Chloroarenes (aryl chlorides) and bromoarenes (aryl bromides) can be easily prepared by direct chlorination or bromination of benzene or other aromatic hydrocarbons. These reactions are carried out in dark, at ordinary temperatures (310–320 K) in the presence of Lewis acid catalyst such as anhydrous ferric or aluminium halides (FeCl₃, FeBr₃, AlCl₃). These reactions are called electrophilic substitution of arenes. The Lewis acid acts as a catalyst and its function is to carry the halogen to the aromatic hydrocarbon and is also called halogen carrier. In actual practice, iron filings in the presence of chlorine or bromine are commonly used. The halogens react with iron filings to form corresponding Lewis acids.

Which derivative has pharmaceutical or dyeing properties?

Bromine

The correct answer is option 3. Bromine.

The bromine derivative sometimes has certain advantages because of the greater ease in effecting the replacement of this halogen in subsequent reactions or because it possesses certain pharmaceutical or dyeing properties.

Bromine is a more reactive halogen than iodine, so it is easier to replace bromine with another element in subsequent reactions. This makes bromine derivatives more versatile than iodine derivatives.

Bromine also has certain pharmaceutical and dyeing properties that iodine does not have. For example, bromine derivatives are used in the production of antiseptics, disinfectants, and dyes.

Therefore, bromine derivatives sometimes have certain advantages over iodine derivatives because of their greater reactivity and their pharmaceutical or dyeing properties.

Here are some examples of bromine derivatives that have pharmaceutical or dyeing properties:

Iodoform (CHI₃) is a yellow, crystalline compound that has antiseptic properties. It is used to treat cuts and scrapes.

Bromothymol blue is a dye that is used to test for acids and bases. It is a blue dye in acidic solutions and a yellow dye in basic solutions.

P-Bromoaniline is a compound that is used to make dyes. It is a colorless solid that turns yellow when it is exposed to light.

These are just a few examples of the many bromine derivatives that have pharmaceutical or dyeing properties.