Does KMnO4 really cleave double/triple bonds?

[thebillsfan]

I thought it only oxidized to alcohols...under what conditions can it cleave pi bonds?

Also, what's the different between hot/acidic KMnO4 and cold/dilute KMnO4?

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[G1SG2]

I thought it only oxidized to alcohols...under what conditions can it cleave pi bonds?

Also, what's the different between hot/acidic KMnO4 and cold/dilute KMnO4?

Hot/acidic KMnO4-cleaves double bonds to their carbonyl products, and even oxidizes the aldehydes to carboxylic acids.

Cold/dilute KMnO4-makes a glycol/diol.

 

[thebillsfan]

Hot/acidic KMnO4-cleaves double bonds to their carbonyl products, and even oxidizes the aldehydes to carboxylic acids.

Cold/dilute KMnO4-makes a glycol/diol.

pookiez,

so wouldnt it always oxidize to carboxylic acids, since cleavage of a double bond would always lead a terminal carbonyl (ie aldehyde)

 

[G1SG2]

pookiez,

so wouldnt it always oxidize to carboxylic acids, since cleavage of a double bond would always lead a terminal carbonyl (ie aldehyde)

No, cleavage of a double bond does not always lead to an aldehyde. Consider R2C=CRH. The KMnO4 cleaves the double bond to give R2C=O, a ketone and RCH=O, an aldehyde, which then gets oxidized to RCOOH, a carboxylic acid. Just picture yourself erasing the double bond and replacing it with two O's (that are not attached to each other, of course).

 

[loveoforganic]

For terminal alkynes, it oxidizes to a carboxylic acid and CO2. For an internal alkyne, it oxidizes to two carboxylic acids. ('it' being hot, acidic kmno4).

 

[G1SG2]

For terminal alkynes, it oxidizes to a carboxylic acid and CO2. For an internal alkyne, it oxidizes to two carboxylic acids. ('it' being hot, acidic kmno4).

Yeah, also if it's neutral, then it'll oxidize an internal alkyne to a diketone.

 

[loveoforganic]

Cool, never knew that