Influence of the ammonium salts used in the Brønsted acid catalyzed hydrothermal decomposition of D-glucose towards 5-HMF
In this work, we compare the effect of two ammonium salts used as promotors in the hydrothermal decomposition of D-glucose with the results obtained in the presence of sulfuric acid. The two ammonium salts used were ammonium sulfate and ammonium acetate. For the first time, we demonstrate that the ammonium acetate is not a good promotor due to the low conversion of D-glucose. Conversely, the ammonium sulfate appears as a much more promising promotor. Indeed, even if a large amount of humins is observed, 5-HMF is obtained in good yield with a fast conversion of D-glucose. After isolation and characterization of the liquid and solid phases, the role of the ammonium sulfate was thoroughly investigated. A structural characterization of the humins obtained from D-glucose and ammonium salts is also proposed. In addition, we demonstrated that with an ammonium-containing promotor, part of the nitrogen atoms is inserted in the humins structure as pyrrole derivatives.