Acetone is not caustic AT ALL. It is a neutral solvent.
Most folks think that it is a vile dangerous chemical because it is very offensive to your health, it is highly flammable, and it is a VERY effective solvent for many organic materials. Unlike water, which is very "Polar", acetone has different properties that make it very effective on pine sap.
It might also damage some ropes by dissolving the material they are made of, so I would try a washing machine first. Buying enough acetone to wash a rope would be expensive.
If I had a real sappy rope, and laundry didn't get it off, I would use paint thinner to dissolve the sap, then put the rope through the laundry again after the thinner has evaporated.
I used to wash greasy coveralls & grease rags in gasoline (back when it was cheaper and I didn't have a uniform service). We would soak the offensive fabric in a 5 gallon bucket of gas, then spash it around until mostly clean. Then wring it out, and throw in the washer. I told one of my guys how to do this once, and I told him to make sure that the lid on the washer did not get closed until the spin cycle came up, 'cause the gasoline vapors were explosive. He didn't listen, it blew up the washing machine. BIG BOOM, but the lid just banged up against the wall, and the washer kept working!
If you wash your rope following acetone, paint thinner, or gasoline, leave the lid open until the spin cycle!