Azo dyes are commonly used in organic chemistry courses to demonstrate electrophilic aromatic substitution and combinatorial effects. This study developed methods of crystallization of azo dye compounds and obtained a library of crystal structures. Naphthol-derived azo dyes were crystallized through solvent evaporation, vapor diffusion, and solvent-solvent layering and characterized by single crystal X-ray diffraction. The library consists of 20 crystal structures of azo dyes originating from combinations of three different naphthol coupling compounds and variously substituted aniline derivatives. Crystal structures are used by undergraduate organic chemistry students to visualize the molecular structures and concepts such as aromaticity, conjugation, and hydrogen bonding. Interestingly, most of the crystal structures displayed N-H hydrazone tautomeric form rather than the typically drawn O-H azo form. This data matches the literature on azo dyes but is not often reflected in the organic chemistry laboratory procedures for students.

Development of a crystal structure library of azo dyes for the undergraduate organic chemistry laboratory

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