Question

They yield of acid amide in the reaction, $RCOCl+N{H}_3\to RCON{H}_2$ , is maximum when

• A. Acid chloride and ammonia are treated in equimolar ratio
• B. Acid chloride and ammonia are treated in 1 : 2 molar ratio
• C. Acid chloride and ammonia are treated in 2 : 1 molar ratio
• D. All the three gives nearly similar result

Answer 1

The correct option is B

Acid chloride and ammonia are treated in 1 : 2 molar ratio

For the complete conversion of an acid chloride molecules into acid amide, ammonia should be used 1 : 2 molar raio : because one molecule of ammonia acts a nucleophile while the other as a Bronsted base to remove the acid formed during the reaction.
$RCOCl+N{H}_3\to RCON{H}_2+HCl\frac{HCl+N{H}_3\to N{H}_{4}Cl}{RCOCl+2N{H}_3\to RCON{H}_2+N{H}_{4}Cl}$
In case the two reactants are taken in 1 : 1 molar ratio, one half of acid chloride will remain unreacted.
$RCOCl+N{H}_3\to \frac{1}{2}RCON{H}_2+\frac{1}{2}N{H}_{4}Cl+\frac{1}{2}RCOCl$
However, the above reaction can be forced to completion if it is carried out in presence of some other base, like NaOH, which reacts with the acid formed and thus allowing the whole $N{H}_3$ a weaker base to react only with RCOCl.
$RCOCl+N{H}_3\stackrel{NaOH}{\to }RCON{H}_2+NaCl+H_{2}O$