DFT investigation of green stabilizer reactions: curcumin in nitrocellulose-based propellants.

Context: Nitrocellulose, widely used in energetic materials, is prone to thermal and chemical degradation, compromising safety and performance. Stabilizers are molecules used in the composition of nitrocellulose-based propellants to inhibit 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, known for its antioxidant properties and a potential green stabilizer, was investigated using Density Functional Theory (DFT) focusing on its interaction with nitrogen dioxide. Two mechanisms were analyzed: aromatic ring nitration and free radical formation. 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 the activation enthalpy (∆H°) for two different temperatures, 298.15 K (room temperature) and 363.15 K (typical temperature 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. The radical-based mechanism favors improved kinetics. These findings demonstrate curcumin's potential as an effective stabilizer, providing comparable performance to traditional compounds with lower environmental impact.

Methods: DFT calculations were carried out using Gaussian 09 and Orca 5.0.1 packages. The ωB97M-V, B3LYP, and M062X functionals were employed with the 6-311 + G(d) and 6-311G(d) basis sets. Solvent effects were modeled using the Conductor-like Polarizable Continuum Model (CPCM) and Solvation Model based on Density (SMD) continuum solvent models. Thermochemical data were computed using the same levels of calculation.