Aromatic nitrile hydrogenation: a journey from a single batch process to sustained primary amine production

McAllister, Mairi I. (2020) Aromatic nitrile hydrogenation: a journey from a single batch process to sustained primary amine production. PhD thesis, University of Glasgow.

Abstract

Primary amines are industrially valuable intermediate species which are recurrently used in the synthesis of many products, including plastics, pharmaceuticals, and agrichemicals. Whilst various synthetic methods to afford primary amines are available, it is the heterogeneously catalysed hydrogenation of nitriles which is the methodology of choice in an industrial setting. Thus, the liquid phase hydrogenation reactions of various aromatic nitriles are used to probe the reactions progress from nitrile to primary amine. In the first instance, the substrate 4 hydroxybenzyl cyanide was examined before efforts were moved to the cyanohydrin mandelonitrile. It is here that the majority of the investigation was focused. Finally, preliminary studies into the hydrogenation reaction of 1,2-dicyanobenzene were also undertaken. Detailed analysis of the reaction systems, principally by HPLC, provides the basis for this study.

Efforts were focused on understanding the interconnectivity of the reactions which typically accompany a nitrile hydrogenation reaction. Whilst no hydrogenolysis was observed in the 4-hydroxybenzyl cyanide hydrogenation reaction, coupling reactions were detected. Moreover, it was shown that the careful tuning of reaction parameters effectively removed unwanted products, affording the desired primary amine with complete selectivity.

The mandelonitrile hydrogenation reaction system was found to be significantly more complex. Despite this, analysis of the product distribution from the corresponding deuteration reaction allowed some of the finer mechanistic details to be elucidated. The single batch reaction conditions, employed for the mechanistic studies, were found not to be suitable in the assessment of catalyst longevity and durability. The reaction protocol was modified from a single batch regime, to a repeat batch regime, thus allowing the more industrially relevant fed batch protocol to be mimicked.

Utilising the insight gleaned from the mandelonitrile hydrogenation reaction studies, a dinitrile substrate system was preliminarily explored. No prior work had been conducted within the Lennon group on the hydrogenation reaction of 1,2-dicyanobenzene. Hence, suitable methodology and an appropriate analytical protocol were not in place. Whilst aspects of this reaction system were found to be somewhat problematic, an enhanced understanding has been achieved. This minor sub-section of the project is presented as an appendix and is now ready for additional investigation.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: nitrile hydrogenation/deuteration, hydrogenolysis, Pd/C catalyst.
• Subjects: Q Science > QD Chemistry
• Colleges/Schools: College of Science and Engineering > School of Chemistry
• Funder's Name: Syngenta
• Supervisor's Name: Lennon, Professor David
• Date of Award: 2020
• Depositing User: Mairi McAllister
• Unique ID: glathesis:2020-81503
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 15 Jul 2020 08:36
• Last Modified: 05 Dec 2025 13:38
• URI: https://theses.gla.ac.uk/id/eprint/81503

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