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In preparation of alkene from alcohol using $Al_2O_3$ which is effective factor : -
A
Porosity of $Al_2O_3$
B
Temperature
C
Concentration
D
Surface area of $Al_2O_3$
Detailed Solution
When alcohol vapour is passed over heated alumina, it is dehydrated. The product depends mainly on the temperature:
At about 523 K (250 °C), intermolecular dehydration gives an ether: $2C_2H_5OH \xrightarrow{Al_2O_3,\ 523\ K} C_2H_5OC_2H_5 + H_2O$
At about 633 K (360 °C), intramolecular dehydration gives an alkene: $C_2H_5OH \xrightarrow{Al_2O_3,\ 633\ K} CH_2=CH_2 + H_2O$
So temperature is the effective factor that decides whether an alkene is formed.
At about 523 K (250 °C), intermolecular dehydration gives an ether: $2C_2H_5OH \xrightarrow{Al_2O_3,\ 523\ K} C_2H_5OC_2H_5 + H_2O$
At about 633 K (360 °C), intramolecular dehydration gives an alkene: $C_2H_5OH \xrightarrow{Al_2O_3,\ 633\ K} CH_2=CH_2 + H_2O$
So temperature is the effective factor that decides whether an alkene is formed.