Of course whether raising the minimum wage will result in net employment or unemployment is subject to situational market factors (though when you're talking such an extreme hike, it's not really debatable that it would lower employment); But if the goal is to help the lowest income earners, it is basic common sense that as you raise wages beyond their worth, you begin to price them out of the market in favor of better employees or technology.
For example, unfortunately I'm on the go a lot and have to eat more fast food than I'd like. I'm continually amazed how little many fast-food employees don't give a shit about their jobs. You're lucky if your order is even right, but hey, cheap labor, cheap food, you get what you pay for, right?
The counter-argument is, "well, if you paid them more money, they'd show more effort". I know that is not the case from my experience with some of my colleagues, plenty who were making well beyond minimum wage. Some people's skills and motivations delegates them to end up with lesser jobs.
What you are doing when you raise wages, especially so dramatically, is make it tougher for them to even have these crappy jobs, because guys like me with a college degree, experience and credibility are all of the sudden interested in a minimum wage job if it pays that well.
Sure that might mean much better service at the McDonalds (assuming they don't opt to replace me with a machine that's now more effective), but it means the tradeoff of probably having to pay more for the same shitty burgers. Is that a world you really want to live in?
