Efficient 5-hydroxymethylfurfural production in ChCl-based deep eutectic solvents using boric acid and metal chlorides

Abstract

Bio-based 5-hydroxymethylfurfural (5-HMF) production in DESs has garnered significant attention due to its effectiveness and environmental friendliness. In this study, acidic ChCl-based DESs and ChCl–fructose DES were compared in terms of 5-HMF production in the presence of four acids, namely boric acid, oxalic acid, citric acid, and p-toluenesulfonic acid. Simultaneously, two types of ChCl–fructose and ChCl–glucose DESs were explored in combination with boric acid for 5-HMF production respectively. The 5-HMF yield was optimized by varying parameters such as the mass ratio of ChCl to carbohydrate, catalyst usage, temperature, time, and water content. The results indicated that ChCl–fructose DES exhibits better performance in converting fructose to 5-HMF than acidic ChCl-based DES. A 5-HMF yield of 65.2% was obtained in ChCl–fructose DES (6 : 4 w/w) with 20% water and 80 mg boric acid at 120 °C for 120 minutes. Similarly, a 5-HMF yield of 33.7% from glucose was presented in ChCl–glucose DES (6 : 4 w/w) with 20% water, 120 mg boric acid, and 25 mg CrCl₃·6H₂O at 120 °C for 120 minutes. The addition of an appropriate amount of water is beneficial for promoting 5-HMF production in ChCl–fructose and ChCl–glucose DESs. The high viscosities of ChCl–fructose and ChCl–glucose DESs can be attributed to a strong intermolecular force, resulting in a large mass transfer resistance. Overall, this work provides an efficient and inexpensive approach for producing 5-HMF in ChCl–fructose and ChCl–glucose DESs.