The synthesis of higher-carbon sugar alcohols via indium-mediated acyloxyallylation as potential phase change materials

In recent years, sugar alcohols have gained significant attention as organic phase change materials (PCMs) for thermal energy storage due to their comparably high thermal storage densities up to 350 J/g. In a computational study, outstandingly high values of up to ~ 450–500 J/g have been postulated for specific higher-carbon sugar alcohols. These optimized structures feature an even number of carbon atoms in the backbone and a stereochemical configuration in which all hydroxyl groups are in an 1,3-anti-relationship, as found in the natural hexitol d-mannitol. However, these manno-configured higher-carbon sugar alcohols have not been experimentally investigated as PCMs yet and described synthetic routes are elaborate multiple steps syntheses. Therefore, we aimed to synthesize sugar alcohols of the manno-series with a concise synthetic protocol based on the indium-mediated acyloxyallylation (IMA) of aldoses. En route the C2-epimers were easily accessible, namely gluco-configured sugar alcohols, bearing one set of hydroxyl groups in a suboptimal 1,3-syn-realtionship. The synthesized compounds were found to possess thermal properties consistent with the predicted values, and the “perfect” higher-carbon sugar alcohol with eight carbon atoms was found to have indeed an outstanding high latent heat of fusion of ~ 380 J/g with a melting point of 260 °C.

Graphical abstract