Synthesis and thermal stability of dimethyl adamantanes as high-density and high-thermal-stability fuels

Alkyl-adamantane fuels are appealing for aerospace vehicles due to their high density, good low-temperature performance and thermal stability. Here we reported a facile route to synthesize dimethyl-adamantane fuels via solvent-free rearrangement. The thermodynamic preference of six products (dimethyl-adamantane isomers) was revealed by Density Functional Theory (DFT) calculation and experiment, and the reaction pathway was further discussed. The reaction conditions including catalyst, catalyst dosage, temperature, and solvent were optimized, with the dimethyl-adamantane yield of 88.7%. We synthesized two typical dimethyl-adamantane fuels (with different compositions of isomers) by adjusting the reaction conditions and then evaluated their properties. It is found the two fuels show different fuel properties (e.g., density, heating value, thermal stability) due to the difference in methyl substitution position, although both with high density and good low-temperature fluidity. Specifically, the dimethyl-adamantane with methyl on the tertiary carbon shows better thermal stability than JP-10 and decalin. This work presents dimethyl-adamantanes as good high-density and high-thermal-stability fuels, and suggests the position of methyl substitution on adamantane has considerable effect on their properties.