Dissociation energy for the P2S2 ring in a family of thionation reagents and the corresponding chemical reactivity of separated species: a density functional theory analysis

In this work, 11 members of a 1,3,2,4‐dithiadiphosphetane 2,4‐disulfides family are analyzed from a theoretical point of view. These reagents are involved in thionation processes, where the first step implies the breaking bond between sulfur and phosphorus atoms to destroy the P2S2 ring, which is characteristic of these compounds. Thus, we estimate this breaking bond by analyzing the Gibbs energy over several temperatures, concluding that 3 of the most representative reagents of this family (Belleau, Davy, and Lawesson) are dissociated to yield 2 symmetrical species, for temperatures less than 400 K. This estimation, in gas phase, is reasonably good with respect to experimental information where these 3 reagents react at temperatures below 383 K. These 3 reagents present the lowest dissociation energies for several temperatures due to enthalpic and entropic contributions. Reagents and their monomers were analyzed by using the density functional theory framework to show that among the studied reagents, 3 of them exhibit similar behavior between themselves and correspond to the most used reagents in experimental thionation processes. For the separated species, the density functional theory chemical reactivity predictors indicate that the phosphorus atom has the biggest response when the system accepts electrons and sulfur atoms have the biggest response when the system gives electrons. This result is totally in accord with experimental suggestions for this kind of processes.