The Thermodynamics of 2-methylthiophene Homocoupling

Abstract

The homocoupling of 2-methylthiophene to yield 5,5’-dimethyl-2,2’-bithiophene was observed with the following chemical oxidants: hydrogen peroxide (H2O2), cerium (Ce4+), dichromate (Cr2O7 2-), and persulfate (S2O8 2-). The reaction kinetics and equilibrated system concentration for the homocoupling of 2-methylthiophene was quantified using 1H-NMR spectroscopy. Under the conditions studied the system equilibrated in under 48 hours. Using the oxidant hydrogen peroxide the equilibrium concentrations of 2-methylthiophene and 5,5’-dimethyl-- 2,2’-bithiophene were 0.0994M, and 7.398 x ^(-4) M. The equilibrium constant for the homocoupling in the presence of hydrogen peroxide was calculated to be 0.146 at 25 °C. Using this equilibrium constant, the reduction potential of 5,5’-dimethyl-2,2’-bithiophene to 2-methylthiophene was calculated to be 1.80 V..