orgo q

[tadizhere]

hi guys
does anyone know what kmno4 does in a reaction when its dilute, cold, and hot. oh and they would be in seperate rxns off course. thnx

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[Sama951]

KMnO4 is used to synthesize 1,2-diols from alkenes with syn stereochemistry (the OH's add to the same face of the double bond)

I know the reaction has to be done under cold temperatures to prevent the OH's from reacting any further with the KMnO4... I'm guessing it being dilute would have the same effect but I don't know for sure

 

[doc3232]

KMnO4 is used to synthesize 1,2-diols from alkenes with syn stereochemistry (the OH's add to the same face of the double bond)

I know the reaction has to be done under cold temperatures to prevent the OH's from reacting any further with the KMnO4... I'm guessing it being dilute would have the same effect but I don't know for sure

I agree. I think cold and dilute is a general rule for correct use of it.

 

[userah]

as the person above has stated, in cold dilute KMnO4, you get syn, vicinal diols. But KMnO4 in heat gives you 2 carboxylic acids. That's if the alkene is internal. If the alkene is terminal, you get carboxylic acid (or ketone) and CO2. Again this is for alkene. For general purposes, KMnO4 is a pretty strong acid that it will convert the substituents all the way to carboxylic acids. For these reactions, it doesn't mention anything about whether they are being done in the cold or with heat so not sure about that. I guess that's what the two people meant by cold and dilute being a general rule. Regardless, I think the only time where you'll have to worry about it is when it's an alkene being oxidized, otherwise i believe you just take it all the way to carboxylic acids.

if i'm mistaken, please feel free to correct me on the matter =)

btw, when i say substituents, i mean like alcohol, aldehyde, nitriles, etc.