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ochem question

Discussion in 'DAT Discussions' started by tuan209, Jul 31, 2006.

  1. tuan209

    tuan209 Member
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    Hi,

    Im looking through the Kaplan book over carboxylic acids, and it mentioned that in ONE step a carboxylic acid can form an amide. Is this true? I recall from Ochem II that a carboxylic acid cannot form an amide.
     
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  3. lintydent

    lintydent member
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    I checked my ochem textbook and it says:

    "Amides undergo hydrolysis to yield carboxylic acids plus amine on heating in either aqueous acid or aqueous base......acidic hydrolysis reaciton occurs by nucleophilic addition of water to the protonated amide, followed by loss of ammonia........basic hydrolysis occurs by nucleophilic additino of OH- to the amide carbonyl gropu, followed by deprotonation of the -OH group and elimination of amide ion (-NH2)"

    ...so yes, the kaplan book is right, occurs by one step via all those intermediate actions.

    EDIT: ahh man, i read your question backwards....
     
  4. allstardentist

    allstardentist All-Star
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    I think he's talking about COOH to amide not amide to COOH. tuan, what page did u get that from?
     
  5. RockstarDMD

    RockstarDMD sUcCeSs iS mY OnLY OpTioN
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    Usually you will see a carboxy acid hit with PBr3 first..........
     
  6. lintydent

    lintydent member
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    It's in the "review problems" of the -COOH section....problem #12

    "Carboxy acids can be reacted in one step to form all of the following compounds EXCEPT:

    a. acyl halides
    b. amides
    c. alkenes
    d. alcohols

    Ans. C"

    a. reacts with SOCl2
    b. NH3
    c. NaBH4....-OH comes out
    d. LiAlH4


    yes?
     
  7. allstardentist

    allstardentist All-Star
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  8. tuan209

    tuan209 Member
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    Thats the problem I am talking about. But that doesnt make any sense. NH3 is a base, and COOH is an acid. The base will pull off the Hydrogen of the COOH. Your products should be a COO- + NH4. I tried drawing it and its mechanistically impossible.
     
  9. dat_student

    dat_student Junior Member
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    "NH3 + R-COOH" is an acid and base rxn. It won't give you an amide.
     
  10. tuan209

    tuan209 Member
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    Thanks, that was what I was thinking as well.
     
  11. dat_student

    dat_student Junior Member
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    I am 100% sure the products are NH4+, RCOO-
    Good Luck :)
     
  12. issa

    issa Senior Member
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    R-COOH + NH3 -------------> R-CONH2 (an amide)
     
  13. dat_student

    dat_student Junior Member
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    NO, see above ;)
     
  14. issa

    issa Senior Member
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    the question

    "Carboxy acids can be reacted in one step to form all of the following compounds EXCEPT:

    a. acyl halides
    b. amides
    c. alkenes
    d. alcohols

    Ans. C"

    is this question wrong?
     
  15. dat_student

    dat_student Junior Member
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    It has more than one correct answer (B & C) :) Kaplan tests, books,etc. have a ton of errors. Last year, I reported 40-50 mistakes to Kaplan.
     
  16. allstardentist

    allstardentist All-Star
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    DAT student is correct. Amide cannot by synthesized from COOH. It's acid-base rxn. The solution from kaplan is wrong.
     
  17. dental#1

    dental#1 Fla DDS
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    - LialH4 is a reducing agent: It reduces CH3COOH --> Primary alcohol;
    - NaBH4 is also a reducing agent: (*Note it doesn't reduce Carbo and Esters) Aldehyde --> primary alcohol.
    - SOCl2 is Alcyl Halides
    -Amid Condensation RXN: RCOR + NH3 --> RCNHR ( its the only one I could come up with for this ?)
    - The alkene answer is correct because, KMnO4 with heat on the double bond on C2 is cleaved and therfore you get 2 Carbo. If it is Terminal bond you get a ketone and a CO2 molecule. These are Oxidative reaction.
    Alkene--> Carbo Not Carbo --> Alkene.

    So finally conclusion C could be the right answer In my opinion :D
     
  18. grapeflavorsoda

    grapeflavorsoda Senior Member
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    hello there,

    yes it is true.

    typcially intro. orgo texts mention the amide synthesis rxn using carboxylic acid and amine only briefly or not at all.

    anyhoo, at typical room-temperature setting the dominant reaction between carboxylic acid and amine is acid-base reaction. And carboxylate is the most stable form of the typical carboxylic acid derivatives. So other rxn pathways leading to other carboxylic acid derivatives will not be observed at mild setting.

    however, when you increase the temperature(around 200-300 celcius), the ammonium carboxylate salt that was formed after the kinetically fast acid-base rxn, will lose water and subsequently form the amide.

    although it involves two mechanistically distinct steps, synthesis of amide using carboxylic acid and amine is typically carried out by dumping these two reagents and simply heating it. thus it is considered as a single step synthesis rxn.
     
