Reaction XXXII.—Action of Alkalis on certain a-di-ketones

Reaction XXXII. Action of Alkalis on certain a-di-ketones. (A., 25, 25 31, 324 B., 14, 326 19, 1868 41, 1644.)—When benzil is fused with potassium hydroxide, or digested with alcoholic potash, or heated for a long time with aqueous potash, a molecular re-arrangement not unlike the pinacoline transformation (p. 79) takes place, and benzilic acid is formed. 

The acid can also be obtained directly from benzil by the action of air and caustic potash. 

Anisil and cuminil in a similar way yield anisilic and cuminilic acids. 

50 gms. (excess) of caustic potash are melte d with a small quantity of water in a silver, nickel, or copper crucible. The liquid is allowed to cool to 150° (for combined thermometer and stirrer, and precautions to be taken in alkali fusions, see Fig. 53), and 10 gms. of dry, finely powdered benzil are added with constant stirring. The benzil melts and the whole soon sets to a solid mass of potassium benzilate. When all the oil has disappeared, the melt is cooled, dissolved in water, and benzilic acid precipitated by acidifying with hydrochloric acid. The precipitate is cooled with cold water and, to free it from traces of benzoic acid, is boiled in a dish with water until the smell of the latter has disappeared. On cooling, 

—90% theoretical (20 gms.). Colourless needles sparingly soluble in cold water readily in hot water, and in alcohol M.P. 150°. (B 4, 1644.) 

---