Kinetic study of the reactions of some 5-nitro-2-(4-nitrophenoxy)-3-x-thiophenes with aniline and 4-methoxyaniline in methanol

The rate constants of the title reactions have been measured at various amine concentrations. The second-order kinetic constant for the amino substitution increases in a hyperbolic way as a function of the nucleophile concentration. The k3Am/k-1 ratio for each catalysed system is not a monotonic function of the X substituent. This result has been rationalized in the framework of the SB-GA (Specific Base-General Acid) mechanism of base catalysis.