Solvent and crown ether/cryptand effects on the oximate-promoted 1,2-elimination from β-phenylmercaptoethyl p-nitrophenolate. Formation and reactivity of a crown ether-complexed potassium oximate ion pair

1994 ◽  
Vol 72 (2) ◽  
pp. 437-447 ◽  
Author(s):  
Erwin Buncel ◽  
Anurag Kumar ◽  
Hai-Qi Xie ◽  
Robert Y. Moir ◽  
J. Garfield Purdon
Keyword(s):  
Crown Ether ◽  
Metal Ion ◽  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Ion Pair ◽  
Rate Coefficients ◽  
Complexing Agents ◽  
Specific Rate ◽  
Reaction Products ◽  
Rate Of Reaction

The reactions of β-phenylmercaptoethyl p-nitrophenolate (1) with three potassium oximates, viz. potassium 2,3-butanedione monoximate (BDOK), acetophenone oximate (APOK), and acetone oximate (AOK) have been investigated in two nonhydroxylic dipolar aprotic solvents, tetraglyme and dimethyl sulfoxide (DMSO). The reaction products, as determined by 1H NMR spectroscopy, were p-nitrophenoxide ion and phenyl vinyl sulfide, in accord with an elimination process. A kinetic spectrophotometric study showed that in tetraglyme, the addition of oxime and water in small amounts drastically decreased the rate of reaction of 1 with APOK as a result of hydrogen-bonding interactions with the oximate anion. In tetraglyme as solvent the addition of 2.2.2 cryptand greatly enhanced the reactivity of the oximates but the macrocyclic crown ether DC-18-C6 had much smaller effect on rate. The results are consistent with formation of a crown ether-complexed potassium oximate ion pair, which is much less reactive than the free anion formed in the presence of 2.2.2 cryptand but more reactive than the potassium oximate ion pair. The kinetic data were analyzed to obtain specific rate coefficients for reaction of APOK as the dissociated anion, the ion-paired species, and as the crown ether-complexed oximate; equilibrium constants for potassium oximate ion pair formation and for the crown ether-complexed ion pair were obtained. In DMSO as solvent the rate of reaction remained unaffected on addition of the metal ion complexing agents, indicating that ion pairing is not important in this solvent. The reactivity of the free oximate anions in both solvents increased in the order BDOK < APOK < AOK, which parallels the pKa's of the corresponding oximes in DMSO. The unusually high reactivity of oximates in the low polarity tetraglyme compared to polar DMSO could be explained on the basis of stabilization of the transition state in tetraglyme. Trends in kTG/kDMSO for the oximates follow reactivity–selectivity considerations.

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.

Mechanism of interference with the Jaffé reaction for creatinine.

1987 ◽  
Vol 33 (7) ◽  
pp. 1129-1132 ◽  
Author(s):  
M H Kroll ◽  
N A Roach ◽  
B Poe ◽  
R J Elin
Keyword(s):  
Carbonyl Group ◽  
Equilibrium Constants ◽  
Molar Absorptivity ◽  
Reaction Products ◽  
Cyclic Ketones ◽  
Common Structure ◽  
Aliphatic Ketones ◽  
Rate Of Reaction ◽  
The Common

Abstract We investigated the mechanism of the Jaffé reaction for determination of creatinine by studying the spectrophotometric, kinetic, and equilibrium properties of the reaction of picrate with creatinine and with cyclic and aliphatic ketones. Absorbance spectra for the reaction products of picrate with all the ketones were superimposable with that of creatinine (Amax, 490 nm). Cyclic ketones not containing nitrogen had a molar absorptivity less than half that of creatinine and equilibrium constants approximately 0.01 that of creatinine. Aliphatic ketones, except for benzylacetone, had molar absorptivities similar to that of creatinine, but all of these compounds had equilibrium constants approximately a tenth or less that of creatinine. The common structure for all of the compounds reacting with picrate is the carbonyl group. The variable magnitude of interference for aliphatic and cyclic ketones is ascribable to the different rate constants, molar absorptivities, and equilibrium constants as compared with creatinine. Structures adjacent to the carbonyl group significantly affect the absorptivity and equilibrium constant, but steric hindrance is the major factor affecting the rate of reaction. We postulate that the carbonyl group is required for the Jaffé reaction, and we suggest a mechanism for the reaction.

Micelle formation as a factor influencing the mode(s) of metal ion partitioning into N-alkylpyridinium-based ionic liquids (ILs): implications for the design of IL-based extraction systems

2017 ◽  
Vol 19 (23) ◽  
pp. 5674-5682 ◽  
Author(s):  
James L. Wankowski ◽  
Michael J. Kaul ◽  
Mark L. Dietz
Keyword(s):  
Ionic Liquids ◽  
Crown Ether ◽  
Metal Ion ◽  
Alkaline Earth ◽  
Micelle Formation ◽  
Ion Pair ◽  
Neutral Complex ◽  
Ion Partitioning ◽  
Alkaline Earth Cations ◽  
Complex Ion

In the extraction of alkali and alkaline earth cations by a crown ether into certain N-alkylpyridinium-based ILs, the balance between neutral complex/ion-pair partitioning and ion exchange is significantly altered by the formation of micelles in the aqueous phase involving the IL cation.

