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

Abstract

In recent years, sugar alcohols have gained significant attention as phase change material (PCM) for thermal energy storage within organic materials due to their high thermal storage densities of up to 350 J/g. In a computational study (a), even higher values of up to 500 J/g have been postulated for higher-carbon sugar alcohols with structural features as they can be found in D-mannitol or galactitol: (1) Linear elongation, (2) even number of carbon atoms, and (3) separate distribution of all hydroxyl groups (1,3-anti). However, these sugar alcohols have not been experimentally investigated as PCMs yet and described synthetic routes for the compounds of interest are elaborate multiple step syntheses. Within our work, we took on the challenge to develop concise synthetic protocols for substances of this class based on the indium-mediated acyloxyallylation (IMA) of aldoses and evaluate their thermal properties. Via IMA and subsequent ozonolysis with a reductive workup protocol we synthesized some of the theoretical investigated manno-configured sugar alcohols and their C2-epimers, bearing one set of hydroxyl groups in a suboptimal 1,3-syn-relationship. The synthesized compounds were found to possess thermal properties consistent with the predicted values and the C8 sugar alcohol fulfilling all the stated criteria was found to have indeed an outstanding high latent heat of fusion of ~380 J/g. We additionally set our interest to the synthesis of galacto-configured higher-carbon sugar alcohols and developed a synthetic protocol with high control of stereoselectivity for the introduced hydroxyl groups. We aimed to further demonstrate the influence of the chain length and distribution of the hydroxyl groups on the melting point and melting enthalpy of sugar alcohols, as it has been discussed by Inagaki and Ishida (a), by including examples not matching all stated criteria.

(a) T. Inagaki, T. Ishida, J. Am. Chem. Soc. 2016, 138, 11810.