Degradation of 1-phenyl-2-propanone during long-term storage: useful information for methamphetamine impurity profiling

Abstract

1-Phenyl-2-propanone (P2P) is a main precursor of methamphetamine. The authors investigated the formation of P2P degradation products during long-term storage and the factors that affected P2P degradation. Samples of neat P2P, 1 mg/mL P2P in methanol and in ethyl acetate were prepared. These samples were stored at room temperature or 4 °C for 1, 3, and 6 months; then the samples were analyzed by gas chromatography–mass spectrometry. A similar experiment (but stored only for 1 month) was also performed for phenylacetylcarbinol. Neat P2P stored at room temperature gave degradation products after 3-month storage, and the degradation proceeded over the next 3 months. Benzaldehyde, benzoic acid, benzyl acetate, 1-phenyl-1,2-propanedione, phenylacetylcarbinol, 1-acetoxy-1-phenyl-2-propanone, and 1,1-diphenylacetone were identified as degradation products after 6-month storage. The degradation was prevented incompletely by storage at 4 °C and almost completely by storage in the organic solvents. Neat phenylacetylcarbinol stored at room temperature was remarkably decomposed. Benzaldehyde, benzoic acid, 1-phenyl-1,2-propanedione, and 1-acetoxy-1-phenyl-2-propanone were regarded as the degradation products. The degradation was prevented incompletely by storage at 4 °C and almost completely by storage in the organic solvents. These results suggested that P2P and phenylacetylcarbinol were oxidized by oxygen in air and that the organic solvents inhibited the oxidation. P2P was presumed to be initially oxidized to phenylacetylcarbinol, then it was converted to benzaldehyde, benzoic acid, 1-phenyl-1,2-propanedione, and 1-acetoxy-1-phenyl-2-propanone. Production of phenylacetylcarbinol from P2P is useful information for methamphetamine impurity profiling because phenylacetylcarbinol is a precursor of ephedrines, the other methamphetamine precursors.