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.^[1] Squaramides exhibit 10-50x greater affinity for halides than do thioureas.^[2] Squaramides also find application in medicinal chemistry, metabolomics and material science due to their ability to selectively conjugate amines^[3][4]

Squaramide

Names
IUPAC name 3,4-diaminocyclobut-3-ene-1,2-dione
Identifiers
CAS Number	5231-89-0
3D model (JSmol)	Interactive image
PubChem CID	2781329
CompTox Dashboard (EPA)	DTXSID40381784
InChI InChI=1S/C4H4N2O2/c5-1-2(6)4(8)3(1)7/h5-6H2 Key: WUACDRFRFTWMHE-UHFFFAOYSA-N
SMILES C1(=C(C(=O)C1=O)N)N
Properties
Chemical formula	C4H4N2O2
Molar mass	112.088 g·mol−1
Appearance	white solid
Melting point	338–340 °C (640–644 °F; 611–613 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Squaramide is prepared by ammonolysis of diesters of squaric acid:^[5][6]

O₂C₄(OEt)₂ + 2 NH₃ → O₂C₄(NH₂)₂ + 2 EtOH

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