Personally I'd always make the change to something that seems like it might interest me more and could potentially lead to career advancement. The med school application process is such a crap shoot, it doesn't hurt to explore alternative careers that you might enjoy if for whatever reason you didn't become a doctor. Industrial chemistry seems like something that might be a bit more useful to your learning in med school compared to being in sales at a steel company, but ultimately I think the real gain would be in maybe finding something you could talk about with great interest during interviews rather than expressing, "meh, it's a job that's just a placeholder that pays enough." I'm sure med school interviewers hear the later all the time, but it gives you a leg up if you've got an interesting job that you enjoy talking about and seem like a go-getter.