Question

Catalytic dehydrogenation of primary alcohol gives a:
A) secondary alcohol
B) aldehyde
C) ketone
D) ester

Answer 1

Hint:
Dehydrogenation is a process that leads to the removal of hydrogen. This process is meant for only the removal of one or more hydrogens. This is an elimination reaction and for dehydrogenation of a primary alcohol, it involves $E2$ elimination.

Complete answer:
1) The catalytic reaction involves the use of a catalyst such as metal surface which in this case is copper.
2) When the vapors of primary alcohol are passed through a heated copper metal surface it gives product as mechanized bellow:
$C{H}_{3}C{H}_2-OH\underset{\mathrm{\Delta }}{\overset{Cu/{300}^{\circ }c}{\to }}C{H}_3-CHO+H_2$
3) In the above reaction, the copper metal surface is used as a catalyst in presence of heat which gives aldehyde as the main product, and hydrogen is removed as a dehydrogenated product.
4) There is no further reaction that happens once the aldehyde is formed in the reaction product.

Hence, option B will be the correct answer.

Additional information:
This is a type of endothermic reaction and it requires appropriate heat input for further reaction. Catalytic dehydrogenation reactions can be done by using different catalysts such as silver metal catalysts in presence of oxygen which convert primary alcohol into an aldehyde. This same reaction can be done in absence of oxygen by using a palladium or platinum catalyst. These reactions are followed to form fine chemicals and good product yield. In this type of reaction pressure increases and decreases during the conversion. This reaction is also preferred at high temperatures.

Note:
The dehydrogenation type of reaction involves the removal of hydrogen that is why it is also called an oxidation reaction. Hence, one can use this concept to solve questions as primary alcohols when oxidized gives the aldehyde as a product.