Hydrogen/Chlorine Exchange Reactions of Gaseous Carbanions

Gas-phase reactions of three typical carbanions CH2NO2−, CH2CN−, and CH2S(O)CH3− with the chloromethanes CH2Cl2, CHCl3, and CCl4, examined by tandem mass spectrometry, show a novel hydrogen/chlorine exchange reaction. For example, reaction between the nitromethyl anion CH2NO2− and carbon tetrachloride CCl4 forms the ion CHClNO2−. The suggested reaction mechanism involves nucleophilic attack by CH2NO2− at the chlorine of CCl4 followed by proton transfer within the resulting complex [CH2ClNO2 + CCl3−] to form CHClNO2− and CHCl3. Two other carbanions CH2CN− and CH2S(O)CH3− also undergo the novel hydrogen/chlorine exchange reactions with CCl4 but to a much smaller extent, their higher nucleophilicities favoring competitive nucleophilic attack reactions. Proton abstraction is the exclusive pathway in the reactions of these carbanions with CHCl3. While CH2CN− and CH2S(O)CH3− promote mainly proton abstraction and nucleophilic displacement in reactions with CH2Cl2, CH2NO2− does not react.