Is an acid catalyzed hydro-alkoxy addition the same as an acid-catalyzed alkoxyation?
1 Answer
Assuming by "acid-catalyzed hydro-alkoxy addition", you mean the alkoxy addition catalyzed by protonated water (
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In an acid-catalyzed alkoxylation, the water is protonated by some strong acid such as
#H_2SO_4# . -
The alkene or alkyne breaks a pi bond, sends an electron for the proton, and deprotonates the water so that it's just water again, gaining one proton.
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For Alkenes:
Then, the alkoxide, seeing the carbon adjacent to the carbon that just donated a pi electron as cationic and electrophilic, acts as a good enough nucleophile that it can attach onto the cationic, less-substituted site (standard, Markovnikov addition).
For Alkynes:
Then, the alkoxide, seeing that an unstable triangular pi-bond-banana-bond complex formed, attacks the less substituted carbon (standard, Markovnikov addition) and attaches to improve the stability of the molecule. -
After attaching, the alkoxide is considered protonated (and cationic), so the previously-discussed, unprotonated water comes in and deprotonates the alkoxide, finishing the mechanism and regenerating the acid catalyst that began the reaction.