Introduction
I represent to BB audience Methamphetamine synthesis method of 1-phenyl-2-propanon (P2P) reductive amination by NaBH4. Following method allows obtaining and large batches of product. The hardest problem of this method is the heat generating during exothermic reaction of imine reduction. Extremely important keep temperature in described frames and keep all reagent and reaction atmosphere dry (use drying tubes with CaCl2). Also, manipulations with NaBH4 is quite dangerous and take a lot of attention because this reagent has toxic effects, reacts with water and alcohols with releasing enormous amount of hydrogen and form the corresponding borate, it may cause an explosion, burns and injuries. You have to use chemical glass, gloves, chemical coat and respirator.
Equipment and glassware:
- Ceramic mortar;
- 2 L (x2), 0.5 L (x2) and 200 ml (x2) beakers;
- 2 L (x2) and 10 L Erlenmeyer flask;
- Measuring cylinder for 100 ml;
- 2 L three-necked round bottom flask with plugs;
- 2 L round bottom flask with vacuum quickfit or Schlenk flask;
- 0.5 L Simple dropping funnel with Claisen flask and drying tube or 0.5 L equal pressure dropping funnel;
- 1 L Separator funnel;
- 2 L Evaporation flask;
- Pyrex dish 0.5 L;
- Magnetic stirrer with heating plate;
- Silicone-oil bath;
- Icecubes/methanol bath (-10 °C) or Mashed ice with salt (-10 °C);
- Laboratory scale (1 g-1 kg is suitable);
- Oven;
- Aspirator;
- Drying tube x2;
- Rotavap machine with water bath;
- Filter paper.
Reagents:
- 138 gram P2P (1 mole) (1-phenyl-2-propanone);
- 10% Methylamine in Methanol (w/w) - 1000 ml with 100 g MeNH2 (~3 moles);
- Magnesium Sulfate - 36 g (MgSO4·7H2O, oven dry at 300 °C for 2h MgSO4·1H2O) [For drying MeOH/MeNH2 solution];
- Silica Gel (3-5 mm balls) - 200 ml (dry at 300 °C/2h, they will darken!) [For absorbing 2 mol H2O during rxn];
- 15 gram NaBH4 as a reducing agent for the formed (water-free!) imine;
- 5-7 L distilled water + ~5 L distilled water to filling rotavap machine bath;
- 1 L Dichloromethane (DCM);
- 0.5 L Acetone.
Important: the reaction is very sensitive to any water (fluid or vapour in the air!).
Note: hold all manipulations in pull out probe or under exhaust hood; methylamine is a rather toxic substance, do not let its vapors enter the respiratory tract. Using respiratory mask is required. Inhalation of methylamine causes severe skin irritation, eyes and upper respiratory tract. Firstly, leads to excitement and then to depression of the central nervous system. Death can occur from respiratory arrest.
Note: hold all manipulations in pull out probe or under exhaust hood; methylamine is a rather toxic substance, do not let its vapors enter the respiratory tract. Using respiratory mask is required. Inhalation of methylamine causes severe skin irritation, eyes and upper respiratory tract. Firstly, leads to excitement and then to depression of the central nervous system. Death can occur from respiratory arrest.
Procedure
Precursors drying
First quickly crunch your pre-dried (oven, 300 °C, 3 hrs.) dry MgSO4 to pop corn shaped rocks in a mortar, sieve the powder out, and directly put the rocks under max. mixing in the Methanol/Methylamine mix (1000 ml) and close the pot to let no water from the air in. Keep mixing for 10 minutes, then all the water will be taken up to the MgSO4. Let stand and wait till all the MgSO4 is on the bottom. Now quickly tap off the now dry MeOH/methylamine (MA) mix in a 2 L three-necked round bottom flask and close that one. Wash directly your empty pot with lots of water, to remove the smell of methylamine, so you can safely store it.
SynthesisFirst quickly crunch your pre-dried (oven, 300 °C, 3 hrs.) dry MgSO4 to pop corn shaped rocks in a mortar, sieve the powder out, and directly put the rocks under max. mixing in the Methanol/Methylamine mix (1000 ml) and close the pot to let no water from the air in. Keep mixing for 10 minutes, then all the water will be taken up to the MgSO4. Let stand and wait till all the MgSO4 is on the bottom. Now quickly tap off the now dry MeOH/methylamine (MA) mix in a 2 L three-necked round bottom flask and close that one. Wash directly your empty pot with lots of water, to remove the smell of methylamine, so you can safely store it.
Now add the 200 ml (measure in beaker, neglect the free spaces) dry Silicagel beads (2-5 mm) and a magnetic mixer bar also in the 2 L flask and close again. Keep 2 L flask in Silicone-oil bath at 20 °C. Silicone-oil only slowly warms up! Do not apply heat now, it's only meant as a cooling medium in this stage. Now add slowly via a dropping funnel the 138 g P2P to the 2 L flask under strong mixing. The temperature rises to 23 °C during the (water-free) Imine forming. The water from this reaction is taken up by the dried Silicagel! This takes 30 minutes. Let, then mix for another hour. The reaction mix color changes from light yellow to coffee+milk color. Temp 23 °C.
