I asked this same question about 7 months back..Didnt get a reply
Asking again.....
In case of 2,4-dinitoalkylbenxene ,if NH4HS or Na2S is used as reducing agent,nitro group at para position is reduced ,while if SnCl2/HCl is used then nitro group at ortho position is reduced.WHY ???
1SEE IF IT HELPS
Actually , SnCl2/HCl is a reagent used for selective reduction. here , at ortho position if NO2
is attacked, then some benzaldehyde is formed. thus the deactivating group nearer to the alkyl group ( activating ) is now converted into an activating group. thus,this phenomenon is supported.
but,Na2S is perhaps not a hydrogenating reducing agent, it attacks the oxy-atom of nitro group at para position.
1presence of an methyl group at ortho position make the nitro group out of plane so that the attack of the H+ becomes easier while in later it is just the less hindered position
