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Question: Aldol condensation between which of the following two compounds followed by dehydration gives methyl...

Aldol condensation between which of the following two compounds followed by dehydration gives methyl vinyl ketone?
A.Formaldehyde and acetone
B.Formaldehyde and acetaldehyde
C.Two molecules of acetone
D.Two molecules of acetaldehyde

Explanation

Solution

In order to find an answer to this question, we have to see the aldol condensation reaction that gives vinyl ketone as the product. This type of reaction occurs only in compounds having alpha hydrogen and alpha carbon. This is a type of electrophilic substitution reaction.

Complete step by step answer:
Let us first learn about aldol condensation;
The condensation of Aldol happens only in carbonyl compounds containing alpha hydrogen. Aldehydes and ketones are carbonyl-compounds. Such alpha hydrogen is acidic, so the bases are quickly removed and carbanion is given. Then this carbanion reacts to give the aldol product with another carbonyl molecule.
Let us look into the aldol condensation reaction of the first option which is formaldehyde and acetone;
 CH2O+CH3COCH3→HOCH2−CH2−CO−CH3 \,C{H_2}O + CH_3COC{H_3} \to HOCH_2 - C{H_2} - CO - C{H_3}\,
Here, when this product is heated;
 HOCH2−CH2−CO−CH3→ΔCH2=CH−CO−CH3 \,HOC{H_2} - C{H_2} - CO - C{H_3}\xrightarrow{\Delta }C{H_2} = CH - CO - C{H_3}\,
We get vinyl ketone as the product. So, this option is correct.
In option B, crossed aldol condensation occurs between formaldehyde and acetaldehyde and the product formed is  3−hydroxy propanal \,3 - hydroxy\,propanal\,. Hence, this is not the correct answer.
In option C, Aldol condensation product of two acetone yields  4−methyl−pent−3−en−2−one \,4 - methyl - pent - 3 - en - 2 - one\, Hence, this option is also not correct.
In option D, the aldol condensation of two acetaldehydes result in the formation of  CH3−CH(OH)−CH2−CHO \,C{H_3} - CH(OH) - C{H_2} - CHO\,. Hence, this is also not the correct option.

Hence, option A is the correct answer.

Additional information: Crossed aldol condensation is a variation of aldol condensation in which the condensation reaction is undergone jointly by two separate carbonyl compounds each having alpha hydrogens. Up to four different products can be formed in such reactions.
For the direct conversion of syngas and propene into  2− \,2 - \, ethyl hexanol, the Aldox procedure is an industrial modification of the aldol condensation reaction. This compound is formed by hydroformylation of the butyraldehyde reactants, subsequent condensation of the aldol into  2− \,2 - \, ethyl hexane and hydrogenation of the reactant into  2− \,2 - \, ethyl hexanol

Note:
Only aldehydes having at least one alpha hydrogen or alpha carbon can undergo aldol condensation. Formaldehyde, for example, does not contain alpha carbon. However, as it cannot undergo self-aldol condensation, acetone helps it to initiate the electrophilic reaction.