When vapours of a secondary alcohol are passed over heated copper at 573 K, the alcohol undergoes dehydrogenation (removal of hydrogen). The molecule loses one hydrogen atom from the hydroxyl group (-OH) and one from the alpha-carbon atom, forming a ketone.

Reaction: $R-CH(OH)-R' \xrightarrow{Cu, 573 K} R-CO-R' + H_2$

Comparison:

• Primary alcohols under the same conditions form aldehydes.
• Tertiary alcohols undergo dehydration to form alkenes because they lack an alpha-hydrogen.