[Edited on 29-6-2015 by blogfast25]AJKOER - 30-6-2015 at 14:24
Potassium manganate is an intermediate in the preparation of Potassium permanganate.
I would guess the answer is below 240 C as that is the temperature at which the Potassium permanganate decomposes per Wikipedia.Texium - 30-6-2015 at 14:34