Biomass represents an important potential source of organic chemicals to replace fuels and chemical feedstocks currently obtained from petroleum. The furanic molecule 5-hydroxymethylfurfural (HMF) is an important bio-based platform chemical, as it can be produced from hexose sugars by dehydration without breaking carbon-carbon bonds and can be processed further to produce a wide variety of chemical functionalities, including monomers for plastic production and promising fuel molecules. Many catalysts have been developed to facilitate this process, but many of these systems rely on toxic heavy metals or require the use of expensive ionic liquids to obtain good yields of HMF from glucose. We have developed a metal-free process to obtain high yields of HMF directly from glucose using substituted phenylboronic acids as non-toxic Lewis acid catalysts, along with a small amount of chloride as a co-catalyst. HMF yield and selectivity show a marked dependence on the chloride concentration, with low concentrations giving low conversions and higher concentrations diverting a large amount of material to polymeric humin byproducts. Our optimal catalyst, 2-carboxyphenylboronic acid, showed unique reactivity relative to other boronic acids, and mechanistic analyses indicate a unique mechanism relative to other reported phenylboronic acids for the production of HMF. The process also proved functional with other sugars present in biomass, including mannose, xylose, and fructose, and was capable of converting disaccharides such as sucrose and cellobiose. Though currently not scalable, further optimization could lead to a convenient and rapid process for HMF production while avoiding the toxicity of transition metal Lewis acids.

Biomass conversion using boronic acids: Efficient transformation of carbohydrates into furanics

256th National Meeting (2018)

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