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Reduction of Aldehydes and Ketones to Their Corresponding Alcohols in 1- Butyl-3-Methylimidazolium Tetrafluoroborate

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Reduction of Aldehydes and Ketones to Their Corresponding Alcohols in 1- Butyl-3-Methylimidazolium Tetrafluoroborate REDUCTION OF ALDEHYDES AND KETONES TO THEIR CORRESPONDING ALCOHOLS IN 1- BUTYL-3-METHYLIMIDAZOLIUM TETRAFLUOROBORATE Josiane Ayingeneye Dissertation submitted in fulfilment of the academic requirements for the degree of Master of Science in the School of Chemistry and Physics, University of KwaZulu-Natal, Durban. Supervisor: Prof Vincent O. Nyamori February 2018 Abstract The use and release of volatile organic solvents (VOS) to the atmosphere have become detrimental to both human health and his environment. In addition, the non-recyclability and the excessive consumption of these solvents in chemical industry influence their high costs. This has incited the growing need towards the design of new processes and benign solvents, helping in minimizing these raised issues. Ionic liquids (ILs) which are acknowledged as green and environmentally friendly solvents, are assigned as promising alternatives for replacing these VOS. The review of some ILs aspects such as structure, synthesis methods, physicochemical properties, solvent applications in reduction reactions, and their recyclability gave an impressive trend and a motivation towards our work. Synthesis of 1-butyl-3- methylimidazolium tetrafluoroborate ([BMIM][BF4]), as typical IL and investigation of its solvent efficiency, in the reduction of aldehydes and ketones to their corresponding alcohols, were the core objectives of this research. [BMIM][BF4] was synthesized via microwave (MW) and conventional methods. The characterization of the synthesized [BMIM][BF4] was done by means of Fourrier transform infrared (FTIR), nuclear magnetic resonance (1H- and 13C-NMR,) and liquid chromatograph- mass spectroscopy (LC-MS) techniques. Physicochemical properties of [BMIM][BF4] related to its solvent application, such as water content, density, viscosity and thermal stability, were explored. It was observed that synthesis method impacted on the purity and yield of the 1 products, as well as the reaction times. H-NMR spectrum of [BMIM][BF4] showed the high resonance peak of hydrogen atom on carbon at position-two, (C2)-H, around 8.66 ppm, implying the high polarity of this hydrogen atom towards reduction reactions. [BMIM][BF4] solvent property, in comparison with normal organic solvent viz. ethanol, was investigated through the reduction reactions. The reduced aldehydes and ketones were benzaldehyde (Ph-CHO), acetophenone (Ph-COCH3), ferrocenecarboxyaldehyde (Fc-CHO), and acetylferrocene (Fc-COCH3). Two different methods viz. conventional or ultrasound (US) were also employed in aldehydes and ketones reduction by NaBH4, as reducing agent, in either synthesized [BMIM][BF4] or dry ethanol as solvent. Further to this, similar reduction reaction was carried out under solvent-free conditions for a better investigation of solvent effect. Additionally, reduction reaction of similar substrates under H2 gas with 10% palladium supported on activated charcoal (10% Pd/C), as catalyst, was also investigated. ii | The obtained alcohols were characterized by FTIR and NMR. The recyclability of [BMIM][BF4] was studied by use of both reducing agents, in the reduction of Ph-CHO, as typical example. Under similar reaction conditions, [BMIM][BF4] provided higher product yields than dry ethanol. This showed that during reduction process, [BMIM][BF4] was fast proton donor than 1 dry ethanol, as correlating with H-NMR spectrum of [BMIM][BF4]. This observation together with its efficient recyclability make [BMIM][BF4] more efficient and cost effective. Furthermore, green approaches such as MW and US examined in this study showed high potential in terms of better product yields and short reaction times. iii | Preface The experimental work presented in this dissertation was conducted in the School of Chemistry and Physics, Westville campus, University of KwaZulu-Natal, Durban, South Africa. This work was carried out from February 2015 to October 2017 and was supervised by Prof Vincent O. Nyamori. The presented studies compiles original work by the author and have not been submitted in any form for a completion of any degree or diploma to any tertiary institution. Where use has been made of the others‘ work, it is accordingly acknowledged in the text. …………………………………………. ………………………………………….. Josiane Ayingeneye Date iv | Declarations Declaration 1 - Plagiarism I, Josiane Ayingeneye, declare that: 1. The research reported in this thesis, except where otherwise indicated, is my original research. 2. This thesis has not been submitted for any degree or examination at any other university. 3. This thesis does not contain other persons’ data, pictures, graphs or other information, unless specifically acknowledged as being sourced from other persons. 