Write the name of the reagent to transform Allyl alcohol to Propanal.
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Solution and Explanation
Step 1: Look at what must change
Allyl alcohol is $\mathrm{CH_2{=}CH{-}CH_2OH}$. Propanal is $\mathrm{CH_3CH_2CHO}$. So the double bond must go away, and the $\mathrm{-CH_2OH}$ must become a $\mathrm{-CHO}$.
Step 2: Remove the double bond
First we add hydrogen across the $\mathrm{C{=}C}$ using $\mathrm{H_2}$ with a palladium catalyst $\mathrm{(H_2/Pd)}$. This gives n-propanol $\mathrm{CH_3CH_2CH_2OH}$.
Step 3: Oxidise gently to the aldehyde
Now we oxidise the primary alcohol, but only mildly, so it stops at the aldehyde and does not go all the way to an acid. PCC (pyridinium chlorochromate) is the gentle oxidant that does this, giving propanal.
Answer: First $\mathrm{H_2/Pd}$ to reduce the double bond, then PCC to oxidise gently, giving propanal.
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