Solvent-free synthesis and crystal structures of s-cis and s-trans N,N′-bis(2-hydroxycyclohexyl)ethane-1,2-diamine

The symmetrical amino alcohol synthesis via ring opening of cyclohexene oxide with ethylendiamine is illustrated by synthesis and characterization of beta-amino alcohols s-cis-(SSSS)-cy(2)en (1) and s-trans-(SSRR)-cy(2)en (2) (cy(2)en = N,N'-bis(2-hydroxycyclohexyl)ethane-1,2-diamine) in one step and with high yield. The reaction was carried out in a microwave reactor under solvent-free conditions. These products were characterized by IR and Raman spectroscopy, elemental analysis, thermal methods (TGA, DTG and DTA), mass spectrometry and H-1 and C-13 NMR spectroscopy. The crystal structures of 1 and 2 were determined by single crystal X-ray structural analysis, followed by DFT calculations. Intramolecular hydrogen bond was observed in 1 with C (2) symmetry, but not in 2 with C (i) symmetry. The nature of intramolecular hydrogen bond in 1 has been investigated by AIM and NBO analyses. The molecules in 1 are linked into an infinite chain along the [001] direction, giving rise to R (4) (4) (8) graph-set motif, while the molecules in 2 are linked into a 2D network in the bc plane, giving rise to R (2) (2) (10) and R (3) (3) (12) motifs. The protonation equilibria of 1 and 2 have been studied by pH-potentiometry, with pK (1) 9.01 and pK (2) 5.50 determined for 1 and pK (1) 8.58 and pK (2) 5.26 determined for 2.