4. This thesis does not contain other persons' writing, unless specifically acknowledged as being sourced from other researchers. Where other written sources have been quoted, then: a. Their words have been re-written but the general information attributed to them has been referenced. b. Where their exact words have been used, then their writing has been placed in italics and inside quotation marks, and referenced. 5. This thesis does not contain text, graphics or tables copied and pasted from the Internet, unless specifically acknowledged, and the source being detailed in the thesis and in the References sections. …………………………………………. ………………………………………….. Josiane Ayingeneye Date v | Declaration 2 - Scientific contributions Oral presentation Josiane Ayingeneye and Vincent O. Nyamori, “Reduction reactions in ionic liquids: Reduction of aldehydes and ketones by NABH4 in [BMIM][BF4] to their corresponding alcohols”, at the 42nd National Convention of the South African Chemical Institute, Southern Sun Elangeni Hotel, Durban, South Africa, 29 November – 4th December 2015. Poster presentation Josiane Ayingeneye and Vincent O. Nyamori, “Synthesis and application of 1-butyl-3- methylimidazolium tetrafluoroborate in reduction of aldehydes and ketones using ultrasound method”, at the College of Agriculture, Engineering and Science Postgraduate Research and Innovation Day 2017, Westville campus, University of KwaZulu-Natal, Durban, South Africa, 26 October 2017. Workshops 1. South Africa Chemical Institute (SACI), “Green chemistry workshop”, Southern Sun Elangeni Hotel, Durban, South Africa, 29 November 2015. 2. PerkinElmer, “Innovation Tour-South Africa”, Olive Convention Centre, Durban, South Africa, 23 June 2015. Publication Josiane Ayingeneye and Vincent O. Nyamori, “Reduction of aldehydes and ketones to their corresponding alcohols in 1-butyl-3-methylimidazolium tetrafluoroborate: A comparison between sodium borohydride reduction and catalytic hydrogenation approaches” (manuscript in preparation). …………………………………………. ………………………………………….. Josiane Ayingeneye Date vi | Dedication This dissertation is dedicated to my beloved husband Antoine Ayinkamiye and my daughter Dorcas Ishimwe Ayinkamiye. I am so blessed to have them as the most highly important persons in my life. This achieved success is the recompense of their huge sacrifice in so many different ways. vii | Acknowledgments All my humble thanks and gratitude are offered to Almighty God who has been all in all for getting where I am today. His unconditional love strengthened me and was my shield throughout this study. My sincere gratitude goes to my supervisor, Prof Vincent O. Nyamori, for initiating this project. His invaluable support, through knowledge sharing and constructive critism, lifted me to any high scientific level compared to where I was before. His patience and encouragement helped me to surpass hard times and challenges encountered during this research journey. I am sincerely thankful to Prof Bice Martincigh and Dr Bernard Owaga for their input through insightful suggestions and positive comments offered during group meeting presentations. I learnt a lot from your expertise and surely your contribution has improved my academic background. I would like to acknowledge the technical and instrumental contribution provided by technical staffs, especially, Gregory, Anita, Unathi and Malini. I wish to extent my appreciations to Dr Lucy M. Ombaka and Dr Eric Njogu for initiating me to the laboratory works. It was not easy to me but with their experience and patience, I became familial to the experimental domain. I also appreciate my laboratory mates, Tabitha Amollo, Kudzai Mugadza, Ayomide Labulo, Hassan Shoyiga, Samantha Ndlovu, Nonjabulo P. Ngidi, Wisdom Munzeiwa, Tonderai Mombeshora and Mkhize Muthokozisi. Your mutual interactions made this research interesting and rewarding experience. I would like to thank University of KwaZulu-Natal for funding this project. The School of Chemistry and Physics for allowing the project to run. My gratitude also goes to my late father, who was a source of inspiration to me, and of course I will not forget my wonderful mother, my mother-in-law and my grand-mother for their love and prayers. Many thanks to my first born, Ayinkamiye Ishimwe Dorcas for her moral contribution. Finally, my appreciation also goes to the love of my life, my husband, Antoine Ayinkamiye for his love, understanding, encouragement, supports and prayers during the course of this research. viii | Table of Contents Contents Pages Abstract ii Preface iv Declaration 1: Plagiarism v Declaration 2: Scientific contributions vi Oral presentation vi Poster presentation vi Workshops vi Publication vi Dedication vii Acknowledgments viii Table of contents ix List of figures xv List of tables xviii List of schemes xx List of abbreviations
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