US patent 3821303 Preparation of Oximes
(Rated as: excellent)
US Patent 3821303
Improvements in or Relating to the Manufacture of Cyclohexanone Oxime from Cyclohexanone
To the cyclohexanone (98.09g, 1.0mol) in a one-liter, three-necked flask fitted with a water cooled condensor and a stirrer was added 1000ml of water, 104g of sodium nitrite (1.5mol), 80.25g of ammonium chloride and carbon dioxide was passed therein at a slow rate. Zinc dust (100g, 85% purity) was added in small portions. The reaction became exothermic, and the addition of Zn dust was done in such a way that the temperature was maintained around 60-70*C. After all the Zn dust had been added, the reaction was allowed to continue for 1 hour, during which it returned to RT. The oily layer was decanted, the residue was extracted with benzene (500mL). The benzene was added to the decanted oil. The solution was distilled in vacuo (10-12mmHg) to remove the benzene and then unreacted cyclohexanone. As the solvent and untouched reactants were removed, the cyclohexanone oxime crystallized as a material of 95.3% purity. Yield : 60-65%
The Zinc reacts to form Zn carbonate as a precipitate.
The carbon dioxide is introduced as a means of controlling temperature (no external heat necessary), maintaining slightly acidic conditions and eliminating O2 from the reaction mixture.