Aspirin that has been stored for a long time may give a vinegar odor and give a purple color with fecl3. what reaction would cause this to happen

There would be production of acetic acid from moisture that gets inside the bottle. What happens is that water molecules reacts with the aspirin protonating an oxygen in the acetic group and allowing it to detach from the molecule producing acetic acid which is the main cause of the vinegar smell.