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Topic: Acetone reaction scheme  (Read 30002 times)

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Offline Rutherford

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Re: Acetone reaction scheme
« Reply #30 on: February 12, 2013, 12:15:01 PM »
Okay, V is the corresponding oxime. After H2 is added, all double bonds are saturated now. What is the use of CF3COOH?
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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #31 on: February 12, 2013, 12:24:58 PM »
OK you got the Curtius rearrangement.
this gives after hydroxyl amine treatment V
O=C(OC(C)(C)C)NC(C1)CC1(C/2)CC2=N\O

The hydrogenation reduces the oxime to the amine
NC1CC2(CC(NC(OC(C)(C)C)=O)C2)C1

What is left, the TFA, what is the standard method for removal of a t-butyl carbamate? And what is the product?
The product is W 8)
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Offline Rutherford

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Re: Acetone reaction scheme
« Reply #32 on: February 12, 2013, 12:33:39 PM »
Then the tbutyl leaves and -OCOCF3 joins the molecule. Why is the bicarbonate used?
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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #33 on: February 12, 2013, 12:37:49 PM »
No, think ester hydrolysis, bicarb is used to neutralise any excess acid and generate the product free from a possible TFA salt.
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Offline Dan

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Re: Acetone reaction scheme
« Reply #34 on: February 12, 2013, 12:47:12 PM »
How did the ketone survive LAH without protection though?
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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #35 on: February 12, 2013, 12:50:59 PM »
I ask myself that question!
Something is wrong here, but we went with the assumption that it did survive and he is learning some new chemistry anyway!
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Offline Dan

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Re: Acetone reaction scheme
« Reply #36 on: February 12, 2013, 12:53:15 PM »
I think I got it - the structure of P is incorrect, and O is not (quite) 1,3-dibromoacetone.

Hint: Br+ is a Lewis acid

Structure A is OK though.
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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #37 on: February 12, 2013, 12:55:41 PM »
OK, but may we finish the scheme we were working on, even although it is probably not correct?
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Offline Dan

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Re: Acetone reaction scheme
« Reply #38 on: February 12, 2013, 01:13:40 PM »
Quote from: discodermolide on February 12, 2013, 12:55:41 PM
OK, but may we finish the scheme we were working on, even although it is probably not correct?

Yes, I was unclear, sorry - if I'm right, then your structure for T and those that follow as you have it now are correct.
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Offline Rutherford

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Re: Acetone reaction scheme
« Reply #39 on: February 12, 2013, 01:18:50 PM »
Quote from: Dan on February 12, 2013, 12:53:15 PM
I think I got it - the structure of P is incorrect, and O is not (quite) 1,3-dibromoacetone.

Hint: Br+ is a Lewis acid

Structure A is OK though.
Was Br added to the carbonyl group then? But then there aren't two isomers made.


Quote from: discodermolide on February 12, 2013, 12:37:49 PM
No, think ester hydrolysis, bicarb is used to neutralise any excess acid and generate the product free from a possible TFA salt.

Is the final product NH2-R-NH-COOH?

Edit: D'oh. I see it's the diamine. I got just confused.

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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #40 on: February 12, 2013, 01:24:43 PM »
No, hydrolysis of a carbamic acid ester gives the alkyl part and CO2. In this case isobutene and CO2. The amine is produced as a TFA salt, which is neutralised by bicarb to give product W which is.

NC1CC2(CC(N)C2)C1

I suggest you got through all this chemistry again and make sure you understand every step, what the reagents do, what the mechanisms are and so on. Get to recognise standard chemical reactions, synthesis with malonate esters, the Curtius rearrangement, Wolff rearrangement Beckmann rearrangement (although it was not in this scheme)and other Named reactions, they crop up all the time, the hydrolysis of carbamates and so on. Basic stuff.
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Offline Rutherford

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Re: Acetone reaction scheme
« Reply #41 on: February 12, 2013, 01:39:33 PM »
Okay, I will learn those three guys' rearrangements. Why wasn't the carbonyl group hydrogenated in the last reaction? Can I look at the carbamic acid ester as an tbutyl amide?
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Offline discodermolide

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Re: Acetone reaction scheme
« Reply #42 on: February 12, 2013, 01:52:12 PM »
There is more to organic chemistry than those there guys' rearrangements. All I am saying is that when you see certain functionality present or being made in a molecule it should trigger off the memory, e.g. when I saw acid chloride/acyl azide/heat/alcohol I immediately recognised that a Curtius was being carried out. In my case most of organic chemistry is ingrained in my brain cell, some details are sketchy but I like to think that most of it is there, but I have been doing it for nearly 40 years, and one does forget. Some things I say may not be 100% correct but if they put you on the right track then that's ok.

A carbamate ester is not an amide and you can't apply amide chemistry to a carbamate. Carbamates are typical protecting groups for amines, e.g. Boc, t-Boc and the like. They are almost tuneable to the other functionality in your molecule, that is you can choose your carbamate so that it can be removed without destroying the rest of the molecule.

Also you should not just take a guess at the products, you need to slow down and think, not panic, and remember your chemistry. We are not there in the exam!
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Offline Rutherford

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Re: Acetone reaction scheme
« Reply #43 on: February 12, 2013, 02:07:55 PM »
I am currently very confused, so I will need some rest. I don't know how I thought that it is an amide. Anyway tomorrow or in two days (more probably), I will try to write the whole scheme in chemdraw.
I know that organic chemistry is a very comprehensive field of chemistry and I like it very much. As I am just a novice in exploring it, I will need some time to get all those rearrangements and reactions.
Thanks for the help. There is one more scheme in this problem.
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Offline Dan

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Re: Acetone reaction scheme
« Reply #44 on: February 12, 2013, 02:14:19 PM »
Quote from: Raderford on February 12, 2013, 01:18:50 PM
Quote from: Dan on February 12, 2013, 12:53:15 PM
I think I got it - the structure of P is incorrect, and O is not (quite) 1,3-dibromoacetone.

Hint: Br+ is a Lewis acid

Structure A is OK though.
Was Br added to the carbonyl group then? But then there aren't two isomers made.

The 1,3-dibromoacetone is probably an intermediate, and may even be N - is it stated in the question that N and O are isomers?

Remember the solvent is MeOH, and there is a Lewis acid (Br2). What do you get if you mix a ketone (like 1,3-dibromoacetone), excess alcohol and a Lewis acid?
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