Protonation of some substituted phenylthiophen-2-ylmethanones in sulfuric acid

Abstract

Within the framework of research carried out on the behaviour of ArCOY compounds the title reaction has been investigated in order to gain information on the influence of Ar and of Y on the interaction between Y and CO and between Ar and CO, respectively, when Ar = 4-substituted phenyl and Y = 5-substituted thiophen-2-yl. The pK_BH⁺ values collected in this work have been analysed by linear free energy relationship and the calculated p values (0.98 and 2.15 for substitution in the phenyl group and thiophen-2-yl ring, respectively), as well as the mean value (0.97) of m*, have been compared with those of 5-substituted-2-acetylthiophenes 2 and 4-substituted acetophenones 3. From the above comparisons we conclude that solvation has a role, as important as that of the electronic density on the basic centre, in determining the degree of protonation of weak bases even if they are structurally similar.