Concerted SN2 mechanism for the hydrolysis of acid chlorides. Comparison of reactivities calculated by the density functional theory with experimental data

Ferenc Ruff (1) , Ödön Farkas (2)

1 Organic Chemistry
2 Department of Organic Chemistryí

DFT computations have been performed in acetone and water solvents in order to investigate the mechanism of hydrolysis of acid chlorides. Acetyl chloride and chloroacetyl chloride hydrolyze via concerted, one-step SN2 mechanism, with the attack of water at the sp2 hybridized carbon atom of the C=O group, and the transition state (TS) has distorted tetrahedral geometry. Solvent molecules act as general base and general acid catalysts. The TS of chloroacetyl chloride is tighter and less polar than the TS of acetyl chloride. The structure of the SN2 TS for the hydrolysis of benzoyl chlorides changes with the substituents and the solvent. Tight and loose TSs are formed for substrates bearing electron withdrawing (e-w) and electron donating (e-d) groups, respectively. In acetone, only the e-w effect of the substituents increase the reactivity of the substrates, and the change of the structure of the TSs with the substituents is small. In water, polar and very loose TSs are formed in the reactions of benzoyl chlorides bearing e-d substituents, and the rate enhancing effect of both e-d and e-w groups can be computed at higher level of theory. Calculated reactivities and the changes of the structure of the TSs with substituents and solvent are in accordance with the results of kinetic studies. In SN2 nucleophilic substitutions late/early TSs are formed if the attacking reagent is poorer/better nucleophile than the leaving group, and loose/tight TSs are formed for substrates bearing e-d/e-w substituents and in protic/aprotic solvents.

Mots clés: Physical Sciences

Ferenc Ruff, Ödön Farkas. Concerted SN2 mechanism for the hydrolysis of acid chlorides. Comparison of reactivities calculated by the density functional theory with experimental data. Journal of Physical Organic Chemistry, 2010, 24 (6), pp.480. ⟨10.1002/poc.1790⟩. ⟨hal-00599807⟩