Spectroscopy of Hydrothermal Reactions 20:  Experimental and DFT Computational Comparison of Decarboxylation of Dicarboxylic Acids Connected by Single, Double, and Triple Bonds

Abstract

The kinetics and pathways of decarboxylation of aqueous acetylenedicarboxylic acid at pH = 0.97−8.02 were studied in situ at 80−160 °C and 275 bar by using an FT-IR spectroscopy flow reactor with sapphire windows. The first-order (or pseudo first-order) rate constants and corresponding Arrhenius parameters were obtained for the neutral acid, monoanion, and dianion. The decarboxylation rates are in the order: HO2CC⋮CCO2 - > HO2CC⋮CCO2H > -O2CC⋮CCO2 -. The decarboxylation mechanisms of these reactants and the propiolic acid product were analyzed by B3LYP/6-31+G(d) density functional theory. The transition state structures were found for the neutral acids and monoanions. In gas phase the transition state structure is a four-member ring involving C−C(O)−O−H. In aqueous solution a cyclic structure incorporating at least one water molecule forms. A comparison of transition state structures for the decarboxylation of β-saturated (succinic) and β-unsaturated (maleic, fumaric, and acetylenedicarboxylic) aliphatic diacids was made with and without incorporating a water molecule. Consistent with experiment, the calculated activation energy for H-atom transfer to the α carbon atom in the decarboxylation step follows the order C⋮C < CC < C−C.

Two Three-Dimensional Lanthanide Frameworks Exhibiting Luminescence Increases upon Dehydration and Novel Water Layer Involving in Situ Decarboxylation

“…Decarboxylation can occur under hydro(solvo)-thermal conditions, 2 which can proceed via C−C bond cleavage. 3 Although decarboxylation reactions will increase the difficulty of the syntheses of compounds with required structures, they generate some novel compounds containing interesting organic species that are difficult to obtain by routine synthetic methods. 4 There have been many reports that transition metals such as Cu(II), Mn(II), Zn(II), and Cd(II) ions play a unique catalytic role in decarboxylation reactions.…”

Spectroscopy of hydrothermal reactions, part 26: Kinetics of decarboxylation of aliphatic amino acids and comparison with the rates of racemization

“…Direct decarboxylation of the zwitterions of the carboxylic acid and carboxylate ion, such as occurs in amino acids, has been found 28–31. Generally, the decarboxylation of aliphatic carboxylic acids is strongly dependent on the group attached and the bond type at the β‐position 30–35. For example, an aromatic ring acts as an electron sink that dissipates the developing negative charge on the α‐carbon atom during the decarboxylation of aromatic acids 35.…”

“…For example, an aromatic ring acts as an electron sink that dissipates the developing negative charge on the α‐carbon atom during the decarboxylation of aromatic acids 35. A general water‐molecule‐catalyzed transition state involving a six‐member ring has been suggested for decarboxylation 34–38. The decarboxylation of protein amino acids takes place at high temperatures.…”

Assembly of a novel Ag(I) supramolecular architecture constructed from flexible ligand containing asymmetrical tricarboxylate

“…These results indicate that Ag(I) atom plays an important role in the decarboxylation under hydrothermal conditions. Although the decarboxylation of carboxylic acids can happen both by homolytic and heterolytic cleavage of the C-C bond by a variety of mechanisms (with a heterolytic pathway occurring most frequently under hydro(solvo)thermal conditions) [29], we have not yet determined the mechanism by which the decarboxylation takes place on H 4 odp ligand, which is necessary to further study in this field.…”