Density functional and MP2 calculations with extended basis sets were performed on the species participating in both the previously suggested and a newly proposed mechanisms of partial dechlorination of chloropicrin by simple sulfur species, both in gas phase and in a simulated water environment. Thermochemistry of both mechanisms in the gas phase was also studied using the chemical models G3 and G4. It is shown that the previously proposed reductive dehalogenation is not thermodynamically feasible at room temperature, as it should be according to the experimental evidence. Although inclusion of the solvent improves the results with respect to gas phase, the thermodynamics of the proposed mechanism by Zheng et al. is still unfavorable for obtaining the experimental products. An alternative mechanism is then proposed, involving the formation of HSCl, which is the intermediate that then undergoes redox reactions. Such a mechanism is exothermic and spontaneous, according to the computational results, and produces elementary sulfur in agreement with the experimental facts.