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The lithium-cation basicity (LCB=Gibbs energy of adduct dissociation) of methyl benzoate, and the three isomeric dimethyl phthalates (phthalate, iso- and tere-phthalate) has been determined by Fourier transform ion cyclotron resonance (FT-ICR), using the kinetic method. The dimethyl phthalate ester appears to be a relatively strong base toward Li + , as compared to the other isomers and to methyl benzoate. This is attributed to the chelation effect of the two carboxyl groups. The previously unknown protonic gas-phase basicity of dimethyl phthalate was also determined. Chelation makes also dimethyl phthalate a much stronger base than the two other isomers toward H + , but its protonated form decomposes readily by loss of a methanol molecule. |
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