Reactions of alcohol/ethers with hydrogen halides [duplicate]








**This question already has an answer here**:
 
 




[Ether cleavage with conc HBr](/questions/32102/ether-cleavage-with-conc-hbr)

 (1 answer)
 

Closed 6 years ago.



General equation - 


Alcohol - $\ce{ROH + HX -> RX + H2O} $ 


Ethers - $\ce{ROR + HX -> RX + ROH} $


I've been told that X = $\ce{Cl-}$ , $\ce{Br-}$ , $\ce{I-}$


Then I wonder ... 


* How Cl , Br and I nucleophile is going to Attack OH ?


All of the 3 are weaker nucleophile than OH as well as a better leaving group. So ... 


* How does it replace and substitute OH ?


Or 


* OR (with ethers)?




This reaction generally takes place in an environment where there are free $\ce{H3O+}$ ions. The oxygen atom in the alcohol or ether takes up $\ce{H+}$ from these ions. Now the leaving group is $\ce{H\bond{-}O+\bond{-}H}$ or $\ce{H\bond{-}O+\bond{-}R}$ which are much better leaving groups than $\ce{O\bond{-}H}$ or $\ce{O\bond{-}R}$. This makes the substitution of the halide ions easier.


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