Phosgene in deteriorated chloroform: presumptive cause of production of 3,4-dimethyl-5-phenyl-2-oxazolidones in methamphetamine

Purpose The trans- and cis -forms of 3,4-dimethyl-5-phenyl-2-oxazolidone (DPO) are impurities found in methamphetamine, but their production mechanism has been unclear. Here, the authors examined whether DPOs were produced by the reaction of ephedrines (ephedrine and pseudoephedrine) with deteriorated chloroform containing phosgene. Methods Two sources of chloroform were used in this experiment: amylene-stabilized chloroform, which had been stored on a laboratory table after opening the bottle, and ethanol-stabilized chloroform, which had been stored without opening the bottle. Samples 1–4 were prepared and analyzed by gas chromatography/mass spectrometry. Sample 1 was prepared by extracting hydrochloride salts of ephedrines with chloroform under basic conditions. Sample 2 represented a chloroform solution of pseudoephedrine hydrochloride. Sample 3 was a methanol solution of pseudoephedrine hydrochloride, which had been exposed to chloroform prior to dissolution. Sample 4 was prepared by extracting pseudoephedrine hydrochloride, which had been exposed to chloroform prior to the extraction, with ethyl acetate under basic conditions. Results Phosgene was detected in amylene-stabilized chloroform but not ethanol-stabilized chloroform. The amylene-stabilized chloroform almost completely converted ephedrines to DPOs in samples 1 and 2, and partially converted pseudoephedrine to trans- DPO in samples 3 and 4. In contrast, the ethanol-stabilized chloroform did not give DPOs in any sample. Conclusions The experimental results indicated that DPOs were produced by the reaction of ephedrines with deteriorated chloroform containing phosgene and that the reaction proceeds regardless of chemical forms, even at room temperature. DPOs are useful markers of contact between ephedrines and deteriorated chloroform.