# questions about the synthesis of iodobenzene from aniline

I am conducting an experiment about synthesis of iodobenzene from aniline, referring to this site(and various sites) (http://www.prepchem.com/synthesis-of-iodobenzene/). Below is my experimental process.

1. Put $$\pu{9.5mL}$$ of conc. $$\ce{HCl}$$, $$\pu{9.5mL}$$ of distilled water, $$\pu{2mL}$$ ($$\pu{0.0215mol}$$) of aniline in a $$\pu{100mL}$$ round flask with ice bath, and wait until the temperature of mixture drops below $$\pu{5℃}$$.

2. Dissolve $$\pu{1.56g}$$ ($$\pu{0.0226mol}$$) of $$\ce{NaNO2}$$ in $$\pu{50mL}$$ of distilled water, and cool it with ice bath.

3. Once the temperature of mixture dropped below $$\pu{5℃}$$, put the solution of $$\ce{NaNO2}$$. the solution must be poured very slowly not to raise temperature above $$\pu{10℃}$$.

4. Stir the mixture for $$\pu{10 min}$$.

5. Dissolve $$\pu{ 3.58g}$$ ($$\pu{0.0216mol}$$) of $$\ce{KI}$$ in distilled water. I used the water in very small quantities because $$\ce{KI}$$ is very soluble in water.

6. Put solution of $$\ce{KI}$$ to the mixture, then color of the mixture turns to be black, and gas bubbles (may be nitrogen gas) rise from the mixture.

7. After $$\pu{1-2 h}$$, gently heat the mixture (I set the temperature about $$\pu{50-70 ℃}$$).

8. Again after $$\pu{1-2 h}$$, it seemed that there are no more gas bubbles, so I stopped stirring and heating.

9. Layer separation occurred, (I guess) because iodobenzene is insoluble in water. so I moved it to separatory funnel and took the black oily organic layer presumed to be iodobenzene.

10. Here is the stage I am stuck on. according to the reference site, it says "use $$\ce{NaOH}$$ to decolorize the iodobenzene" (iodobenzene is colorless liquid). I put $$\ce{NaOH}$$ and made the pH of mixture 7, but its color is still black.

Question 1. Do I have to make the mixture basic to decolorize it? (actually, I tried making it basic, but it was not decolorised. Should I wait a moment after making it basic?)

Question 2. According to the reference site, iodobenzene have to be distilled using steam-distillation, but should I distill it with steam-distillation, not just ordinary distillation?

Question 3. Are there any problems with my experimental process?

• The boiling point of iodobenzene is about $\mathrm{188~^oC}$, thus, it's better to purify using fractional didtillation under reduced pressure (if you are reluctant to purify it by chromatography). Nov 22 '18 at 18:08