymeric units. These ionic liquids provide both ester and ethoxy groups as interaction sites for Li+ ions enhancing the Li+ ion transportation, resulting in ionic conductivity of 10−3 Scm−1 at 25 °C, which is of 103 factor higher than ethoxy containing polyethylene oxide solid polymer electrolyte. It's noteworthy that the conductivity increases as ethoxy units are increased from one to three units, followed by a decrease for the polymeric ethoxy unit. Electrochemical stability window of these ionic liquids improves as the ethoxy groups are added to imidazolium cation. The Li/LiFePO4 cell fabricated with [ME3AMIm][TFSI] electrolyte shows good initial discharge capacity of 98.5 mAhg−1 at 0.05 C‐rate at room temperature, which gradually decreases with cycling. Systematic investigation of electrode surfaces by using SEM and EDX shows deposition of passivation layers on their surfaces. Ionic liquids fabricated by this facile method provide a promising model system for understanding the molecular interactions in promoting the lithium‐ion conduction mechanism. The advantages and the limits associated to series of ionic liquid electrolytes are critically investigated.
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