Benzaldehyde nitration by mixed acid under homogeneous condition: a kinetic modeling

2-Nitrobenzaldehyde and 3-nitrobenzaldehyde are important isomers involved in the synthesis of a variety of products for the bulk and fine chemicals industry. They can be both obtained by direct nitration of benzaldehyde in mixed acid. The meta substituted isomer is the main reaction product even though it has been recently pointed out that the yields of the two compounds (ortho and meta isomers) are affected by the mixed acid composition. In this work, a reaction network consisting of equilibrium and irreversible reactions and a mathematical model are proposed. For each of the reactions the kinetic and thermodynamic parameters were estimated in order to explain and predict the changes in the reactivity and selectivity at varying conditions. Moreover, a simplified approach was successfully used to describe the kinetics of the secondary oxidation pathways of the organics in the nitrating mixtures leading to benzoic and nitrobenzoic acids. The parameter estimation suggested that the ortho-oriented nitration is mainly due to the rearrangement of the complex of benzaldehyde with the nitronium ion rather than to the direct nitration of the organic substrate. On the other hand, the nitration of benzaldehyde and of the complex are both relevant for the meta-oriented isomer formation.