  19. grapeflavorsoda

    grapeflavorsoda Senior Member
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    PBr3 or SoCl2 is typically used with carboxylic acid when alpha-halogenation of the carboxylic acid is desired.
     
  20. grapeflavorsoda

    grapeflavorsoda Senior Member
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    yes. and that salt can undergo dehydration(at higher temp) rxn forming corresponding amide.

    even though you might not be familiar with this rxn, i am sure you have encountered the urea synthesis rxn involving carbon dioxide and ammonia; combine these two reagents and simply heat.

    mechanically, it is very similar, if not same.
     
  21. dat_student

    dat_student Junior Member
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    The question says "ONE STEP." It doesn't say SEVERAL STEPS involving (1) acid-base rxn (2) dehydration (3) etc etc etc. Yes, I agree with you that in many steps you can make an amide from a carboxylic acid. What you said is true but it cannot happen in one step. It's as if someone says we dump 10 reagents in one container and boil it and because they are all in one container and we add them all at once it's one step.

    Last year, I had a similar question. I emailed my question to Kaplan and I received the following reply:

    "Yes, you are quite right here. The acid-base proton transfer is much
    faster than any other possible reaction and will occur first..."
     
  22. grapeflavorsoda

    grapeflavorsoda Senior Member
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    it is considered one step.

    see any text on any advanced orgo text.

    or ask your orgo professor.
     
  23. grapeflavorsoda

    grapeflavorsoda Senior Member
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    dat_student if we use your categorization to define the "one-step" then none of them can be formed in "one-step."

    for choice (a) typically involves nuceophilic attack. formation of intermediate(not transition state). after that acid-base rxn, which is followed by another nucleophilic attack. and then another acid-base rxn step.

    for choice (b) you typically convert carboxylic acid into more thermodynamically unstable species like esters, acyl halides.
    and then you add reagents such as amine. this rxn takes multiple rxn pathways such as acid-base rxn, nucleophilic attack, etc.

    for choice (d) you need to reduce first. but reduction step with metal hydride such as LiH4 is not single step rxn; if first goes through termolecular rxn resembling acid-base rxn. after that it goes through multiple lewis acid-base rxn. After forming adducts it also goes multiple steps.

    mechanistically simple rxn is single step-rxn but converse is not true.
    the reason for this is organic definition of whether a rxn is single-step or not is based on the actual empirical step you take when you run the experiment.

    single-step rxn is not equal to simple-rxn.

    simple-rxn involves only one mechanism(therefore overall rxn is equal to its mechanism), but not the single-step rxn.
     
  24. DonExodus

    DonExodus Dentist in Virgin Islands
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    You cant reduce a COOH to alkene in one step... recuding it with LiALH4, not NaBH4 will yield an alcohol, not C=C
     
  25. tuan209

    tuan209 Member
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    I asked my Orgo teacher, and he replied that YOU CANNOT make an amide from a carboxylic acid.
     
  26. grapeflavorsoda

    grapeflavorsoda Senior Member
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    reduction of carbonyl to alcohol. why u tripping?

    by the way, one step means one empirical step. if a particular rxn has a single rxn mechanism step, it is called simple rxn not one step rxn.

    that's why reduction of ketone/aldehyde to alcohol with NaBH4 is considered one-step rxn where as the reduction with LiAl4 is considered two step rxn since you need to add after the metal-anion adduct complex formation rxn is completed. mechanistically they are same and not a simple rxn.
     
  27. grapeflavorsoda

    grapeflavorsoda Senior Member
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    lol

    where did he get his ph.D?

    better yet does he have any teaching experience?

    here i googled some for you. i hope my 10 wasted minutes will enlighten some of the future people who will take out my cavaties.

    http://www.chemguide.co.uk/organicprops/amides/preparation.html

    http://members.aol.com/logan20/outlin18.html(see section amide)

    http://en.wikipedia.org/wiki/Amide

    www.hamline.edu/~rmajerle/Chem3460/Slides/April2406.ppt

    acstaff.bloomu.edu/mpugh/108Chpt17S06.pdf

    http://www.cem.msu.edu/~reusch/VirtTxtJml/amine1.htm

    www.utdallas.edu/~biewerm/20+21.pdf

    and you can go on and on to find more.

    i personally checked these websites so it will have the one-step amide synthesis rxn using carboxylic acid and amine.
     
