Why aspirin gives voilet clr with ferric chloride?

Ferric chloride, or iron(III) chloride will not react with aspirin. It will, however, react with salicylic acid, which is used to synthesize aspirin. In this light, adding an aqueous ferric chloride solution to a sample of aspirin is a good way to see if there is any unreacted salicylic acid. A purple color is an indication of salicylic acid. A sample of pure aspirin should not exhibit any color change.