1,3,5-Trithiane is the chemical compound with the formula (CH2S)3. This heterocycle is the cyclic trimer of the otherwise unstable species thioformaldehyde. It consists of a six-membered ring with alternating methylene bridges and thioether groups. It is prepared by treatment of formaldehyde with hydrogen sulfide. It is the trimer of thioformaldehyde. Trithiane is a building block molecule in organic synthesis, being a masked source of formaldehyde. In one application, it is deprotonated with organolithium reagents to give the lithium derivative, which can be alkylated. (CH2S)3 + RLi → (CH2S)2(CHLiS) + RH (CH2S)2(CHLiS) + R’Br → (CH2S)2(CHR’S) + LiBr (CH2S)2(CHR’S) + H2O → R’CHO + …. Trithiane is the dithioacetal of formaldehyde. Other dithioacetals undergo similar reactions to the above. It is also a precursor to other organosulfur reagents. For example, chlorination in the presence of water affords the chloromethyl sulfonyl chloride: (CH2S)3 + 9 Cl2 + 6 H2O → 3 ClCH2SO2Cl + 12 HCl