The effect of Brønsted acids on the hydrothermal dehydration of fructose to 5-hydroxymethylfurfural (HMF), a promising platform chemical from renewable resources, exceeds the sole donation of catalytically active protons.

Within the past years, hydrothermal processes have gathered much attention as promising conversion technologies for especially wet biomass. Amino acids are an integral component of biomass, zoo biomass in particular. However, what happens to them during hydrothermal treatment? Reviewing the available literature going back to the mid of the 20th century revealed an astonishing, but still fragmentary view. In fact, two universal degradation reactions could be identified (i. e., deamination and decarboxylation), competing with each other. Thereby, small structural differences may obviously have huge impacts on the fate of individual amino acids. Nevertheless, the amount of available experimental data is relatively scarce in many cases. In this work, the available knowledge about the degradation of 20 proteinogenic amino acids under hydrothermal conditions was presented and discussed critically. The hydrothermal conversion of proteinaceus biomass as well as the Maillard reaction, both extensively reviewed elsewhere, were only touched on.

The hydrothermal treatment of sugars features a promising technology for the production of fine and platform chemicals from renewable resources. In this work the hydrothermal decomposition of fructose was studied in a buffered medium at a pH range between 2.2 and 8.0. It is demonstrated that at lower pH values mainly 5‐hydroxymethylfurfural (HMF), levulinic acid and humin are generated, while lactic acid and acetic acid are produced at higher pH values. The work shows that the use of moderate acidic conditions may have advantages for the hydrothermal HMF production over the use of strongly acidic conditions, as especially the degradation into levulinic acid is suppressed. Besides, this study deals with a rather complex reaction network, hence limitations and need for adaption of the kinetic model are discussed.

5-Hydroxymethylfurfural (HMF) is a valuable platform chemical that can be produced by an acid-catalysed triple dehydration of hexoses, in particular ketoses. The mechanism of HMF formation is not fully understood, i.a. it has been hypothesised that anions could be involved in the reaction, provided that they are present. In this work, the effect of different monovalent, weakly nucleophilic anions on the HMF formation from fructose and tagatose is studied in order to elucidate their possible role in the mechanism. All anions investigated cause an acceleration of the initial HMF formation compared with the salt-free sample, i.e. there is a reaction order with respect to the anion concentration between 0.12 and 0.68. Merely higher concentrations of nitrate inhibited the HMF formation. Furthermore, by studying the insertion of ¹⁸O from labelled water into fructose using LC-MS, a hydroxyl group exchange could be identified giving rise to the assumption that substitution reactions play an important role.