Squaramide

Squaramide is the organic compound with the formula O2C4(NH2)2. Not an amide in the usual sense, it is a derivative of squaric acid wherein the two OH groups are replaced by NH2 groups. Squaramides refer to a large class of derivatives wherein some of the H's are replaced by organic substituents. Exploiting their rigid planar structures, these compounds are of interest as hydrogen-bond donors in supramolecular chemistry and squaramide catalysis. Squaramides exhibit 10-50x greater affinity for halides than do thioureas. Squaramides also find application in medicinal chemistry, metabolomics and material science due to their ability to selectively conjugate amines

Squaramide is prepared by ammonolysis of diesters of squaric acid:
 * O2C4(OEt)2 + 2 NH3   →   O2C4(NH2)2  +  2 EtOH

N-Substituted squaramides are prepared similarly, using amines in place of ammonia.