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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Zalzul on May 01, 2018, 03:12:39 PM

Title: Ozonolysis of pent-1-en-4-yne
Post by: Zalzul 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.

Title: Re: Ozonolysis of pent-1-en-4-yne
Post by: Mitch 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.
Title: Re: Ozonolysis of pent-1-en-4-yne
Post by: Zalzul 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.
Title: Re: Ozonolysis of pent-1-en-4-yne
Post by: Mitch on May 01, 2018, 06:24:45 PM
That's what caught my eye as well.