Chloroacetone

At STP it is a colorless liquid with a pungent odor.

[3] On exposure to light, it turns to a dark yellow-amber color.

Chloroacetone is used to make dye couplers for colour photography, and is an intermediate in chemical manufacturing.

[6] Chloroacetone purchased from commercial suppliers contains 5% impurities including mesityl oxide, which is not removed by distillation.

Mesityl oxide can be oxidized using acidified KMnO4 to form a diol (followed by separation with ether), which is removed on subsequent distillation.