Solvation and metal ion effects on structure and reactivity of phosphoryl compounds. Part 4. Dealkylation of phosphate esters by thiophenoxide ion in methanol

1994 ◽  
Vol 72 (9) ◽  
pp. 1933-1936 ◽  
Author(s):  
Marian Mentz ◽  
Agnes M. Modro ◽  
Tomasz A. Modro
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Rate Constants ◽  
Metal Ion ◽  
Ion Pairs ◽  
Phosphate Esters ◽  
Phosphoryl Group ◽  
Ion Effects ◽  
Metal Ion Effects ◽  
Catalytic Effects

Second-order rate constants for the demethylation of three phosphate esters by thiophenoxide salts, PhS−M+ (M+ = Me4N+, K+, Na+, Li+) in methanol-d4 at 25 °C have been measured. In contrast to the demethylation by iodide salts, metallic counterions do not exhibit any catalytic effects on the demethylation rate. The absence of the catalysis indicates that the salts react exclusively as ion pairs, in which an alkali metal ion is not available for the interactions with the phosphoryl group in the transition state.

Solvation and metal ion effects on structure and reactivity of phosphoryl compounds. Part 2. Alkali metal ion catalysis in the demethylation of methyl di(3-nitrophenyl)phosphinate by iodide ion

1993 ◽  
Vol 71 (4) ◽  
pp. 469-472 ◽  
Author(s):  
Agnes M. Modro ◽  
Tomasz A. Modro
Keyword(s):  
Alkali Metal ◽  
Metal Ions ◽  
Crown Ethers ◽  
Rate Constants ◽  
Metal Ion ◽  
Reaction Rate ◽  
Retarding Effect ◽  
Metal Ion Catalysis ◽  
Ion Effects ◽  
Metal Ion Effects

Second-order rate constants for the demethylation of methyl di(3-nitrophenyl)phosphinate by iodide in acetone-d6 at 25 °C have been measured. For a series of iodide salts the rate increased in the order: NBu4I < KI ≤ NaI < LiI. The addition of crown ethers or D2O has a retarding effect on the reaction rate. The results are discussed in terms of the increase of the nucleofugality of the phosphinate group via the complexation of metal ions with the phosphoryl function.

Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. III. Catalysis vs. inhibition by metal ions in the reaction of p-nitrophenyl benzenesulfonate with ethoxide

1990 ◽  
Vol 68 (10) ◽  
pp. 1846-1858 ◽  
Author(s):  
Marko J. Pregel ◽  
Edward J. Dunn ◽  
Erwin Buncel
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Ground State ◽  
Rate Constants ◽  
Metal Ion ◽  
Ion Pairs ◽  
Alkali Metal Ions ◽  
Complexing Agent ◽  
Metal Ion Catalysis

The rate of the nucleophilic displacement reaction of p-nitrophenyl benzenesulfonate (1) with alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For lithium ethoxide, sodium ethoxide, potassium ethoxide, and cesium ethoxide, the observed rate constants increase in the order LiOEt < NaOEt < CsOEt < KOEt. The effect of added crown ether and cryptand complexing agents was also investigated. Addition of complexing agent to the reaction of KOEt results in the rate decreasing to a minimum value corresponding to the reaction of free ethoxide. Conversely, addition of complexing agent to the reaction of LiOEt results in the rate increasing to a maximum value that is identical to the minimum value seen in the reaction of KOEt in the presence of excess complexing agent. In complementary experiments, alkali metal ions were added in the form of unreactive salts. Addition of a K+ salt to the reaction of KOEt increases the reaction rate, while addition of a Li+ salt to the reaction of LiOEt decreases the rate. The involvement of metal ions in the reaction of 1 is proposed to occur via reactive alkali metal – ethoxide ion pairs. The kinetic data are analyzed in terms of an ion pairing treatment that allows the calculation of second-order rate constants for free ethoxide and metal–ethoxide ion pairs; the rate constants increase in the order LiOEt < EtO−< NaOEt < CsOEt < KOEt. Thus, Li+isaninhibitorofthereactionofethoxidewith1, whiletheothermetalsionsstudiedareallcatalysts. Equilibrium constants for the association of the various metal ions with the transition state are calculated using a thermodynamic cycle, and are compared to association constants in the ground state. Consistent with the observed kinetic results, Li+ is found to stabilize the ground state more than the transition state, while Na+, K+, and Cs+ all stabilize the transition state more than the ground state. The trend in the magnitude of the transition state stabilization is interpreted in terms of interactions of the transition state with bare or solvated metal ions. It is concluded that the transition state for the reaction of 1 with ethoxide forms solvent separated ion pairs with alkali metal ions. Analogous data were available for the reaction of p-nitrophenyl diphenylphosphinate (2) with ethoxides, where Li+, Na+, K+, and Cs+ all function as catalysts, and the results are analyzed as above. In contrast to the sulfonate system, it is proposed that the phosphinate transition state forms contact ion pairs with alkali metal ions. The difference is attributed to a greater localization of negative charge in the phosphinate transition state, leading to stronger interactions with metal ions, which overcome metal ion – solvent interactions. Keywords: nucleophilic substitution at sulfur, alkali metal ion catalysis.

