Self-Catalyzed Deconstruction of Acid-Modified k-Carrageenan for Production of 5-Hydroxymethyl Furfural

k-Carrageenan is a major constituent of red seaweeds composed of inherent repeating sulfated galactan units having potential to produce 5-hydroxymethyl furfural (5-HMF). The presence of inherent alkali sulfate functionality generates catalytically active acid sites on the backbone of k-carrageenan. In the present study, catalyst-free synthesis of 5-HMF was studied by inducing acid active sites on alkali-sulfated functionalities of k-carrageenan. The presence of -SO3H active sites on acid-imparted k-carrageenan were accountable for the self-catalytic property to deconstruct k-carrageenan into galactose units and further dehydration into 5-HMF. A plausible mechanism for the self-catalytic deconstruction of k-carrageenan into 5-HMF has been proposed. The comparative study of catalytic and noncatalytic reactions in DMSO resulted 43% and 41% yield of 5-HMF, respectively. Of the tested solvents (DMF, DMSO, IPA, TBA, and IAA), DMSO was found as the best solvent for deconstruction. Furthermore, the ease of solvent recovery is achieved by using IPA as a green solvent in combination with DMSO, which resulted in 50% yield of 5-HMF. The use of a catalyst-free protocol by using IPA as a green and low boiling reaction medium promotes development of green processes.