A new polymorph of 2,6-diaminopyridine

Area of Science:

• Materials Science
• Crystallography
• Organic Chemistry

Background:

• 2,6-Diaminopyridine (26-DAP) is a crucial intermediate in synthesizing aromatic azo chromophores.
• Azo chromophores are extensively utilized in the dyes and pigments industry.

Purpose of the Study:

• To investigate the solid-state forms of 2,6-Diaminopyridine.
• To characterize a newly discovered polymorph of 26-DAP.

Main Methods:

• Sublimation of commercial 26-DAP powder.
• Recrystallization of 26-DAP from acetone and toluene.
• Thermal analysis (Differential Scanning Calorimetry, Thermogravimetric Analysis) to determine phase transitions.

Main Results:

• A new polymorph, Form II, was obtained as colorless orthorhombic needles.
• Form II was the major phase when recrystallized from acetone or toluene.
• Thermal analysis confirmed Form II is less stable than Form I, converting at 335 K.

Conclusions:

• Discovery and characterization of a new polymorph (Form II) of 2,6-Diaminopyridine.
• Form II is a metastable phase that transforms into the known Form I upon heating.
• Understanding 26-DAP polymorphism is important for its industrial applications in dyes and pigments.