Oxidative cleavage of alkenes

  • Thread starter Clari
  • Start date
62
0
Alkenes are oxidatively cleaved to alts of carboxylic acids, by hot basic permanganate solutions. However, I dont understand why the solutions need to be basic and hot? Why cant it be cold or acidic?

Please tell me. :confused:
 
Hot reactions proceed faster than cold reactions simply because the molecules have more energy, and also they collide more often. acidic or basic usually has to do with some sort of catalytic reaction IDK much aboot organic chem, so I will leave that question to other members.
 

movies

Science Advisor
283
1
I think that an excess of OH- in solution facilitates the reaction by cleaving the reduced manganese species off of the organic substrate. It's probably also necessary to initiate the final oxidation from aldehyde to carboxylic acid. In acidic solution then there wouldn't be any good nucleophiles, just water.
 
1,100
0
A primary alchol can become a carboxylic acid but the alchol needs an acidificed dichromate solution (e.g. potassium dichromate solution) or sulphuric acid (well simply concentrated acid). If I have understood the question, you are asking how to make a carboxylic from an alchol. So I would say it has to be acidic.

To make an alchol from an alkene does need a base for the electrophilic addition.

The Bob (2004 ©)
 

movies

Science Advisor
283
1
In the case of a chromium oxidation you need the acid to facilitate making chromic acid, which is the active oxidizing agent. It's a different mechanism.
 
1,100
0
That would explain it then. That is the only mechanism I have come across at the moment.

The Bob (2004 ©)
 

movies

Science Advisor
283
1
I read that acidic KMnO4 can also oxidize alcohols and aldehydes to carboxylic acids, so maybe the "basic" part isn't so important for that. I also read that hydroxide accelerates the cleavage of the manganese species after the dihydroxylation step of the alkene cleavage process. So, I would guess that the nucleophile is most important there.

The same effect is true with OsO4. If you use a stoichiometric amount of the osmium, then you have to do a workup that is capable of cleaving the osmium-organic complex before you can isolate the dihydroxylation product.
 

Related Threads for: Oxidative cleavage of alkenes

  • Posted
Replies
1
Views
3K
  • Posted
Replies
8
Views
9K
  • Posted
Replies
4
Views
10K
Replies
1
Views
1K
  • Posted
Replies
2
Views
2K
  • Posted
Replies
4
Views
916
Replies
3
Views
11K
Replies
5
Views
3K

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top