For most purposes, (CAS NO. ) can be purified sufficiently by shaking with conc H₂SO₄ until free from , then with H₂O, dilute NaOH and water, followed by drying (with P₂O₅, sodium, LiAlH₄, CaH₂,4X Linde molecular sieve, or CaSO₄, or by passage through a column of silica gel, for a preliminary drying, CaCl₂ is suitable), and distn. A further purification step to remove thiophene, acetic acid and propionic acid, is crystn by partial freezing. The usual contaminants in dry thiophene-free Benzene are non-benzenoid hydros such as cyclohexane, methylcyclohexane, and heptanes, together with naphthenic hydrocarbons and traces of toluene. Carbonyl-containing impurities can be removed by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine, phosphoric acid and H₂O. (Prepared by dissolving 0.5g DNPH in 6mL of 85% H₃PO₄ by grinding together, then adding and mixing 4mL of distd H₂O and 10g Celite.) Benzene has been freed from thiophene by refluxing with 10% (w/v) of Raney nickel for 15min, after which the nickel was removed by filtration or centrifugation.

Dry it was obtained by doubly distilling high purity Benzene from a soln containing the blue ketyl formed by the reaction of sodium-potassium alloy with a small amount of benzophenone.

Thiophene has been removed from Benzene (absence of bluish-green coloration when 3mL of Benzene is shaken with a soln of 10mg of isatin in 10mL of conc H₂SO₄) by refluxing the Benzene (1Kg) for several hours with 40g HgO (freshly pptd) dissolved in 40mL glacial acetic acid and 300mL of water. The ppte was filtered off, the aq phase was removed and the Benzene was washed twice with H₂O, dried and distd.

Alternatively, Benzene dried with CaCl₂ has been shaken vigorously for half an hour with anhydrous AlCl₃ (12g/L) at 25-35 °C, then decanted, washed with 10% NaOH, and water, dried and distd. The process was repeated, giving thiophene-free Benzene.

After shaking successively for about an hour with conc H₂SO₄, distd water (twice), 6M NaOH, and distd water (twice), Benzene was distd through a 3-ft glass column to remove most of the water. Abs EtOH was added and the Benzene-alcohol azeotrope was distd. (This low-boiling distn leaves any non-azeotrope-forming impurities behind.) The middle fraction was shaken with distd water to remove EtOH, and again redistd. Final slow and very careful fractional distn from sodium, then LiAlH₄ under N₂, removed traces of water and peroxides. Benzene liquid and vapour are very toxic and highly flammable, and all operations should be carried out in an eficient fume cupboard and in the absence of naked flames in the vicinity.

Rapid purification: To dry Benzene, alumina, CaH₂ or 4A molecular sieves (3% wlv) may be used (dry for 6h). Then Benzene is distd, discarding the first 5% of distillate, and stored over molecular sieves (3A, 4A) or Na wire.