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2 Polish Journal of Chemistry

2 1998

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Studies on mechanism of 2-pyridinecarboxaldehyde oxidation by dichromates in strongly acidic aqueous solutions. The unusual reaction order on concentration of the aldehyde

Kita E., Kita P., Uścińska G.

Polish Journal of Chemistry

1998

Vol. 72, nr 8

1949-1957

2-Pyridinecarboxaldehyde (pyad) has been oxidized by Cr2O7(-2) ion at pH range 0-1 to 2-pyridinecarboxylic acid (pyac). The produced CR(III) exists in the form of three complex ions: [CR(pyac)(H2O)4](2+), [Cr(pyac)2(H2O)2](+) and [Cr(H2O)6](3+). The reaction follows unusual mixed fourth-order rate law: first-order on concentrations of H(+)-aq and CR(VI) and second-order on concentration of the aldehyde. Mechanism of the reaction has been discussed.

Studies on kinetics and mechanism of oxidation of pyridoxal by dichromates in aqueous HClO4 solutions

Kita E., Kita P., Pietkiewicz A., Wrzeszcz G., Rozpłoch F.

Polish Journal of Chemistry

1998

Vol. 72, nr 3

573-581

Oxidation of pyridoxal (PL) by Cr2O7(2-) ion has been studied using an excess of the aldehyde under air or argon atmospheres. The reaction leads mainly to two Cr(III) complexes: [Cr(PA)(H2O)4](2+) and [Cr(H2O)6](3+) and to uncoordinated pyridoxic acid (PA). The rate of PL oxidation follows a mixed third order rate law: first order in concentrations of Cr(VI), Pl and H3O(+). The reduction of Cr(VI) toCr(III) proceeds through chromium(V) intermediate complex, which has been detected by the EPR method. Mechanism of the reaction has been discussed.