72758-70-4Relevant academic research and scientific papers
Reactions in Strongly Basic Media. Part 10. Base-catylysed Isomerisation of Z- to E-substituted Chalcones
Bowden, Keith,Duah, Christiana K.,Ranson, Richard J.
, p. 109 - 112 (2007/10/02)
The rate coefficients for the methoxide-catalysed isomerisation of substituted (Z)-chalcones have been measured in methanolic dimethyl sulfoxide (DMSO) at 30.0 deg C, as well as for (Z)-chalcone at several temperatures.The reactions are first order in substrate and base.Further, log k1 for the reaction of (Z)-chalcone and (Z)-4-nitrochalcone correlate with an acidity function, Ha, having slopes equal to 0.53 and 0.45, respectively.The effect of substitution has been assessed using the Hammett equation, with ρ equal to 1.99 for the β-phenyl group and 1.93 for the benzoyl group.For the (Z)-chalcone, the enthalpy and entropy of acti vation are 14.2 kcal mol-1 and -14 cal mol-1 K-1, respectively, and the kinetic solvent isotope effect, k2MeOD/k2MeOH, is ca. 2.0.The rate coefficients for the amine-catalysed isomerisation of (Z)-chalcone and (Z)-4-nitrochalcone in DMSO have been measured at 30.0 deg C.The amino bases are a series of secondary aliphatic amines and the Bronstedt coefficients, β, are given as 0.39 and 0.38, respectively.The isomerisation is considered to proceed by rate-determining attack of the base at the β-carbon of the (Z)-chalcone to form a carbanion.The "cis"-conformer of the carbanion then rotates to form the "trans"-conformer, which eliminates the base to give the (E)-chalcone.
