How would you synthesize #N#-methylacetamide from methyl bromide and any other inorganic reagents?

1 Answer
Jan 18, 2016

First we do a retrosynthesis, and then we do the synthesis.

Explanation:

A. Retrosynthesis (Planning a synthesis backwards)

The target molecule is #"CH"_3"CONHCH"_3# (an amide).

How to make an amide? From an amine!

#"CH"_3"CONHCH"_3 ⇒ "CH"_3"CO"^+ + ""^(-)"NHCH"_3color(white)(l)("CH"_3"CO-Cl" + "H-NHCH"_3)#

How to make an acid chloride? From the acid!

#"CH"_3"COCl" ⇒ "CH"_3"CO"^+ + "Cl"^(-) ("CH"_3"CO-OH" + "Cl-SOCl")#

How to make a carboxylic acid? From a Grignard plus #"CO"_2#!

#"CH"_3"COOH" ⇒ "CH"_3^(-) + ^(-)"COOH"color(white)(l)("CH"_3"-MgBr" + "CO"_2)#

How to make the Grignard? From methyl bromide!

#"CH"_3"MgBr" ⇒ "CH"_3^(-) + ""^+"MgBr"color(white)(l)("CH"_3"-Br" + "Mg")#

How do we make a substituted amine? From an alkyl halide and ammonia!

#"CH"_3"NH"_2 ⇒ "CH"_3^+ + ""^(-)"NH"_2color(white)(l)("CH"_3"-Br" + "H-NH"_2)#

B. Synthesis (Putting it all together)

#"CH"_3"Br" stackrelcolor(blue)("NH"_3color(white)(X))(→) "CH"_3"NH"_2 #

#"CH"_3"Br" stackrelcolor(blue)("Mg/Dry ether"color(white)(Xl))(→) "CH"_3"MgBr"#

#"CH"_3"MgBr" stackrelcolor(blue)("1. CO"_2; 2. "H"^+color(white)(Xl))(→) "CH"_3"COOH"#

#"CH"_3"COOH" stackrelcolor(blue)("SOCl"_2color(white)(Xl))(→) "CH"_3"COCl"#

#"CH"_3"COCl" + "CH"_3"NH"_2 → "CH"_3"CONHCH"_3#

And we did it using only #"CH"_3"Br"# and other inorganic reactants!