Impurity profiling of an alternative pathway to ephedrine/pseudoephedrine and methamphetamine from the precursors benzaldehyde and nitroethane

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Methamphetamine is produced using various routes from two predominant precursors, ephedrine/pseudoephedrine or phenyl-2-propanone (P2P). The multitude of synthetic routes results in many possible impurities (by-products or intermediates). Impurity profiling of methamphetamine by gas chromatography-mass spectrometry (GC–MS) is an important tool for the forensic chemist and investigators to assist in identification of the synthetic pathway and linking seizures. With the emergence of alternative routes, continued research into impurity profiles is important. One such alternative route is an ephedrine/pseudoephedrine-based pathway using the precursors typically associated with the phenyl-2-propanone (P2P) route, benzaldehyde and nitroethane. Benzaldehyde and nitroethane were condensed to form 2-nitro-1-phenyl-1-propanol. Subsequent reduction led to the corresponding 2-amino-1-phenyl-1-propanol. Cyclization-methylation with dimethyl carbonate to 3,4-dimethyl-5-phenyl-2-oxazolidinone, followed by catalytic hydrogenolysis or basic hydrolysis formed methamphetamine and ephedrine/pseudoephedrine, respectively. This paper presents the impurity profile of the alternative route. The conditions for the reduction of the intermediate 2-nitro-1-phenyl-1-propanol to 2-amino-1-phenyl-1-propanol was found to influence the by-products observed in the methamphetamine product. Notable by-products were amphetamine, N-ethylamphetamine and N-hydroxymethamphetamine.