Chemisch katalysierte Epimerisierung von D-Fructose für die Herstellung von D-Allulose

• Chemically catalysed epimerization of D-fructose for the production of D-allulose

Drabo, Peter; Palkovits, Regina (Thesis advisor); Weinhold, Elmar (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2023

Abstract

This work deals with the chemocatalytic conversion of D-fructose into D-allulose using basic catalysts. In addition to the investigation of the reaction network, this work addresses the identification of the catalytically active species in polar and non-polar solvents and contributes to knowledge-based catalyst development. By screening different catalysts and solvents, a yield of D-allulose of 14 % was obtained with a selectivity of up to 33 %. The alkaline conversion of D-fructose mainly leads to the saccharides D-allulose, D-glucose and D-mannose. A method was introduced for the analysis of the saccharides, which proposed the separation of acidic decomposition products by using basic and acidic ion-exchange resins. Subsequently, the saccharides were converted into their isopropylidene derivatives and analyzed by gas chromatography, which allowed the assignment of unique signals to the sugars in the chromatograms obtained. Using CaO, SrO, MgO and Ba(OH)2, as catalysts for the conversion of D-fructose in water, a D-allulose yield of 7 % was obtained. By incorporating kinetic approaches, filtration and contact tests, and continuous analysis of pH and leached metal species, it was shown that hydroxide-ions were the catalytically active species for the reaction in water. Furthermore, isomerization of D-fructose was tested in the presence of a variety of structurally different basic amines. Hydroxide ions are formed in aqueous phase in the presence of amines. By incorporating a kinetic approach, it was shown that these ions play a crucial role in catalysis. While D-glucose was predominantly formed as the main product in the protic solvents water and methanol, a significant increase in selectivity towards D-allulose could be observed in DMF and DMSO. Incorporating operando 13C NMR data, it was found that D-fructopyranoses (the predominant species in water and methanol) preferentially converted to D-glucose, while the formation of D-allulose proceeded predominantly from D-fructofuranoses (the dominant moiety in DMSO and DMF). This explains the significantly increased yield and selectivity of D-allulose in the aprotic solvents. Further studies showed the high potential of phosphazenes for the catalytic conversion of D-fructose. The strongly basic compounds exhibited high catalytic activity upon isomerization in DMF and, along with amines, can be used as starting materials for the synthesis of tailor-made solid catalysts.

Institutions

• Department of Chemistry [150000]
• Chair of Heterogeneous Catalysis and Technical Chemistry [155310]