Racemic Structures of (±)-α-Methylbenzylamine Salts with Organic Acids and Optical Resolution of the p-t-Butylbenzoate by Preferential Crystallization

Abstract

The racemic structures of (±) -α-methylbenzylamine salts with organic acids have been studied. The organic acids employed were benzenesulfonic acid (BS), p-methylbenzenesulfonic acid (MBS), p-ethylbenezenesulfonic acid (EBS), sulfanilic acid (SU), p-t-butyl. b enzoic acid (TBB) phenoxyacetic acid (PA), isovaleric acid (IVA), pivalic acid (Pe), methacrylic acid (MC), and 2, 2-bis (hydroxymethyl) propionic acid (HMP). It was concluded based on the comparison of the infrared spectra, melting points and solubilities of these (±)-salts with those of the corresponding (-)-salts that the (±)-TBB salt was conglomerate. It was unable to presume the racemic structures of the other (±)-salts by these comparisons. The enthalpies of fusion values (ΔHf) of (±)-BS, MBS, EBS, SU, PA, MC, and HMP salts were higher than those of the (-)-salts. The 4H values of (±)-IVA and PI salts were lower than those of the (-)-salts. However, these (±)-salts were concluded to form racemic compound, since the free energies of formation of racemic compound values (ΔG∅) were negative. The ΔG∅value of the (±)-TBB salt, being conglomerate, was positive. These results were supported by the binary phase diagrams of melting point. The optical resolutions of (±)-TBB salt were carried out in tetrahydrofuran under the conditions of several degrees of supersaturations (112, 122 and 133%) at 20°C. The (±)-TBB salt was able to be resolved by preferential crystallization procedure and the (-)-salt having a high optical purity was obtained.