Question

Dehydration of tertiary alcohols with Cu at 573 K gives :

• A. Ketones
• B. Alkenes
• C. Aldehydes
• D. Carboxylic acid

Hint:

A tertiary alcohol has no hydrogen on the carbinol carbon, so over Cu at 573 K it loses water and gives an alkene.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
When alcohol vapour is passed over heated copper at 573 K, the reaction depends on the type of alcohol.
Primary and secondary alcohols lose hydrogen. Tertiary alcohols behave differently.

Step 2: Reaction of each type:
A primary alcohol gives an aldehyde. \[ \mathrm{RCH_2OH} \xrightarrow{\mathrm{Cu,\ 573\ K}} \mathrm{RCHO + H_2} \]
A secondary alcohol gives a ketone. \[ \mathrm{R_2CHOH} \xrightarrow{\mathrm{Cu,\ 573\ K}} \mathrm{R_2C{=}O + H_2} \]

Step 3: Tertiary alcohol:
A tertiary alcohol has no hydrogen on the carbon that carries the OH group. So it cannot form a C=O bond.
It loses a water molecule instead and forms an alkene. \[ \mathrm{(CH_3)_3C{-}OH} \xrightarrow{\mathrm{Cu,\ 573\ K}} \mathrm{(CH_3)_2C{=}CH_2 + H_2O} \]

Step 4: Why the other options are wrong.
Ketones come from secondary alcohols. Aldehydes come from primary alcohols. A carboxylic acid needs a strong oxidising agent and a primary alcohol, and Cu at 573 K does not give it.

Final Answer:
Tertiary alcohols give alkenes, which is option (B).\[ \boxed{\text{Alkenes}} \]