An organic chemist intends to synthesize the ether 2-ethoxypropane from 2-bromopropane utilizing the — Haloalkanes and Haloarenes Chemistry Question
Question
An organic chemist intends to synthesize the ether 2-ethoxypropane from 2-bromopropane utilizing the standard Williamson ether synthesis. However, the reaction massively fails, yielding a highly significant amount of propene gas instead. How should the chemist specifically modify the reagents to overwhelmingly favour the desired substitution product ($S_N2$) and practically eliminate the troublesome alkene byproduct?
💡 Solution & Explanation
2-Bromopropane is a secondary ($2^\circ$) alkyl halide. When treated with sodium ethoxide (which is both a very strong base and a strong nucleophile), $E2$ elimination aggressively competes with $S_N2$ substitution, producing a massive amount of propene. To synthesize the desired asymmetrical ether efficiently, the chemist must minimize the steric hindrance at the electrophilic carbon to heavily favour $S_N2$. By switching to a primary ($1^\circ$) halide (like 1-bromopropane) while reacting it with the unhindered ethoxide ion, the backside attack becomes kinetically extremely rapid, completely outcompeting the $E2$ pathway. (Option A strongly promotes $E2$. Option C leads entirely to alcohol formation via hydrolysis. Option D at high temperatures heavily promotes $E1$ elimination).