Abstract
An efficient microwave-assisted methodology for the oxidation of free carbohydrates to corresponding aldonates is described. Supported gold catalyst, hydrogen peroxide, and a mineral base were used to perform the oxidation reaction in water under microwave irradiation. These conditions combined with Au/Al2O3 catalyst allowed to reach in 10 min a quantitative conversion of glucose. The catalyst was highly selective and reusable, and only 0.004 mol % of gold compared to sugar was used. The reaction was performed using a variety of substrates (mono- or oligosaccharides, neutral or acidic sugars), and good to excellent conversion yields and selectivity to corresponding aldonates were obtained. After filtration and freeze-drying, sodium or potassium aldonates were obtained without any purification. Thanks to very high turnover frequencies (up to 438 000 h(-1)), this methodology significantly improves the previously described methods for the gold-catalyzed oxidation of carbohydrates.