Hydrolysis of acetals to give aldehydes and ketones

Description: Addition of aqueous acid to acetals will transform them into ketones (or aldehydes)

Notes:

Acid may be written simply as “H+” . Many different acids will suffice here.
The reaction is an equilibrium. Alcohol (R’–OH here) is generally used as the solvent. Since it is present in vastly greater excess relative to waterthe reverse reaction is negligible. Because it’s assumed that alcohol is the solvent, you won’t often see “2 equiv” as you do here.
Acid is catalytic
The reaction can be used to “protect” the carbonyl against attack, since acetals are not reactive.

Examples:

Notes: Example 3 is an example where both alcohols come from the same molecule, this makes a cyclic acetal

Mechanism: The reaction begins by protonation of one of the oxygens of the acetal (Step 1, arrows A and B), which makes a better leaving group, 1,2-elimination of the alcohol (Step 2, arrows C and D) leads to an oxonium ion, which is then attacked by water in a 1,2-addition (Step 3, arrows E and F). Proton transfer from water to alcohol (Step 4, arrows G and H) again makes the alcohol a better leaving group, which is displaced through 1,2-elimination (Step 5, arrows I and J) forming a protonated ketone. This is then deprotonated (Step 6, arrows K and L) to give the neutral ketone.

Notes:

There are other reasonable mechanisms for proton transfer in step 3.
Furthermore there are several other species that could act as bases in step 6. TsO(–) is chosen for simplicity.
Although each step is reversible, single arrows are shown here for simplicity.