1,3,5-Trithiane

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 and thioether groups. It is prepared by treatment of formaldehyde with hydrogen sulfide.

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 in turn 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 chloromethylsulfonyl chloride:
 * (CH2S)3 +  9 Cl2  +  6 H2O   →   3 ClCH2SO2Cl  +  12 HCl