Question

write two preparation of alkenes​

Answer 1

1) Alkenes can be prepared by the Dehydration of alcohols by concentrated Sulphuric acid acid at 170 °C or with Al2O3 as a dehydrating agent at 350°C .    

                Al2O3/350°C

C2H5OH ------------------> C2H4 + H-OH

2) Alkenes can also be prepared by a process called Dehydrohalogenation. This is done by reacting alcoholic KOH (with Ethanol) with an alkyl chloride.

It involves removal of a hydrogen and halogen atom from the Alkyl halide.

This reaction takes place at room temperatures.

                                                                (room temperature)

C2H5Br(Bromoethane) + KOH(alcoholic) ---------> C2H4 + KBr + H-OH