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Hydroxylation with Osmium Tetraoxide

  • #1
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Homework Statement


I know that alkenes when treated with OsO4 in pyridine undergo syn 1,2-dihydroxylation. This forms an osmate ester which when treated with NaHSO3 in water gives a diol by syn addition.
However, in one of the problems, 1-methylcyclohexene treated with OsO4 and then H2O2 gave a diol by anti addition.
The attempt at a solution
I think that it won't add by anti fashion in the first place. Even if it is possible, would it be by some free radical mechanism?
Please explain.
 

Answers and Replies

  • #2
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Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.
?
 
  • #3
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Hey! Hasn't anybody seen this...
@Borek @TeethWhitener @Ygggdrasil Come on say something....Anything
I suscpect that this question is wrong but I need clarification. It's useless bumping it again, it might backfire.
I know I'm being a cranky kid but still...please
 
  • #4
Borek
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Sorry, organic chemistry is something I don't touch even with a long stick.
 
  • #5
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You got the ozonolysis question...
Never mind
 
  • #6
Ygggdrasil
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I also can't figure out why the product would be anti. If this is part of a class, perhaps ask your professor or a teaching assistant.
 
  • #7
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I also can't figure out why the product would be anti. If this is part of a class, perhaps ask your professor or a teaching assistant.
Unfortunately, my professor isn't doubt friendly. Plus, the book I'm referring to is wayyy out of our syllabus (but I know the theory well), so she wouldn't even look at it. I tried...
 
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  • #8
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Can you ask any other Mentor or Organic Chemistry expert you know to take a look at this?
I know @TeethWhitener & @DrClaude can look at this, but both of them are inactive for a while now...
(P.S. Sorry I have to resort to such means...wandering like a door-to-door salesman...but the discussion hasn't triggered even after a week...)
 
  • #9
TeethWhitener
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OsO4 can be rendered catalytic with judicious use of a sacrificial oxidant like H2O2. I doubt this affects stereospecificity.
 
  • #10
Ygggdrasil
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Physics Fourms may lack the organic chemistry expertise to answer your question. Perhaps try www.chemicalforums.com or reddit.com/r/chemistry
 
  • #11
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Physics Fourms may lack the organic chemistry expertise to answer your question. Perhaps try www.chemicalforums.com or reddit.com/r/chemistry
I'll give it a shot.
It's not that we lack the expertise, it's just that we're relying too much on @TeethWhitener (no offence to you). He's the only one I know who helps regularly with organic chemistry homework.
If there were more experts, even his job would've been easier. I'm not saying he's unreliable...but you know, more experts-more inputs-better inputs is the way it works.
 
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  • #12
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I know even @DrClaude can look at this, but he's gone cold for over a month. Oh wait, I just remembered that even @mjc123 and @SammyS can look at this. Maybe, they can figure it out.
 
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  • #13
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Coincidentally, OsO4 is so expensive that you can't even perform this reaction in a lab to check the outcome.
Plus, 1-methylcyclohexene is probably not even isolable, so we'd have to generate it in situ in some other reaction. So even if everything else is available, it's too much of a fuss.
 
  • #14
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If you think about the mechanism of this, the osmate ester intermediate must give a syn diol. An anti outcome has to mean that a free radical mechanism is initiated by the H2O2 (as in our usual HBr anti Markovnikov addition). But howwww?
 
  • #15
TeethWhitener
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If you think about the mechanism of this, the osmate ester intermediate must give a syn diol. An anti outcome has to mean that a free radical mechanism is initiated by the H2O2 (as in our usual HBr anti Markovnikov addition). But howwww?
In my experience, H2O2 simply regenerates OsO4 from OsO2(OH)2 (hence the catalytic activity), so the syn intermediate isn't changed.
 
  • #16
TeethWhitener
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OsO4 is so expensive
It's not that expensive, especially if you use it as part of a catalytic system.
I'm not saying he's unreliable
I was on vacation for a week.
 
  • #17
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I was on vacation for a week.
No dude, don't get pissed. I said that not because you were inactive but because you're the only one I know who actively engages in organic chemistry questions.
Take this question's case itself as an example. We started bombarding you as soon as you were back from your vacation.
So if there are more active expects, we don't need to rely on you. As I said,
more experts-more inputs-better inputs
 
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  • #18
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In my experience, H2O2 simply regenerates OsO4 from OsO2(OH)2 (hence the catalytic activity), so the syn intermediate isn't changed.
I even watched the Khan Academy video, and they seem quite alright with the syn product even with H2O2. So probably, there's a misprint in my book. A huge one that could've cost me.
 
  • #19
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Thank you @Borek & @Ygggdrasil for helping me as much as you could. I know that mentioning someone in a message to draw their attention is unethical. I'll avoid doing it again.
And @TeethWhitener , if you're pissed, I'm sorry.
 

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