Catalytic pathways in the ethanolysis of fenitrothion, an organophosphorothioate pesticide. A dichotomy in the behaviour of crown/cryptand cation complexing agents

2001 ◽  
Vol 79 (2) ◽  
pp. 157-173 ◽  
Author(s):  
Vimal K Balakrishnan ◽  
Julian M Dust ◽  
Gary W vanLoon ◽  
Erwin Buncel
Keyword(s):  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Metal Ion ◽  
Alkali Metals ◽  
Rate Coefficients ◽  
Nucleophilic Attack ◽  
Complexing Agents ◽  
Product Analysis ◽  
Aliphatic Carbon

The rates of displacement of 3-methyl-4-nitrophenoxide ion from the pesticide, fenitrothion, by alkali metal ethoxides in anhydrous ethanol were followed spectrophotometrically. Through product analysis experiments, which included 31P NMR and GC-MS, as well as spectrophotometric analysis, three reaction pathways were identified: nucleophilic attack at the phosphorus centre, attack at the aliphatic carbon, and a minor SNAr route ([Formula: see text]7%). Furthermore, a consecutive process was found to occur on the product of attack at the phosphorus centre. For purposes of kinetic treatment, the processes at the aliphatic and aromatic carbon were combined (i.e., the minor SNAr pathway was neglected), and the observed reaction rate constants were dissected into rate coefficients for nucleophilic attack at phosphorus and at aliphatic carbon. Attack at phosphorus was found to be catalyzed by the alkali metal ethoxides in the order KOEt > NaOEt > LiOEt. Catalysis arises from alkali metal ethoxide aggregates in the base solutions used (0–1.8 M); treatment of the system as a mixture of free ethoxide, ion-paired metal ethoxide, and metal ethoxide dimers resulted in a good fit with the kinetic data. An unexpected dichotomy in the kinetic behaviour of complexing agents (e.g., DC-18-crown-6, [2.2.2]cryptand) indicated that the dimers are more reactive than free ethoxide anions, which are in turn more reactive than ion-paired metal ethoxide. The observed relative order of reactivity is explained in the context of the Eisenman theory in which the free energy of association of the metal ion with the rate-determining transition state is largely determined by the solvent reorganization parameter. In contrast with displacement at the phosphorus centre, attack at the aliphatic carbon was not found to be catalyzed by alkali metals. In this case, the free ethoxide anion was more reactive than either the ion-paired metal ethoxide or the dimeric aggregate. The differing effects of alkali metals on the two pathways is ascribed largely to the leaving group pKa. For carbon attack, the pKa value estimated for demethyl fenitrothion, 2.15, is sufficiently low that metal ions are not required to stabilize the rate-determining transition state. In contrast, for phosphorus attack, 3-methyl-4-nitrophenoxide, with a pKa of 7.15, requires stabilization by metal ion interactions. Hence, alkali metal ions catalyze attack at phosphorus, but not attack at the carbon centres.Key words: organophosphorothioate, pesticide, fenitrothion, ethanolysis, alkali metal ethoxide, ion-pair reactivity, dimers, catalysis, competitive pathways.

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

1989 ◽  
Vol 67 (9) ◽  
pp. 1440-1448 ◽  
Author(s):  
Edward J. Dunn ◽  
Erwin Buncel
Keyword(s):  
Crown Ether ◽  
Alkali Metal ◽  
Transition State ◽  
Metal Ions ◽  
Ground State ◽  
Metal Ion ◽  
Complexing Agents ◽  
Transition State Stabilization ◽  
Nucleophilic Displacement ◽  
Metal Ion Catalysis

