Linear free energy ortho-correlations in the thiophene series. Part 12. The kinetics of piperidinodebromination of some 2-bromo-3-X-4-methyl-5-nitrothiophenes in methanol

Abstract

The rates of piperidinodebromination of some 2-bromo-3-X-4-methyl-5-nitrothiophenes (I; X = Me, H, Br, CONH₂, CO₂Me, SO₂Me, CN, or NO₂) have been measured in methanol. The logarithm of the rate constants gives an excellent straight line when plotted against the logarithm of the rate constants of piperidinodebromination for the corresponding 2-bromo-3-X-5-nitrothiophenes (III)(except for X = CONH₂) and against σ^–(except for X = Br and CONH₂). The good fit obtained confirms the applicability of Hammett-type relationships to fully ortho-tetrasubstituted thiophene derivatives. Kinetic data show the occurrence of a significant secondary steric effect in the piperidinodebromination of compound (Id).