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Topic: Ozonolysis of pent-1-en-4-yne  (Read 1213 times)

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Offline Zalzul

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Ozonolysis of pent-1-en-4-yne
« on: May 01, 2018, 03:12:39 PM »
In performing ozonolysis on C=CCC#C, specifically with the procedure of (step 1) O3 @ -78 °C and (step 2) (CH3)2S in water, I came up with 3 different products:

C(=O), C(=O)CC(=O)O, and C(=O)O

Given the subsequent reaction (reduction with sodium borohydride in methanol followed by acidic workup), I was confused as to the point of trying to generate multiple products: methanol, glycolic acid, and acetic acid.  According to the book, the only product to consider is the middle one: C(=O)CC(=O)O, with the end product (following the aforementioned reduction and subsequent treatment with hot sulfuric acid) being prop-2-enoic acid.  This acid then goes on to be the dienophile in a Diels-Alder reaction.

In reflecting on this, I cannot reason as to why one would discount the methanol and acetic acid, for fear of unwanted ether and/or ester products given the hot and acidic environment once the sulfuric acid is added.

Can someone clarify for me as to why I needn't consider either formaldehyde or acetic acid in the ozonolysis of pent-1-en-4-yne?  Thanks in advance.

« Last Edit: May 01, 2018, 04:56:43 PM by Zalzul »

Offline Mitch

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Re: Ozonolysis of pent-1-en-4-yne
« Reply #1 on: May 01, 2018, 03:56:07 PM »
I think the trick is to stop it from letting the reaction go all the way to completion. It should react with the triple bond first and more often than not.
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Offline Zalzul

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Re: Ozonolysis of pent-1-en-4-yne
« Reply #2 on: May 01, 2018, 04:55:20 PM »
Ah, I see; perhaps then that's what meant by the cold temperature during the ozonolysis step.

Offline Mitch

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Re: Ozonolysis of pent-1-en-4-yne
« Reply #3 on: May 01, 2018, 06:24:45 PM »
That's what caught my eye as well.
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