When HI is in excess and the reaction is carried out at high temperature,
ethanol reacts with another molecule of HI and is converted to ethyl iodide Step 3:
Mechanism
Mechanism
Mechanism
Mechanism
Mechanism
However, when one of the alkyl group is a tertiary group, the halide
formed is a tertiary halide CH
C
CH +HI
CH OH +CH
C
I
3
3
3
3
CH3
CH3
CH3
CH3
O
It is because in step 2 of the reaction, the departure of leaving group
(HO–CH3) creates a more stable carbocation [(CH3)3C
+], and the reaction
follows SN1 mechanism In case of anisole, methylphenyl
oxonium ion, 
 is
formed by protonation of ether