CHEMISTRY OF SUSTAINABILITY – PART I: CARBON DIOXIDE AS AN ORGANIC SYNTHON AND PART II: STUDY OF THERMODYNAMICS OF CATION EXCHANGE REACTIONS IN SEMICONDUCTOR NANOCRYSTALS

Open Access
Author:
Sathe, Ajay Arun
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 29, 2016
Committee Members:
  • Robert Martin Rioux Jr., Dissertation Advisor
  • Robert Martin Rioux Jr., Committee Chair
  • Raymond Edward Schaak, Committee Member
  • Ayusman Sen, Committee Member
  • Chunshan Song, Outside Member
Keywords:
  • Carbon dioxide conversion
  • Flow Chemistry
  • Isothermal Titration Calorimetry
  • Cation Exchange Reactions in Nanoparticles
Abstract:
Sustainability is an important part of the design and development of new chemical and energy conversion processes. Simply put sustainability is the ability to meet our needs without sacrificing the ability of the next generations to meet theirs. This thesis describes our efforts in developing two orthogonal strategies for the fixation of CO2 by utilizing high energy intermediates which are generated via oxidative or reductive processes on common organic substrates and of thermochemical measurements of cation exchange reactions which will aid the development of new materials relevant for energy conversion and storage. The first chapter lays a background for the challenges and opportunities for the use of CO2 in organic synthesis. The rapidly growing field of continuous flow processing in organic synthesis is introduced, and its importance in the development of sustainable chemical conversions is highlighted. The second chapter describes the development of a novel route to α-amino acids via reductive carboxylation of imines. A mechanistic proposal is presented and the reaction is shown to proceed through the intermediacy of α-amino alkyl metal species. Possible strategies for designing catalytic and enantioselective variants of the reaction are presented. The third chapter describes the development of a catalytic oxidative carboxylation of olefins to yield cyclic carbonates. The importance of flow chemistry and membrane separation is demonstrated by allowing the combination of mutually incompatible reagents in a single reaction sequence. While the use of carbon dioxide for synthesis of organic fine chemicals is not expected to help reduce the atmospheric carbon dioxide levels, or tackle climate change, it certainly has the potential to reduce our dependence on non-sustainable carbon feedstocks, and help achieve a carbon neutral chemical life cycle. Having described the use of carbon dioxide and flow chemistry for sustainable chemical conversion, the fourth chapter introduces the role of nanomaterials in sustainable solar energy conversion and storage. The use of cation exchange reactions in nanocrystals to access novel materials is highlighted. Despite having shown tremendous promise in the synthetic applications, the fundamental measurements of the thermodynamic and kinetic parameters of a cation exchange reaction are largely non-existent. This impedes the future growth of this powerful methodology. The technique of isothermal titration calorimetry is introduced, and its importance to studying the thermochemical changes occurring during cation exchange is outlined. The final chapter presents results obtained from the isothermal titration calorimetry on the prototypical cation exchange reaction between cadmium selenide and silver ions. The role of nanoparticle size, identity of the silver salt, solvent, surface ligands and temperature is studied. Recommendations for future investigations using ITC as well as other characterization techniques for discerning the kinetics of cation exchange are presented. I believe that a more unified mechanistic understanding of the cation exchange process in nanomaterials will aid the development of more efficient and robust materials for applications in a wide variety of fields.