Accidentally splashed surgical alcohol on a plaster wall
Alcohol acts like a paint remover. So rather than thinking of this as a stain on the surface that can be washed away you have to realize that the paint finish has been partially degraded.
This means you will have to repaint a small area of the wall. Often you will find that touching up does not blend very well so you may need to repaint the affected wall from corner to corner to get a good result