Preparation of 5-methylfurfural from starch in one step by iodide mediated metal-free hydrogenolysis

Abstract

Starch is available in large quantities and at cheap price, especially that from stale rice, root and tuber crops, etc., which makes it desirable for conversion to value-added products. A metal-free approach to convert starch to 5-methylfurfural (5-MF) using hydrochloric acid, sodium iodide and hydrogen in a biphasic solvent system has been developed. 5-MF is an important fine chemical, widely used in food, medicine, pesticides, cosmetics and other industries, and is also considered to be an important bio-gasoline precursor. I⁻ has superior nucleophilic substitution properties and high reactivity towards C–O bond cleavage, which is crucial for this transformation. Under optimal reaction conditions, 38.0% of 5-MF and 45.6% of total organic products can be obtained from starch with 22.5% levulinic acid as the main side product. Besides, 80.8% 5-MF can be directly obtained from 5-hydroxymethylfurfural (HMF) through the same process. To the best of our knowledge, this is the first reported example of a metal-free process to convert starch and HMF directly to 5-MF. The reaction mechanism was well studied. The catalyst system was proved to be stable and was recycled five times without loss of activity.