Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Blackrose on January 03, 2013, 09:55:23 AM
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Hi there, I am new here and I really need help with a reaction mechanism.. I've literally drawn it out like at least 20 times and I'm still doing it wrong, I'm just horrible when it comes to curly arrows and all..
Attached is the reaction itself, if someone can please have a look at it and draw out for me how the reaction happened with the arrows.. I need to explain how it took place and what exactly happened but I can't because I don't understand how it happened!! I'm freaking out here, I really need to have the right mechanism so I can explain it right in my dissertation, any help would be highly appreciated..!
I'm sorry if it sounds as if I want someone to do it for me, I really have tried I just don't know how to get it right and I don't have much time left to play around with it..
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What happens when NaOH comes into play with both starting materials? Are there any acidic protons somewhere?
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Hello!
I guess this is essentially an Aldol reaction that undergoes ring closure...
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Look at the functional groups, carboxylic acid, aldehyde, methyl ketone.
Also the base can pick up another proton (there are 2 carbonyl group, 1 with α protons) .
Give it a try
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Ok, if you guys don't mind, I'm going to post the reaction in small steps so you can see what I'm doing..This way you can tell me whether I'm on the right track or not, and I will be able to see where I go wrong as I'm very confused on my own.. Do keep patient with me, I've never been good at this.. =$
Ok so this is the first step in the reaction, if I understood your help right..
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Step 2..
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Step 3..
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I can't believe I spent over 4 hours on this..!! Please ignore my other posts, I think they are wrong..
This is the complete reaction, I hope I've done it right this time, it seems ok but I still have a feeling I missed something out or have some mistakes somewhere, so I would really really appreciate it if someone could look it over for me and give me any feedback.. Thanks for your hints, they really did help a lot!
Ok, I'm off to bed, It seems I'm going to see curly arrows and structures in my dreams, they are dancing in front of my eyes at the moment.. :-\
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As far as I can make out that looks OK, except for the ring closure. The carboxylate attacks the C=C in a Michael type of reaction. Thus the electrons move into the C-O bond moving the one of the C=O pairs fully onto the oxygen atom to produce an enolate. So the negative charge you have on that carbon is delocalised into the pi system of the C=O. Pushing the charges back that carbon picks up the proton to give the product. I can draw it if you wish.
But well done anyway.
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As far as I can make out that looks OK, except for the ring closure. The carboxylate attacks the C=C in a Michael type of reaction. Thus the electrons move into the C-O bond moving the one of the C=O pairs fully onto the oxygen atom to produce an enolate. So the negative charge you have on that carbon is delocalised into the pi system of the C=O. Pushing the charges back that carbon picks up the proton to give the product. I can draw it if you wish.
But well done anyway.
If you can please, I'm not quite understanding what you mean..
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Here is just the last part I was talking about, compare it with yours.
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Oh I see, I thought you were talking about the other carbonyl group, but that one stays untouched.. I'll draw the reaction mechanism out again in chemdraw and then place it here.. Now it's complete :).. Thanks a lot..!
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I think you did very well, I would not even take a mark off in an exam for what you produced.
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Just an opinion, if you treated the lactone with NaOH, it would hydrolyze the lactone. Acidification would recyclize it. I think there had to have been an acidification step to isolate the lactone. I also expect excess base was present to neutralize the carboxylic acid and enolize the ketone.
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Just an opinion, if you treated the lactone with NaOH, it would hydrolyze the lactone. Acidification would recyclize it. I think there had to have been an acidification step to isolate the lactone. I also expect excess base was present to neutralize the carboxylic acid and enolize the ketone.
I don't understand how to do the above.. But does that mean that my reaction is wrong..?
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Alright then.. Here is the complete (hopefully right) reaction.. :) Anything I need to remove or include..? Any minor detail is important, so feel free to be picky.. Also when I would want to explain it.. Would it be right to say the reaction is an aldol reaction, followed by a michael's type of reaction for cyclization, like you guys suggested..?
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That looks OK.
The sequence is 1) esterification, 2) Aldol condensation, 3) ring closure via a Michael type addition to an α,β-unsaturated ketone.
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That looks OK.
