MALDI-TOF, 13C NMR and FTIR analysis of the cross-linking reaction of condensed tannins by triethyl phosphate

•Catechin, tannins and resorcinol cross-linked with triethyl phosphate (TEP).•Catechin as model reacts with TEP mainly on the OH of the aromatic B-ring.•Tannins/TEP reaction is mainly on the C3 site of the flavonoid heterocycle ring.•Tannins/TEP reaction occurs also on the aromatic C4′, C5′ carbons of the B-ring.•TEP does not appear to react on the C5 and C7 sites of the flavonoid A-ring. Reaction of condensation and cross-linking of catechin monomer as a model of condensed (flavonoid) tannin extracts and of mimosa tannin itself, as well as of resorcinol with triethyl phosphate (TEP) have been investigated. FTIR, solid state CP-MAS 13C NMR, 31P NMR and MALDI-ToF spectroscopy studies revealed that reaction occurs mainly on the C3 of the flavonoid heterocycle ring and on the aromatic C4′ and C5′ carbons of the flavonoids B-ring, while TEP does not appear to react on the A-ring. A difference in the relative proportions of these two reaction sites for tannin and catechin has been noticed. The reactions appear to be dependent on the temperature. According to the thermogravimetric analysis, materials obtained from the reaction of tannin with TEP showed high thermal stability.