Does Water Clustering Accelerate Acetylacetone Tautomerization Reaction?
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𝛽-diketone tautomerization is a key reaction in synthetic chemistry that is known to be accelerated in polar protic solvents, such as water. However, the mechanism and number of water molecules for optimal catalytic effect remain unclear. To investigate this aspect, we employed a hybrid cluster-continuum approach using water clusters, (𝐻2𝑂)𝑛, 𝑛 = 1 ∼ 4, to simulate tautomerization of acetylacetone (AA). We utilized CBS-Q energies, along with the geometries and solvation energies obtained from B3LYP/6-311+G(2d,2p), using the polarizable continuum model. The addition of one water molecule was shown to lower the activation energy (Ea) by 24 kcal/mol by actively participating in the proton transfer. Additional water molecules can further lower the Ea by 5 to 10 kcal/mol; however, the decrease in Ea saturates at n = 3 water molecules. Water molecules also help stabilize AA with a solvation energy of −6 kcal/mol per 𝐻2𝑂. These findings highlight the critical role of explicit water clusters in promoting the tautomerization reaction for AA.
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