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Alcohol + SOCl2 Without Base --> ???

Discussion in 'DAT Discussions' started by FROGGBUSTER, Jul 24, 2011.

  1. FROGGBUSTER

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    R-OH (primary or secondary) + SOCl2 (no base) --> R-SO2Cl + HCl

    And with base it's:

    R-OH + SOCl2 (Pyrimidine) --> R-Cl

    Is this correct?
     
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  3. wired202808

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    Primary and Secondary Alcohols Only

    R-OH + SOCl2 ---> R-Cl + SO2 + HCl

    I believe the answer is the same whether Pyrimidine is used or not. I've never seen SO2CL attached to anything.
     
  4. HannibalLecter

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    Hmm I was looking into this last night for frogger and I think you can attach thionyl chloride with primary and secondary alcohols without the addition of a base. Now the HCl leaves off as itself because it is more stable like that and you have the thionyl group attached to the oxygen. But, dont forget that the thionyl group is a good leaving group as itself with oxygen and this product is usually used for another subsequent reaction as an intermediate.

    And yes as Wired said, primary and secondary alcohols only due to steric hindrance.
     
  5. FROGGBUSTER

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    So was what I wrote in my original post correct?
     
  6. wired202808

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    Primary and Secondary Alcohols Only

    R-OH + SOCl2 ---> R-Cl + SO2 + HCl

    I believe the answer is the same whether Pyrimidine is used or not. I've never seen SO2CL attached to anything.
     
  7. FROGGBUSTER

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    I didn't ignore your first post. Hannibal seems to be saying otherwise; I'm trying to ask for clarification from him.
     
  8. Troyvdg

    Troyvdg Dentistry not Debtistry
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    R-OH (primary or secondary) + SOCl2 (no base) --> R-Cl + HCl

    And with base it's:


    R-OH + SOCl2 (Pyrimidine) --> R-Cl
    no HCl formed, instead pyrimidine is protinated

    both reactions will replace the alcohol with a halide without inversion. Pyrimidine acts as a base ("proton sponge") to prevent HCl from forming
     
  9. FROGGBUSTER

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    Hm, are you absolutely sure of this?

    The reason I'm asking is because Kaplan actually states: "R-OH + SOCl2 --> R-SO2Cl + HCl" in its Subject Test #2.

    I too thought Cl replaced the OH in both cases until I read that...
     
  10. Troyvdg

    Troyvdg Dentistry not Debtistry
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    I'm 100% sure. I have emailed kaplan so many times about errors in their subject tests regarding orgo...clearly the makers of those tests never mastered the subject before they started writing questions about it


    for example. what happens when you add SOCl2 with a carboxylic acid? ...you form an acid halide. you don't form a carbonyl with SOCl2 attached.

    or when you want to make a gringard from an alcohol, before the addition of magnesium, you can add SOCl2, you don't get a carbon with SOCl2 attached, you get a halide
     
    #9 Troyvdg, Jul 24, 2011
    Last edited: Jul 24, 2011
  11. wired202808

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    i dunno i thought he was saying the same thing as me. Ignore Kaplan and their silly mistakes! or better yet google it! I have yet to see SO anywhere. I understand it always leaves any you're left with a halide.
     
  12. Troyvdg

    Troyvdg Dentistry not Debtistry
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    Iwas :thumbup:, I just elaborated a little more... I think he just needed to hear it more than once
     
  13. FROGGBUSTER

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    Alright thanks guys.
     
  14. wired202808

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    no problem man! i like your curiosity in fact im actually going back over the threads you posted to see the questions posed and answer answered! maybe ill learn something new thats crucial for the dat!
     
  15. FROGGBUSTER

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    Oh cool, yeah I've learned a lot just asking stuff on this forum, hopefully you can glean something from them.
     
  16. HannibalLecter

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    Ok my bad for not getting back to you until now Frogger. I am saying that you are actually right with your first reaction. Just remember the product that is formed "R-SO2Cl" is an intermediate just like the intermediate formed like O-Ts just like:

    http://www.curvedarrow.com/chem/tosylate_formation.jpg

    Now I think this is how it goes down but it would be great if someone backed me up because I am not 100% sure on this but this mechanism should run like tosylate formation as well. And we all know that tosylate molecule is just an intermediate on other rxns.
     
  17. wired202808

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    ok i remember this now! good find hannibal! ots is a great leaving good right?

    This is what I have from chad's notes:

    Alcohols can participate in Sn1/Sn2 if -OH is turned into a better leaving group by one of three methods:

    A) Protonating it
    B) Converting to a tosylate (OTs)
    C) Form an inorganic ester

    so you convert it intso OTs and then its a better leaving group for alkyl halides?

    I hope this makes sense. Although just remember OTs is an intermediate so R-Cl would still be the product but it is good to know OTs. I remember doing a problem on it once and not recalling it, only to kick myself bout it later.
     
  18. HannibalLecter

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    I don't know if it is only restricted to replacement by halides but I know its a very very very good leaving group even better than like -I but not H2O obviously. So I think you can essentially use sh*tty nucleophiles as well I think thats why they use OTs, its because you have a very low reactive nucleophile that you wouldn't see reacting in a reaction like this but with a great leaving group anything looks attractive.

    I was just trying to compare the reaction that frogger states with this one but I don't necessarily think halogenating it is the only option, other nucleophiles could work too after that step.
     
  19. FROGGBUSTER

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    Thanks guys, I understand now. It makes sense that that would be the intermediate.
     

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