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G.Patton

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Introduction
YvLRnBsu93

L-Ephedrine is obtained from dried plants of various species of the genus Ephedra by initial treatment with alkali, followed by extraction with organic solvent. Extraction, purification and isolation of these drugs is time-consuming, costly and complicated by the presence of undesired byproducts. L-Phenylacetylcarbinol (L-PAC; (1)) which is a precursor for ephedrine is produced by biotransformation of benzaldehyde using yeast cultures. The chemical conversion of L-PAC to ephedrine has proved to be more advantageous than the extraction route. L-PAC could be converted by a chemical reductive amination with methylamine to optically pure L-ephedrine. The use of microwave irradiation for chemical synthesis is of increasing importance, since it provides a simple alternative to classical chemical routes with rapid reactions yielding high conversion and selectivity. The present work was undertaken to explore the possibility of conducting the synthesis using microwaves as an alternative to these routine chemical synthetic reactions. A two-step simple synthetic reaction was carried out in a homogeneous reaction medium under exposure to microwaves. A homogeneous reaction medium ensures better thermal homogeneity under microwave heating and facilitates scale-up of the reaction. The procedure is superior to methods involving complex hydrogenation procedures and those involving reduction of protected cyanohydrins. Also, you can read other topics concerns ephedrine manufacturing.

Equipment and glassware:

  • 100 mL Round-bottom flask;
  • Ice;
  • pH indicator paper;
  • Paster pipete;
  • 100 mL Drip funnel with equalize pressure;
  • Retort stand and clamp for securing apparatus;
  • Magnetic stirrer;
  • 100 mL x4; 50 mL x2 Beakers;
  • 500 mL Separatory funnel;
  • Calcium chloride (CaCl2) tube;
  • Flash chromatography kit (middle column and silica gel 60 ± 120 mesh);
  • IFB Neutron kitchen oven (760 W output and 2450 MHz frerequest);
  • Vacuum source;
  • Glass rod and spatula;
  • Rotovap machine;
  • Laboratory scale (0.01-100 g is suitable) [depends on synthesis load];
  • Measuring cylinder, 100 mL.

Reagents:

  • L-PAC (0.03 moles, 4.5 g) [CAS Number 1798-60-3];
  • Ethanol (EtOH) ~150 mL;
  • Hydrochloric acid conc. (HCl) aq. solution ~20 mL;
  • Methylamine 40% (v/v) solution (CH3NH2) 9 mL;
  • Diethyl ether (Et2O) 200 mL;
  • Sodium bicarbonate (NaHCO3) ~50 g;
  • Distilled water, 65 mL;
  • Sodium sulphate anhydrous (Na2SO4) or magnesium sulfate (MgSO4) ~100 g;
  • Ethyl acetate (EtOAc) ~500 mL;
  • Toluene ~400 mL
  • Sodium borohydride (NaBH4) 0.09 moles, 3.24 g.
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Procedure

Conversion of L -phenylacetylcarbinol (L -PAC) (B) to 2-(methylimino)-1-phenyl-1-propanol (2)
L -PAC (0.03 moles, 4.5 g) was placed in a 100 mL round-bottom flask containing 10 mL of ethanol, cooled in crushed ice and the pH adjusted to 4, by dropwise addition of conc. HCl. Three mL of a 40% (v/v) solution of methylamine was added dropwise with constant stirring. The reaction mixture was brought to ambient temperature (30 +/- 2 °C) and was irradiated for 3 min at 50 % power in a modified domestic microwave* oven in previous flask with CaCl2 tube (connection with atmosphere). The reaction was further continued for 6 min (two cycles of 3 min at 50 % power) with addition of 3 mL 40 % methylamine solution during each irradiation cycle. After exposure to the microwaves, the reaction mixture was cooled in crushed ice with 10 mL of added water. The pH of the reaction mixture was adjusted to 4 and the reaction mixture was washed with ether (25 mL x 3) to collect unreacted L-PAC (1). The aqueous layer was neutralized with NaHCO3 and the pH value adjusted to between 7 and 8. The aqueous layer was extracted with ether (25 mL x 3) and the combined ether layers were washed again with 15 mL of cold water. The ether layer was dried by passing through anhydrous sodium sulphate (Na2SO4); ether was removed in a rotavap to obtain the product (2) as a yellow oil. This oil was further purified by silica gel (60 ± 120 meshes) column (flash) chromatography using ethyl acetate and toluene (6:4) as eluent. Yield 55 %.

