and why do you need to do this?also use fire.
If you want to make the data unreadable, scratching the surface won't do. The inner side is the information, it's mostly clear plastic. You'd have to break them and such, melt.
If you scratch the polycarbonate side enough, it won't reflect properly. Take it outside, put the data side on the ground and rub it on the sidewalk for a few minutes.
Obviously someone who specialized in data recovery could get data off a scratched CD, I just want this destroyed enough that some garbage man isn't going to pick my old CDs out of the garbage and pick through them for the lulz.