Studies on the synthesis, physical properties, and stability of benzyl ethers as potential heat transfer fluids

Heat transfer fluids (HTFs) play a crucial role across a broad range of industrial operations, absorbing and conveying thermal energy in applications such as process heating, metal fabrication, and machinery cooling—particularly within the aerospace, automotive, and marine sectors. HTFs serve as essential components in the generation of electricity through concentrating solar power systems. Here, they function as reservoirs of sensible heat, enabling thermal energy storage for use when direct solar radiation is unavailable, thereby ensuring continuous power conversion.

Previously, we have reported on the preparation of extended dibenzyl ethers as potential heat transfer fluids utilizing Williamson-type ether synthesis in combination with Suzuki reactions, often in one-pot reactions [1]. In the current contribution, we extend the scope of benzyl ethers that can be prepared under these conditions. Furthermore, we investigate the physical properties such as the heat capacity and the temperature-dependent density of selected dibenzyl ethers, and compare the values with computational data using incremental methods for the estimation of group contributions within the structures towards the macroscopic properties of the compounds. Finally, it was realized that while some of the dibenzyl ethers were stable even at 300 °C, studied benzyl ethers were found to degrade oxidatively in air at rt over longer time periods. Thus, after 365 days at rt dibenzyl ethers were found to have degraded to mixtures of benzaldehydes, benzoic acids and aryl benzoates. Possible mechanisms for these transformations are discussed.

[1] Thiemann et al., 3^rd World Sustainability Forum, Sciforum Electronic Conference Series, Vol. 3, 2013, d-002.