Methyl vinyl ketone reaction with sodium C-1-C-3 mercaptides of a spent sulfide-alkaline solution at 20degreesC was found to yield 5-thiahexan-2-one (80%) and 5-thiaheptan-2-one (2%). The addition of formaldehyde gives mainly 1,1-bis(methylthiomethyl)propanone (62%) and 6-thia-4-hepten-2-one (18%). Increasing reaction temperature (50degreesC) and sodium hydroxide concentration in the reaction medium results in the formation of sulfur compounds with a higher molecular mass.