Laurel and John set up identical reactions for the conversion of a-chloro-2, 6-

Question

Laurel and John set up identical reactions for the conversion of a-chloro-2, 6- dimethylacetanilide to alpha (N, N. diethylamino)-2, 6-dimethylacetanilide. The reactions were identical in scale, amounts of reagents and solvents, and source of reactants. After refluxing for one hour, both reactions had gone to 40% completion (40% conversion of starting material to products average rate of 10% per quarter hour). John continued refluxing her reaction whereas Laurel was impatient and decided to distill off the reaction solvent and begin the workup. After distilling away the solvent (this required 15 minutes) and before extractive workup, Laurel checked her reaction and found that it was now 100% converted! She told John who checked his refluxing reaction. John found to his dismay that his reaction had progressed only to 42% conversion (note: at an average rate of 10% per quarter hour, John's should have been at 50%). BRIEFLY explain why Laurel's reaction was complete whereas John's was actually slowing down. Be sure to name the reaction mechanism and state its rate equation.

Explanation / Answer

The rate of the reaction will be,
rate = k [ reactant ]2 the reactant is same as given in the question
It is bi-molecular SN2 type of reaction.
It is told in the question that Laurel distilled off the solvent, this triggered an increase in the
concentration of reactants which in turn increases the rate of the reaction. As the rate of reaction
increases the reaction proceeds towards completion fastly. That is the reason why Laurel's reaction
reached completion whereas John's was actually slowing down.

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