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

Abstract

The symmetrical amino alcohol synthesis via ring opening of cyclohexene oxide with ethylendiamine is illustrated by synthesis and characterization of β-amino alcohols s-cis-(SSSS)-cy2en (1) and s-trans-(SSRR)-cy2en (2) (cy2en = 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 1H and 13C 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.