The racemisation describes the process by which an optically active (chiral) amine is converted into a racemic mixture (equal parts of both enantiomers).
Means of racemisation under PtO₂/H₂:
• PtO₂ is Adams’ catalyst (platinum(IV) oxide), used for catalytic hydrogenation.
• Under hydrogenation conditions (H₂ with PtO₂), chiral amines like L-N-Methylphenylisopropylamine (L-Methamphetamine) can undergo racemisation.
The racemisation can be represented as follows:
Step 1: Setup
• Dissolve L-methamphetamine (8,25mol) in ethanol (10l)
Step 2: Catalyst Addition
• Add a catalytic amount of 50 g platinum(IV) oxide (pre reduced) (PtO₂, also known as Adams’ catalyst) to the solution.
Step 3: Hydrogenation
• Evacuate and purge the reaction vessel alternately with inert gas and then with hydrogen to ensure that no atmospheric oxygen remains.
• Introduce hydrogen gas (H₂) at 1 atm to the reaction vessel.
• Stir or shake the mixture to ensure thorough mixing and contact of all components.
Step 4: Reaction
• Allow the reaction to proceed at room temperature or slightly elevated temperature (commonly 20–40 °C). The temperature must be kept under 45 °C because otherwise the product will be destroyed.
• During this time, the chiral methamphetamine adsorbs onto the PtO₂ surface, where reversible hydrogenation and dehydrogenation facilitate the interconversion of (D)- and (L)-enantiomers.
Step 5: Completion
• Monitor the reaction progress by removing small samples for polarimetry to check for loss of optical activity (formation of racemate).
• Once racemisation is complete (no optical rotation), stop the reaction.
• After completion, filter catalyst, evaporate solvent, recover racemic amine.
Expected Yield:
Racemisation simply interconverts enantiomers, so theoretically, all the starting material remains intact (100% yield of racemic mixture), unless there is side reaction or loss during work-up.
Means of racemisation under PtO₂/H₂:
• PtO₂ is Adams’ catalyst (platinum(IV) oxide), used for catalytic hydrogenation.
• Under hydrogenation conditions (H₂ with PtO₂), chiral amines like L-N-Methylphenylisopropylamine (L-Methamphetamine) can undergo racemisation.
The racemisation can be represented as follows:
Step 1: Setup
• Dissolve L-methamphetamine (8,25mol) in ethanol (10l)
Step 2: Catalyst Addition
• Add a catalytic amount of 50 g platinum(IV) oxide (pre reduced) (PtO₂, also known as Adams’ catalyst) to the solution.
Step 3: Hydrogenation
• Evacuate and purge the reaction vessel alternately with inert gas and then with hydrogen to ensure that no atmospheric oxygen remains.
• Introduce hydrogen gas (H₂) at 1 atm to the reaction vessel.
• Stir or shake the mixture to ensure thorough mixing and contact of all components.
Step 4: Reaction
• Allow the reaction to proceed at room temperature or slightly elevated temperature (commonly 20–40 °C). The temperature must be kept under 45 °C because otherwise the product will be destroyed.
• During this time, the chiral methamphetamine adsorbs onto the PtO₂ surface, where reversible hydrogenation and dehydrogenation facilitate the interconversion of (D)- and (L)-enantiomers.
Step 5: Completion
• Monitor the reaction progress by removing small samples for polarimetry to check for loss of optical activity (formation of racemate).
• Once racemisation is complete (no optical rotation), stop the reaction.
• After completion, filter catalyst, evaporate solvent, recover racemic amine.
Expected Yield:
Racemisation simply interconverts enantiomers, so theoretically, all the starting material remains intact (100% yield of racemic mixture), unless there is side reaction or loss during work-up.
