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The sugarcane bagasse (SCB) can be utilized to obtain various value-added products like levulinic acid, glucose, xylose, ethanol, etc. with suitable pretreatment and subsequent extraction and isolation processes. There are several ways to pretreat SCB and one among them is by using ionic liquids (ILs). The ILs are non-volatile and versatile solvents used mainly due to their efficiency in promoting cell disruption and by altering cellulose crystallinity, thereby making the SCB more accessible to the enzymes. The pretreatment is followed by enzymatic hydrolysis and fermentation to obtain a variety of products. The first objective of this minireview is to put forward an up-to-date survey of pretreating renewable SCB using non-volatile ILs to form value-added products, thus helping in selection of the best IL for this purpose. The second objective is to understand various ways to open doors for use of ILs in biorefineries by reducing cost of IL, by recycling and reusing the ILs or by reducing loading amounts of ILs. A link between ILs and solid wastes recovery as well as their reuse is presented in a circular bioeconomy aspect. In future, biorefineries may use ILs in the processing of lignocellulose.

Ionic liquids (ILs) have found applications in the pretreatment of waste lignocellulosic biomass by interacting with the carbohydrate molecules present in the biomass materials. Pretreatment is an essential step prior to biomass conversion into valuable chemicals, fuels, and many other value-added products. This comparative study mainly focused on the pretreatment ability of four ILs having acetate or triflate as a common anion with different cations. Among various studied ILs, diazabicyclo[5.4.0]undec-7-ene (DBU)-based acidic ionic liquid when used as a dual solvocatalyst showed significant structural modifications of the rice straw (RS) sample, through C6-O bond breakage assisted by the tertiary nitrogen in DBU cation. Structural modifications due to the pretreatment were confirmed through SEM, PXRD, and FTIR analysis. Elemental analysis confirmed that carbon content in original RS is reduced to 29% and 20% upon ionothermal treatment of RS with IL at 90 °C and 120 °C, respectively. Additionally, TGA indicated that further pyrolysis could be easier with the pretreated rice straw yielding biochar upto 9% thereby reducing wastes. Conversion of RS was found to be 60 % which reduced marginally to 50 % after three cycles of recycling IL. The findings of this work provide the proof of concept that studied ILs with high thermal stability and recyclability should act as a potential solvocatalyst in sustainable pretreatment and other biomass applications.

The solvation strength of N,N-dialkylethanolammonium based protic ionic liquids (PILs) have been determined by normalised Reichardt's parameter (ETN ) and molecular polarizability (αP). The solvation strength depends on the intermolecular interactions which are governed by the functional group and molecular structure of the species. So here in this work, the influence of functional groups such as –OH, –RCOOH and –R, on solvatochromic parameters of studied PILs have been discussed in terms of experimental results and relevant literature. Further the intermolecular interactions of PILs have been analyzed with the help of temperature dependant experimental refractive index data. Additionally, a positive correlation was obtained between the polarity and the refractive index of the studied PILs.

Glycerol carbonate is a key multifunctional compound used as solvent, additive, and building block in alternative chlorine-free processes. Here, we report the synthesis of glycerol carbonate from renewable materials (glycerol and dimethyl carbonate, DMC) using basic ionic liquids (ILs) as catalysts. After process optimization, it has been possible to isolate pure glycerol carbonate in quantitative yield using a three-fold excess of DMC and ca. 15 % of IL. The IL could be reused at least four times without any significant reduction in the conversion yield.

N -Alkyl- N -methylmorpholinium and N -alkyl substituted 1,4-diazabicyclo[2.2.2]octane (DABCO) based ionic liquids (ILs), N -alkyl-DABCO, bearing short alkyl chains are characterised by a low toxicity to Vibrio fischeri , although toxicity significantly increases on increasing the alkyl chain length. Alkyl chain length affects also biodegradability in the 28 days tests; the higher level of biodegradation was found in both the series in the case of the ethyl (C2) derivatives. In the case of N -ethyl DABCO based IL, although biodegradability is still around 40%, and consequently this IL cannot be classified as “readily biodegradable”, this value is similar to the more biodegradable functionalized imidazolium based ILs.

A series of new room temperature ionic liquids based on N-alkyl-N-methylmorpholinium cations (the alkyl chain ranging from ethyl to nonyl) and a hydrophilic anion (dicyanamide), a mostly unexplored class of room temperature ionic liquids (RTILs), has been synthesized and characterized. Selected physico-chemical properties (density, viscosity and ionic conductivity) have been measured and the salts' propensity to organize into ionic clusters has been explored. The inspection of their Walden plots and electrospray ionization spectra strongly prompts for the occurrence of clustering phenomena, especially for salts bearing long alkyl chains. This structural organization has been confirmed using X-ray scattering techniques and the existence of a high degree of intermediate range order has been detected, as fingerprinted by distinct diffraction features at low Q. These evidences are rationalized in terms of a structural model where, similarly to other RTILs, the alkyl chains tend to segregate from the charged moieties.

Bronsted acidic ionic liquids (ILs) have been synthesized and investigated as catalysts in esterification and transesterification reactions: simple and non-corrosive salts characterized by aliphatic cations associated with an “acidic” anion (in particular, [HSO4]−) gave the higher yields. A quite good correlation between IL acidity (H0) and catalytic ability was found although also the hydrophilic nature of the ionic medium probably affects the process efficiency.

Acidic ionic liquids (ILs) are key systems in synthesis and their performances depend greatly on their cation and anion structure and their liquid-state organization. This microreview reports several examples of Bronsted and/or Lewis acidic ILs that have been selected to highlight the main peculiarities of these systems potentially fundamental for rational design and development of new ionic media and catalysts. Fundamental physico-chemical properties, optimization of which through tailoring of molecular structures could favor more efficient and sustainable applications, are discussed.

We found that in a scCO2-ionic liquid hybrid reaction system, Mannich reaction of benzaldehyde, aniline and acetophenone can be remarkably accelerated and the yield of Mannich base 1,3-diphenyl-3-(phenylamino)propan-1- one was significantly high. This system would be available for the green reactions with good performance. © The Royal Society of Chemistry 2011.