Kinetics and isotope effects of the Dehydrochlorination of 1,1‐dichloro‐2,2‐bis‐(4‐nitrophenyl) ethane with 1,5‐diazabicyclo [4.3.0] non‐5‐ene in aprotic solvents

The kinetics of the reaction of 1,1‐dichloro‐2,2‐bis‐(4‐nitrophenyl)ethane (1) with 1,5‐diazabicyclo‐[4.3.0]non‐5‐ene(DBN) in acetonitrile (MeCN), dichloromethane (DCM), tetrahydrofuran (THF), isopropylether (IPE) and hexane (Hex) solvents are reported. The reaction is a simple β‐elimination forming 1‐chloro‐2,2‐bis‐(4‐nitrophenyl)ethane (2) (100% conversion). The rate constants are similar for MeCN, THF, IPE, but lower by a factor of 2 and 7 for DCM and Hex respectively. The deuterium kinetic isotope effects kH/kD are between 10 and 6 for MeCN and Hex solvents. The entropies of activation (ΔS≠) are negative and large and show no correlation with the polarity of the solvents. The free enthalpies of activation (ΔG≠) are rather small (about 68 kJ mol−1). The results are interpreted in terms of E2H with a contribution of (E1cB)I mechanism.