A mixture of 40 gm (0.2 mole) of benzophenone oxime, 70 ml of methanol, and a solution of 33 gm (0.8 moles) of sodium hydroxide in 180 ml of water is warmed gently with stirring until a clear solution has been produced. The solution is cooled and, with vigorous stirring, 40 gm (0.32 mole) of dimethyl sulfate (caution, toxic reagent) is added dropwise over a 2-hr period. The reaction mixture is cooled in an ice bath overnight. The nitrone is extracted from the cold reaction mixture with ether. The ether solution is dried with anhydrous sodium sulfate and filtered. The filtrate is evaporated to dryness. The residue is stirred with 300 ml of petroleum ether (b.p. 30-50°C) until it becomes powdery (crude yield 22 gm). Upon crystallization from ligroin (b.p. 60-70°C), approximately 20 gm (47.4%) of a,a-diphenyl-N-methylnitrone is isolated, m.p. 102-103°C.
A mixture of 2 gm (0.01 mole) of α,α-diphenyl-N-methylnitrone and 50 ml of 8% hydrochloric acid is refluxed for 15 min. The aqueous solution is evaporated under reduced pressure. The crude residue is dissolved in absolute alcohol. By fractional precipitation with absolute ether, 1.68 gm of benzophenone (m.p. 47-48°C) and 0.75 gm (95%) of N-methyl-droxylamine hydrochloride (m.p. 87-89°C) are isolated.
The free base has been prepared by treating the hydrochloride salt with potassium hydroxide pellets and distilling repeatedly in high-vacuum train equipment. The properties of iV-methylhydroxylamine are reported as m.p. 38.5°C, b.p. 115.0°C/760 mm Hg.
