Theoretical Study of the Mechanism and Regioselectivity of the Alkylation Reaction of the Phenoxide Ion in Polar Protic and Aprotic Solvents

Publication date: Available online 15 June 2018 Source:Computational and Theoretical Chemistry Author(s): Isac C. Nogueira, Josefredo R. Pliego Alkylation of the phenoxide ion in the solution phase can take place on the oxygen atom (O-alkylation) and the carbon atoms of the aromatic ring in the ortho- and para-positions (C-alkylation). The reaction outcome depends on the alkylating molecule and the solvent. This work presents a density functional theory calculation (X3LYP and M08-SO functionals) of the possible reaction pathways for alkylation of phenoxide ions with ethyl chloride in the following solvents: water, methanol, and dimethyl sulfoxide. The solvent effect was included through the SMD and PCM models. Our results pointed out that O-alkylation was much more favorable than C-alkylation in the gas phase. Solvent effect favors C-alkylation, although it was unable to change the reactivity preference of O-alkylation, even in aqueous solution. Alkylation on the meta-carbon atom corresponded to a second-order saddle point and was the most unfavorable pathway. The calculations indicated that only O-alkylation would be observed, with an activation free energy of 23.6 kcal mol-1 in dimethyl sulfoxide solution, in good agreement with the experimental barrier of 20.8 kcal mol-1. Graphical abstract
Source: Computational and Theoretical Chemistry - Category: Chemistry Source Type: research
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