Forssten, Camilla Sofia; (2002) Electrochemical control of organic reactions involving phase transfer. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Phase transfer catalysis reactions are reactions where the reactants are soluble in different solvents. The phase transfer catalyst facilitates the transfer of a reactant from one phase to another, hence enabling the reaction. This can be explained electrochemically: By partitioning between the phases, the catalyst establishes a potential difference across the interface, which drives the transfer of reagent into the other phase (usually an inorganic anion is being transferred into the organic phase), or controls the reaction at the interface. A similar potential difference can also be applied with electrochemical instrumentation and the reactions can be investigated in electrochemical systems. Electrochemistry at ITIES (Interface between Two Immiscible Electrolyte Solutions) provides a fast, convenient and simple way of investigating the electrochemistry of a synthetic phase transfer reaction. The organic syntheses were also carried out to confirm the electrochemical results. Using an SN2 reaction involving a catalytic step, it has been shown how to use electrochemical measurements of ion transfer across the aqueous-organic interface to understand the reactions following this ion transfer. The reaction investigated was the reaction between 2-bromo-3-methyl butyric acid and iodide and hydroxide. The experiments show that mechanistic details of consecutive steps in organic reactions, inseparable when carrying out the organic experiments, can be observed when the reaction is carried out electrochemically. Another reaction that has been investigated is a two-phase oxidation reaction, where cis-cyclooctene in an organic solvent is oxidised by aqueous permanganate. These experiments prove that ITIES can be used for investigations of two-phase reactions, which are too slow to be investigated on a normal cyclovoltammetric timescale. Again, the first reaction step can be investigated separately. In synthetic methods the further reaction of the intermediate makes the determination of the rate constant of the initial step difficult, whereas this rate constant is obtainable through simulations of the electrochemical experiments. Also, the experiments show that through electrochemical experiments at a liquid-liquid interface, it is possible to determine in which phase the initial step of a two-phase reaction takes place. An SN1 reaction has been investigated using synthetic methods. SN1 reactions with a chiral substrate normally proceed by racemisation. The reaction chosen was the hydrolysis of [alpha]-phenylethyl chloride. By using a two-phase system the reaction mechanism was altered to preserve optical rotation through inversion of configuration.

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