Methamphetamine from Phenyl-2-Propanone
Introduction
The procedure is an adaption from the reductive amination of MDP2P with methylamine in Pihkal #109
Procedure
In a 1000ml wide-mouthed erlenmeyer flask, 19 grams of aluminum foil cut to 3x3cm pieces was amalgamated in a solution of 500mg mercuric chloride (HgCl2) in 700ml warm water until the solution became greyish, and hydrogen bubbles was evolved in a steady rate from the aluminum surface. The water was decanted off, and the aluminum amalgam was washed with 2x500ml cold water.
To the aluminum amalgam there was added 29.5g methylamine hydrochloride (1.02 mol, 7 eqv) dissolved in 30ml hot water, 75 ml isopropanol, 70ml 25% NaOH, 19.75g (0.147 mol) phenyl-2-propanone (P2P) and finally 175ml isopropanol. Hydrogen was vigorously evolved from the aluminum amalgam, and the temperature of the solution rose quickly. The reaction rate was controlled by immersing the reaction flask in cold water during 2h, whereafter it was allowed to stand at room temperature with magnetic stirring overnight, with attention being given to the reaction mixture during the first hour so that the temperature did not rise over 50°C.
To the reaction mixture there was added another 50ml 25% NaOH, and the reaction mixture was stirred for 30min and then allowed to settle. The clear supernatant was decanted, and 100ml isopropanol was added to the grey sludge, and it was stirred for 15min, and the supernatant again decanted. The aluminum sludge at the bottom of the flask was now filtered through celite in a buchner funnel and washed with 2x50ml THF (methanol can also be used). All the decantations and washes were combined, and the solution concentrated under vacuum.
The residue was taken up in 1000ml water, acidified by the addition of conc HCl, and washed with 3x50ml DCM, basified with 25% NaOH, and extracted with 3x100ml DCM. The combined DCM extracts were dried over MgSO4, filtered and the solvent distilled off. The residue was distilled twice under aspirator vacuum at 100-110°C to give 14.65g (67%) of methamphetamine freebase as a water-white oil. The hydrochloride salt can be prepared by dissolving the oil in 10x the volume of diethyl ether and gassing the solution with dry HCl gas until no more precipitate forms. The methamphetamine hydrochloride is filtered off with suction and washed with diethyl ether and air dried.
