Thermoreversible Transformations of the Cyanosubstituted 2‐Oxopyrrole Derivative by the Action of Amines for the Creation of Novel High‐Contrast Coloration/Decoloration Systems

Abstract A new efficient approach to the synthesis of intensely colored 2‐(2‐oxo‐3 H ‐pyrrol‐3‐ylidene)malononitrile ( OP ) was developed. Using the reaction of OP with amines, a series of previously unknown colorless organic salts – dicyano(2‐oxo‐2,5‐dihydro‐1 H ‐pyrrol‐3‐yl)methanides were synthesized, bearing in the structure two fragments of same or diverse amines of different nature (covalent and ionic). TGA‐DTA study of the synthesized salts showed a thermal reversibility of their formation. The introduction of violet OP into paper followed by treatment with amine vapors revealed prospects of using such a system for naked‐eye detection of volatile amines. It was also shown that OP ‐based rewritable paper can be created, to which a data can be applied by local heating and erased by the action of amine or temperature.