A novel solventless process is described for the preparation of imidazole-2-thiones. The new solventless process tolerates a variety of bases as co-reactants which introduces feedstock flexibility into the process while the solventless feature renders the process more environmentally friendly by eliminating volatile organic solvents from the process, reducing energy consumption (associated with solvent recovery and/or recycling), and allows shorter reaction time and workup. Furthermore, the elimination of solvents enhances workplace safety by obviating the need for flammable and/or toxic solvents.