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SOCl2 added to R-OH

Discussion in 'DAT Discussions' started by joonkimdds, Dec 27, 2008.

  1. joonkimdds

    joonkimdds Senior Member
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    [​IMG]

    I learned from my OCHEM class and Destroyer that
    R-OH + SOCl2 ==> R-Cl

    but according to the picture from Kaplan,
    R-OH + SOCl2 ==> R-OSOCl

    why does this happen? is there an exception to this rule?
     
  2. Panther85

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    a common method of converting OH to alkyl halides involves the formation of inorganic esters, which readily undergo SN2 rxns. alcohols react with thionyl chloride to produce an intermediate inorganic ester (a chlorosulfite) and HCl. the chloride ion of HCl displaces SO2 and regenerates Cl-, forming the desired alkyl chloride.


    the strucutre u have is correct except its NOT finished!!! another mole of Cl- will attack the methyl group in ur structure. thus the end products of ur reaction will be: ClCH3 + SO2 + Cl-
     
  3. doc3232

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    Exactly, to add to it. the reason the reaction is so favorable is that the formation of the gas SO2 is entropically favorable (very lethal gas).
     
  4. joonkimdds

    joonkimdds Senior Member
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    I am not sure if I fully understood what you guys said.
    The way I understand now is
    R-OH + SOCl2 ==> R-O-SOCl + HCl (This is the picture I posted)
    and then it's not done yet and we add SOCl2 again,
    R-O-SOCl + SOCl2 ==> R-Cl (This is the final product that DAT destroyer shows?)

    am I right? and if so, how do I know if I should stop the reaction before the 2nd SOCl2 comes or not?
     
  5. doc3232

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    THIS HAPPENS:
    R-OH + SOCl2 ==> R-O-SOCl + HCl

    THEN: Cl- attacks the R group. At the same time, Cl leaves the S and the sulfur is oxidized to SO2.
     
  6. joonkimdds

    joonkimdds Senior Member
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    I think I understand the whole mechanism now :) Thanks.

    Another question I have is, how do I know if it will stop at
    R-O-SOCl and proceed to the next reaction
    or if it will go all the way to R-Cl and then proceed to the next reaction?

    In other word, what if the question asks for the product and the answer choices are
    1) R-OSOCl
    2) R-Cl
    which one should I pick?
     
  7. doc3232

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    This reaction is very exothermic. The first part has a Cl kicked off when the oxygen attacks the Sulfer.
    The second part is extremely exothermic, remember how I said the SO2 leaving is very entropically favorable.
    I doubt the test would expect you to know the mechanism of SOCl2.
     
  8. joonkimdds

    joonkimdds Senior Member
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    Thank you all. U guys are genius.
     
  9. Panther85

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    hahahah... i wish... i just happened to have read that in my kaplan bb this week :laugh:
     

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