Date of Award
Campus Access Thesis
Master of Science (MS)
This work describes the heterogenous catalytic hydrogenolysis in aqueous medium for the development of environmentally benign reductive approaches as a potential alternative to currently used methods in synthetic chemistry. The conventional methods often have disadvantages such as harsh reaction conditions, including high temperature and/or high pressure, a large amount of hazardous reducing reagents and the use of flammable organic solvents. These conditions are not suitable to the current environmental standards of sustainable chemistry. In our catalytic system, the use of explosive gas is eliminated as water is employed as the H or D atom source and reaction medium, which makes this approach safer and greener without the need of handling in explosive gas. The major advantage of the method is based on the slow dissolution of Al in water that results in the controlled in situ generation of hydrogen gas and the additional metal component serves as the hydrogenation catalyst. The method is tunable by using different possible hydrogenation catalysts (Ni or Pd) depending on the substances employed and applied in the projects.
The first project describes the selective deprotection of benzyl (Bn-), benzyloxycarbonyl (Cbz-), and allyloxycarbonyl (Alloc-) protected alcohols, amines, and amino acids using both Ni-Al alloy and Pd/C-Al in H2O systems under mild conditions. Both catalytic systems successfully achieved high yields, which shows the efficacy of the method. The reusability of Pd/C-Al-H2O system showed good results in five consecutive cycles.
Continuing our interest in the development of these catalytic systems, the second project describes the application of a Pd/C-Al-D2O system for the selective deuterodehalogenation of a broad variety of small organic compounds. Various methods have been reported for deuteration transformations; however, those protocols have not found to be environmentally friendly. In our approach, a commercially available Pd catalyst was used with the combination of Al powder in D2O medium, which generates D2 gas in situ from the reaction of Al and D2O. The catalytic exchange of halogen to deuterium was accomplished in good to excellent yields with high selectivity under mild conditions.
Zorigt, Naranchimeg, "Development of Environmentally Benign Reductive Methods through Metal-Al-Water Facilitated Hydrogenolysis" (2020). Graduate Masters Theses. 647.