Solid state debromination of C 60 Br 24 back to C 60 with cesium iodide: kinetics, thermodynamics and mechanism

AbstractThe bromofullerene C60Br24 undergoes a complete and quantitative debromination to C60 when it is mixed and ground in the solid state with cesium iodide (CsI). The kinetics of this unique solid state debromination reaction was studied with FT-IR spectroscopy on C60Br24 embedded in CsI pellet. The debromination rate constant was measured k = 8.4 x 10−4 s−1 and found independent from the C60Br24 concentration. Chemical thermodynamics calculations show that the C60Br24 debromination in CsI matrix is characterized by a largely favorable free energy of reaction (ΔGr) and the reaction is exothermal. A debromination mechanism is discussed in terms of concerted elimination of the bromide anions and formation of carbocations on the fullerene cage in agreement with the E1 type elimination reaction mechanism. The carbocations sites are reduced to radicals and stabilized as trivinylmethyl radicals (the reduction occurs by the action of iodide ions of CsI which are oxidized to molecular iodine) and then a rearrangement of the double bonds leads back to C60 quantitatively.Keywords: BromofullereneC60Br24solid state debrominationcaesium iodidekineticschemical thermodynamicsdebromination mechanism Disclosure statementNo potential conflict of interest was reported by the author(s).Additional informationFundingWe acknowledge support from State Research Agency (AEI) of the Spanish Ministry of Science and Innovation (MICINN) under grant PID2020-115758GB-I00. This article is based upon work from COST Action NanoSpace, CA21126, supported by COST (European Cooperation in Science and Technology).