Among different functionalities that can be embedded in ionic liquids (ILs), the incorporation of organocatalytic attributes is attracting a rapidly increasing attention in synthetic chemistry. Some ILs can offer dual functionalities by acting simultaneously as a solvent for reactants and a catalyst, for example carbene, for organic transformation reactions. Recently, some of us reported that 1-ethyl-3-methylimidazolium acetate (EmimOAc) can serve not only as a facile solvent for cellulose but also as an activating reagent for a transesterification reaction of cellulose hydroxy groups with isopropenyl acetate (IPA) as an ester donating reagent. The synthetic protocol employed enabled facile and promising transesterification of cellulose without any additional catalysts and activating reagents. To understand detailed insight into the organocatalytic properties of EmimOAc for transesterification of cellulose, we synthesyzed several different imidazolium-based ionic liquids with acetate anion. The key question we tackled is whether or not carbene species plays a crucial catalytic role in the transesterification processes. The proton at the C-2 position of imidazolium cations is rather acidic, so that its transfer to a base–if it occurs–generates carbene. Experimental results suggeste that it is not nessesary that carbene produced from the imidazolim cation can act as a catalyst. According to model transesterification reactions using the newly sinthesyzed imidazolium-based ILs and their computational analysis, acetate anion of ILs plays an essential role in the promotion of the reactions.

Ionic liquids as catalysists for biomass conversion

255th National Meeting (2018)

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