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Alkylation of substituted phenols in DMF by MeI using TMGN (bis- 1,1,8,8-(tetramethylguanidino)naphtalene) a proton sponge as base: a kinetics study by NMR spectroscopy
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1  Université de Lille 1, Sciences et Technologies, UMR CNRS USTL 8009, Organic and Macromolecular Chemistry, FR CNRS USTL 2638, Eugène-Michel CHEVREUL Institute, Villeneuve d’Ascq, France

Abstract: Evaluation of a new proton sponge, bis-1,1,8,8-(tetramethylguanidino)naphtalene (TMGN), in substituted phenols O-alkylation by methyl iodide in DMF has been studied. Kinetic measurements were performed in N,N-dimethylformamide-d7 and followed by 1H NMR using stoichiometric amounts of reagents. Plot of the results shows that the reaction follows an almost perfect second order rate law. However the Hammett plots for substituted phenols are not linear but bell shaped. In order to separate the deprotonation and alkylation contribution to the kinetics, deprotonation of phenols by TMGN has been investigated by quantitative 13C NMR. By combining these data a linear Hammett plot with a negative slope was obtained for the alkylation step and substituted phenol acidity constants in DMF, not accessible by NMR measurements, were determined which are in agreement with literature data.