Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: pdffree on November 30, 2008, 03:52:26 PM
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How do you get 2-pentanol from formaldehyde?
Anyone?
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Do you know the grignard reaction? Can you see the part of 2-pentanol that may have come from formaldehyde?
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Do you know the grignard reaction? Can you see the part of 2-pentanol that may have come from formaldehyde?
Not only me but everyone in the class is having hard time!< Morever its an online class and he posts notes that doesn't help the class!.
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I'm sorry, if you came here expecting the answer, you should have read the forum rules first. That's not how it works. We ask you questions, and help guide you to the correct answer, so you can learn the material and understand how to solve the problem in the future.
If I just give you the answer, you would have gained little to no knowledge about the underlying mechanisms and things you should consider in solving the problem. So if the structure were changed slightly, you wouldn't have the basic understanding in order to solve it, and you would be stuck again.
The teacher sucks, fine. But you're in college, put in the effort that is expected of you, and do some studying.
So, I'll ask again, have you heard of the grignard reaction?
Do you have a textbook that you were required to buy for the class (online classes can still have a textbook).
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yea!
I have the textbook! looking at the book!
and unfortunately we had him in ORG 1, and thats why we are having hard time!
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Ok, good. Now look up the chapter on the alcohols, find the section that talks about grignard reaction. What are the two pieces of a grignard reaction?
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Ok, good. Now look up the chapter on the alcohols, find the section that talks about grignard reaction. What are the two pieces of a grignard reaction?
I can see similar reactions in the book but in reverse direction!1. (RMGX, ether 2. H3O+
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What reacts with the RMgX?
What is formed as the product?
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What reacts with the RMgX?
What is formed as the product?
i am looking at this link:
http://depts.washington.edu/chemcrs/bulkdisk/chem238A_win05/notes_14_06_10.pdf
and see that Grignard reagents react with formaldehyde to give primary alcohols.
but I want it the other way!
you can see it the attachment!
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Oh, no that is an organic notation. The open arrow like that means "make the left side from the right side", so you are looking at turning formaldehyde into a secondary alcohol?
So, what carbonyl do you use to make a secondary alcohol?
Can you make that type of carbonyl from a primary alcohol (look at oxidations of alcohols)?
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Oh, no that is an organic notation. The open arrow like that means "make the left side from the right side", so you are looking at turning formaldehyde into a secondary alcohol?
So, what carbonyl do you use to make a secondary alcohol?
Can you make that type of carbonyl from a primary alcohol (look at oxidations of alcohols)?
do i have to use Cro3/H2so4 for the oxidation of alchol?
and at the end alcl3 to remove Ch3Ch2?
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Well, CrO3 with H2SO4 will give you a carboxylic acid.
What is the type of carbonyl that is used to make a secondary alcohol from? There is a milder oxidation that will convert a primary alcohol into this type of carbonyl.
Also, if you read through that pdf in there, it talks about how to break apart a alcohol into pieces. You are going to have to break yours twice.
First time, you'll get one type of carbonyl and a grignard reagent.
Second time, you'll break your carbonyl into two pieces and then you'll get your formaldehyde and another grignard reagent.
I'm not sure what you meant about the alcl3 to remove CH3CH2.
EDIT: By the way, I'm glad to see you decided to take a proactive approach about this instead of saying you can't do it because your teacher sucks.
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i did this . What do you do next? see the image attached.
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Answer this question before we continue:
What type of carbonyl compound when reacted with a grignard reagent forms a secondary alcohol?
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Answer this question before we continue:
What type of carbonyl compound when reacted with a grignard reagent forms a secondary alcohol?
aldehydes
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Ok good!
So, you need to find an oxidation that can convert primary alcohols into aldehydes.
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is it H2so4?
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Nope.
Start here:
http://en.wikipedia.org/wiki/Alcohol#Oxidation
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so the first step is oxidation and than grignard reaction?
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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.
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can you check this?
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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.
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i didnt understant how you want me to do it!
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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.
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check!
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That will only give you three carbons. You need 5 right? ;)
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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 ;)
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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)
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Azmanam to the rescue with his awesome pictures! :D
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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. :-(