Benzil (CAS NO.: ), which is also known as dione, diphenyl-, could be produced through the following synthetic route.

In a 12-l. flask, fitted with a mechanical stirrer and mercury seal, a reflux condenser and an inlet tube for the introduction of air, is placed a mixture of 4100 g. (16.4 moles) of crystalline copper sulfate, 4000 g. of technical pyridine and 1600 g. of water. This is heated on a steam bath with stirring until the copper sulfate is completely dissolved and then 1696 g. (8 moles) of benzoin (p. 94; unrecrystallized material is satisfactory) is added and heating and stirring continued for two hours. The reaction mixture becomes dark green in color and the melted benzil forms the upper layer. After cooling, the copper sulfate-pyridine solution is decanted and the benzil washed with water and then heated with 3–4 l. of 10 per cent hydrochloric acid. After cooling, the benzil is filtered, washed with water, dried and recrystallized from carbon tetrachloride (2 l. of solvent per kg. of benzil). By concentration of the mother liquors a certain amount of benzil is always obtained. The total yield is 1450 g. (86 per cent of the theoretical amount) of recrystallized material melting at 94–95°.

The copper sulfate-pyridine mixture is readily reoxidized by passing a current of air through it for thirty-six hours. To this resulting solution is now added 200 g. of pyridine and it is then used for oxidizing another 1696 g. portion of benzoin.