Hydration and Hydrolysis with Water Tolerant Lewis Acid Catalysis in High Temperature Water.

Abstract

The purpose of this work was to develop the technique of performing organic reactions in high temperature water (HTW) with water-tolerant Lewis acids (WTLAs). We define high temperature water as liquid water above its normal boiling point. A water-tolerant Lewis acid is a Lewis acid that is not deactivated in the presence of water. Our work is the first application of WTLAs to HTW reaction media.

We studied two basic reactions in HTW with WTLA catalysis: alkyne hydration to form ketones, and ether hydrolysis to form alcohols. We used a model alkyne, 1-phenyl-1-propyne to carry out a catalyst comparison study. In(OTf)3 was the best catalyst of those tested: In(OTf)3,InCl3, Sc(OTf)3,Yb(OTf)3, HCl, and H2SO4. Reactions at different temperatures (150, 175, 200, and 225˚C) allowed us to determine activation energy and frequency factor to be 21.4 $pm$ 0.6 kcal/mol and 10^(8.8±0.3} L/mol s, respectively. Experiments with additional alkynes helped define the scope and limitations of the method.

Anisole served as our model ether for hydrolysis. We tested the same acid catalysts as above and found indium triflate to be the best catalyst of those tested. Experiments at different temperatures (200, 225, 250, 275, and 300˚C) allowed us to determine that activation energy and frequency factor to be 31±1 kcal/mol and 10^(10.6±0.5} L/mol s, respectively. We tested additional ethers toward hydrolysis to determine the limitations of the procedure.

We tested the effects that our reactor vessel may be exerting upon the reaction. For alkyne hydration, we found that the use of a capillary quartz reactor slowed the reaction dramatically, likely due to transport limitations. For ether hydrolysis, we found that the presence of quartz or statinless steel decreased reaction progress, perhaps due to interaction between the surface and the indium triflate catalyst. These experimental results identify an important phenomenon that had previously gone unrecognized in the field.

The overall significance of our work is our demonstration that the use of WTLAs in HTW presents potential as a novel medium for organic synthesis. For hydration and hydrolysis, this previously unexplored reaction medium can be competitive with traditional techniques in terms of rate and yield