Environmentally benign chemical processing in near- and supercritical fluids and gas expanded liquids

As industry begins to acquire a greater concern for public health and the environment, research in both academic and industrial settings has begun to focus on solvent remediation and catalyst removal. In many cases, solvents must be completely removed and recovered after reaction and catalysts are often recycled due to their expense but quite often, especially with acid catalysts, they require neutralization then disposal of the resulting salts. Therefore, replacement solvent systems must be environmentally benign and allow for facile separation after reaction. Catalysts must also be tailored for these solvents systems to allow for fast rates of reaction and ease of separation and recycle. This thesis addresses these issues with benign alternatives to conventional chemical processing that avoid hazardous solvents, reduce the need for catalyst separation, neutralization, and disposal, and allow for facile separation.; Hazardous solvents have been replaced with more benign solvents at elevated temperatures and pressures that can be tuned to act as the solvent and catalyst while being easily separated from the final products. First, nearcritical water (NCW) is evaluated as solvent and catalyst for the hydrolyses of benzoate esters to gain a more thorough understanding of hydrolysis processes taking place in this medium. Supercritical carbon dioxide is then used as both solvent and reactant in conjunction with hydrogen peroxide to facilitate the epoxidation of olefins. Supercritical carbon dioxide is further investigated as a medium for performing phase-transfer catalyzed reactions through the design and use of CO₂-philic phase-transfer catalysts. Next, gas expanded liquids (GELS) are examined for reactions and separations. First, the interaction of alcohols expanded with gaseous CO₂ for the in situ formation of alkylcarbonic acids is confirmed. Diastereomer salts dissolved in methanol are separated using gas antisolvent crystallization by expanding the liquid solution with gaseous CO₂. Finally, a novel method for the preparation of 5-phenyl-1H-tetrazole is developed where reactions are run neat in benzonitrile with definitive control over the potential amount of the hydrazoic acid being formed in the system.