  28. dat_student

    dat_student Junior Member
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    I looked at some of your references:

    This is what one of them says:

    http://www.hamline.edu/~rmajerle/Chem3460/Slides/April2406.ppt

    "Some ammonium salts of carboxylic acids can be dehydrated to the amide at high temperatures
    This is generally a poor method of amide synthesis"

    If temperature is not high it is not even possible.... You need to heat it up to make it go through a second step. As your reference suggests this method doesn't work for all cases and is a very very very very poor method to make amides.

    This is one of the usual ways to make amides in labs:

    McMurry 4th edition page 1079 (McMurry is a professor at University of Pennsylvania)
    the mechanism of amide formation by reaction of a carboxylic acid and an amine with DCC (dicyclohexylcarbodiimide)
    Figure 27.8

    1)
    the carboxylic acid first adds to the carboiimide reagent to yield a reactive acylating agen (at this point we no longer have COOH, instead we have RCOO-(DCC) << This is done to prevent acid & base rxn)

    2)
    nucleophilic attack of the amide on the acylating agent gives a tetrahedral intermediate

    3)
    The intermediate loses dicyclohexylurea and yields the desired amide.

    I don't consider that one step. If you think that's one step, fine it's one step. I don't think the question is asking for exceptional cases and exceptional set of parameters.
     
  29. tuan209

    tuan209 Member
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    Im certain he knows what he is talking about. He got his B.S. at City College of New York, M.S AND Ph.D at Yale. Those are some pretty nice schools if you ask me.
     
  30. grapeflavorsoda

    grapeflavorsoda Senior Member
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    omg. are u for real? you are fun, yet dumb. no wonder you chose dental school. lol. good thing though my lab is closed down for 2 days and i got absolutely nothing to do today.

    anyway,

    everything is done in one step. let me just reminds you again and again that the number of experimental steps you take defines the rxn steps. if you add sugar and heat up until it dissolves, it is considered one step. if you add sugar stir until dissolves partially, and then you heat to melt more sugar, it is considered as a two step.

    for the amide synthesis pathway i was talking about, you dump all the reagents and heat up all at one step. no additional separate steps are required. you dont heat separately after the acid-base rxn is done or not.

    you just do all the step at once. dump and heat. leave it alone for a while.

    first of all, like all the amide formation rxn with carboxylate derivatives, the reacting amine must not be tertiary. guess why? it needs to form a bond with carbonyl carbon and nitrogen-carbon bond is not as unstable as N-H bond. thus any tertiary amine will not form amide with any carbonyl compounds unless reaction condition is really harsh.

    of course, the tertiary amine can act as base so it will form acid-base pair with the carboxylate. but it wont be able to make any new bonds with carbon. it could at certain temperature but it will be such extreme condition, the carbon chain will crack. you have heard about cracking, right? petroleum purification, modification, etc.

    anyway, let me address some reasons why your copying and pasting of orgo. lab manual does no good in defending your case.

    when you add DCC to carboxylic acid, you doing a different synthesis pathway from the one i was talking about earlier which involves salt.(do you even understand intro orgo?).

    anionic oxygen of the carboxylate attacks the DCC, thus forming a better leaving group than oxygen. it is similar to acylation of carboxylic acid with SOCl2, PBr3, etc. another organic reagent you could use instead of DCC for the rxn you mentioned is HOBt.

    so this particular pathway, you mentioned, requires the prior formation of carboxylate-DCC adduct before the addition of the amine. by the way, carbxylate-DCC adduct is functionally similar to anhydride.

    you FIRST do the reaction that forms more reactive species. only AFTER the adduct rxn is completed(so you wait for this rxn to be completed before doing anything else to the rxn vessel) you add amine. now let me ask you why the hell amine was not added along with carboxylic acid and DCC ?

    i will just give you the answer since it seems like you cannot think at all.

    amine will react with carboxylic acid, so carboxylate-DCC adduct will form faster. but amine will be protonated, thus won't be able to function as good nucleophile. another reason is that amine can react with DCC thus reducing the effective concentratino of free DCC. therefore, two separate and distinct empirical steps are required for the amide synthesis pathway you mentioned.

    back to the carboxylate-DCC pathway. as i stated above carboxylate-DCC is functionally similar to anhydride.
    that is why it undergoes the typical addition-elimination rxn of the carboxylic-acid derivatives which involves the tetrahedral intermediate.

