Turn on thread page Beta
    • Thread Starter
    Offline

    0
    ReputationRep:
    Hey,
    could someone check a mechanism for me, if I send it?
    It's for the alkylation of salicylic acid with acetic anyhydride and a H3PO4 catalyst
    Thanks in advance
    Offline

    1
    ReputationRep:
    (Original post by _scott)
    Hey,
    could someone check a mechanism for me, if I send it?
    It's for the alkylation of salicylic acid with acetic anyhydride and a H3PO4 catalyst
    Thanks in advance
    Yeah sure. You should end up with Aspirin btw.
    Offline

    19
    You could just post it up here (you can attach files to posts) so you can get a few peoples opinions
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by jam12)
    Yeah sure. You should end up with Aspirin btw.

    (Original post by EierVonSatan)
    You could just post it up here (you can attach files to posts) so you can get a few peoples opinions
    Thanks

    Name:  step 2 mech.png
Views: 101
Size:  22.1 KB
    Offline

    19
    (Original post by _scott)
    Thanks
    I'm afraid you got a couple of errors in there. Just use the phosphoric acid as an acid i.e. a H+ source that can protonate the anhydride. Then use the OH from the salicylic acid to attck it
    Offline

    1
    ReputationRep:
    You can't simply take OH's off a molecule and plonk them on another. Drawing OH groups fully e.g. O-H will help you understand that only H's are involved, hence these steps are called protonation/deprotonation.

    Btw, remember mechanistic arrows can only come from a bond or lone pair - remember to do draw them on!
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by EierVonSatan)
    I'm afraid you got a couple of errors in there. Just use the phosphoric acid as an acid i.e. a H+ source that can protonate the anhydride. Then use the OH from the salicylic acid to attck it

    (Original post by jam12)
    You can't simply take OH's off a molecule and plonk them on another. Drawing OH groups fully e.g. O-H will help you understand that only H's are involved, hence these steps are called protonation/deprotonation.

    Btw, remember mechanistic arrows can only come from a bond or lone pair - remember to do draw them on!
    Ah yeah, I feel silly now :P obviously wasn't thinking properly when I said the acid loses the OH- !
    So during the protonation of the anhydride, would the C=O be attacked or the C-O-C ?
    Offline

    12
    ReputationRep:
    (Original post by _scott)
    Ah yeah, I feel silly now :P obviously wasn't thinking properly when I said the acid loses the OH- !
    So during the protonation of the anhydride, would the C=O be attacked or the C-O-C ?
    Protonate a C=O oxygen and then have the OH lone pair from salicylic acid attack the other C=O carbon. This way you can draw arrows to spit out a molecule of acetic acid. I don't think you could do this by protonating the C-O-C oxygen. Well, you could but you'd end up having to transfer the proton onto the C=O oxygen at some point anyway.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Kyri)
    Protonate a C=O oxygen and then have the OH lone pair from salicylic acid attack the other C=O carbon. This way you can draw arrows to spit out a molecule of acetic acid. I don't think you could do this by protonating the C-O-C oxygen. Well, you could but you'd end up having to transfer the proton onto the C=O oxygen at some point anyway.
    Okay, thanks!
    Would this be ok?Name:  step 2 mech.png
Views: 68
Size:  22.5 KB
    Offline

    19
    Hmm no. In the first step use the lone pair on the oxygen from the C=O bond to form C=O+-H then use the R-OH (on the salicylic acid's aromatic ring) to attack the carbon in the C=O+-H with a lone pair from the oxygen.

    This might be simpler for you if you draw the mechanism without the acid catalyst?
    Offline

    1
    ReputationRep:
    (Original post by Kyri)
    Protonate a C=O oxygen and then have the OH lone pair from salicylic acid attack the other C=O carbon. This way you can draw arrows to spit out a molecule of acetic acid. I don't think you could do this by protonating the C-O-C oxygen. Well, you could but you'd end up having to transfer the proton onto the C=O oxygen at some point anyway.
    The OH attacks the protonated carbonyl group, not the other one.

    @OP, draw without the full acid catalyst structure like EierVorSatan has suggested. The catalyst is only there to protonate one of the C=O groups (to C=O+-H) making it more electrophilic.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by EierVonSatan)
    ...

    (Original post by jam12)
    ...
    Hi, sorry I haven't been on the computer for a few days. Sorry to bother you again, but would this be okay?

    Name:  step 2 mechanism.png
Views: 67
Size:  18.4 KB
    Offline

    19
    This is quite tricky, so I think I'll just save some time and post it up - if you have any questions please ask
    Attached Images
     
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by EierVonSatan)
    This is quite tricky, so I think I'll just save some time and post it up - if you have any questions please ask
    Thanks for your help!
    Since it's quite tricky, do you think I should just leave this out my investigation report? It's for Advanced Higher chemistry
    Offline

    19
    (Original post by _scott)
    Thanks for your help!
    Since it's quite tricky, do you think I should just leave this out my investigation report? It's for Advanced Higher chemistry
    No, it's just a bit above A-level/Advanced higher in my opinion so it'd look good in a report. Again, if there is something you don't understand - just ask
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: April 18, 2011
The home of Results and Clearing

1,256

people online now

1,567,000

students helped last year

University open days

  1. Bournemouth University
    Clearing Open Day Undergraduate
    Fri, 17 Aug '18
  2. University of Bolton
    Undergraduate Open Day Undergraduate
    Fri, 17 Aug '18
  3. Bishop Grosseteste University
    All Courses Undergraduate
    Fri, 17 Aug '18
Poll
Will you be tempted to trade up and get out of your firm offer on results day?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.