*For chemical reactions using microwave irradiation, a modified IFB Neutron kitchen oven (760 W output and 2450 MHz frerequest) was used.
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2-(methylamino)-1-phenyl-1-propanol (3) (Ephedrine)
The imine (2) 2-(methylimine)-1-phenyl-1-propanol (0.03 moles, 4.89 g) was placed in a 100 mL round-bottom flask containing 10 mL of ethanol. To this solution NaBH4 (0.09 moles, 3.24 g) was added in increments of 0.02 moles for each microwave irradiation of 2 min at 50 % power. The total reaction time under microwave exposure was 10 min (2 min x five cycles of 50 % power). After exposure to the microwaves, the reaction mixture was cooled in ice and quenched by adding 10 mL of ice-cold water and some pieces of ice. This solution was then extracted with ether (25 mL x 3). The combined ether layers were washed twice with 15 mL of cold water in a separatory funnel and dried by passing through anhydrous sodium sulphate (Na2SO4) in a beaker. The ether layer was removed in a rotavap to give the oil containing product and unreacted imine (2). The mixture was separated by column chromatography using silica gel (60 ± 120 mesh) and ethyl acetate±toluene (8:2) as eluent. The isolated product obtained after elution of the column was recrystallized in hot ethanol and dried to give ephedrine. Yield 64 %.
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mp_

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Multiple times in this synthesis was the topic of a rotavap mentioned. As they are expensive, could one evaporate the ether layer/solvent at normal pressure?

Or is it like in the case of LSD where the product must be evaporated under reduced pressure due to it being so unstable?
 

btcboss2022

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Any option to replace the microwave by normal heating obviously changing temp and time?
 

btcboss2022

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Any option to replace the microwave by normal heating obviously changing temp and time?
btcboss2022@G.Patton Won't be enough with a standard reductive amination of the L-PAC?
Ethanol + methylamine (40% in water) + L-PAC and left to react at room temperature for 30 min, to allow imine formation.
The mixture was cooled to around 0 C and reduced using NaBH4.
The mixture was then basified and extracted with DCM
Dried dried anhydrous sodium sulphate, filtered and evaporated.
 

Consider

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Please i have tried this method i have rotary evaporator followed all the procedure, please i need someone to teach me this procedure properly, or any other method of synthesis ephedrine Hcl. Please i really need help from friends in the group.
 

Consider

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Please i did not purify using silica gel mesh chromatography please how do i do it, guess that may have affected my product, please guide me friends here
 

rampage

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does anyone have the recipe for making l-pac
 

Throw-off

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does anyone have the recipe for making l-pac
rampageThere's a study from a Australian University where they used yeast and benzaldehyde in a hot water bath for an hour to achieve a 30% yield if I remember correctly.. It can be found on sciencedirect website.
 

OrgUnikum

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The problem with l-PAC is that it racemizes quick to d/l-PAC what yields not the wanted l-Ephedrine but d/l-ephedrine what in consequence leads to racemic Meth as made from P2P.
We want d-Meth or at least predominantly d-Meth.
Two factors drive racemisation of l-PAC: First alkaline environment, say the presence of bases of any kind and transition metal ions, say any salts of iron etc. present even in minuscule amounts as they work catalytically.

Now many reduction systems are alkaline as is NaBH4, so its clear what would happen. Therefor besides storing and handling the l-PAC properly and adding something like oxalic acid and/or stannic acid or EDDA to take care of any metal salts around one chooses an acidic reduction system or one which works in slightly acidic conditions at least. I would recommend to use STAB whats an acidic derivative of NaBH4 and works especially well in reductive aminations. Methylamine is then used as the acetate, say the acetic acid salt of methylamine and all together as one pot one go Imine formation/Imine reduction whats called reductive amination.
Information on how to make STAB from NaBH4 and GAA is all over the net and also on how to use it. Yields are excellent.
Zinc-Borohydride would be another easily prepared possibility if one has anhydrous ZnCl2.
Al/Hg is also possible bust it must be done in THF or diethylether.
But a native acidic system as STAB or Zinc-Boro is best.

