Butane conjugated molecule

A typical example treats butanal (21) with NaOEt in refluxing ethanol, and an aqueous acid second step (known as a reaction workup) gives 22 in 75% yield. This new product contains eight carbons and it is clear that one molecule of the aldehyde must react with a second molecule of the same aldehyde. When the reaction is repeated, but treated in the second step with hot and concentrated acid, a conjugated aldehyde product (23) is formed in over 90% yield, and it also contains eight carbons. If 22 is isolated, purified, and then heated with aqueous acid, 23 is the product. 

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