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During acetal/ketal formation and deprotection, the same thing is used essentially which is acid and some sort of alcohol like ethylene glycol. And once deprotection occurs by the use of acid, ethylene glycol would be in solution so it would be essentially the starting material for the protection of a ketone or aldehyde. Is there some sort of external factors that favour acetal/ketal formation and others that favour deprotection or am I missing something here?

M.L
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  • very similar to https://chemistry.stackexchange.com/questions/10722/what-makes-c-o-more-stable-that-coh%e2%82%82 – napstablook Jun 25 '21 at 05:39
  • I don't think it is the same because my question is about protection and deprotection, not essential about the bond stability of the two products of ketone/aldehyde and acetal/ketal – M.L Jun 25 '21 at 05:49
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    acidic medium promotes "deprotection" and basic medium vice versa. This is because H+ in acidic medium makes one of the oxygen linkage a good leaving group enabling the other oxygen to remove it since the carbocation is stable. – napstablook Jun 25 '21 at 05:53
  • But aren't they both done in acidic medium? – M.L Jun 25 '21 at 05:56
  • no only "deprotection" is done in acidic medium. acetals are pretty unstable in acidic medium. – napstablook Jun 25 '21 at 05:56
  • Wait then why do most mechanisms involve H3O+ in acetal formation. – M.L Jun 25 '21 at 06:00
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    The protection is done in anhydrous acidic media often with removal of water (D-S reflux). The deprotection is done in aqueous so that the molecules of alcohol/glycol that are removed are vastly outnumbered by the water present and there is very little chance of the acetal reforming. – Waylander Jun 25 '21 at 06:52

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