scholarly journals Metal ion catalysis in nucleophilic displacement reactions at carbon, phosphorus, and sulfur centers. II. Metal ion catalysis in the reaction of p-nitrophenyl diphenylphosphinate with alkali metal phenoxides in ethanol

1990 ◽  
Vol 68 (10) ◽  
pp. 1837-1845 ◽  
Author(s):  
Edward J. Dunn ◽  
Robert Y. Moir ◽  
Erwin Buncel ◽  
J. Garfield Purdon ◽  
Robert A. B. Bannard
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Metal Ion ◽  
Ion Pairs ◽  
Rate Coefficients ◽  
Complexing Agents ◽  
Specific Rate ◽  
Nucleophilic Displacement ◽  
Metal Ion Catalysis

The reactions of p-nitrophenyl diphenylphosphinate (1) with lithium, sodium, potassium, and benzyltrimethylammonium phenoxides (BTMAOPh) have been studied by spectrophotometric techniques in anhydrous ethanol at 25 °C. The reactivity (kobs) of the alkali metal phenoxides increases in the order BTMAOPh < KOPh < NaOPh < LiOPh. The rate of reaction of 1 with LiOPh is enhanced when lithium salts (LiSCN, LiNO3, LiClO4, LiOAc) are added to the reaction media. The addition of the alkali metal complexing agents dicyclohexyl-18-crown-6 ether or [2.2.2]cryptand for Na+, and [2.1.1]cryptand for Li+, to each of the alkali metal phenoxide reactions resulted in a decrease in rate, indicating catalysis by the alkali metal ions. The kinetic data are analyzed to obtain specific rate coefficients of reactions of phenoxide and ethoxide as the dissociated ions and as alkali metal – phenoxide ion pairs. Reactivities follow the order [Formula: see text]; [Formula: see text]; [Formula: see text]; [Formula: see text]. A mechanism is proposed in which the ion-paired metal phenoxide is more reactive towards the substrate than is the dissociated phenoxide. Analysis of the data in terms of initial state and transition state interactions with metal ions indicates that the increased reactivity of the ion-paired species results from greater stabilization of the negatively charged transition state relative to stabilization of the ion-paired nucleophile. Keywords: nucleophilic displacement at phosphorus by phenoxide, alkali-metal-ion catalysis.

Metal ion effects on the acid hydrolysis of pyrophosphate

1964 ◽  
Vol 26 (8) ◽  
pp. 1415-1420 ◽  
Author(s):  
J.M. Rainey ◽  
M.M. Jones ◽  
W.L. Lockhart
Keyword(s):  
Acid Hydrolysis ◽  
Metal Ion ◽  
Ion Effects ◽  
Metal Ion Effects ◽  
Hydrolysis Of

Metal Ion Effects on Fullerene/Porphyrin Cocrystallization

2019 ◽  
Vol 19 (11) ◽  
pp. 6743-6751 ◽  
Author(s):  
Mrittika Roy ◽  
Marilyn M. Olmstead ◽  
Alan L. Balch
Keyword(s):  
Metal Ion ◽  
Ion Effects ◽  
Metal Ion Effects
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