Foundations of chemical microscopy, 2 derivatives of primary phenylalkylamines with 5-nitrobarbituric acid.

5-Nitrobarbituric acid (dilituric acid) was extensively used with great success as a chemical microscopic reagent for the qualitative identification of primary phenylalkylamines. This methodology was based on the characterization of observed crystal morphologies, since a unique crystal habit could be associated with each adduct product. To understand the scientific foundations which permitted chemical microscopy to function as a useful analytical technique, the products formed between dilituric acid and a series of primary phenylalkylamines were characterized using polarizing optical microscopy, powder X-ray diffraction, thermal analysis, and solid-state nuclear magnetic resonance. It was deduced that the origins of the different crystal morphologies associated with each of the crystalline adducts arose from the ability of the systems to form differing structural types and/or hydrates upon crystallization. The degree of hydration in the crystalline phenylalkylamine adducts appeared to increase as additional carbon atoms were added between the aromatic ring and the terminal amine group of the aliphatic sidechain.