THERMAL DEGRADATION OF BIS (2-CHLOROETHYL) SULFIDE (MUSTARD GAS)

The thermal degradation of mustard gas (ClCH 2 CH 2 SCH 2 CH 2 Cl, "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°C, 91% HD remains (80% with 5% water). After 40 days at 140°C, 30% HD remains (24% with 5% water) and black "tar" precipitates form. The apparent E a is 22.4 kcal/mol. Major products include Q (ClCH 2 CH 2 SCH 2 CH 2 SCH 2 Cl), 1,2-dichloroethane, 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 "mustard heels." The decomposition does not go to completion due to the equilibrium nature of the reaction at these temperatures.