    the formation of amide by heating carboxylic acid and amine mixture does NOT undergo same mechanistic pathway. it involves salt as intermediate. the rxn pathway you have mentioned actually prevents the ammonium carboxylate salt formation.

    so when doe the salt forms in your rxn pathway?

    as you can see clearly, why compare two rxns that are totally different?
    Furthermore how can you draw a conclusion as you did?

    to be clear, let me just mention again the fact that the urea/amide synthesis pathway i mentioned earlier using carbon dioxide and ammonia w/ heat involves no addition of DCC or any electrophiles that will ultimately serve as leaving group. also, addition of DCC to carboxylic acid prior to separate addition of amine prevents the formation of the ammonium carboxylate salt formation, which is central to the amide synthesis pathway i was talking about before.

    so your supposedly counter-example does not refute or have any relevance to the fact that the synthesis i was talking about was one step.

    it is one step.

    also whether a particular rxn's yield(which defines whether a synthesis pathway is poor method or not) is poor or not does affect whether a rxn is single step or multiple step rxn. it just tells that there might alot of competing rxn.

    then again, your stupidity was more than exposed when you got confused between single step rxn and simple rxn. where is the defense for that? :eek:

    lol. :laugh:
     
  31. grapeflavorsoda

    grapeflavorsoda Senior Member
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    so where is his excuse?
     
  32. tuan209

    tuan209 Member
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    im not going to argue with you as this seems pointless. ive asked 2 professors at my school which have said the samething. Ill take their words over yours, end of discussion.
     
  33. DrGeek

    DrGeek Member
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    I just did a quick search:

    http://glory.gc.maricopa.edu/~tbunag/Exam%203CHM%20236%20Spring%2006%20Answers.htm
    "19. ANS: Since NH3 is a base and a carboxylic acid is an acid, they go through an acid/base reaction instead."


    http://www.chemguide.co.uk/organicprops/amides/preparation.html
    "
    Ammonium salts tend to split into ammonia and the parent acid on heating, recombining on cooling.
    "


    http://72.14.203.104/search?q=cache:96Mig1z2RkwJ:www.bama.ua.edu/~kshaughn/chem232/notes/chapter18.pdf+%22amides+from+carboxylic+acids%22&hl=en&gl=us&ct=clnk&cd=41&client=opera
    "
    Synthesis of amides: Amides are easily made from acid chlorides or anhydrides. Unlike esters,
    amides are very difficult to make from carboxylic acids..."
    Prepared by Dr. Kevin Shaughnessy
    The University of Alabama, Tuscaloosa, AL, 2003


    http://chemistry2.csudh.edu/rpendarvis/aminrxn.html
    "
    In the case of making amides from carboxylic acids, the difficulty comes because the carboxylic acid is a stronger acid (pKa ~5) than the ammonium salt (pKa ~10). The result is that there is very little amine and carboxylic acid at equilibrium. so there is very little nucleophile present. Also, the O- in the carboxylic acid is a very poor leaving group. This reaction doesn't look promising at all
    "


    http://v3.espacenet.com/textdes?IDX=WO0058490&CY=nl&LG=nl&DB=EPODOC&QPN=WO0058490
    enzymatically catalyzed reaction:
    "To avoid the problem of reagents precipitating as salt, the prior art preparation of primary amides using an enzymatically catalyzed reaction involves esterification of the carboxylic acid prior to contacting the ester with the ammonium compound."
     
  34. dat_student

    dat_student Junior Member
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    I apologize for misunderstanding you. I felt you heat "separately" based on one of your references:

    http://www.chemguide.co.uk/organicprops/amides/preparation.html

    "For example, ammonium ethanoate is made by adding ammonium carbonate to an excess of ethanoic acid.

    2CH3COOH + (NH4)2CO3 ---> 2CH3COONH4+ + H2O + CO2

    When the reaction is complete, the mixture is heated and the ammonium salt dehydrates producing ethanamide.

    CH3COONH4 ---> CH3CONH2 + H2O
    .......
    Ammonium salts tend to split into ammonia and the parent acid on heating, recombining on cooling. If dissociation happened in this case, the ammonia would escape from the reaction mixture and be lost.
    "

    P.S. I don't want to argue with you. I apologize again for misunderstanding you. Let's use this forum to exchange opinions and help each other instead of attacking dentistry, predental and dental students. People can have different opinions. In your eyes and based on your knowledge I am wrong. I respect your opinion but disagree. I apologize once again.
     

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