You are given a mixture of three compounds: phenanthrene (0.25 g), 1,4-dibromobe

Question

You are given a mixture of three compounds: phenanthrene (0.25 g), 1,4-dibromobenzene (0.05 g) and 4-aminoacetophenone (0.20 g). The mixture can be dissolved in either diethyl ether or methylene chloride. Write a brief separation scheme that will isolate these compounds using extraction and recrystalization techniques (you only need to separate two out of the three).

Reagents available: 1M NaOH, 6M NaOH, 1M HCl, 6M HCl, 1M NaHCO3, saturated sodium chloride, diethyl ether, 95% ethanol, methanol, isopropyl alcohol, acetone, hexane, toluene, methylene chloride, and granular anyhydrous sodium sulfate.

Explanation / Answer

Phennathrene is non-polar ring system and hence dissolves in non-polar organic solvent diethyl ether

1,4-dibormo benzene is slighly polar due to bromides present [halogens are electronegative, acquire partial negative charge from the atoms they are attached to [here ring atoms of benzene]

4-amino acetophenone NH2 -C6H6-CO-CH3 is highly polar deu to amino NH2 group and also due to Carbonyl group C=O

Both dibormo benzene and 4-amino acetophenone are polar and hence are soluble in polar solvents [methylene chloride]

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So when ether and CH2Cl2 solvent are added to mixture of all three, pehnanthrene gets separated out along with ether later and ether layer can be isolated and then later evoporated to islate the phenanthrene compound. Inthe remaining aqueous layer [CH2Cl2 layer], both dibormo benzene and 4-amino acetophenone are dissolved.To this aq. layer, add an acid 1M HCl which protonates the NH2 group of 4-amino acetophenone to +NH3--C6H6-CO-CH3

So HCl forms Ammonium salt which is insoluble in acetone and alcohol. So after salt is formed, which exist as dissolved salt, add acetone/alcohol which precipiates out the salt of 4-amino acetophenone.

Thus the 2nd compound can be separated out

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