Croconate blue
Croconate blue or 1,2,3-tris(dicyanomethylene)croconate is a divalent anion with chemical formula C
14N
6O2−
2 or ((N≡C−)2C=)3(C5O2)2−. It is one of the pseudo-oxocarbon anions, as it can be described as a derivative of the croconate oxocarbon anion C
5O2−
5 through the replacement of three oxygen atoms by dicyanomethylene groups =C(−C≡N)2. The term Croconate Blue as a dye name specifically refers to the dipotassium salt K
2C
14N
6O
2.
The anion was synthesized and characterized by A. Fatiadi in 1978, together with croconate violet. He obtained the corresponding acid, croconate acid blue C
14H
2N
6O
2 by treating croconic acid C
5H
2O
5 with malononitrile in water solution at 80–90 °C.
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