Question

Adding concentrated H2SO4 to alcohol reduces and gives alkene but not oxidise and gives ketone?

Answer 1

I have a compound HO2CCH2CH(OH)CO2H that is added with concentrated H2SO4, I my suggestion the answer should be HO2CCH2COCO2H because secondary alcohol oxidizes to ketones. But the answer came out to be HO2CCH=CHCO2H, which is an alkene. How is it possible? H2SO4 is a reducing agent?

Answer 2

You can NEVER have a primary carbocation.

Answer 3

The mechanism that you have there is a dehydration reaction with a very concentrated (possibly dilute) acid (H2SO4).
Under certain conditions, such as temperature and how concentrated the acid is (dil H2SO4, 85% H3PO4 or 50% H2SO4 etc.,). they each perform different reactions with alcohols.
I can't remember the exact conditions, but I think for primary alcohols, you need dilute H2SO4 and the concentration essentially gets weakers as you go from 1º to 2º and 3º alcohols. From dilute -> 50% -> 25%

Answer 4

Consider this example: