2-Acetonyl-2-hydroxyindan-1,3-dione

In the title compound, C12H10O4, the five-membered ring adopts an envelope conformation, with the Csp 3 atom at the flap [deviation = 0.145 (2) Å]. In the crystal structure, molecules are linked by intermolecular O—H⋯O and C—H⋯O hydrogen bonds, forming a three-dimensional network.

In the title compound, C 12 H 10 O 4 , the five-membered ring adopts an envelope conformation, with the Csp 3 atom at the flap [deviation = 0.145 (2) Å ]. In the crystal structure, molecules are linked by intermolecular O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds, forming a three-dimensional network.

Comment
Ninhydrin is used to detect α-amino acids, proteins and dipeptides. When it reacts with free amines, a deep blue or purple colour known as Ruhemann's purple (RP) is evolved (Ruhemann, 1910). Ninhydrin is also used to monitor deprotection in solid phase peptide synthesis (Kaiser Test) (Kaiser et al., 1970). It is one of the most widely used reagents for chemical development of fingerprints on porous surfaces. We herein present the crystal structure of the title compound, a derivative of ninhydrin.

Experimental
The title compound was synthesized by the reaction of ninhydrin (1.78 g), trichloroacetic acid (1.64 g) and catalytic amount of magnesium in presence of acetone. Ninhydrin and tricholoro acetic acid in molar ratio 1:1 were allowed to reflux with acetone in presence of Mg turnings for 1 h. The reaction mixture was dried under reduced pressure and was purified by chromatography over silica gel column. Elution of the column with petroleum ether-diethyl ether (4:1) followed by crystallization with petroleum ether-chloroform (1:1) afforded fine crystals of the title compound (120 mg, m.p. 399 K).

Refinement
Atom H1O3 was located in a difference Fourier map and refined freely. The remaining H atoms were positioned geometrically and refined using a riding model, with C-H = 0.93-0.97 Å and U iso (H) = 1.2 and 1.5 U eq (C). A rotating-group model was applied for the methyl group. In the absence of significant anomalous dispersion, 1513 Friedel pairs were merged for the final refinement. Fig. 1. The molecular structure of the title compound, showing 50% probability displacement ellipsoids and the atom-numbering scheme.

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cyrosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.