Sciencemadness Discussion Board

manganates

budullewraagh - 25-11-2004 at 17:21

we all know permanganates exist, but little is said/found of manganates. seriously. do a search online for manganates and all you will find are manganate (VII) which are really just permanganates. i found one site that mentioned the electrolytic oxidation of manganates...but theyre not even listed in the merck index and i cant find them on chemfinder. anybody know why theyre so elusive?

BromicAcid - 25-11-2004 at 17:35

From Descriptive Inorganic Chemistry, Third Edition, Geoff Rayner-Canham and Tina Overton
Quote:

The deep green manganate ion, [MnO4]2-, or tetraoxomanganate (VI), is also strongly oxidizing, but it disproportionates readily to the permanganate ion and manganese (IV) oxide; thus it is of little importance.

So, it's kind of like ferrate, the compound can exist but it dosn't stick around usually and has no specific industrial purpose and therefor it has little information available on it. I believe it can be formed by fusing manganese metal with sodium hydroxide and sodium nitrate. I remember it from the discussion in the thread on making high oxidation states though fusing with sodium hydroxide, that manganese will only go to the manganate stage through fusion and the final step to permanganate is accomplished though adding to water.

Googled around some:
Quote:
Manganates.These salts are derived from manganic acid H2MnO4. Those of the alkali metals are prepared by fusing manganese dioxide with sodium or potassium hydroxide in the presence of air or of some oxidizing agent (nitre, potassium chlorate, &c.); MnOi+2KHO+O=K2MOO4+H2O. In the absence of air the reaction proceeds slightly differently, some manganese sesquioxide being formed; 3MOO2 +2KHO = K2MnO4 + Mn2O3 + FI2O. The fused mass has a dark olive-green color, and dissolves in a small quantity of cold water to a green solution, which is, however, only stable in the presence of an excess of alkali. The green solution is readil converted into a pink one of permanganate by a large dilution wit water, or by passing carbon dioxide through it: 3K2MnO4+2CO2= 2K2CO,+2KMnO4+MnO2.

From an article on manganese.

Edit #2: ..... hummmm ....
Quote:
Manganese trioxide, MnO3, is obtained in small quantity as an unstable deliquescent red solid by dropping a solution of potassium permanganate in sulphuric acid on to dry sodium carbonate (B. Franke, Jour. prak. Chem., 1887 C. it decomposes into the dioxide and oxygen. It dissolves in water forming manganic acid, HiM nO4.

Seems exotic .....

[Edited on 11/26/2004 by BromicAcid]

budullewraagh - 25-11-2004 at 19:32

Quote:
Those of the alkali metals are prepared by fusing manganese dioxide with sodium or potassium hydroxide in the presence of air or of some oxidizing agent (nitre, potassium chlorate, &c.); MnOi+2KHO+O=K2MOO4+H2O.

i take it that if you use the hydroxide and a permanganate instead of manganese dioxide and an oxidizing agent you would have the same result, right?
Quote:
Manganese trioxide, MnO3, is obtained in small quantity as an unstable deliquescent red solid by dropping a solution of potassium permanganate in sulphuric acid on to dry sodium carbonate (B. Franke, Jour. prak. Chem., 1887 C. it decomposes into the dioxide and oxygen. It dissolves in water forming manganic acid, HiM nO4.

i see. so... when you oxidize methanol to methanoic acid by means of a permanganate salt, what exactly happens? the permanganate loses oxygen but it's not like there is an MnO3- anion in existence...as far as i know. so im thinking you get MnO2 and is it XOH?