Snoop Dog performs a recrystallization of N-bromosuccinimide (NBS, MP-175 degree

Question

Snoop Dog performs a recrystallization of N-bromosuccinimide (NBS, MP-175 degrees C) in ethanol. Instead of adding boiling ethanol slowly to the flask containing NBS as instructed, he adds his impure NBS directly to a flask containing 50 mL of boiling ethanol. The NBS dissolves immediately. Snoop Dog removes the NBS solution from the hot plate. Once the flask has cooled to room temperature, he transfers it to an ice bath, but even after prolonged cooling no crystals form. What hypotheses could explain the lack of crystal formation? Check all that apply. Snoop Dog added too much ethanol. Snoop Dog added too little ethanol. The NBS boiled away O The NBS melted Ethanol may not be an appropriate recrystallization solvent

Explanation / Answer

First of all ,known recrystaling solvents for NBS are water or acetic acid. So, there can be two possibilities concluded, one ethanol taken in excess which prevents recrystalization else choice of solvent( ethanol) used for recrystalization.

Further, 152-157 melting point has been found which indicates the presence p-chloro benzoic acid isomer (impure 3 isomer) with 3-chloro benzoic acid impurity.Since, by adding impurity there is depression in melting point not the elevation so the presence of first isomer (2-chloro benzoic acid) can be ruled out easily as its mp=138-140. Further, 3-chloro benzoic acid cant be present as there is usually around 10 -15 oC decrease in mp by presence of impurity. Therefore, it is impure 3 isomer with 3-chloro benzoic acid impurity.

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