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

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.

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.