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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: dornishthunder on January 20, 2013, 07:10:30 PM

Title: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 20, 2013, 07:10:30 PM

Could someone help me synthesize 3-hydroxypentanal? I may have named it wrong but the structure is CH3CH2CH(OH)CH2CH=O

I'm only allowed to use propene for a carbon source so I'm having trouble. I don't understand how I could build something that is five carbons given only a 3 carbon source? I've been trying to figure this out for a few days now.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 20, 2013, 07:29:08 PM

Well you must find 2 carbons from somewhere and they must come from propene.
So what reactions of alkenes do you know?

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 20, 2013, 08:00:09 PM

Ozonolysis might create the O= but carbon is never a leaving group so after you put two propenes together you'll have six carbons and from my limited knowledge I know that getting rid of a carbon is almost impossible.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 20, 2013, 11:54:10 PM

What does ozonolysis do to an alkene?
Say in the case of propene?
Hint: it gives two fragments, how many carbons has each fragment?

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 21, 2013, 11:58:54 AM

So CH3CH=CH2 + O3 -> CH3CH=O


And CH3CH=CH2 + H2SO4/H2O -> CH3CH2CH2OH

But now I need to put them together and I'm not sure how. If I use Grignard I foresee it will alter the structure of the final product to something I don't want.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 21, 2013, 12:06:43 PM

Why not convert the alcohol into an aldehyde and see where you can go from there?

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 21, 2013, 12:41:00 PM

So if I convert the alcohol into an aldehyde say CH3CH2CH2OH + PCC/CH2Cl2 - > CH3CH2CH=O

CH3CH=O + Cl2 h.v. + Mg -> MgClCH2CH=O which then attacks CH3CH2CH=O and gives the product

CH3CH2CH(OH)CH2CH=O

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 21, 2013, 12:45:30 PM

Not the Grignard reagent. You cannot make these ones as they react with themselves.
I was thinking of an aldol reaction. Make the anion of the acetaldehyde CH₃ and react it with the other aldehyde. NaOH (conc) should do it.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 21, 2013, 01:40:00 PM

We haven't covered that yet so I'm not sure what you mean.

1) From what I think I can grasp is CH3CH=O + OH- -> CH2=CH-O^-

CH2=CH-O^-  + CH3CH2CH=O   ->

CH3CH2CH(OH)CH2CH=O

Or is it

2) CH3CH2CH=O + OH- -> CH3CH=CH-O^-
CH3CH=CH-O^- + CH3CH=O  -> CH3CH2CH(OH)CH2CH=O

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 21, 2013, 05:49:20 PM

It's version 1.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: dornishthunder on January 21, 2013, 05:55:04 PM

Thank you for your guidance. I'll have to look into these aldol reactions for future reference. I'm sure they'll come up in class eventually.

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: discodermolide on January 21, 2013, 06:20:05 PM

They surely will, lots of them!

Title: Re: Synthesis of this 3-hydroxypentanal?
Post by: orgopete on January 22, 2013, 10:06:58 AM

I would consider a strategy of converting propene to propanal and adding a Grigard (derived from propene) to the aldehyde. Ozonolysis with reductive workup would give the desired product.