1,3-Indandione

1,3-Indandione is an organic compound with the molecular formula C₆H₄₂CH₂. It is a β-diketone with indane as its structural nucleus. It is a colorless or white solid, but old samples can appear yellowish or even green. It is a popular chemical scaffold, and derivatives antagonize Vitamin K receptors.

Structural properties

Solid 1,3-indandione is a diketone, As a solution in water, it is partially enolized. The enolate anion exhibits significant delocalization, and the highest electron density is on the second carbon. This acid-base behavior explains many properties of the compound.

1,3-Indandione was first obtained by Claisen condensation of ethyl acetate and dimethyl phthalate. A related route entails the reaction of benzoyl chloride with malonyl dichloride. It also can be obtained by oxidation of indane.

The structure of the title compound has been confirmed by X-ray crystallography. Unlike some other 1,3-diketones, it does not crystallize as the enol.
The carbon at the C-2 position is alpha to both carbonyls, and thus can act as a nucleophile. It undergoes self-aldol condensation easily, resulting in bi- and triindone.
Bromination occurs at the 2-position:
One or both carbonyl groups can be reduced to alcohol groups or methylene groups, depending on the method used.

image: Diphenadione2.svg|thumb|left|Diphenadione a commercial rodenticide derived from 1,3-indandione|130px
1,3-Indandiones with a substituent at the 2-position are potent rodenticides. Commercial products include pindone, chlorophacinone, and diphenadione. These compounds function as vitamin K antagonists, inducing hemorrhage in the affected animals.