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TPR Ochem - Possible mistake?

5words

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Dec 31, 2016
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    Extraction question:



    Which of the following compounds are most likely to be found in Et2O layer D?

    I. Boric acid
    II. Alcohol
    III. Ester
    A. I only
    B. II only
    C. III only
    D. II and III only

    Chose C but the answer is D, which isnt making any sense. Although, alcohol are less acidic than phenol since NaOH is mostly used to removed/ extract phenol, the alcohol is still acidic. And as a matter of fact, the OH- of the Sodium Hydroxide is strong enough to remove the alpha protons of ketones and aldehydes, both are less acidic than the alcohol. And alcohol can H-hond with water as well, so the NaOH isnt necessarily needed. So why wouldn't it convert the acohol into it's anionic form thereby making it soluble in water. So, is this a mistake?

    @aldol16 @neurodoc
     

    aldol16

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      The pKa of NaOH is around 14. The pKa of alkyl alcohols are in the 16 range. This means that the alcohols are still more basic than NaOH and you most likely won't be able to deprotonate all or most of the alcohol. You might get some alkoxide into the water phase but there will definitely be alcohol left in the ether.

      Further, you can use NaOH to make enolates but because alpha protons have pKas of around 20, you will again not get much of the enolate - it'll mainly be in the keto form. For reactivity, that might not matter because the enolate is only an intermediate and will be consumed by reaction with an electrophile. Since enolate formation is reversible, the equilibrium will be pulled to the right by subsequent reaction of the enolate. We typically use t-butoxide (pKa around 17) or LDA (pKa around 36) to make enolates.
       
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      5words

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      Dec 31, 2016
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        The pKa of NaOH is around 14. The pKa of alkyl alcohols are in the 16 range. This means that the alcohols are still more basic than NaOH and you most likely won't be able to deprotonate all or most of the alcohol. You might get some alkoxide into the water phase but there will definitely be alcohol left in the ether.

        Further, you can use NaOH to make enolates but because alpha protons have pKas of around 20, you will again not get much of the enolate - it'll mainly be in the keto form. For reactivity, that might not matter because the enolate is only an intermediate and will be consumed by reaction with an electrophile. Since enolate formation is reversible, the equilibrium will be pulled to the right by subsequent reaction of the enolate. We typically use t-butoxide (pKa around 17) or LDA (pKa around 36) to make enolates.
        omg, thats just insane... Would the AAMC ask anything like this? who would have thunk that alcohol are less acidic than NaOH?
         
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