Solubility of organic compounds in scCO2

Abstract The growing environment, health, and economic concerns about using organic solvents have led to efforts for the search of unconventional solvents. Water, ionic liquids (ILs), and supercritical fluids (SCFs) are driving attention for their use as alternative solvents. SCFs are desirable as they combine the properties of both liquid and gaseous state. Their liquid state properties (lower surface tension and viscosities, variable densities, and polarity) and good gaseous behavior make these as smart nonconventional solvents. Contrary to organic solvents, the solvent characteristics of SCFs can be tuned through easy modulation of their densities by pressure conditioning. Supercritical carbon dioxide (scCO2) is a fitting SCF due to its convenient critical conditions and unique physicochemical properties such as low toxicity, nonflammability, recyclability, and natural abundance. The tuning of analyte solubility in scCO2 allows its use for novel fractional separation techniques. Some selected applications where scCO2 has been investigated include natural product extractions (coffee and pharmaceuticals) and recovery of precious metal ions, besides, scCO2 is also a solvent of choice for reaction medium in dyeing industry polymerization, oxidation, free radical reactions, etc. The use of scCO2 in place of VOCs as reaction medium brings additional benefits of no workup, enhanced selectivity, newer reactivity, easy separation, and efficient solvent recyclability for zero emission. Using solid support catalyst immobilization technique flow type reactors involving scCO2 as solvent are possible. The distinct solvent characteristics of scCO2 bring kinetic promotion and enhanced stereoselectivity of many reactions in it. Some important reactions like C-H activation of alkanes, cyclization of amines, etc. which are difficult to carry out in conventional solvents can be selectively performed in scCO2 after reactivity modulation. The significant solubility of fluorinated compounds in scCO2 has placed these as benign replacements to ozone depleting chlorofluorocarbons. In summary scCO2 is promising solvent system for separation and allied technologies. This work is aimed for a systematic insight into the solubility of different classes of compounds in scCO2 reported in the recent literature. The chapter can be useful for the pedagogic buildup of readers and can also interest researchers in designing and exploration of their targets leading to the expansion of knowledge and technological development.