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Topic: Synthesis -2-pentanol from formaldehyde  (Read 22228 times)

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Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #15 on: November 30, 2008, 08:28:20 PM »
Ok good!

So, you need to find an oxidation that can convert primary alcohols into aldehydes.

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #16 on: November 30, 2008, 08:32:18 PM »
is it H2so4?

Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #17 on: November 30, 2008, 08:37:23 PM »

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #18 on: November 30, 2008, 08:43:45 PM »
so the first step is oxidation and than grignard reaction?

Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #19 on: November 30, 2008, 10:09:32 PM »
so the first step is oxidation and than grignard reaction?
Exactly, so write up the whole sequence now, and then instead of R1 and R2, replace them with the appropriate grignard reagents that will give you the methyl and the propyl groups attached to the alcohol.

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #20 on: November 30, 2008, 10:41:19 PM »
can you check this?

Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #21 on: November 30, 2008, 11:06:46 PM »
Hmm...not quite.

I think you are mixing up two things.  Take the problem step by step, you had the right start in your first picture, now build off of that.

So, in your first picture, you are at the primary alcohol.  Next, you know you need to oxidize and then perform another grignard, try drawing the whole thing now.  So, add on to your first picture that ended with the primary alcohol.

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #22 on: November 30, 2008, 11:10:18 PM »
i didnt understant how  you want me to do it!

Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #23 on: November 30, 2008, 11:16:52 PM »
i didnt understant how  you want me to do it!
It's ok.  You seem to be grasping the concepts, we just need to work on meshing them together.

So you can create a primary alcohol, which you can oxidize and then perform another grignard reaction to create your secondary alcohol.  Did you read the part in the pdf about the analysis for synthesis near the end of the pdf?

So step one:

Draw two reactants that when combined make your final product.  You should draw an aldehyde a grignard reagent.

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #24 on: November 30, 2008, 11:39:28 PM »
check!

Offline Mitch

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #25 on: December 01, 2008, 12:30:36 AM »
That will only give you three carbons. You need 5 right? ;)
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Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #26 on: December 01, 2008, 12:52:53 AM »
check!
Sort of the right idea but not quite.  Think about it this way:

If you look at your alcohol, you break off each side chain (so you'd break off a methyl group from the left, and a propyl group from the right).  This is called disconnection.

In order to add these groups, your compound needs to be a carbonyl.

So if we take the starting compound, and break off the methyl group, we see that in order to form it, we need an aldehyde that is of the structure CH3CH2CH2CHO.  We can then add CH3MgBr to it.

Well, now how did we make CH3CH2CH2CHO?  That is an aldehyde, and we discussed that we can make those from primary alcohols by oxidation (although, we have yet to identify the oxidation that will stop at an aldehyde).  So we can say that the CH3CH2CH2CHO came from CH3CH2CH2CH2OH.

Ok, awesome!  Now, where did CH3CH2CH2CH2OH come from.  Well, how did we say we make primary alcohols?  Those came from formaldehyde and a grignard reagent.  So, if we break off the other side chain, we can see our initial starting products were CH2O and CH3CH2CH2MgBr.

Can you draw that process out?  The last thing you need to identify is the type of oxidation that will go from a primary alcohol to an aldehyde, and the answer is in the wikipedia link I gave you above.

Sorry I can't draw this, but my chem draw software isn't installed yet.  Maybe Azmanam will see this and drop by with a pretty colored picture for us ;)

Offline azmanam

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #27 on: December 01, 2008, 06:40:02 AM »
Well... Since you asked...

(it's just a retrosynthesis based on macman's last comment. It needs to be inverted to the correct forward synthesis with complete reagents in the forward direction)
Knowing why you got a question wrong is better than knowing that you got a question right.

Offline macman104

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #28 on: December 01, 2008, 10:03:14 AM »
Azmanam to the rescue with his awesome pictures! :D

Offline pdffree

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Re: Synthesis -2-pentanol from formaldehyde
« Reply #29 on: December 02, 2008, 10:55:19 AM »
Thanks a lot ! both of you!
When you try to learn it, it seems easy.. I wish i had a professor like you guys! Anyway, i will try to study ORG 1 during the break. I hope I will be able to cuz I borrow books all the time during the break just to study in advance and don't open the book at all. :-(

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