Question

The Claisen-Schmidt type reaction is a variant of the aldol condensation and an example of an addition-elimination where carbon acids function as nucleophiles reacting with unsaturated carbon centered electrophiles. Consider the acid catalyzed reaction of the two reactants below. Describe the mechanism and products of such a reaction.

(CH3)3C-C(=0)-CH2 + C6H5CH=0

Describe the mechanism and products in words please.

Answer 1

First, in the presence of an acid, tert-butyl methyl ketone will undergo enolisation and then the enol via its nucleophilic carbanion center attack the electrophilic carbon atom of the ketonic group in aromatic aldehyde. n elimination, it gives α,β-unsaturated carbonyl compound.

Note: Aromatic aldehyde is more electrophilic than the aliphatic ketone one because

a. ph has its electron withdrawing effect.

b. the aldehydic C atom is more electrophilic than that of ketone.

Note: A reaction between two different carbonyl compounds gives an aldol product or α,β-unsaturated product is named as the crossed aldol condensation. The disadvantage of this reaction is that it produces mixture of products. To overcome this limitation of formation of a mixture of products one of the carbonyl compounds used should be chosen in such a way that it won’t have any alpha-hydrogen atoms. Such a crossed aldol condensation is called the Claisen-Schmidt condensation. In such a case, a smaller number of different products will be formed and only one of them will be the major product.