'Periodica Polytechnica Budapest University of Technology and Economics'
Abstract
We have recognized a new nucleophilic addition reaction between L-ascorbic acid and
formaldehyde in biological circumstances (pH 7.4, T = 300 K). UV spectroscopic investi-
gation showed that the C2=C3 double bond of ascorbic acid rapidly disappears during
the reaction, verifying that the addition breaks the double bond. On the other hand, 13C
NMR studies have proved that on atom C2 an additional C-C single bond is formed. Ex-
act interpretation of the reaction mechanism is possible only by using quantum chemical
argumentations. Ab initio calculations show that in ionized (anionic) form of L-ascorbic
acid in water solution the Mulliken excess atomic charge is strongly negative on atom C2
while C1 and C3 exhibit significant positive net charges. Coulombic attraction arranges
formaldehyde's C=O double bond over the C2=C3 double bond of ascorbic acid and the
interaction of the two loose π-electron systems causes forming of a new σ C-C bond. The
described reaction plays a protective role in biological systems, since in this way the toxic
carcinogenic formaldehyde can be eliminated