Novel Direct Access to Enantiomerization Barriers from Peak Profiles in Enantioselective Dynamic Chromatography: Enantiomerization of Dialkyl-1,3-allenedicarboxylates

摘要

The axially chiral allenes dimethyl-1,3-allenedicarboxylate 1 and diethyl-1,3-allenedicarboxylate 2 show characteristic plateau formation during enantioselective GC separation on the chiral stationary liquid phase Chirasil-β-Dex. The elution profiles, obtained from temperature-dependent dynamic GC (DGC) experiments (1: 100-140 ℃; 2: 110-150 ℃) were evaluated with the recently derived approximation function (F) k_1~(approx) = f(t_R~A, t_R~B, w_h~A, h_(plateau, N) to yield the enantiomerization rate constant directly k_1. These values were compared with those obtained by computer-aided simulation with ChroWin. The Eyring activation parameters of the experimental interconversion profiles were determined to be: ΔG~#(298.15 K) = 103.6 ± 0.9 kJ mol~(-1), ΔH~# = 44.7 ± 0.4 kJ mol~(-1), ΔS~# = -198 ± 7 J K~1 mol~(-1) for dimethyl-1,3-allenedicarboxylate 1, and ΔG~#(298.15 K) = 103.5 ± 1.1 kJ mol~(-1), ΔH~# = 44.7 ± 0.5 kJ mol~(-1), ΔS~# = -197 ± 9 J K~(-1) mol~(-1) for diethyl-1,3-allenedicarboxylate 2. The approximation function (AF) presented here allows the fast determination of rate constants k_1 and activation barriers of enantionmerization ΔG~# from chromatographic parameters without extensive computer simulation.