Question

In a lab experiment, Dibenzalacetone was produced from a cross condensation between an Benzaldehyde and Acetone. identify two other base initiated reactions that could conceivably occur involving either or both of these reactants (benzaldeyde and acetone). suggest reasons why these reactions do not result in the formation of large quantities of by products

Answer 1

1. In the first step in this reaction, the cyanide anion (as sodium cyanide) reacts with the benzaldehyde in a nucleophilic addition.

2. Rearrangement of the intermediate results in polarity reversal of the carbonyl group, which then adds to the second carbonyl group in a second nucleophilic addition.

3. Proton transfer and elimination of the cyanide ion leads benzoin as the product.

Another base initiated recation:

acetone reacts with base to give an enolate.

When an enolate forms from an aldehyde, the enolate will normally react with unreacted aldehyde to undergo the "aldol addition" or "aldol condensation" reaction.

Since ketones are less reactive toward nucleophilic addition, the enolate formed from a ketone can be used to react with an aldehyde, a modification called the Claisen-Schmidt reaction.

In cases where the product formed still has a reactive alpha hydrogen and a hydroxide adjacent to an aromatic ring, the reaction will quickly undergo dehydration leading to the condensation product.

These reactions do not lead to large products because they do not undergo to completion but they are reversible reactions and there is always some of the product being converted back to reactants when products are hydrolysed because of abosrbing mositure from atmosphere [or] in cases where water [by product] is not removed as soon as the condensation product is formed