A couple of years ago I started a company with 3 other people. After about 6 months and some internal conflicts I decided to leave. Even though in terms of financial gain the results were null, in terms of experience the outcome was quite positive. Is it worthwhile mentioning in the statement of purpose?

Not sure what a statement of purpose is, but I worked for a company run by a man who didn't know his a*s from a hole in the ground, and consequently the whole thing went belly up. But I still include it on my CV cos despite the nastiness, I learned a lot about how to manage difficult situations.