Hydroxylation with Osmium Tetraoxide

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Discussion Overview

The discussion revolves around the hydroxylation of alkenes using osmium tetraoxide (OsO4) and the resulting stereochemistry of the products. Participants explore the mechanisms of syn and anti addition in the context of a specific example involving 1-methylcyclohexene, questioning the validity of a problem statement regarding anti addition and the role of H2O2.

Discussion Character

  • Debate/contested
  • Homework-related
  • Exploratory

Main Points Raised

  • One participant states that alkenes treated with OsO4 in pyridine undergo syn 1,2-dihydroxylation, forming an osmate ester that yields a diol upon treatment with NaHSO3.
  • Another participant expresses skepticism about the claim that 1-methylcyclohexene treated with OsO4 and H2O2 gives a diol by anti addition, suggesting it may not be possible and questioning if a free radical mechanism is involved.
  • Several participants mention their inability to understand why the product would be anti, with one suggesting consulting a professor or teaching assistant for clarification.
  • One participant notes that OsO4 can be used catalytically with H2O2, but doubts this affects stereospecificity.
  • Another participant points out the high cost of OsO4 and the impracticality of performing the reaction in a lab setting.
  • Some participants discuss the potential for a free radical mechanism initiated by H2O2 to explain an anti outcome, while others argue that the osmate ester intermediate should lead to a syn diol.
  • One participant mentions that H2O2 may regenerate OsO4 from OsO2(OH)2, suggesting that the syn intermediate remains unchanged.
  • There is a mention of a possible misprint in a textbook regarding the expected product stereochemistry.

Areas of Agreement / Disagreement

Participants express differing views on the stereochemistry of the product formed from the reaction of 1-methylcyclohexene with OsO4 and H2O2. There is no consensus on whether the product is anti or syn, and the discussion remains unresolved.

Contextual Notes

Some participants note limitations in their understanding due to the complexity of the mechanisms involved and the reliance on external resources that may not align with their coursework. The discussion also highlights the challenges of accessing certain reagents and the implications for experimental verification.

baldbrain
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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.
 
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
 
Sorry, organic chemistry is something I don't touch even with a long stick.
 
You got the ozonolysis question...
Never mind
 
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.
 
Ygggdrasil said:
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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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...)
 
OsO4 can be rendered catalytic with judicious use of a sacrificial oxidant like H2O2. I doubt this affects stereospecificity.
 
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  • #10
Physics Fourms may lack the organic chemistry expertise to answer your question. Perhaps try www.chemicalforums.com or reddit.com/r/chemistry
 
  • #11
Ygggdrasil said:
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
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
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
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
baldbrain said:
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
baldbrain said:
OsO4 is so expensive
It's not that expensive, especially if you use it as part of a catalytic system.
baldbrain said:
I'm not saying he's unreliable
I was on vacation for a week.
 
  • #17
TeethWhitener said:
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,
baldbrain said:
more experts-more inputs-better inputs
 
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  • #18
TeethWhitener said:
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
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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