Zn<sup>2+</sup>-Catalyzed Methanolysis of Phosphate Triesters: A Process for Catalytic Degradation of the Organophosphorus Pesticides Paraoxon and Fenitrothion
Bibliographic record
Abstract
The methanolyses of two neutral phosphorus triesters, paraoxon (1) and fenitrothion (3), were investigated as a function of added Zn(OTf)(2) or Zn(ClO(4))(2) in methanol at 25 degrees C either alone or in the presence of equimolar concentrations of the ligands phenanthroline (4), 2,9-dimethylphenanthroline (5), and 1,5,9-triazacyclododecane (6). The catalysis requires the presence of methoxide, and when studied as a function of added NaOCH(3), the rate constants (k(obs)) for methanolysis of Zn(2+) alone or in the presence of equimolar 4 or 5 maximize at different [(-)OCH(3)]/[Zn(2+)](total) ratios of 0.3, 0.5, and 1.0, respectively. Plots of k(obs) vs [Zn(2+)](total) either alone or in the presence of equimolar ligands 4 and 5 at the [(-)OCH(3)]/[Zn(2+)](total) ratios corresponding to the rate maxima are curved and show a nonlinear dependence on [Zn(2+)](total). In the cases of 4 and 5, this is explained as resulting from formation of a nonactive dimer, formulated as a bis-mu-methoxide-bridged form (L:Zn(2+)((-)OCH(3))(2)Zn(2+):L) in equilibrium with an active monomeric form (L:Zn(2+)((-)OCH(3))). In the case of the Zn(2+):6 system, no dimeric forms are present as can be judged by the strict linearity of the plots of k(obs) vs [Zn(2+)](total) in the presence of equimolar 6 and (-)OCH(3). Analysis of the potentiometric titration curves for Zn(2+) alone and in the presence of the ligands allows calculation of the speciation of the various Zn(2+) forms and shows that the binding to ligands 4 and 6 is very strong, while the binding to ligand 5 is weaker. Overall the best catalytic system is provided by equimolar Zn(2+), 5, and (-)OCH(3), which exhibits excellent turnover of the methanolysis of paraoxon when the substrate is in excess. At a concentration of 2 mM in each of these components, which sets the pH of the solution at 9.5, the acceleration of the methanolysis of paraoxon and fenitrothion relative to the methoxide reaction is 1.8 x 10(6)-fold and 13 x 10(6)-fold, respectively. A mechanism for the catalyzed reactions is proposed which involves a dual role for the metal ion as a Lewis acid and source of nucleophilic Zn(2+)-bound (-)OCH(3).
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".