Question

$B{F}_3$ is used as catalyst in several industrial processes due to its:

• A. strong reducing nature.
• B. weak reducing action.
• C. strong Lewis acid nature.
• D. weak Lewis acid character.

Answer 1

Answer: (C)

strong Lewis acid nature.

The boron trihalides are covalent in nature and exist as monomeric molecules having planar triangular geometry. In these halides, boron assumes $s{p}^2$ hybrid state and the three $B-X$ bonds are formed by the axial overlap of $s{p}^2$ hybrid orbital of boron and p-orbital of halogen as shown in Fig. Since there are only six electrons in the valence shell of a boron atom in boron trihalides, therefore, they have a great tendency to accept two more electrons in order to acquire stable octet.

Hence, boron trihalides act as Lewis acids. They rapidly combine with electron donors such as $N{H}_3,F^{-}ion$, amines, ether, sulphides or phosphorus.