The crystal structure and characterization of a co-product in the synthesis of a Schiff base give evidence of its zwitterionic nature in the solid state

During the synthesis of the Schiff base 2-methoxy-6-{[(tiophen-2-methyl)imino]methyl}phenol (o-HVATPNH2), a co-product was isolated and characterized. The crystal structure of this molecule, 4,10-dimethoxy-13-(thiophen-2-ylmethyl)-6,12-dihydro-6,12-epiminodibenzo[b,f][1,5]dioxocane, namely (o-VA)(2)TPNH2 for short, was determined by X-ray diffraction methods. The chiral compound crystallizes as a racemate in the triclinic space group P1 with 2 molecules per unit cell. The (o-VA)(2) molecular fragment in (o-VA)(2)TPNH2 shows a non-crystallographic two-fold axis that enables the two molecular stereogenic centers to have the same chirality. The formation reaction mechanism for (o-VA)(2)TPNH2 is proposed and the structural properties of the Schiff base o-HVATPNH2 were revised. Evidence of the presence of the zwitterionic form of a Schiff base in the solid state was found.

Automated summary

The co-product (o-VA)(2)TPNH2 was isolated and characterized during the synthesis of the Schiff base o-HVATPNH2. Its crystal structure was determined by X-ray diffraction methods, revealing a specific chiral structure. The proposed formation reaction mechanism and revised structural properties of (o-VA)(2)TPNH2 were presented, along with evidence of the presence of the zwitterionic form of a Schiff base in the solid state.