Generation and reactions of anionic sigma-adducts of 1,3-dinitrobenzene and 1,3,5-trinitrobenzene with carbanions in a gas phase, using an electrospray ion source as the chemical reactor.
Di- and trinitrophenide anions generated by decarboxylation of the anions of 2,4-, 3,5-, and 2,6-dinitrobenzoic acids and 1,3,5-trinitrobenzoic acid in the medium-pressure region of an electrospray ion source react locally with various C-H acids delivered in the form of vapors mixed with the curtain gas, yielding anionic sigma-adducts. Positive results were obtained for aliphatic aldehydes, ketones, esters and nitriles. All three dinitrobenzoic acids bearing NO(2) groups in the meta position to each other gave the same sigma-adducts which can be rationalized by a reaction sequence including proton transfer from the C-H acid to the nitrophenide anion and subsequent formation of the sigma-adduct by the reaction of 1,3-dinitrobenzene with the carbanion within the ion-molecule complex. It was found that such a reaction is possible only for C-H acids with a gas-phase acidity lying within a narrow, strictly defined range whose location on the acidity scale depends on the acidity of the nitroarene. The sigma-adduct formed in the reaction of the 2,4-dinitrophenide anion with CH(2)Cl(2) undergoes rapid HCl elimination yielding an anion with the same composition as that produced by the Vicarious Nucleophilic Substitution of hydrogen reaction but with a different structure.