The Application of Radiochemical Techniques to the Study of Surface Reactions

Affrossman, Stanley (1961) The Application of Radiochemical Techniques to the Study of Surface Reactions. PhD thesis, University of Glasgow.

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Abstract

The aim of the investigation was to find the mechanism of selective catalysis in the Rosenmund reaction, i.e. the catalytic hydrogenation of acid chlorides to aldehydes under such conditions that no further hydrogenation takes place. Benzoyl chloride was chosen as the primary reactant in all the experiments. A detailed examination was made of the purity of the reagents. The reaction conditions were investigated to find the procedure necessary in order to give an optimum yield of aldehyde. The effect of controlled amounts of added impurities in the reaction mixture and in the synthesis of the catalyst was also examined. A range of selective poisons for the reaction was investigated and it was found that the most powerful poison, i.e. the one which gave the largest yield of aldehyde with the minimum amount of poison added, was tetramethylthiourea. It was shown that decomposition or hydrogenation of all the poisons took place during the reaction. Elementary sulphur was found to be an efficient poison if added under the correct conditions. Palladium sulphide (PdS) catalysts decomposed with loss of sulphur under the reaction conditions and required addition of a sulphur poison in order to give a yield of aldehyde. The effect of temperature on the reaction was also studied and it was found that the reaction products varied with the temperature. To distinguish between consecutive and simultaneous reaction mechanisms, C14 labelled aldehyde was added to a hydrogenation. A loss of activity showed that the reaction proceeded in a stepwise manner, i.e. the primary reaction product could react further by being readsorbed on the catalyst surface. As an aid to the elucidation of the mechanism, the adsorption of reactants on the catalyst surface was investigated by means of a liquid scintillation counter. An accurate method of determining the partition ratio of a reactant, between solvent and catalyst, in the presence of scintillation quenching effects was discovered. The adsorption of aldehyde was examined and there was shown to be a correlation between the amount of aldehyde on the catalyst surface and the rate of reaction at the corresponding concentration A mechanism for the selective action of the poison in the Rosenmund reaction was postulated to explain these results.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1961
Depositing User: Enlighten Team
Unique ID: glathesis:1961-79397
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 05 Mar 2020 10:06
Last Modified: 05 Mar 2020 10:06
URI: http://theses.gla.ac.uk/id/eprint/79397

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