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Thread: Preparing butanoic acid from 2-butanol.

  1. #1 Preparing butanoic acid from 2-butanol. 
    ape
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    Hi, I have to solve the following organic synthesis exercise ( Prepare X from Y). My book however is very unclear with the rules so Im asking this question here. First of all I managed to figure out 2 ways of preparing butanoic acid. In the first "method" Im confused with step 1 (pink) & step 2 (red).

    Step1: I dont know about the elimination reaction, when solving this kind of exercise, isnt there a rule that says we can only prepare for example here 1-butene OR 2-butene (I dont know the rule though if it exists)? Or are both possible?

    Step2: My book didnt say anything on where I should place the OH & H group, does this again mean we have 2 options for the addition of water in unsaturated hydrocarbons? So if for example they said " Prepare 2-butanol from 1-butene" or "Prepare 1-butanol from 1-butene": could we use dehydratation in both cases, or is there a rule that determines the place of both OH & H?



    Thank you!


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  3. #2  
    ape
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  4. #3  
    Bullshit Intolerant PhDemon's Avatar
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    You won't make butanoic acid from 2-butanol, as it is a secondary alcohol you can only oxidise it as far as the ketone (2-butanone).

    You might find this page useful: oxidation of alcohols

    EDIT: Sorry misread your post, you are not trying to do it in one step.
    If you carry out an elimination reaction on 2-butanol you will get a mixture of 1-butene and cis- and trans-2-butene due to carbocation rearrangement in the E1 mechanism (see links in this thread).

    For the oxidation of the alkenes to acids you may find this page useful: Carboxylic acid synthesis by oxidation of alkenes or alkines but bear in mind when oxidising alkenes in this way you get cleavage of the C=C bond so the resulting acid will not be butanoic acid...


    EDIT: 2 just saw your diagrams, I forgot about alkene hydrolysis! In H+/H2O you will make a mixture of alcohols from the mixture of alkenes with the "OH" group adding to the more substituted carbon of each alkene (due to relative carbocation intermediate stabilities -- see here, Additions to Alkenes)

    DISCLAIMER: My organic chemistry was done a long time ago and I wasn't great at it (that's why I'm a physical chemist), maybe someone will correct me or give a better answer.
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  5. #4  
    ape
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    You won't make butanoic acid from 2-butanol, as it is a secondary alcohol you can only oxidise it as far as the ketone (2-butanone).
    But what about the second method? Is it correct(?):

    This method above does not have any steps in which oxidation of secondary alcohols takes place.



    About the first method:

    In this method according to the rules you provided, the first step (pink) is possible since both 1-butene & 2-butene will be formed ("you will get a mixture of 1-butene and cis- and trans-2-butene"), but the second step is not, because you wrote that the OH will add to the C-atom which is more substituted (=less H's) so therefore the whole method is incorrect.


    I have one problem though with the rule for alkene hydratation you provided:
    EDIT: 2 just saw your diagrams, I forgot about alkene hydrolysis! In H+/H2O you will make a mixture of alcohols with the "OH" group adding to the more substituted carbon (due to relative carbocation intermediate stabilities -- see here, Additions to Alkenes)
    Can it be that the word "mixture" is inappropriate here, because the rule says that we get only 1 type of alcohol since the OH goes onto the C-atom with less H's and the H goes onto the C-atom with more H's. If I use the word mixture in the rule, then I get the impression that both 1-butanol and 2-butanol are correct, while its only 2-butanol!
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  6. #5  
    Bullshit Intolerant PhDemon's Avatar
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    Yes the second method looks better and would likely work (but as I say my org. chem was a while back).

    As for the first method you are right, it is probably not viable as you get the more substituted alcohol. By "mixture" I was meaning you would get the more substituted alcohol from each of the 1-butene and cis-and trans 2-butene but thinking about it they are all the same (2-butanol - which is what you started with!) so in this special case of butenes "mixture" is inappropriate but if there were a longer carbon chain each alkene would give different alcohols (this is what I was thinking of when I posted).
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  7. #6  
    ape
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    Thank you for clarifying everything! I appreciate your help immensely!!
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  8. #7  
    Bullshit Intolerant PhDemon's Avatar
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    No problem, glad to help.
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  9. #8  
    KJW
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    From 1-butene, hydroboration with BH3•THF, then oxidation with H2O2, gives 1-butanol.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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  10. #9  
    Bullshit Intolerant PhDemon's Avatar
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    What does it make from 2-butene which will also be present after the first step?
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  11. #10  
    KJW
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    2-butanol (it can't form anything else from the symmetry).
    There are no paradoxes in relativity, just people's misunderstandings of it.
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  12. #11  
    KJW
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    2-butanol is reacted with p-toluenesulfonyl chloride in pyridine to form the "tosylate". Elimination with a sterically-hindered base will yield predominately 1-butene.
    There are no paradoxes in relativity, just people's misunderstandings of it.
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  13. #12  
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    Quote Originally Posted by KJW View Post
    2-butanol (it can't form anything else from the symmetry).
    Thought so but I was too lazy to think about it

    Quote Originally Posted by KJW
    2-butanol is reacted with p-toluenesulfonyl chloride in pyridine to form the "tosylate". Elimination with a sterically-hindered base will yield predominately 1-butene.
    and this looks like a better way of doing the first step.
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