Separation of Closely Boiling Isomers and Identically Boiling Isotopomers via Electron-Transfer-Assisted Extraction

Mixtures of isotopomers with identical molecular weights (ethyl-d 5-benzene + ethylbenzene-d 5 and tert-butyl-d 9-biphenyl + tert-butylbiphenyl-d 9) have been partially resolved by making use of their differing solution electron affinities. EPR analysis of the anion radicals resulting from the partial potassium reduction of mixtures of the isotopomers (*R and R, respectively) in tetrahydrofuran show that the equilibrium constant for the reaction R•-,M+ + *R = R + *R•-,M+ deviates from unity. These EPR results predict that a separation of anion radical from neutral molecule would effect a separation of the isotopomers. Removal of the solvent leaves a solid mixture of neutral and potassium anion radical salt forms of the isotopomers. Subsequent dissolution of the neutral materials from the anion radical salts yields a mixture that is enriched in the ring-deuterated isotopomer, and reoxidation of the anion radical with iodine yields a mixture that is enriched in the ring-protiated isotopomer. Analogous experiments were also used to separate closely boiling geometric isomers.