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Reaction with water

  1. Jul 1, 2009 #1
    1. The problem statement, all variables and given/known data
    Arrange the following compounds inorder of increasing reactivity with water,

    1.allyl halide
    2.primary aryl halide
    3.RMgX
    4.acidanhydride
    5.aliphatic acid chloride
    6.tertiary alkyl halide


    2. Relevant equations

    n/a

    3. The attempt at a solution

    I thought since water is a nucleophile, this would be a nucleophilic reaction,so the stronger the electrophilic nature of the organic compound,the faster would be its reaction,with water.

    Am I correct to assume this?

    I was told in another forum that I should start by arranging the compounds inorder of nucleophilic strength,so,

    tertiary alkyl halide> allyl halide> I got as far as this but, now I don't know if acid anhydride is more nucleophilic than RCOCl,
    I think it might be more nucleophilic,cause an acid anhydride has 2 carbonyl groups whereas an acid chloride has only 1,but I'm not very sure?

    I don't know what I should do.

    I know that all of the above compounds react with water (to some extent)based on my knowledge of their reactions with water(except acid anhydride,I haven't still learnt any of its reactions),but,I'd like to know,
    what exactly is the property that an organic compound should have,inorder to react with water?

    Hope my problems clear.

    Thank you.
     
  2. jcsd
  3. Jul 1, 2009 #2

    chemisttree

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    Your list consists of several general classes of compounds... organic halides (primary, allyl and tertiary ones), organic acids or their derivatives (anhydride and acid chloride) and a generalized Grignard reagent (RMgX). Investigate these three classes and determine their reactivity with water.
     
  4. Jul 2, 2009 #3
    Thanks for replying.

    Ok,so I went through my notes once again,and I think the grignard's reagent would react the fastest,cause it has two highly polar covalent bonds,next,
    I think would be the acid derivatives,but I still can't figureout if an anhydride or an acid chloride would react faster.
    An acid chloride has a carbonyl group and a chloride ion which is a good leaving group,so it incresaes the electrophilic nature of the carbon atom of the carbonyl group,but an acid anhydride has two carbonyl groups,so...
    would an acid chloride be more prone to nucleophic attack than an acid anhydride?

    THANK YOU
     
  5. Jul 5, 2009 #4
    I would still like to know how to do this.
    I'm hopeful someone could help me out ,here.
    THANK YOU
     
  6. Jul 6, 2009 #5
    Acid chloride is more prone to attack. The anhydride does have two C=O bonds, but the site of attack is the middle O atom.
     
  7. Jul 6, 2009 #6

    chemisttree

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    Right answer, wrong reason.

    Consider that hydrolysis of acid chlorides and acid anhydrides is catalyzed by acid. Also consider that most acid anhydrides and acid chlorides are not appreciably soluble in water. Which class of compounds do you think would be more soluble in water (all things being equal, of course) and which would react more readily? Remember to consider the products of the reaction in your analysis as well.
     
    Last edited: Jul 6, 2009
  8. Jul 6, 2009 #7
    Really?
    I haven't learnt it like that,(but then I've learnt only the reaction of acid chloride with water)
    Acid chloride+H2O[tex]\rightarrow[/tex] RCOOH +HCl(is the HCl the catalyst you were referring to,i wonder?)

    As for acid anhydride based on your hint to queenofbabes,I think we would get 2RCOOH,
    if this were true the acids obtained in this hydrolysis would be weaker,so (once again if this reaction were true)this would mean an acid anhydide would be less reactive right?
     
  9. Jul 6, 2009 #8

    chemisttree

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    Right. You should remember that acid derivatives (amides, esters, acid halides and anhydrides) all will hydrolyze and that all are catalyzed by acid. You should be able to find that info in your book....
     
  10. Jul 6, 2009 #9
    Thank You so much,sir & I will try to remember that,
    So,
    for RMgX,how do I know how fast it reacts by looking at the reaction,
    RMgX + H2O [tex]\rightarrow[/tex] RH + MgX,
    is it cause it doesn't need a catalyst?,or is it cause of the highly polar bonds?

    So far I have,inorder of reactivity,
    RMgX > RCOCl > acid anhydride > ...
    so for the rest,
    allyl halide
    primary aryl halide
    tertiary alkyl halide,
    I think after arranging it in increasing order of stability of carbocations,I get,
    primary aryl halide > allyl halide > tertiary alkyl halide

    Would this also be (reason?for)the increasing order of reactivity of the above 3 compounds?

    THANK YOU
     
  11. Jul 6, 2009 #10
    ohdear. You're right >.< My chemistry is abit rusty

    The more stable the carbocation, the more likely it is for it to form, thus making the reaction more likely
     
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