Catalytic Effect of Cesium Cation Adduct Formation on the Decarboxylation of Carboxylate Ions in the Gas Phase

Abstract

The effect of Cs(+) ligation on the decarboxylation of malonic acids (unsubstituted and methyl-, dimethyl-, ethyl-, and phenyl-substituted) in their carboxylate form was studied in the gas phase using tandem mass spectrometry. The study is based on the comparison of the decarboxylation of the bare monoanion (hydrogen malonates) and of the cesium adduct of the cesium salt (Cs(+) [cesium hydrogen malonates]) under collisional activation. Energy-resolved dissociation curves of the negative and positive ions exhibit major differences. Decarboxylation of the cationic adducts of substituted malonic acid salts occurs at significantly lower collisional activation than for the corresponding bare hydrogen malonate anions. The conclusions from these experiments are supported by DFT calculations. The calculated activation parameters (enthalpy and Gibbs energy) confirm that the cesium cation coordination assists the decarboxylation of the carboxylate form.

Origin of the Base‐Dependent Facial Selectivity in Annulation Reactions of Nazarov‐Type Reagents with Unsaturated Indolo[2,3‐a]quinolizidine Lactams

“…On the other hand, although the presence of ionic pairs when DBU is used cannot be ruled out, delocalization of the positive charge in the amidinium unit and the much larger size of DBU compared with the localized unit charge and smaller size of the Cs + cation (and hence the stronger electrostatic potential) suggests that the presence of ionic pairs should be more relevant for the Cs + cation. Further support comes from both experimental and theoretical evidence about the formation of cesium‐coordinated aggregates of diketones and carboxylic acids …”

Beyond Conventional Carbon Activation: Creating Porosity without Etching Using Cesium Effect

“…Further, Cs ions can effectively interact with oxygen-containing functional groups in organic compounds, promoting the elimination of these functional groups and the formation of covalent networks. [9,11] For example, Cs ions effectively catalyze dehydration and decarboxylation accelerating condensation reactions, [12] and activate carbonyl groups generating enolate anions, thus facilitating reactions such as substitution, addition, or macrocyclization. [9,13] Furthermore, the activation process involving Cs can occur at notably lower temperatures (≈600 °C) than K or Na compounds (>800 °C), due to lower melting points and decomposition temperatures of Cs compounds.…”