Reactions of sulfur with alkaline substances such as hydroxides can yield sulfides, thiosulfates or sulfites. For example, the reaction between sulfur and sodium hydroxide can be represented by the following equation:

S + 2 NaOH -> Na2S + H2O

This is a redox reaction, in which sulfur is oxidized from an oxidation state of 0 to -2 in sodium sulfide, while sodium is reduced from an oxidation state of +1 to 0.