Question

(i) In the presence of light, chloroform is slowly oxidised by air to an extremely poisonous gas called ________.
(ii) How is chlorobenzene converted into 1-chloro-2-methyl benzene?

• A.
• B.
• C.
• D.

Hint:

Remember: Friedel-Crafts reactions require a Lewis acid catalyst like anhydrous $\textAlCl_3$ to generate the electrophile ($\textCH_3+$ in this case).

Answer 1

The Correct Option is A

Concept: The question covers the chemical stability of haloalkanes and the electrophilic substitution of haloarenes: Oxidation of Chloroform: Chloroform ($\textCHCl_3$) is sensitive to light and air, undergoing a radical reaction to form a toxic gas. Friedel-Crafts Alkylation: An electrophilic substitution reaction where an alkyl group is introduced into the benzene ring in the presence of a Lewis acid catalyst.
Step 1: Oxidation of Chloroform.\ Chloroform reacts with atmospheric oxygen in the presence of light to produce Phosgene ($\textCOCl_2$), which is highly toxic. $$ 2\textCHCl_3 + \textO_2 \xrightarrow\textlight 2\textCOCl_2 + 2\textHCl $$ To prevent this, chloroform is stored in dark-colored bottles and often mixed with a small amount of ethanol, which converts phosgene into harmless diethyl carbonate.
Step 2: Conversion of Chlorobenzene.\ To convert chlorobenzene into 1-chloro-2-methyl benzene (o-chlorotoluene), we use methyl chloride in the presence of anhydrous $\textAlCl_3$. Since the chlorine atom on the ring is ortho-para directing, a mixture of ortho and para isomers is formed. $$ \textC_6\textH_5\textCl + \textCH_3\textCl \xrightarrow\textanh. AlCl_3 \texto-chlorotoluene + \textp-chlorotoluene $$ 1-chloro-2-methyl benzene is the ortho product.