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1 Polish Journal of Chemistry

1 2001

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Acid-Catalyzed Cleavage of Some Chromone, Coumarin and Pyrone Derivaties of Aminomethylphosphonic Acid. Products and Kinetics of the ReactionB

Boduszek B., Latajka R., Walkowiak U.

Polish Journal of Chemistry

2001

Vol. 75, nr 1

63-69

Treatment of chromone-2, coumarin-4 and pyrone-2 derivatives of N-benzylaminomethylphosphonic acid with strong mineral acids leads to formation of the corresponding heterocyclic amines and phosphoric acid. Kinetic studies of this cleavage reaction demonstrate that protonation has a remarkable influence on a cleavage of C-P bonds. In aq. H2SO4, cleavage of the acids 1-3 exhibits a kinetic dependence on [H+]. The measured solvent isotope effect (kH/kD) was about 1.5 for the 1 and 2 and only 1.1 for the 3. The existence of the isotope effect shows that protons are involved on the rate-determining step. The data obtained suggest that the protonated phosphonate molecule is split by a dissociative mechanism with A-SE2 character and this is combined with an elimination of the phosphonate group as a positive-charged phosphorus moiety.