[portugal]

Phenol doesnt change KMno4 from purple to brown does it and it also doenst react with H2 gas either does it??

[macman104]

Off the top of my slightly inebriated head, no.

[azmanam]

what chemistry takes place in the KMnO4 test?  can phenol do that?

what chemistry takes place in the H2/Pd test (although it's not really a qualitative test)?  will phenol do this?

[minimal]

what chemistry takes place in the KMnO4 test?  can phenol do that?

what chemistry takes place in the H2/Pd test (although it's not really a qualitative test)?  will phenol do this?

Sorry to butt in but I'm unsure about this as well.  Could phenol not be oxidized to the ketone?

[azmanam]

Start by drawing out a generic alcohol and it's generic ketone counterpart.  What has changed between the two?  What bonds are formed (1), what bonds are broken (2).  Then draw phenol and carry out the same bond breaking/bond forming operations on phenol.  Are you able to? 

[minimal]

No they're not the same, but they don't have to be.  A secondary alcohol to ketone mechanism grabs an H off the O and an H off the C.  With a phenyl ring, there is only the H grabbed off the hydroxyl group, and then aromaticity is lost on the ring.  I don't see the problem there. 

[azmanam]

Loss of aromaticity = bad. 

Plus that's not what's going on here.  It's not as simple as pulling off a proton from carbon to complete the oxidation.  Pulling off a proton requires the electrons that were in the carbon hydrogen bond to go somewhere within the carbon-containing molecule.

First, there is no proton on the carbon directly bonded to the phenolic oxygen.  So you'll have to go to the next carbon over (which is outside the scope of KMnO₄ oxidation, but let's assume for a second that it wasnt).

On one side of the phenolic carbon, there is a double bond.  Taking the proton from that side will create a triple bond (and a carbon with 5 bonds), that would have to tautomerize to an exocyclic ketene-like structure that will be far to strained to exist, and it will stil have a carbon with 5 bonds..  The other side is a carbon-carbon single bond, but taking that proton creates a cumulated double bond, and again a carbon with 5 bonds.

So you see, there is no way to oxidize phenol to a ketone or ketone-like structure.  It will fail a KMnO₄ test.

[minimal]

Loss of aromaticity = bad. 

Plus that's not what's going on here.  It's not as simple as pulling off a proton from carbon to complete the oxidation.  Pulling off a proton requires the electrons that were in the carbon hydrogen bond to go somewhere within the carbon-containing molecule.

First, there is no proton on the carbon directly bonded to the phenolic oxygen.  So you'll have to go to the next carbon over (which is outside the scope of KMnO₄ oxidation, but let's assume for a second that it wasnt).

On one side of the phenolic carbon, there is a double bond.  Taking the proton from that side will create a triple bond (and a carbon with 5 bonds), that would have to tautomerize to an exocyclic ketene-like structure that will be far to strained to exist, and it will stil have a carbon with 5 bonds..  The other side is a carbon-carbon single bond, but taking that proton creates a cumulated double bond, and again a carbon with 5 bonds.

So you see, there is no way to oxidize phenol to a ketone or ketone-like structure.  It will fail a KMnO₄ test.

Why wouldn't it go to benzoquinone?

[azmanam]

Perhaps if it started as hydroquinone, but phenol is lacking a second alcohol in the para position.  Good thinking though.  It's good to see you thinking outside the textbook to try to make sense of the concepts.

[minimal]

I don't see why you'd need that in the first place.  Surely assuming the hydrogen was lost off the only hydroxyl group, the resulting charge shift (don't know if this would be considered transition state or reactive intermediate) would be enough to grab an oxygen off of an adjacent potassium permangenate? The one double bond hops to the side, the other double bond hops to the oxygen double bond that is now formed in the para position. 

edit: the only thing that makes me wonder about this is the resulting stability of the MnO3.  I've looked up Manganese oxidation states and apparently +6 is something it does.  But I can't find any references to MnO3.  If it were to have another taken off it would be KMnO2.

[azmanam]

I don't have anything quantitative for you, but I don't think that the negative charge is going to be nucleophilic enough - nor the manganese species electrophilic enough - to transfer an oxygen atom to the benzene ring.

I don't know.  I can't remember seeing it done, but I suppose that doesn't mean it's not possible.  I think you'd need something other than manganese, though.

[Transmutation]

I betcha piranha solution would react with it.