Thermal Degradation of Allyl Isothiocyanate in Aqueous Solution

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Abstract
Allyl isothiocyanate in an aqueous solution was heated and refluxed at 100 °C for 1 h. The reaction mixtures were then extracted with methylene chloride and analyzed using gas chromatography (GC) and gas chromatography−mass spectrometry (GC−MS). The mixtures in aqueous phase were analyzed by high-performance liquid chromatography (HPLC) and liquid chromatography−mass spectrometry (LC−MS) equipped with an atmospheric-pressure chemical ionization (APCI) interface. The compounds identified in the methylene chloride extracts included diallyl sulfide, diallyl disulfide, diallyl trisulfide, diallyl tetrasulfide, allyl thiocyanate, 3H-1,2-dithiolene, 2-vinyl-4H-1,3-dithiin, 4H-1,2,3-trithiin, and 5-methyl-1,2,3,4-tetrathiane. N,N‘-Diallylthiourea, which was the major degradation product in the aqueous phase from the thermal reaction of allyl isothiocyanate, was identified by using LC−MS (APCI+), direct-probe EI-MS, and 1H-NMR. The possible mechanism for the formation of these products was proposed. Keywords: Allyl isothiocyanate; thermal degradation; N,N‘-diallylthiourea; LC−MS; atmospheric-pressure chemical ionization