Question

During the synthesis of 3,6-dibromo-N-propylcarbazole from N-propylcarbazole by bromination, the reaction mixture turned yellowish. After the first recrystallization, the obtained product was white as expected. However, upon attempting a second recrystallization with excess glacial acetic acid and subsequent distillation, the solvent mixture changed from yellowish to green, resulting in green crystals instead of the expected white ones. The change in color did not occur during the first recrystallization. Seeking an explanation for this color change, why did the reaction mixture turn green during the second recrystallization upon heating?

a.The green color indicates the presence of bromine in the solvent, possibly due to incomplete removal during distillation.
b.The product underwent oxidation during the second recrystallization, leading to the green color.
c.The excess glacial acetic acid reacted with the product, causing a change in color to green.
d.The change in color is unrelated to the reaction or the product; it might be due to impurities or an experimental artifact.

Answer 1

The green color during the second recrystallization of 3,6-dibromo-N-propylcarbazole from N-propylcarbazole can most likely be attributed to oxidation of the product.

Step-by-step explanation:

The green color during the second recrystallization of 3,6-dibromo-N-propylcarbazole from N-propylcarbazole can most likely be attributed to option b.

The product underwent oxidation during the second recrystallization, leading to the green color.

Oxidation reactions can produce different colored products due to changes in the electronic structure of the molecules involved.

In this case, the green color indicates the formation of a new compound with different properties.