Carboxylic acids having an a-hydrogen are halogenated at the α-position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give α-halocarboxylic acids. The reaction is known as Hell-Volhard-Zelinsky reaction.

What happens when Propionic acid reacts with two molecules of bromine in the presence of red phosphorus? 

α,α-Dibromopropionic acid 

The correct answer is option 2. α,α-Dibromopropionic acid.

When propionic acid reacts with two molecules of bromine in the presence of red phosphorus, a substitution reaction known as the Hell-Volhard-Zelinsky (HVZ) reaction occurs. This reaction specifically brominates the alpha position of carboxylic acids.

The presence of excess bromine and red phosphorus facilitates further bromination, replacing the second hydrogen atom at the alpha position with another bromine atom to form α,α-dibromopropionic acid.

The final product is α,α-dibromopropionic acid (\( \text{CH}_3\text{CBr}_2\text{COOH} \)).When propionic acid reacts with two molecules of bromine in the presence of red phosphorus, the product formed is α,α-dibromopropionic acid. Therefore, the correct answer is α,α-Dibromopropionic acid.