Aspirin
Aspirin is the brand name for Salicylic acid. It's production on Mars would be part of a larger chemical production system, and it can be used as a model for the complexity of the chemical industry that would be required for a Mars Settlement.
In situ production
Phenol (C6H5OH)
Phenol + sodium hydroxide -> sodium phenoxide (NaOC6H5)
sodium phenoxide +CO2 at 100 atm and 115 °C in a method known as the Kolbe-Schmitt reaction -> sodium salicylate (C7H5NaO3)
sodium salicylate + acidification with sulfuric acid ->
Salicylic acid
It may be more practical to produce aspirin from the bark of the willow tree, that contains the amino acid Phenylalanine. however, this requires the mastery of enzyme catalyzed processes.