Dat Destroyer Aldo Condensation question

[Mrhyde]

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Organic Chem Number 72. )

I have read that Aldo condensations can undergo spontaneous dehydration Even when heat is not listed as a next step. Aldos can dehydrate under acidic, basic, or thermal (heat) ......So I picked answer E , the conjugated , dehydrated more stable form as the Major product----------But the answer chosen as correct was D, the hydrated form.

 

[DAT Destroyer]

Organic Chem Number 72. )

I have read that Aldo condensations can undergo spontaneous dehydration Even when heat is not listed as a next step. Aldos can dehydrate under acidic, basic, or thermal (heat) ......So I picked answer E , the conjugated , dehydrated more stable form as the Major product----------But the answer chosen as correct was D, the hydrated form.

Lets go over the facts.....An Aldol reaction will normally lead to a beta hydroxyaldehyde or ketone, which can then be dehydrated with the addition of heat. We can get dehydration if we use ACID to catalyze the reaction. In base, it stops cleanly before losing water. HOWEVER.....if you are near an Aromatic system, then you are correct, we get the conjugated specie via a dehydration. In this reaction, we do NOT dehydrate. After doing this reaction for over 30 years, I assure you that heating needs to be done !!! If you go to the second addition of the Dr. David Klein text on page 1057, a very similar reaction using butanal was done under these EXACT conditions. Dr.Klein got a 75% yield of the hydroxyl aldehyde.

Hope this helps

Dr. Jim Romano