Halophilic reactions of nucleophiles: 2. Crown ether promoted reactions of dibromodifluoromethane and sodium thiophenoxide1

In ether and benzene, CF2Br2 reacts with PhSNa either very slowly or not at all. However, catalytic amounts of dibenzo-18-crown-6 can accelerate the reactions dramatically, and more notably, the desired product PhSCF2Br (1) can be obtained in high yield, whereas the formation of the by-products PhSSPh (2) and PhSCF2H (3) is significantly suppressed. In ethereal solution containing 2.8 × 10−3 M of the crown ether, ranges of the yields of 1, 2, and 3 were 78–85%, 5–10%, and 1–2%, respectively. These results represent significant improvements over those most recently reported. Possible reaction pathways were discussed and new evidence for an anionic chain mechanism is presented, e.g.: (1) Moisture and other proton-donating species retard the desired reaction but increase the yields of 2 and 3. (2) Protium-donating solvents, light, oxygen and di-tert-butyl nitroxide do not affect the reactions significantly. (3) With CCl4 as the solvent, PhSCF2Cl, BrCCl3 and HCCl3 were also formed, but not CCl3-CCl3. Evidently, PhSCF2Cl was formed from a chlorophilic attack by PhSCF2− on solvent molecules.