Selective Hydrogenation of a Multifunctional Compound: 2-Butyne-1,4-Diol to Cis-2-Butene-1,4-Diol

Cullen, Bernard (2001) Selective Hydrogenation of a Multifunctional Compound: 2-Butyne-1,4-Diol to Cis-2-Butene-1,4-Diol. PhD thesis, University of Glasgow.

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Abstract

A 1% Pd/C catalyst supplied by ICI Synetix has been characterised, and used for the selective hydrogenation of 2-butyne-1,4-diol. The reaction procedure was developed for both an ambient and an elevated pressure reaction vessel, the hydrogenation of 2-butyne-1,4-diol was bench-marked with the 1% Pd/C catalyst. Two 1% Pd/Al2O3 catalysts have been prepared, characterised and used for the hydrogenation of 2-butyne-1,4-diol also. AH three of the 1% supported palladium catalysts have been characterised with CO chemisorption, electron microscopy and BET surface area determination. When the two 1% Pd/Al2O3 catalysts were employed for the selective hydrogenation of 2-butyne-1,4-diol, not only did they exhibit a different rate of hydrogenation of 2-butyne-1,4-diol, but also different final product distributions, with the selectivities towards formation of cis-2-butene-1,4-diol being of the same order (circa 95%) as that achieved when the 1% Pd/C catalyst was employed. An unexpected compound for this type of catalytic hydrogenation called iso- pro poxytetrahydroftiran was formed in all the reactions that employed the 1% supported palladium catalysts. Its formation occurred because of a solvent/bound surface species interaction, in a concerted ring closure process. Iso-propoxytetrahydrofuran has been isolated, purified, characterised with NMR and GC-MS and calibrated for GC analysis. No iso-propoxytetrahydrofuran was formed when a 9.1% Cu/SiO2 catalyst was employed for the selective hydrogenation of 2-butyne-1,4-diol. The 9.1% Cu/SiO2 catalyst offered the advantage of a higher selectivity towards 2- butene-1,4-diol formation than any of the supported 1% palladium catalysts (circa 97%), but at a far slower rate of hydrogenation. By changing the reaction solvent it was possible to produce different furans, and also have an impact of the rate of hydrogenation of 2-butyne-1,4-diol, the rate of hydrogenation in distilled water was around half of that observed when propan-2-ol was employed as the reaction solvent. With distilled water as the reaction solvent, hydroxy-tetrahydrofiiran was produced during the course of the reaction, with w-butanol as the reaction solvent, butoxy-tetrahydrofuran was produced during the course of the reaction. A series of experiments employing mono-substituted alkynes was conducted to try and elucidate the reaction mechanism for the selective hydrogenation of 2-butyne-1,4-diol. It was found from these experiments that a diol functionality was required on the reagent species for the formation of iso-propoxytetrahydrofiiran to occur. Targeted isotope switching experiments, in combination with 1H and 2D NMR spectroscopy and GC-MS were conducted so that all the experimental observations made during the course of the study could be consolidated into one postulated reaction mechanism.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: D Lennon
Keywords: Organic chemistry
Date of Award: 2001
Depositing User: Enlighten Team
Unique ID: glathesis:2001-75965
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 17:11
Last Modified: 19 Nov 2019 17:11
URI: http://theses.gla.ac.uk/id/eprint/75965

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