The isomers of the chemical raw material diaminotoluene are mainly formed by the different positions of the two amino groups on the toluene ring. The common types are ortho, meta and para. The two amino groups of ortho diaminotoluene are located in the adjacent position of the methyl group, the meta position is the two amino groups are located in the meta position of the methyl group, and the para position is the relative position of the amino group to the methyl group. These subtle differences in structure make them show obvious differences in chemical properties and also affect their specific uses in industrial applications.
The chemical activity of ortho diaminotoluene is relatively high, which is related to the spatial position of the two amino groups in its molecule. Because the two amino groups are close to each other, there is a certain electronic effect between them, making it easier to undergo substitution reactions when participating in chemical reactions. When reacting with acid, the amino group of the ortho isomer has a stronger ability to bind protons, and the salts formed are also more stable. However, this structure also makes it easier to decompose under oxidizing conditions to generate some complex oxidation products, so more attention should be paid to isolating from air and oxidants during storage.
In the molecular structure of meta-diaminotoluene, the distance between the two amino groups is moderate and the steric hindrance is small, which makes it show better reaction performance when participating in condensation reactions. For example, when reacting with aldehyde compounds, the meta-isomer can form a stable Schiff base more smoothly, which makes it a more suitable raw material in the synthesis of some polymers. At the same time, the thermal stability of meta-diaminotoluene is relatively good, and it is not easy to decompose at high temperatures, and it can adapt to some reaction processes that require heating conditions.
The molecular structure of para-diaminotoluene has a high symmetry, which makes its chemical properties more stable. The two amino groups are in relative positions, and the electronic influence between them is relatively balanced, so it shows moderate activity in most chemical reactions. In oxidation reactions, the para-isomer has strong resistance and is not easily oxidized and deteriorated, which makes it more advantageous in storage and transportation. At the same time, its symmetrical structure also makes it more regularly arranged when forming crystals, so it has a higher melting point. This physical property also indirectly reflects its chemical stability.
Different isomers have different reaction selectivity with other compounds. Due to the position effect of the amino group, ortho-diaminotoluene is more likely to undergo a substitution reaction on the ring when reacting with halogenated hydrocarbons; while the para-isomer is more inclined to have the hydrogen on the amino group replaced. This reaction selectivity makes them have different focuses when synthesizing different derivatives. For example, the ortho-isomer is more suitable for synthesizing certain heterocyclic compounds, while the para-isomer is more efficient in synthesizing compounds with symmetrical structures.
The stability of each isomer is also different under acidic or alkaline conditions. Ortho-diaminotoluene is prone to intramolecular cyclization under strong alkaline conditions to produce indole compounds; while the meta- and para-isomers are relatively stable under the same conditions and are not prone to such reactions. Under acidic conditions, all three isomers will combine with acid to form salts, but the salt formed by the meta-isomer is more soluble in water, which makes it easier to handle in scenarios where aqueous solution reactions are required.
The difference in the chemical properties of isomers is also reflected in their polymerization reaction performance. When para-diaminotoluene participates in the polymerization reaction, due to the symmetry of the molecular structure, the polymer chain structure formed is more regular, and the mechanical properties and stability are also better; while due to the influence of steric hindrance, the polymerization degree of the ortho-isomer is often low, and the performance of the formed polymer is relatively poor. This difference makes the para-isomer more popular in the synthesis of high-performance polymer materials, while the ortho- and meta-isomers have their application space in some fields that do not require high polymer performance.
