Synthesis of cyclic bis- and trismelamine derivatives and their complexation properties with barbiturates.

Cyclic bis- and trismelamine derivatives were prepared from cyanuric chloride by stepwise substitutions with appropriate amines. The complexation abilities of these melamine derivatives with barbituric acid derivatives were evaluated by UV-vis spectroscopy and (1)H NMR. The structure was also confirmed by X-ray crystallography. Both the acyclic and the cyclic bismelamine derivatives formed a 1 : 1 complex via six hydrogen bonds with barbituric acid derivatives. van't Hoff analyses on the complexation of the bismelamines with the barbituric acid derivative revealed that the complexation of the cyclic bismelamine was entropically favored and enthalpically less favored process than those of the acyclic bismelamine. X-Ray crystallographic analysis and (1)H NMR studies revealed that the cyclic trismelamine bound one barbituric acid derivative into the cavity via six hydrogen bonds by two melamine moieties and another barbituric acid via three hydrogen bonds by the residual melamine moiety.