Question

When light is shined on a mixture of chlorine and ethane, chloroethane is formed besides dichloroethane, trichloroethane and several other products. What reaction condition can optimize the yield of chloroethane?

• A. Higher reaction temperature
• B. High concentration of chlorine gas
• C. Excess of ethane reactant
• D. Low reaction temperature

Answer 1

The correct option is C Excess of ethane reactant

The propogation steps in free radical halogenation of ethane will be:
$C{H}_{3}C{H}_3+C{l}^{\ast }\to C{H}_3-\stackrel{\ast }{C}{H}_2+HCl$ ...(i)
$C{H}_3\stackrel{\ast }{C}{H}_2+C{l}_2\to C{H}_3-C{H}_2-Cl+C{l}^{\ast }$ ...(ii)
Taking excess of ethane (alkane) increases the probability of H-abstraction of ethane in step (i) above, otherwise H-abstraction from previously formed chloroethane also occurs significantly forming di, tri and polychlorinated products.