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How to inhibit Mn2+ autocatalysis in the oxalate-permanganate reaction?
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Nehal Ahmed Khan
How to inhibit Mn2+ autocatalysis in the oxalate-permanganate reaction?
At first the reaction is slow. But when we heat up, the reaction gets catalyzed due to formation of $\ce{Mn^2+}$ ions. It happens due to the fact that $\ce{Mn^2+}$ gets oxidised to $\ce{Mn^3+}$ ions. (Source).
$$\ce{4Mn^2+ + MnO4- + 8H+ -> 5Mn^3+ + 4H2O}$$
So, we have to inhibit the formation of $\ce{Mn^3+}$ ions so as to inhibit the autocatalysis reaction. For this, we have to use phosphonate and carboxylate based chelating agent that solubilize (hydr)oxide-bound $\ce{Mn(III)}$ . The following is some relevant information from the site:
phosphonate-based chelators that solubilize (hydr)oxide-bound
Mn(III) via ligand-promoted and/or reductive dissolution at
circum-neutral pHs.
pyrophosphoric acid (PP), methylenediphosphonic acid (MDP), and
phosphonoacetic acid (PAA), ligand-promoted dissolution is
predominant: from pH 6−8, initial dissolution rates and plateau
concentrations for dissolved Mn(III) decrease in the order PP > MDP >
PAA, and at pH 5, MDP reacts equally well (with birnessite) or more
efficiently (with manganite) than PP, and PAA remains the least
reactive chelator. For manganite reacting with an excess concentration
of aminophosphonate/carboxylate-based chelators, the
aminophosphonate-containing iminodimethylenephosphonic acid and
glyphosate yield appreciable amounts of dissolved Mn(III), but the
aminocarboxylate-based methyliminodiacetic acid yields solely
dissolved Mn(II) via Mn(III) reduction.
At first the reaction is slow. But when we heat up, the reaction gets catalyzed due to formation of $\ce{Mn^2+}$ ions. It happens due to the fact that $\ce{Mn^2+}$ gets oxidised to $\ce{Mn^3+}$ ions. (Source).
$$\ce{4Mn^2+ + MnO4- + 8H+ -> 5Mn^3+ + 4H2O}$$
So, we have to inhibit the formation of $\ce{Mn^3+}$ ions so as to inhibit the autocatalysis reaction. For this, we have to use phosphonate and carboxylate based chelating agent that solubilize (hydr)oxide-bound $\ce{Mn(III)}$ . The following is some relevant information from the site:
phosphonate-based chelators that solubilize (hydr)oxide-bound Mn(III) via ligand-promoted and/or reductive dissolution at circum-neutral pHs.
pyrophosphoric acid (PP), methylenediphosphonic acid (MDP), and phosphonoacetic acid (PAA), ligand-promoted dissolution is predominant: from pH 6−8, initial dissolution rates and plateau concentrations for dissolved Mn(III) decrease in the order PP > MDP > PAA, and at pH 5, MDP reacts equally well (with birnessite) or more efficiently (with manganite) than PP, and PAA remains the least reactive chelator. For manganite reacting with an excess concentration of aminophosphonate/carboxylate-based chelators, the aminophosphonate-containing iminodimethylenephosphonic acid and glyphosate yield appreciable amounts of dissolved Mn(III), but the aminocarboxylate-based methyliminodiacetic acid yields solely dissolved Mn(II) via Mn(III) reduction.
At first the reaction is slow. But when we heat up, the reaction gets catalyzed due to formation of $\ce{Mn^2+}$ ions. It happens due to the fact that $\ce{Mn^2+}$ gets oxidised to $\ce{Mn^3+}$ ions. (Source).
$$\ce{4Mn^2+ + MnO4- + 8H+ -> 5Mn^3+ + 4H2O}$$
So, we have to inhibit the formation of $\ce{Mn^3+}$ ions so as to inhibit the autocatalysis reaction. For this, we have to use phosphonate and carboxylate based chelating agent that solubilize (hydr)oxide-bound $\ce{Mn(III)}$ . The following is some relevant information from the site:
At first the reaction is slow. But when we heat up, the reaction gets catalyzed due to formation of $\ce{Mn^2+}$ ions. It happens due to the fact that $\ce{Mn^2+}$ gets oxidised to $\ce{Mn^3+}$ ions. (Source).
$$\ce{4Mn^2+ + MnO4- + 8H+ -> 5Mn^3+ + 4H2O}$$
So, we have to inhibit the formation of $\ce{Mn^3+}$ ions so as to inhibit the autocatalysis reaction. For this, we have to use phosphonate and carboxylate based chelating agent that solubilize (hydr)oxide-bound $\ce{Mn(III)}$ . The following is some relevant information from the site:
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