Reaction of Vitamin C with Permanganate

Can someone please explain the following reactions?

1. Vitamin C titrated against acidified potassium permanganate

The end point should be pale purple, but the pale purple keeps disappearing when vitamin C is added, later on, the solution turns brown instead of purple.

2. Excess acidified potassium permanganate + Vitamin C

After standing in air for some time, the deep purple colour disappears, solution turns brown. If heated, purple fumes are given out, and small black solids, like little ants, are precipitated.

Thank you!!