Details

Autor(en) / Beteiligte

• Li, Jun
• Brill, Thomas B

Titel

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

Ist Teil von

• The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 2002-10, Vol.106 (41), p.9491-9498

Ort / Verlag

American Chemical Society

Erscheinungsjahr

2002

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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.