Cosolvents, hydrogen-bond donor

The solubility parameter approach was subsequently expanded from three to four terms with the division of the hydrogen-bonding parameter into acidic and basic solubility parameters to quantify electron-donor and electron-acceptor properties [48,49], However, the expansion of these solubility parameter terms did not make the equation any easier to use foptfiBi prediction of solubility in cosolvent systems. 

SCF carbon dioxide is a lipophilic solvent since the solubility parameter and the dielectric constant are small compared with a number of polar hydrocarbon solvents. Co-solvents(also called entrainers, moditiers, moderators) such as ethanol have been added to fluids such as carbon dioxide to raise the solvent strength while maintaining it s adjustability. Most liquid cosolvents have solubility parameters which are larger than that of carbon dioxide, so that they may be used to increase yields, or to decrease pressure and solvent requirements. A summary of the large increases in solubility that may be obtained with a simple cosolvent is given at the top of Table I. Cosolvents, unlike carbon dioxide, can form electron donor-acceptor complexes (for example hydrogen bonds) with certain polar solutes to influence solubilities and selectivities beyond what would be expected based on volatilities alone. Several thermodynamic models have been developed to correlate and in some cases predict effects of cosolvent on solubilities( ,2). They are used extensively in SCF research and development... 

Using ethylammonium nitrate (EAN) as PIL ( . , =0.95, ji = 1.12, a=1.10, P = 0.46), following types of binary mixture models were selected for the analysis and quantification of the microscopic solvent properties (a) [molecular aprotic solvent with HBA ability + PIL cosolvent], (b) [molecular aprotic solvent with both HBD and HBA ability + PIL cosolvent] and (c) [molecular protic solvent + PIL cosolvent] [31]. The molecular solvents included in this analysis were dimethylsul-phoxide (DMSO) ( ., =0.44, 7r = 1.00, a=0.02 and p=0.76) as a polar aprotic HBA solvent, acetonitrile (AN) ( .,. =0.46, 7t =0.75, a=0.19, p=0.40) as polar aprotic HBA/HBD solvent and methanol ( .,. =0.76, 7t =0.60, a=0.98, p=0.66) as a protic solvent. EAN is a N-H-bond donor. In all cases, the pure component part of the mixtures was capable of forming associated species through hydrogen-bonding interactions. For the explored solvent mixtures, empirical parameters . n, a and P were calculated from the wave numbers of the absorbance maxima of the corresponding chemical probes at 25°C. 

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