Indane-1,2,3-trione is the organic compound with the formula C<sub>6</sub>H<sub>4</sub>(CO)<sub>3</sub>. The compound is the dehydrated derivative of C<sub>6</sub>H<sub>4</sub>(CO)<sub>2</sub>C(OH)<sub>2</sub>, known as ninhydrin, which is used to reveal fingerprints.
Indane-1,2,3-trione, which reacts readily with nucleophiles (including water). Whereas for most carbonyl compounds, a carbonyl form is more stable than a product of water addition (hydrate), ninhydrin forms a stable hydrate of the central carbon because of the destabilizing effect of the adjacent carbonyl groups.
To generate the ninhydrin chromophore (2-(1,3-dioxoindan-2-yl)iminoindane-1,3-dione), the amine must condense to give a Schiff base. The reaction of ninhydrin with secondary amines gives an iminium salt, which is also coloured, generally being yellowâÂÂorange.