purified Benzonitrile is colorless but mine is yellow . by TLC I have known that it is impure.
Benzonitrile (CAS NO. 100-47-0) should be dried with CaSO4, CaCl2, MgSO4 or K2CO3, and distd from P2O5 in an all-glass apparatus, under reduced pressure (b 69 °C/10mm), collecting the middle fraction. Distn from CaH2 causes some decomposition of solvent. Isonitriles can be removed by preliminary treatment with conc HCl until the smell of isonitrile has gone, followed by preliminary drying with K2CO3. (This treatment also removes amines).
Steam distd (to remove small quantities of carbylamine). The distillate was extracted into ether, washed with dil Na2CO3, dried overnight with CaCl2, and the ether removed by evaporation. The residue was distd at 40mm (b 96 °C).
Conductivity grade benzonitrile (specific conductance 2x10-8 mho) was obtained by treatment with anhydrous AlCl3, followed by rapid distn at 40-50 °C under vacuum. After washing with alkali and drying with CaCl2, the distillate was vac distd several times at 35 °C before being fractionally crystd several times by partial freezing. It was dried over finely divided activated alumina from which it was withdrawn as required.
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