Acid-catalyzed cleavage of 2-pyridyl and 4-pyridyl derivatives of aminomethylphosphonic acid. Kinetic and chemical arguments for a mechanism with A-SE2 character

Bogdan Boduszek, Rafał Latajka, Wojciech Leśniak

Research output: Contribution to journalArticlepeer-review

Abstract

Studies of the acid-catalyzed cleavage of 2-pyridyl and 4-pyridyl(amino)methylphosphonic acids demonstrate that protonation has a profound effect on the cleavage of C-P bonds. In H2SO4, and other strong mineral acids the cleavage of aminophosphonic acids 1 and 4 exhibits a kinetic depedence on Zucker-Hammett acidity function (h0), with rate law, v = k[phosphonate]·h0, and also fulfil the Bunnett approach on acidity function. The measured solvent isotope effect kH/kD is small, and varied from 1.46 for 1b to 1.18 for 4b. The isotope effect shows that protons are involved on the rate determining step of the cleavage. All of this evidence indicates that the cleavage of 1 or 4 shows A-SE2 character substitution reaction. Calculated activation parameters and some chemical experiments indicate that the protonated phosphonate molecule is split by a dissociative mechanism, combined with formation of a positive-charged phosphorus moiety.

Original languageEnglish (US)
Pages (from-to)53-75
Number of pages23
JournalPhosphorus, Sulfur and Silicon and Related Elements
Volume165
DOIs
StatePublished - Jan 1 2000
Externally publishedYes

Keywords

  • Acidity
  • Catalysis
  • Cleavage reactions
  • Phosphonates
  • Protonations
  • Pyridines

ASJC Scopus subject areas

  • Biochemistry
  • Organic Chemistry
  • Inorganic Chemistry

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