The ene reaction of maleic anhydride with alkenes

Abstract

The kinetics of the ene reaction between maleic anhydride and various alkenes have been investigated. The kinetics, based on a 100% mass balance, have been determined for a number of alk-1-enes ranging from hex-1-ene to dodec-1-ene and for cis- and trans-dec-5-ene. The reaction has been found to follow second-order kinetics up to 75% conversion with no significant solvent effects. The kinetics have been determined over the range 125–224 °C and the Arrhenius parameters have been calculated. In the absence of detectable quantities of cyclobutane derivatives in the product and the negligible effect of free radical inhibitors on the rate of the ene reaction, a concerted mechanism is favoured. The trans-configuration of the products, alkenylsuccinic anhydrides, and the lack of variation of the reaction rate with increasing alkyl chain length of the alk-1-enes point to an exo-transition state. trans-Dec-5-ene appears to favour an exo-transition state whilst the greater negative entropy of activation for cis-dec-5-ene is attributed to steric hindrance favouring an endo-transition state.