Stop mixing after this 1 hour and pour the fluid off into a 2 L glass erlenmeyer with flat bottom and add a mixbar. The remaining Silicagel is washed 3 times with 50 ml dried (use silicagel) methanol, to catch the remaining Imine, and those 2 x 50 ml is also poured into the 2 L erlenmeyer. Now put the 2 L erlenmeier on magn.mixer, in an icecubes/methanol bath (-10 °C) (or mashed ice with salt) and start strong mixing. Put a drip funnel on top of 2 L erlenmeier, in rubber ring. Now start adding, every 5 min., a teaspoonfull (flat off!) of NaBH4 in minimum methanol, wash it from funnel with minimum methanol amount. After every spoonfull, stopper the funnel loosely with a rubber stopper. This takes 2.5 hrs. Do not exceed a temp of more than 20 °C! You can add the next spoon at ±8 °C. Solution color is light clear orange/brown. Let mix in total for 8.5 h (could perhaps be lot fewer hours).
The total volume is ~1900 ml. Add then the mix to 5 L distilled water into a 10 L flask, under magn.mixing. The pH=12. Add then 500 ml DiChloroMethane (DCM) and mix strongly for 30 min. Let oil precipitate and a dark, honey-coloured layer of DCM+oil settle onto the bottom. Decant the water part with an aspirator + siliconetube. Fill the rest (water+DCM+oil) in a seperatory funnel and tap off only the DCM+oil = 550 ml. (DCM b.p. 40 °C). The leftover MgSO4 and boro salts stayed nicely in the waterpart. Then dry the DCM+oil with some dry MgSO4 and decant in 2l erlenmeier. Wash this MgSO4 with some fresh, DRY DCM and add the DCM washings to the now dry DCM+oil. Total volume DCM+oil =1000 ml, colour is honey/red.
Producing methamphetamine hydrochloride
Start now bubbling this 1000 ml with HCl-gas via 2 L Schlenk flask (or round bottom flask with vacuum quickfit), while this 2 L flask stands in ice bath on magn. mixer and blends vigorously. Check pH frequently, proceed until pH 6. Pour the now acidified 1000 ml in a 2 L evaporation flask and put on Rotavap machine. Spee~100 rpm, t° = 80 °C, little vacuum=0.8 bar (water-jet aspirator is enough), to hold the flask. After distillating off nearly all the DCM, suddenly the contents of the flask turns from dark honey colour to creamy milk color, and it dries out to a round cake on the bottom. Remove the ~0.5 L DCM, now in the collector flask, and hang that empty flask on again. Now put full vacuum on to remove the last traces of water.
Cleaning by 3 x recrystallization: put minimum quantity of hot (40 °C) dry DCM (or dry 98%+ ethanol) in the flask until the last remains of the dry stuff dissolves, and add 4x this DCM-quantity in the form of dry acetone. Close with stopper and put 1 hr in freezer. A solid dirty-white crystal mass is formed with a layer of dark red fluid on top of it. Decant the fluid and repeat this step another 2x and 2 hrs. You have, the last time, snow-white crystals of racemic methamphetamine hydrochloride. Dry Weight = 141.5 g, close to quantitative yield.
Methamphetamine purification.
You can use this technique or follow next advices to produce ICE meth: melt this crystal mass in an alu flat bottom pot on a heater plate at 170-175 °C. Then let this melt, very slowly, and do not go higher than necessary to melt it, or its starts smoking (you have your first quick-test then: enjoy!). Cool down to 150 °C again, really slowly, 1 °C/30 min. (regulate with your temp controller!), and you got ICE, after you let it very slowly again cool down to room temperature (with a closed lid on it!, its hygroscopic!). Advantage: you removed all the water in this process!
You can better make the sulfate salt following logical method: Let 10% H2SO4/Ethanol mix acidifying a 1:4 mix of freebase Meth/Ethanol. This is not so hygroscopic. Filter and dry the crystals.
Cleaning by 3 x recrystallization: put minimum quantity of hot (40 °C) dry DCM (or dry 98%+ ethanol) in the flask until the last remains of the dry stuff dissolves, and add 4x this DCM-quantity in the form of dry acetone. Close with stopper and put 1 hr in freezer. A solid dirty-white crystal mass is formed with a layer of dark red fluid on top of it. Decant the fluid and repeat this step another 2x and 2 hrs. You have, the last time, snow-white crystals of racemic methamphetamine hydrochloride. Dry Weight = 141.5 g, close to quantitative yield.
Methamphetamine purification.
You can use this technique or follow next advices to produce ICE meth: melt this crystal mass in an alu flat bottom pot on a heater plate at 170-175 °C. Then let this melt, very slowly, and do not go higher than necessary to melt it, or its starts smoking (you have your first quick-test then: enjoy!). Cool down to 150 °C again, really slowly, 1 °C/30 min. (regulate with your temp controller!), and you got ICE, after you let it very slowly again cool down to room temperature (with a closed lid on it!, its hygroscopic!). Advantage: you removed all the water in this process!
You can better make the sulfate salt following logical method: Let 10% H2SO4/Ethanol mix acidifying a 1:4 mix of freebase Meth/Ethanol. This is not so hygroscopic. Filter and dry the crystals.
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