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Topic: Help needed with reaction mechanism of benzofuranone  (Read 9110 times)

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Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #15 on: January 07, 2013, 06:33:24 PM »
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..?

Offline discodermolide

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #16 on: January 07, 2013, 11:20:09 PM »
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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Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #17 on: January 08, 2013, 07:07:42 AM »
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!

Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #18 on: January 09, 2013, 05:49:25 PM »
Does anyone know whether this is numbered right..?

Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #19 on: January 15, 2013, 04:43:17 PM »
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..?

Offline discodermolide

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #20 on: January 15, 2013, 05:10:42 PM »
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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Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #21 on: January 15, 2013, 05:19:46 PM »
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..

Offline discodermolide

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #22 on: January 15, 2013, 05:49:38 PM »
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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Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #23 on: January 15, 2013, 06:09:45 PM »
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..

Offline orgopete

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #24 on: January 16, 2013, 02:35:25 AM »
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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Offline Blackrose

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Re: Help needed with reaction mechanism of benzofuranone
« Reply #25 on: January 16, 2013, 02:57:30 AM »
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..


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