Thermal degradation of bis (2-chloroethyl) sulfide (mustard gas)

The thermal degradation of mustard gas (ClCH2CH2SCH2CH2Cl, "HD"), with and without 5% added water, is examined. GC/MS, LC/MS and NMR were employed to comprehensively analyze the products. After 75 days at 90 degrees C, 91% HD remains (80% with 5% water). After 40 days at 140 degrees C, 30% HD remain s (24% with 5% water) and black "tar" precipitates form. The apparent E-a i s 22.4 kcal/mol. Major products include Q (ClCH2CH2SCH2CH2SCH2CH2Cl) 1,2-di chloroethane, polysulfides and 1,4-dithiane. With 5% water, oxygenates such as 1,4-thioxane and 2-chloroethanol are produced as are numerous sulfonium ions, including S-(2-chlorethyl)-1,4-dithianium, a major component of "mus tard heels." The decomposition does nor go to completion due to the equilib rium nature of the reaction at these temperatures.