The sequence is 1) esterification, 2) Aldol condensation, 3) ring closure via a Michael type addition to an α,β-unsaturated ketone.
Alright, Thank you!
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Does anyone know whether this is numbered right..?
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Hi again.. I need your help again guys..
So fir this reaction this is what I had written..
The synthesis of benzofuranone follows a three step reaction. The two reactants, 2-carboxybenzaldehyde and the relevant acetophenone, are coupled by an esterification reaction, which is followed by an aldol condensation reaction. The formation of the benzofuran ring system is achieved by the ring closure via a Michael type addition to the α,β-unsaturated ketone (Scheme 3).
However, after showing it to my lecturer he told me to change it to this..
The synthesis of benzofuranone follows a three step reaction. The two reactants, 2-carboxybenzaldehyde and the relevant acetophenone, are first coupled via an aldol condensation reaction. The formation of the benzofuranone ring system is achieved by the ring closure via a Michael type addition to the α,β-unsaturated carbonyl which also forms an internal ester (Scheme 3).
I understand that the aldol reaction takes place first, however is the rest also right.. He confused me and I want to know if the changes he made me make are actually right..?
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Yes he is correct. I must apologise I read the ONa as OMe hence thinking the first step was an esterification, sorry.
The product can be described as an internal ester.
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Yes he is correct. I must apologise I read the ONa as OMe hence thinking the first step was an esterification, sorry.
The product can be described as an internal ester.
Oh you don't need to apologise I'm happy enough you always answer.. :)
One more question.. ;D Is it still right to say it follows a three step reaction now that there is no esterification reaction.. Because there is obviously the last acidification step but would I call it a two step reaction or still a three step reaction..
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Call it two steps, the aldol condensation and the Michael addition/internal esterification. The HCl is there for the work-up.
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Yes he is correct. I must apologise I read the ONa as OMe hence thinking the first step was an esterification, sorry.
The product can be described as an internal ester.
Oh you don't need to apologise I'm happy enough you always answer.. :)
One more question.. ;D Is it still right to say it follows a three step reaction now that there is no esterification reaction.. Because there is obviously the last acidification step but would I call it a two step reaction or still a three step reaction..
Alright... Thanks a million times..
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I would make two points. He is giving you his grade, so he is right. We aren't given the actual reaction conditions, so it does make it difficult to judge, but the reaction is described as a condensation of a benzoic acid, a ketone, and NaOH to give a neutral lactone without an acidification step. I suppose the reaction could give the neutral product plus NaOH, but if I asked you to give the product of that lactone plus NaOH I would expect you to give me the carboxylate of the acid.
There is a condensation that uses similar conditions with sodium acetate and acetic anhydride. The anhydride can react with water generated and the basicity is reduced. The reaction is heated for some time as the equilibria are not towardvenolate formation. Perhaps you lecturer wrote the problem with NaOH to help the class anticipate enol ate formation (and ignoring carboxylate formation), but I find it difficult to believe one could generate NaOH by lactonizing a carboxylate salt. That is why I suggested there must have been an acidification.
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I would make two points. He is giving you his grade, so he is right. We aren't given the actual reaction conditions, so it does make it difficult to judge, but the reaction is described as a condensation of a benzoic acid, a ketone, and NaOH to give a neutral lactone without an acidification step. I suppose the reaction could give the neutral product plus NaOH, but if I asked you to give the product of that lactone plus NaOH I would expect you to give me the carboxylate of the acid.
There is a condensation that uses similar conditions with sodium acetate and acetic anhydride. The anhydride can react with water generated and the basicity is reduced. The reaction is heated for some time as the equilibria are not towardvenolate formation. Perhaps you lecturer wrote the problem with NaOH to help the class anticipate enol ate formation (and ignoring carboxylate formation), but I find it difficult to believe one could generate NaOH by lactonizing a carboxylate salt. That is why I suggested there must have been an acidification.
No you are right, I have changed the reaction mechanism slighty, so now I have a COO- throughout rather than a COONa which means there is no NaOH generated.. And you're also right about the acidification step as I forgot to mention that in my very first post.. I've actually carried out this reaction in lab and the last step was the addition of HCl..