Question

Using your roadmaps as a guide, show how to convert acetaldehyde into racemic 3-hydroxybutanal. You must use acetaldehyde as the source of all carbon atoms in the target molecule. Show all reagents and all molecules synthesized along the way.

Short answer

Answer: The synthesis of racemic 3-hydroxybutanal from acetaldehyde requires a single-step aldol condensation reaction in the presence of an aqueous base, such as NaOH. This reaction leads to dimerization of acetaldehyde, forming the desired product (3-hydroxybutanal) directly.

Step-by-step solution

Dimerization of Acetaldehyde

To obtain a molecule with four carbon atoms, we have to perform a dimerization of acetaldehyde. This can be done via an aldol condensation, where two acetaldehyde molecules react together in the presence of an aqueous base (such as NaOH) to form 3-hydroxybutanal directly. The reaction is as follows: 2 CH3CHO + NaOH → HOCH2CH2CH(OH)CHO + H2O

Isomerize to the desired product

Since the aldol condensation reaction generates the desired target molecule in a single step, no further reaction is necessary. However, the product obtained from the one-step aldol condensation will be racemic, as both the pro-R and pro-S hydrogen atoms at the alpha position (adjacent to the carbonyl group) can be removed by the base, leading to the formation of a new C-C bond. In conclusion, the synthesis of racemic 3-hydroxybutanal from acetaldehyde only requires a single step process that is an aldol condensation with the presence of an aqueous base such as NaOH.