I've looked into preparations of activated manganese dioxide for some time now, and what confused me is the contrast between the original Attenborough method and some of the alternatives.
A solution of MnSO4⋅4H2O (110 g) in H2O (1.5 L) and a solution of NaOH (40%; 1.17 L) were added simultaneously during 1 h to a hot stirred solution of KMnO4 (960 g) in H2O (6 L). MnO2 precipitated soon after as a fine brown solid. Stirring was continued for an additional hour and the solid was then collected with a centrifuge and washed with water until the washings were colorless. The solid was dried in an oven at 100–120 ◦C and ground to a fine powder (960 g) before use.
That is molar ratio MnSO4.4H2O:KMnO4 - 1:8,34
A solution of MnCl2⋅4H2O (200 g) in H2O (2 L) at 70 ◦C was gradually added during 10 min, with stirring, to a solution of KMnO4 (160 g) in H2O (2 L) at 60 ◦C in a hood. A vigorous reaction ensued with evolution of chlorine; the suspension was stirred for 2 h and kept overnight at rt. The precipitate was filtered off, washed thoroughly with H2O (4 L) until pH 6.5–7 and the washing gave a negligible chloride test. The filter cake was then dried at 120–130 ◦C for 18 h; this gave a chocolate-brown, amorphous powder; yield 195–200 g.
Manganese (II) sulphate monohydrate (140 g) was dissolved in 2.66 liters of water and heated to 60°C. Potassium permanganate (97.3 g) in 1.85 liter of water was added over a period of 15 minutes and stirred at 60°C for 1 hour, until manganese dioxide precipitated out. The reaction mixture was filtered and the residue was washed with deionised water until no sulphate ion was present. The solid was dried under suction for 2 hours followed by drying at 70°C under vacuum to a constant weight (about 8 days) to give 115 g of a dark brown powder
In the span of 2h, to 250ml of 5% MnSO4 solution add 200ml of 5% KMnO4 solution while stiring at 50-60C. Filter out the precipitate and wash until the absence of SO42- ions. Dry for 10h at 120C.
Whereas in these examples, it's more closer to 1:1. Why is that, will there be a difference in oxidative abilities? Alternatively, what would be the best way to synthesize this from Mn2+ salts?
Attenburrow, J.; Cameron, A. F. B.; Chapman, J. H.; Evans, R. M.; Hems, B. A.; Jansen, A. B. A.; Walker, T.. 194. A synthesis of vitamin A from cyclohexanone. J. Chem. Soc. 1952, 1094-1111; doi 10.1039/JR9520001094.
Galecki J. Preparatyka nieorganiczna. WNT; Warsaw: 1964. p. 439.