Carboxylic
Acid Catalyzed Hydration of Acetaldehyde
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Abstract
Electronic
structure calculations of the pertinent stationary points on the potential
energy surface show that carboxylic acids can act effectively as catalysts
in the hydration of acetaldehyde. Barriers to this catalyzed process
correlate strongly with the p<i>K</i><sub>a</sub> of the
acid, providing the potential to provide the predictive capacity of
the effectiveness of carboxylic acid catalysts. Transition states
for the acid-catalyzed systems take the form of pseudo-six-membered
rings through the linear nature of their hydrogen bonds, which accounts
for their relative stability compared to the more strained direct
and water-catalyzed systems. When considered as a stepwise reaction
of a dimerization followed by reaction/complexation, it is likely
that collisional stabilization of the prereactive complex is more
likely than reaction in the free gas phase, although the catalyzed
hydration does retain the potential to proceed on water surfaces or
in droplets. Lastly, it is observed that postreactive diol–acid
complexes are significantly stable (∼12–17 kcal/mol)
relative to isolated products, suggesting the possibility of long-lived
hygroscopic species that could act as a seed molecule for condensation
of secondary organic aerosols