Which of the following alcohol vapours passed over heated heavy metal catalyst Cu does not give aldehydes and ketones ?

Question

Accepted Answer

Option 2, $(CH_{3})_{3}C-OH$, is the correct answer because it is tert-butyl alcohol, a tertiary alcohol. When tertiary alcohols are passed over a heated heavy metal catalyst like copper (Cu), they do not undergo dehydrogenation to form aldehydes or ketones. Instead, they tend to undergo dehydration to form alkenes. This is due to the stability of the tertiary carbocation formed during the reaction, which favors elimination over oxidation.

Now, let's examine why the other options are incorrect:

1. **Option 1: $CH_{3}CH_{2}OH$ (Ethanol)**  
   Ethanol is a primary alcohol. When passed over a heated copper catalyst, primary alcohols typically undergo dehydrogenation to form aldehydes. In this case, ethanol would be converted to acetaldehyde ($CH_{3}CHO$).

2. **Option 3: $(CH_{3})_{2}CHOH$ (Isopropanol)**  
   Isopropanol is a secondary alcohol. Secondary alcohols, when passed over a heated copper catalyst, are dehydrogenated to form ketones. Isopropanol would be converted to acetone ($(CH_{3})_{2}CO$).

3. **Option 4: $CH_{3}CH_{2}CH_{2}OH$ (Propanol)**  
   Propanol is another primary alcohol. Similar to ethanol, when passed over a heated copper catalyst, it undergoes dehydrogenation to form an aldehyde. Propanol would be converted to propionaldehyde ($CH_{3}CH_{2}CHO$).

In summary, Option 2 is the correct answer because tert-butyl alcohol does not form aldehydes or ketones when passed over a heated copper catalyst, unlike the other alcohols listed, which do undergo such transformations.