Question

Ethers are prepared by the reaction of sodium alkoxides and alkyl halides . Which of the following reagents should be taken to prepare methyl tert - butyl ether?

• A. $(C{H}_3{)}_{3}C-Br+NaOC{H}_3$
• B. $C{H}_{3}Br+NaOC(C{H}_3{)}_3$
• C. $C{H}_{3}C{H}_{2}Br+NaOC(C{H}_3{)}_2$
• D. $(C{H}_3{)}_{2}C-Br+NaOC{H}_{2}C{H}_3$

Answer 1

The correct option is B $C{H}_{3}Br+NaOC(C{H}_3{)}_3$

The Williamson ether synthesis is an organic reaction, forming an ether from an organohalide and a deprotonated alcohol (alkoxide). It involves the reaction of an alkoxide ion with a primary alkyl halide via an $S_{N}2$ reaction as:

$RONa+R^{\prime }X\to RO{R}^{\prime }$

Since the reaction is $S_{N}2$, the alkyl halide preferably be primary or halide should be least hindered so that alkoxide can easily attack as nucleophile and substitute halide. In case of primary alkoxide, it will act as strong base and the alkyl halide will thus undergo elimination instead of substitution an will result in alkene formation.

For methyl tert-butyl ether i.e. $C{H}_3-O-\stackrel{\underset{|}{C{H}_3}}{\underset{\stackrel{|}{C{H}_3}}{C}}-C{H}_3$

thus for reaction to follow $S_{N}2$ it should be:

$C{H}_{3}Br+NaO-\stackrel{\underset{|}{C{H}_3}}{\underset{\stackrel{|}{C{H}_3}}{C}}-C{H}_3\to C{H}_3-O-\stackrel{\underset{|}{C{H}_3}}{\underset{\stackrel{|}{C{H}_3}}{C}}-C{H}_3$

and $C{H}_{3}ONa+Br-\stackrel{\underset{|}{C{H}_3}}{\underset{\stackrel{|}{C{H}_3}}{C}}-C{H}_3\to \stackrel{\underset{||}{C{H}_2}}{\underset{\stackrel{|}{C{H}_3}}{C}}-C{H}_3$

Therefore, $C{H}_{3}Br+NaOC(C{H}_3{)}_3$ should be taken to prepare methyl tert - butyl ether