Abstract: A method for preparing a compound of formula RSH where R represents an alkyl group, by gas-phase catalytic reaction of hydrogen sulfide with a compound of formula ROH, in the presence of a solid catalyst, according to which method the reaction is performed in the presence of a catalyst which includes one or several pure or mixed rare-earth oxide(s), one or several pure or mixed rare-earth sulfide(s), or one or several pure or mixed rare-earth oxysulfide(s). When the rare earth is lanthanum, the catalyst is a mixed oxide of lanthanum and of at least one metal selected from rare earths or not and when the rare earth is cerium, the catalyst is supported on an alumina.

Abstract: An agent for initiating a radical addition reaction includes a persulfate and one or more transition metals, in elemental form or in an oxidized form, as well as a method for preparing a compound of formula (I) in which X is selected from S, Se and O; by a radical addition reaction in the presence of such an agent.