Naphthalen 1,8 diyl 1,3,2,4 dithiadiphosphetane 2,4 disulfide

A compound related to Lawesson's reagent named NpP₂S₄ has been formed by the reaction of 1-bromonaphthalene with P₄S₁₀, this is a 1,3,2,4-dithiadiphosphetane 2,4-disulfide which has a naphth-1,8-diyl group holding the two phosphorus atoms together. The mechanism by which the NpP₂S₄ forms is unclear, but it is thought to occur through some free radical process, and naphthalene has been detected as a side product in its synthesis. In general NpP₂S₄ has been found to be less reactive than Lawesson's reagent, this result agrees with the hypothesis that the dithiophosphine ylides are responsible for the majority of the chemical reactions of the 1,3,2,4-dithiadiphosphetane 2,4-disulfides.

It has been found that NpP₂S₄ reacts with many hydroxyl compounds, for instance methanol, ethylene glycol and a catechol to form species with oxygen atoms bonded to the phosphorus atoms.

Methanol reacts to form compound which has one O-methyl and one S-methyl bonded to the two phosphorus atoms.