As I know, when you determine COD by using KMnO4 in H2SO4, the organic matter will be oxidized and form CO2 and other inorganic components. Mn in KMnO4 (+7) is reduced to Mn(+2), below is the simple equation for this :
Organic matter + KMnO4 + H2SO4 ==MnSO4 + K2SO4 + CO2 + H2O
But in recent days, people have not used this method more often because KMnO4 just oxidize about 75% organic matter. In stead of using KMnO4, we can use K2Cr2O7.(can oxidize about 90% organic matter)
Good luck