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Question: Maximum number of molecules of methyl iodide that can react with one molecule of methylamine is: A...

Maximum number of molecules of methyl iodide that can react with one molecule of methylamine is:
A) 4{\text{4}}
B) 3{\text{3}}
C) 2{\text{2}}
D) 1{\text{1}}

Explanation

Solution

Hint- It is important to highlight that the methyl iodide is reacted with only one molecule of methylamine. One can draw the reaction for each step until the reaction stops and calculate the molecule's methyl iodide which is consumed in the reaction.

Complete step by step answer:

  1. First of all let's learn about the reaction and write the reaction stepwise. The first step of the reaction is as below,
    CH3−NH2→CH3−ICH3−NH−CH3C{H_3} - N{H_2}\xrightarrow{{C{H_3} - I}}C{H_3} - NH - C{H_3}
    In the above first step, one molecule of methyl iodide is used which reacts with the methylamine and replaces the one hydrogen atom from the amine group, and forms the dimethylamine as a product.

  2. Now the second step will go as below,
    CH3−NH−CH3→CH3−ICH3−N(CH3)−CH3C{H_3} - NH - C{H_3}\xrightarrow{{C{H_3} - I}}C{H_3} - N(C{H_3}) - C{H_3}
    In the above second step of the reaction, the second methylamine molecule is used which reacts with the dimethylamine and replaces the one hydrogen from the amine group with the methyl group and forms the trimethylamine as a product.

  3. Now the third step will go as below,
    CH3−N(CH3)−CH3→CH3ICH3−(I−)N+(CH3)−CH3C{H_3} - N(C{H_3}) - C{H_3}\xrightarrow{{C{H_3}I}}C{H_3} - ({I^ - }){N^ + }(C{H_3}) - C{H_3}
    In the above third step, there is the consumption of the third methyl iodide molecule which is used to react with the trimethylamine group. In this reaction, the nitrogen atom in the trimethylamine group is attacked by the negatively charged halogen that is iodine and there is the formation of the ionic complex as quaternary salt. The reaction stops after the formation of quaternary salt.

  4. There are three molecules of methyl iodide that are consumed. Therefore, the maximum number of molecules of methyl iodide that can react with one molecule of methylamine is 3{\text{3}}

Therefore, the correct option is B

Note:
The quaternary salt formed is called tetramethyl ammonium iodide. In this product, there are partial positive and negative charges that are present on nitrogen and iodine respectively. As the product formed is tertiary amine which is a polar molecule it forms the ionic bond with the iodine.