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Methamphetamine via Reductive Amination of Phenyl-2-Propanone

Using Aluminum Amalgam and Methylamine in wet Isopropanol

Procedure adapted from the synthesis of MDMA from MDP2P in Pihkal #109

Procedure 1: Using Methylamine Hydrochloride

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 (0.44 mol, 3 eqv) dissolved in 30ml hot water, 75 ml isopropanol, 70ml 25% aqueous NaOH (0.44 mol), 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 50C.

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 100-110C 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.

Procedure 2: Using 40% Aqueous Methylamine Freebase

In a 500ml wide-mouthed Erlenmeyer flask, aluminum foil (10g, 0.37 mol) cut to 3x3cm pieces was amalgamated in a solution of 200 mg HgCl2 in 400 ml warm water until the solution became greyish, and hydrogen bubbles was evolved in a steady rate from the aluminum surface. The water was decanted, and the amalgamated aluminum pieces were washed twice with 250ml cold water.

To the aluminum amalgam (still in the above flask) there was added, quickly, a 40% Methylamine solution (43 mL, 0.50 mol), isopropanol (100 mL), Phenyl-2-Propanone (13.42g, 0.10 mol), and finally another 100 mL isopropanol (which was used to rinse the beaker the P2P had been in). The aluminum pieces were poked with a glass rod so that all of them were below the surface of the liquid. Hydrogen began to evolve vigorously from the aluminum surface, and the temperature (which was measured by a small thermometer inserted into the flask) rose quickly. The evaporation of methylamine was attenuated by covering the mouth of the flask with some Al foil (do not plug it tight, or it may explode), and the reaction rate was controlled by immersing the reaction flask in cold water from time to time during the first hour so that the temperature did not rise over 50C. At the 2 hour point most of the aluminum was consumed, and 20 mL 25% aqueous NaOH was added to the solution and magnetic stirring was initiated (keep an eye on the temperature again, and keep it below 50C). At the 3 hour point another 20 mL 25% NaOH was added (no significant temp rise), whereafter it was allowed to stir at room temp overnight and then allowed to settle.

The clear supernatant was decanted, 100ml isopropanol was added to the grey sludge, it was stirred for another hour, and the supernatant again decanted after the particle suspension had settled. The aluminum sludge at the bottom of the flask was now vacuum filtered through an inch of Celite in a buchner funnel and washed with 2 x 50 mL methanol. All the decantations and washes were combined, and the solution concentrated under vacuum.

The residue was taken up in 300 mL water, acidified with conc. HCl, washed with 3x50ml methylene chloride, basified with 25% NaOH, and extracted with 3x100ml ethyl acetate. The combined organic extracts were washed with 75ml brine, followed by drying over anhydrous sodium sulfate with good magnetic stirring for 15 min. The drying agent was removed by filtration from the crystal-clear solution and the solvent distilled off on an oil-bath heated to no more than 110C (as to not risk any evaporation of the freebase). The residue was taken up in 150 mL diethyl ether and with good stirring a solution of 5M HCl in isopropanol was added until the solution was acid to dampened universal pH paper. The precipitate was filtered off with suction using a fritted glass funnel and the filter cake was washed with 2 x 50 mL ether and sucked dry. After air-drying overnight on a plate, the crude product (13.6 g) still had a strong solvent smell, and was recrystallized by dissolving it in 65 mL acetonitrile (5 mL/gram), and quickly vacuum filtering the hot solution through a fritted glass funnel to remove a slight turbidity, and the solution was then left at room temp to crystallize, and after about an hour the white crystalline precipitate was filtered with suction, washed with 2 x 25 mL ether and air dried. The filtrate and ether washes (collected separately) were both cooled to -20C in the freezer, and from the acetonitrile a second crop was collected, while nothing came out of the ether.

The first and second crop weighed 12.0 g and 0.45 g, respectively, making the total yield of Methamphetamine Hydrochloride 12.45 grams, or 67% of theory