Density functional theory investigation of green stabilizer reactions: curcumin in nitrocellulose-based propellants

Stabilizers are molecules used in the composition of nitrocellulose-based propellants for inhibiting the autocatalytic degradation process that produces nitrous gases and free nitric acids. Curcumin – (1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione – is a promising green stabilizer in new formulations of environmental and health-friendly single-base propellants. This work investigates reactions between curcumin and nitrogen dioxide NO2 using density functional theory to unveil their mechanisms. For this purpose, we obtained optimized geometries of equilibrium and transition states, minimum energy paths, and thermochemical data for aromatic ring nitration and hydrogen release reactions. The results indicate that nitration of the aromatic ring of curcumin and the formation of a curcumin-based free radical are viable. The computed Gibbs free activation energy (∆‡G°) and activation enthalpy (∆‡H°) for two different temperatures, 298.15 K (room temperature) and 363.15 K (a typical temperature used in aging tests), are respectively 43.64 kcal/mol and 44.78 kcal/mol for the first reaction, and 31.54 kcal/mol and 35.31 kcal/mol for the second. Therefore, the radical-based mechanism is kinetically favored.