2000 Progress Report: Aqueous Polyglycol Solutions as Environmentally Benign Solvents in Chemical ProcessingEPA Grant Number: R828133
Title: Aqueous Polyglycol Solutions as Environmentally Benign Solvents in Chemical Processing
Investigators: Kirwan, Donald J. , Gainer, John L.
Institution: University of Virginia
EPA Project Officer: Karn, Barbara
Project Period: June 1, 2000 through May 31, 2003 (Extended to May 31, 2004)
Project Period Covered by this Report: June 1, 2000 through May 31, 2001
Project Amount: $335,000
RFA: Technology for a Sustainable Environment (1999) RFA Text | Recipients Lists
Research Category: Sustainability , Pollution Prevention/Sustainable Development
Objective:The objective of the research project is to explore aqueous solutions of polyethylene glycol and polypropylene glycol as environmentally benign alternatives to industrial solvents in chemical processing. Particular emphasis is on the replacement of reaction solvents and precipitation agents in pharmaceutical and fine chemical processes.
Progress Summary:In this first year of the project, significant advances have been made in the exploration of nonvolatile, nontoxic, aqueous PEG and PPG solutions as reaction solvents for reaction classes commonly employed in pharmaceutical syntheses. Reactant and product solubilities and reaction kinetics have been measured at room temperature for the following model organic reactions: Diels-Alder (two reactions), SN1, and SN2; the values were compared with those for the traditional, volatile organic solvents normally used. In general, at greater than 70 percent PEG/PPG, these solvents exhibited significant solubility for the organic reactants studied. For the SN1 reaction, the rate constants were 1 to 3 orders-of-magnitude larger than in traditional solvents; for the Diels-Alder reactions, the rate constants were higher than those in traditional solvents, indicating significant potential as replacement solvents for these reaction classes. For the SN2 reactions, the rate constants were found to be 1 to 2 orders-of-magnitude lower in the polyglycol systems. However, depending upon the balance of environmental and economic concerns, solvent replacement still may be justified.
Future Activities:The next area of investigation for the substitution of reaction solvents will be a study of the temperature dependence of solubilities and kinetics in these alternative solvents. The polyglycol solvents are nonvolatile as compared with traditional solvents that contribute significantly to VOC emissions. Therefore, it is likely that reactions can be operated at higher temperatures without any adverse environmental consequences and thereby have improved reaction productivity. A second area of investigation will be the influence of the solvents on reaction selectivity using a model Diels-Alder reaction. This is an area of extreme importance to economic solvent substitution and must be fundamentally investigated. Finally, modeling of reaction kinetics in these solvents will be undertaken to permit generalization of the results beyond the particular model reactions studied.
We also will initiate further experimental studies and modeling of the solubility capabilities of these solvents. This will have particular relevance to precipitation and crystallization of pharmaceuticals and fine chemicals by anti-solvent addition. Studies of crystal nucleation and growth in these solvents also will be initiated.