Polyethylene glycol-water and polypropylene glycol-water solutionsas benign reaction solvents

Abstract

Aqueous solutions of low molecular weight polypropylene and polyethylene glycol are proposed for use as novel, safe, environmentally friendly solvents. Not only are these solvents relatively nontoxic, but they are also nonvolatile, which eliminates the possibility of fugitive gaseous emissions. Many organic compounds have been found to be soluble in these polyglycol solutions; thus, they could be used as replacement solvents in various chemical processes.One use of the solvents could be as the medium for conducting chemical reactions, and this has been investigated. In particular, three classes of organic reactions, S N 1, S N 2, and Diels-Alder, have been conducted in the polyglycol solutions. Rate constants were obtained and compared to those for the traditional organic solvents. For the S N 1 reaction and the Diels-Alder reactions, the rate constants in the polyglycol solvents were greater than those found for the frequently used organic solvents.

Effect of aqueous PEG or PPG solvents on reaction selectivity and Gibbs energies

“…The rate constants for this reaction are different than those obtained for the previously studied S N 1 hydrolysis reaction of 2-chloro-2-methylpropane (Leininger et al, 2003). For that S N 1 reaction, the rate constants in the PEG 300-H 2 O solutions and 90 mass % PPG 425-H 2 O solution were 2-3 orders of magnitude greater than those obtained in the traditional organic solvents at low water concentrations.…”

“…(1) These results, along with those previously reported (Leininger et al, , 2003, support the idea that low molecular weight polyethylene glycol (PEG 300) and polypropylene glycol (PPG 425) and their aqueous solutions can be used as environmentally friendly reaction solvents for typical pharmaceutical synthesis reactions. (2) Kinetics: For the hydrolysis of the 1-chloro-3-methyl-2-butene (S N 1) reaction, the rate constants obtained at low water content were about an order of magnitude lower than those in the conventional solvents (methanol-H 2 O and acetone-H 2 O).…”

“…We repeated these calculations using the reaction kinetics previously obtained for the hydrolysis of 2-chloro-2-methylpropane (Leininger et al, 2003) and found that the S N 1 transition state was significantly more stabilized (10 -15 kJ/mol) in the 90 mass % PEG 300-H 2 O solutions than in the 90 mass % acetone-H 2 O or 90 mass % methanol-H 2 O. S N 1 transition states generally seem to be stabilized in polyglycol-H 2 O solutions.…”

“…Another consideration is their ability to dissolve various organic compounds. We have previously reported that the solubility of several organic compounds is quite high in the polyglycol-H 2 O solutions (Leininger et al, , 2003. Because of their low volatility, use of these polyglycol-H 2 O solvents would reduce volatile emissions, as well as being useful for higher temperature operations.…”

“…Previously, reaction rate constants for three different classes of organic reactions (S N 1, S N 2, and Diels-Alder) were measured in the polyglycol-H 2 O solutions and compared to those obtained in traditional organic solvents (Leininger et al, 2003). It was found that reaction rate constants in the polyglycol solvents were comparable or higher for the S N 1 and Diels-Alder reactions, but lower for the S N 2 reaction.…”