Reciprocal resolutions between 1-phenylethylamine and carboxyesters of isopropylidene glycerol: improvement of the method by replacing mono-phthalate with 3-carboxy-2-naphthoate

A novel resolving agent, isopropylidene glycerol 3-carboxy-2-naphthoate 2 , was designed on the basis of the consideration that replacement of phenyl group with a naphthyl group would improve the resolving ability of isopropylidene glycerol hydrogen phthalate 1 while also conferring more suitable physicochemical properties for such a specific use. Indeed, 1-phenylethylamine 4 was resolved by 2 more efficiently than by 1 (respective resolution efficiencies, ( S ) 0.88 and 0.81), while 1 and 2 were resolved by 4 with S ranging between 0.54 and 0.59. Furthermore, 2 is a solid, whereas 1 is a viscous oil, and its recovery at the end of the resolution procedure is easier than that of 1 . In order to understand the chiral discrimination mechanism of the two reciprocal resolutions, the binary melting point phase diagrams of the four diastereomeric systems ( S )- 2 ·( S )- 4 /( S )- 2 ·( R )- 4 , ( S )- 2 ·( S )- 4 /( R )- 2 ·( S )- 4 , ( S )- 1 ·( S )- 4 /( S )- 1 ·( R )- 4 and ( S )- 1 ·( S )- 4 /( R )- 1 ·( S )- 4 were determined. The first two systems form ideal conglomerates, characterised by identical diagrams, in which the eutectic corresponds to a 0.10 molar ratio of ( S )- 2 ·( S )- 4 . The same behaviour was shown by the other two systems, whose eutectics, however, correspond to a 0.18 molar ratio of ( S )- 1 ·( S )- 4 . On the basis of the present results, which indicate an excellent resolution ability of 2 for 4 , the application of this new acid to the resolution of other 1-arylalkylamines seems to have very good prospects, worthy of investigation.