Janet L. Scott

Extraction of lignin from lignocellulose at atmospheric pressure using alkylbenzenesulfonate ionic liquid

Lignocellulosic materials are a potentially valuable source of both aromatic compoundsvia the lignin component and sugars from the cellulose and hemicellulose components. However, efficient means of separating and depolymerising the components are required. An ionic liquid mixture containing the 1-ethyl-3-methylimidazolium cation and a mixture of alkylbenzenesulfonates with xylenesulfonate as the main anion was used to extract lignin from sugarcane plant waste at atmospheric pressure and elevated temperatures (170–190 °C). The lignin was recovered from the ionic liquid by precipitation, allowing the ionic liquid to be recycled. An extraction yield exceeding 93% was attained. The lignin produced had a molecular weight of 2220 g/mol after acetylation. The regenerated ionic liquid showed good retention of structure and properties. The other product of the extraction was a cellulose pulp, which can be used in further processing.

Thermal Degradation of Ionic Liquids at Elevated Temperatures

Ionic liquids based on the imidazolium cation are found to degrade, yielding volatile degradation products, at temperatures significantly lower than previously reported and thus a parameter Tz/x (the maximum operating temperature) is developed to provide a more appropriate estimate of thermal stability.

Ionic liquids : The neglected issues

There has been an explosion of interest in ionic liquids in the last five years that has resulted in the discovery of a vast number of new ionic liquids with a wide range of interesting applications. Although ionic liquids are invariably described as highly stable green solvents, thorough investigations quantifying their purity, stability, biodegradability, and toxicity have lagged behind the pace of other research in the area. This review addresses these key issues and summarizes the approaches that have been developed for recycling ionic liquids.

Thermal degradation of cyano containing ionic liquids

The long term thermal stability of ionic liquids containing dicyanamide or tricyanomethide anions is significantly lower than might be expected from temperature ramped TGA studies, and these anions, combined with N-based cations, yield polymeric products during thermal decomposition. Operational upper temperature limits for extended heating have been determined from isothermal decomposition measurements and extraction of t0.99 values, and a simple relationship between onset of decomposition (determined by non-zero 1st derivative) and T0.01/10 (the temperature at which 1% decomposition occurs in 10 h) is derived.

The effect of anion fluorination in ionic liquids : physical properties of a range of bis(methanesulfonyl)amide salts

The bis(trifluoromethanesulfonyl)amide, TFSA, anion is widely used in the genesis of room temperature ionic liquids as it is non-spherical, fluorinated and has a particularly diffuse charge. However, the extent to which each of these structural features is responsible for the low melting point, fluidity and excellent stability of the resultant ionic liquids has yet to be described. We present the synthesis and analysis of a range of analogous, non-fluorinated species containing the bis(methanesulfonyl)amide, NMes2−, ligand. Utilisation of this anion produces ionic liquids that are hydrophilic and extremely low melting, but with decreased thermal and electrical stability and significantly increased viscosity. The crystal structures of the dimethyl pyrrolidinium bis(methanesulfonyl)amide and TFSA species are compared, and the number of close contacts within each is assessed. Comparison of these structural and physical properties provides new insight into the effect of anion fluorination on these ionic liquids.

Green chemistry approaches to the Knoevenagel condensation: comparison of ethanol, water and solvent free (dry grind) approaches

We report a comparative study of the Knoevenagel condensation with a variety of substituted benzaldehydes (17 examples) and cyanoamides (3 examples), using three different methodologies: (a) traditional ethanol reflux; (b) water reflux; and (c) solvent free conditions. Almost without exception these reactions proceeded faster, more cleanly and in higher yields when the reactions were conducted in a solvent-free fashion. Additionally, our solvent free approach allowed the use of nitrobenzaldehydes, which failed to yield the desired products under traditional and water based approaches.

Guest specific solid-state fluorescence rationalised by reference to solid-state structures and specific intermolecular interactions

Guest specific solid-state fluorescence enhancement in 2,7-bis-(3-hydroxy-3,3-diphenylprop-1-ynyl)fluoren-9-one host:guest complexes may be ascribed to changes in the packing modes and hence host–host intermolecular interactions leading to excimer formation in the solid-state and the occurrence (or lack thereof) of specific intermolecular interactions.

Recent advances in solventless organic reactions: towards benign synthesis with remarkable versatility

A paradigm shift away from using solvents in organic synthesis as solventless reactions can lead to improved outcomes, and more benign synthetic procedures, in for example aldol condensation reactions, sequential aldol and Michael addition reactions en route to Kröhnke type pyridines, reactions leading to 3-carboxycoumarins, benzylidenes, 4-aryl-1,4-dihydropyridines and 2-aryl-1,2,3,4-tetrahydroquinazolines, and oligomerisation reactions for the synthesis of cavitands; kinetic considerations for the reaction of two solids can only be explained if a eutectic melt is formed during the reaction.

Liquids intermediate between “molecular” and “ionic” liquids: Liquid Ion Pairs?

Ionic liquids comprised of tetradecyltrihexyl- and tetrabutyl-phosphonium cations paired with chloride or sulfonyl amide anions exhibit properties that reflect strong ion association, including comparatively low viscosity as well as a degree of volatility, and hence exemplify an interesting intermediate state between true ionic and true molecular liquids.

A critical assessment of electrochemistry in a distillable room temperature ionic liquid, DIMCARB

Ionic liquids are frequently advocated as green media for electrochemical studies. However, they are non-volatile and hence difficult to purify or recover. In this paper the electrochemical behaviour of a ‘distillable’ room temperature ionic liquid, DIMCARB, has been investigated. This ionic liquid is unusual because it is readily prepared, in large quantities and at low cost, by mixing of gaseous carbon dioxide with dimethylamine and also easily recovered by decomposition back into its gaseous components followed by reassociation. Almost ideal reversible voltammetry is observed for the Cc+/0 process (Cc = cobalticinium), which therefore is recommended for reference potential calibration. Another IUPAC recommended reference potential process, Fc+/0 (Fc = ferrocene), is only reversible at fast scan rates and occurs near the positive potential limit available. However, decamethylferrocene (DmFc) is reversibly oxidised and behaves ideally as for the reduction of Cc+. The small diffusion coefficients of 1.2 × 10−7 cm2 s−1 (Cc+) and 5.0 × 10−8 cm2 s−1 (DmFc) at 20 °C are attributed to the relatively high viscosity. The potential window of ca. −1.50 V to +0.50 V vs. SHE indicates that DIMCARB is more suitable for electrochemical studies of reductive rather than oxidative processes. Voltammetric studies in DIMCARB reveal a series of reversible reductive processes for the Keggin [α-SiW12O40]4− polyoxometallate. Comparison of reversible potential data reported in other media indicate that the polarity of DIMCARB is intermediate between that of MeCN and the conventional ionic liquid [BMIM][PF6]. The deposition of metallic Pb also has been studied and reveals that Pb(II) is reduced in a single irreversible 2-electron step to the metallic state via a nucleation/growth mechanism. Overall, these studies show that DIMCARB is highly suitable for electrochemical studies, but that it is a potentially reactive medium.