A simple and efficient microwave-assisted HNb(3)O(8) catalytic process is proposed for the dehydration of carbohydrates in the aqueous phase. A 5-hydroxymethylfurfural (HMF) yield of 55.9 % was achieved at a high substrate/catalyst weight ratio of 50 from a 10 wt % fructose solution, which is close to the yield achieved by homogeneous aqueous systems. The critical factor for this performance is the fast in situ exfoliation of layered HNb(3)O(8) with the aid of microwave irradiation, which leads to quasi-homogeneous catalytic behavior. Importantly, the catalytic system is also applicable for the one-pot production of HMF from di- and polysaccharides, such as inulin, through a consecutive hydrolysis-dehydration reaction. Additionally, the unique restacking feature of the exfoliated HNb(3)O(8) ensures the good reusability of the catalyst.
By photoredox-catalysis, alkylation/aryl cyclization of alkynylphosphine oxides towards benzo[b]phospholes has been realized under metal- and oxidant-free conditions at room temperature.
Cellulose without any pretreatment was directly converted into levulinic acid (LA) in a microwave-assisted acidic catalytic system with a high ionic strength. The highest LA yield could reach 67.3 mol% within 60 min even when the cellulose concentration was as high as 10 wt%. It is concluded that high ion strength and microwave irradiation were jointly responsible for the fast cellulose conversion and high LA yield, and a cooperative acceleration mechanism is finally proposed. The high ion concentration provided by alkali metal halides not only accelerated the cellulose hydrolysis but also facilitated glucose conversion into LA by shifting the weak acid ionization equilibria, and microwave irradiation further promoted this salt effect by its characteristic heating way of ion conduction. Such a one-pot catalytic system provides a possibility of practical application for direct highly efficient conversion of cellulose due to its green properties, low cost and efficient characteristics.
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