Hydrocarbon K: Structure and Carboxylic Acid Product Revealed

[tipton12]

Having trouble with this one; I've tried working backwards from the three carbon carboxylic acid product, but to no avail. Please help! I can not figure out 'K'.


"A hydrocarbon K adds one equivalent of H2 upon hydrogenation over a Pt catalyst. When K is oxidized vigorously with hot KMnO4, a single three carbon carboxylic acid is obtained. Give the structures of K and the carboxylic acid."

This seems simple but K is giving me a lot of grief.

 

[chem_tr]

Well, vigorous reaction with hot permanganate is not still enough for pure hydrocarbons, this is an alkene with single double bond, this is okay. Since decarboxylation won't occur with KMnO₄, I think the K hydrocarbon has three carbons. The vinylic hydrocarbon H_3C-CH=CH_2 may be the structure for K and the corresponding carboxylic acid may be HOOC-CH=CH_2. I think the carboxylic acid should be like this, since it is principally similar with an aromatic alkane, say, toluene, which can also be oxidized with permanganate to the acid.

I may be wrong, so you will have to finish the remaining work by yourself.

 

[movies]

Sounds like a symmetrical alkene to me. Probably 3-hexene.

 

[chem_tr]

Hmm, does permanganate cleave double bonds to give carboxylic acid? I couldn't remember this one. However, this is logical. I remember ozonolysis to produce ketones or aldehydes, so this sounds okay to me.

EDIT: I looked up my textbook and saw the example with cyclohexene to give adipic acid with hot permanganate. So your assumption is okay, I think.

 

[tipton12]

I'll play around with both ideas and get back to you on my answers. Thank you both for all your help!

 

[movies]

Yeah, I think KMnO4 first does a dihydroxylation, much like OsO4, and then cleaves the diol, much like NaIO4 does. The resulting aldehydes are then oxidized to the acids.

 

[tipton12]

sorry i never got back to writing my answer. I waited for it to be graded.
This is what I did and it was marked correct:

K ____H2/Pt___K ____Oxidized___KMnO4/heat___ 3-hexene___H2/Pt___hexane w/carbocation on the 3carbon_____warm KMnO4/-OH___>> HO-C-CH2-CH3
ll
O

Thanks for your help!

 

[tipton12]

i don't know why my answer posted that way, but the =O is supposed to be on the Carbon attached to the -OH.