l-PAC production from Benzaldehyde by biosynthesis is not necessarily difficult but it is more of a technical challenge for the large volumes to handle. And first of all one has to find a good strain of yeast for the purpose. With this at hand it is mainly a problem of extracting the l-PAC at the end, a continuous extraction system is a must have here and ether is the solvent of choice.

good luck!
 

yuiopjkl

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The problem with l-PAC is that it racemizes quick to d/l-PAC what yields not the wanted l-Ephedrine but d/l-ephedrine what in consequence leads to racemic Meth as made from P2P.
We want d-Meth or at least predominantly d-Meth.
Two factors drive racemisation of l-PAC: First alkaline environment, say the presence of bases of any kind and transition metal ions, say any salts of iron etc. present even in minuscule amounts as they work catalytically.

Now many reduction systems are alkaline as is NaBH4, so its clear what would happen. Therefor besides storing and handling the l-PAC properly and adding something like oxalic acid and/or stannic acid or EDDA to take care of any metal salts around one chooses an acidic reduction system or one which works in slightly acidic conditions at least. I would recommend to use STAB whats an acidic derivative of NaBH4 and works especially well in reductive aminations. Methylamine is then used as the acetate, say the acetic acid salt of methylamine and all together as one pot one go Imine formation/Imine reduction whats called reductive amination.
Information on how to make STAB from NaBH4 and GAA is all over the net and also on how to use it. Yields are excellent.
Zinc-Borohydride would be another easily prepared possibility if one has anhydrous ZnCl2.
Al/Hg is also possible bust it must be done in THF or diethylether.
But a native acidic system as STAB or Zinc-Boro is best.

l-PAC production from Benzaldehyde by biosynthesis is not necessarily difficult but it is more of a technical challenge for the large volumes to handle. And first of all one has to find a good strain of yeast for the purpose. With this at hand it is mainly a problem of extracting the l-PAC at the end, a continuous extraction system is a must have here and ether is the solvent of choice.

good luck!
OrgUnikumI read a post by someone who synthesized l-ephedrine by refluxing l-PAC with methylformamide, and the yield was about 21g l-ephedrine from 20g l-PAC

I'm not sure if this method will work or not.
 
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OrgUnikum

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I read a post by someone who synthesized l-ephedrine by refluxing l-PAC with methylformamide, and the yield was about 21g l-ephedrine from 20g l-PAC

I'm not sure if this method will work or not.
yuiopjklThere is no reason the Leuckart reaction would not work for making ephedrine from l-PAC, the acidic environment is for sure a big big plus here. Of course it is the Leuckart and results vary widely, most I know did not get results they were happy with. But almost all of them wanted to make Amphetamine and thats anything but sturdy, ephedrine or methamphetamine are far more robust and good yields might be well possible.
Ideally one would react the l-PAC directly after it is extracted with N-benzylmethylamine to get a stereochemically stable Imine and does a double whopper hydrogenation/debenzyation with Pd/C to get l-ephedrine such avoiding all racemisation problems which might arise after extraction.
 

lalalander

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There is no reason the Leuckart reaction would not work for making ephedrine from l-PAC, the acidic environment is for sure a big big plus here. Of course it is the Leuckart and results vary widely, most I know did not get results they were happy with. But almost all of them wanted to make Amphetamine and thats anything but sturdy, ephedrine or methamphetamine are far more robust and good yields might be well possible.
Ideally one would react the l-PAC directly after it is extracted with N-benzylmethylamine to get a stereochemically stable Imine and does a double whopper hydrogenation/debenzyation with Pd/C to get l-ephedrine such avoiding all racemisation problems which might arise after extraction.
OrgUnikumHi. Is there any method that you can suggest?
 

WhyTheFace

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L-Phenylacetylcarbinol that you used, came from?
Do you have any new information on the method for the Bio transformation? ie Quantities, timings, aeration, continuous or batch?
Bit stuck on how to achieve a RQ of 4-5?
Any help be great.
 
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