LAUSR

5-(Hydroxymethyl)furfural (HMF), produced by the acid-catalyzed dehydration of biomass-derived hexoses, is a well-recognized renewable chemical intermediate in the biorefinery research for the productions of fuels, chemicals, and materials. However, the inherent hydrophilicity and poor stability of HMF continue to disfavor its production and value addition from an economic standpoint. In this regard, the superior thermal and hydrolytic stability of the hydrophobic analogs of HMF simplify their isolation and purification from the aqueous (or polar) reaction media while enhancing their shelf life. The analogs show promises in supplanting HMF from its derivative chemistry. The halogenated derivatives of HMF, such as 5-(chloromethyl)furfural (CMF) and 5-(bromomethyl)furfural (BMF), can be produced directly from biomass in good isolated yields. The non-halogenated, hydrophobic derivatives of HMF include esters such as 5-(formyloxymethyl)furfural (FMF) and 5-(acetoxymethyl)furfural (AMF), obtained by the dehydration of carbohydrates in suitable carboxylic acids. The ethers of HMF, such as 5-(ethoxymethyl)furfural (EMF), can be produced directly by the acid-catalyzed alcoholysis of biomass. In addition, partially oxidized or reduced derivatives of HMF, such as 2,5-diformylfuran (DFF) and 5-methylfurfural (5MF), have also found significant interests as hydrophobic analogs of HMF. The production and value addition of various lipophilic analogs of HMF are rather scattered in the literature, and no comprehensive review is available in this area to date. This technical review attempts to fill that gap with up-to-date information with a critical analysis of the achievements and challenges. In this review, the production and derivative chemistry of various hydrophobic analogs of HMF have been discussed. The relative advantages and challenges associated with the preparation and value addition of various hydrophobic analogs of HMF are highlighted.