The effect of macrocyclic crown ether and cryptand complexing agents on the rate of the nucleophilic displacement reaction of p-nitrophenyl diphenylphosphinate by alkali metal ethoxides in ethanol at 25 °C has been studied by spectrophotometric techniques. For the reactions of potassium ethoxide, sodium ethoxide, and lithium ethoxide, the observed rate constant increased in the order KOEt < NaOEt < LiOEt. Crown ether and cryptand cation-complexing agents have a retarding effect on the rate. Increasing the ratio of complexing agent to base results in a decrease in kobs to a minimum value corresponding to the rate of reaction of free ethoxide ion. In complementary experiments, alkali metal ions were added to these reaction systems in the form of unreactive salts, causing an increase in reaction rate. The kinetic data were analysed in terms of ion-pairing treatments, which allowed evaluation of rate coefficients due to free ethoxide ions and metal ion – ethoxide ion pairs. Possible roles of the metal cations are discussed in terms of ground state and transition state stabilization. Evaluation of the equilibrium constants for association of the metal ion with ground state (Ka) and the transition state (K′a) shows that catalysis occurs as a result of enhanced association between the metal ion and the transition state, with (K′a) values increasing in the order K+ < Na+ < Li+. A model is proposed in which transition state stabilization arises largely from chelation of the solvated metal ion to two charged oxygen centers. This appears to be the first reported instance of catalysis by alkali metal cations in nucleophilic displacement at phosphoryl centers. Keywords: nucleophilic displacement at phosphorus, alkali-metal-ion catalysis.

Synthesis and metal ion complexation behavior of polycarboxylate 18-crown-6 ethers derived from tartaric acid

1988 ◽  
Vol 66 (5) ◽  
pp. 1097-1108 ◽  
Author(s):  
Philip J. Dutton ◽  
Thomas M. Fyles ◽  
Susan J. McDermid
Keyword(s):  
Aqueous Solution ◽  
Crown Ether ◽  
Tartaric Acid ◽  
Metal Ion ◽  
Electrostatic Interactions ◽  
Complexing Agents ◽  
Acidity Constants ◽  
Metal Ion Complexation ◽  
Ion Complexation ◽  
Anionic Charge

The metal ion complexation behavior of four 18-crown-6 ethers derived from (+)- and meso-tartaric acid is examined. Preparations of a meso-crown ether diacid and of a crown ether hexacid from three units of (+)-tartaric acid are described. Acidity constants and stability constants for complexation of metal cations in aqueous solution were determined by potentiometric titration. The complexes are substantially stabilized by favourable electrostatic interactions and are of similar stability to complexes of cryptands and EDTA. The complexation behavior of the series can be rationalized in terms of electrostatic interactions, direct coordination of the cations by at least one carboxylate from the crown ether periphery, and rigidification of the ligands as the anionic charge increases. Distributions of charge influence the relative stability of isomeric complexes. Highly charged polycarboxylate crown ethers are effective, but relatively unselective, cation complexing agents for a range of cations. The complexes are stable to pH 3 and the ligands can be used as simultaneous pH and metal ion buffers.

scholarly journals Comparative extraction studies of potassium phenoxide, p-nitrophenoxide, and picrate into methylene chloride by macrocyclic crown ether and cryptand complexing agents

1984 ◽  
Vol 62 (5) ◽  
pp. 926-930 ◽  
Author(s):  
E. Buncel ◽  
H. S. Shin ◽  
R. A. B. Bannard ◽  
J. G. Purdon
Keyword(s):  
Crown Ether ◽  
Aqueous Medium ◽  
Phase Transfer Catalysis ◽  
Methylene Chloride ◽  
Phase Transfer ◽  
Equilibrium Constants ◽  
Complexing Agents ◽  
Extraction Study

The results of a comparative extraction study of potassium phenoxide, p-nitrophenoxide, and picrate, from aqueous medium into methylene chloride in the presence of crown ether and cryptand complexing agents, are reported. The efficiency of extraction varies extremely widely with the nature of the anion and the ligand. An analysis of the results in terms of constituent equilibrium constants, and the factors which influence these, is presented. The significance of the results to other areas including phase transfer catalysis is pointed out.

Spectrophotometric study of the complexation equilibria of cadmium ions with 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-diethylaminophenol (BrPADAP, ClPADAP)

1983 ◽  
Vol 48 (1) ◽  
pp. 52-59 ◽  
Author(s):  
Vlastimil Kubáň ◽  
Miroslav Macka
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Optimal Conditions ◽  
Cadmium Ions ◽  
Brij 35 ◽  
Ethanol Medium ◽  
Triton X ◽  
Derivatives Of

The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the reactions of formation of the ML and ML2 complexes of both reagents with cadmium(II) ions were determined by graphical analysis and numerical interpretation of the absorbance-pH curves by the modified SQUAD-G program. Optimal conditions were proposed for the spectrophotometric determination of Cd in 10% v/v ethanol medium in the presence of 0.1% w/v Triton X-100 or 1% w/v Brij 35. BrPADAP and ClPADAP are the most sensitive spectrophotometric reagents for the determination of cadmium(II) ions (ε = 1.28-1.44 . 105 mmol-1 cm2 at 560 nm and pH 8.0-9.5) with a high colour contrast in the reaction (Δλmax ~117 nm) and a selectivity similar to that of other N-heterocyclic azodyes (PAR, PAN, etc.).

Spectrophotometric study of the acid-base and optical properties of the 5-bromo and 5-chloro derivatives of 2-(2-pyridylazo)-5-(diethylamino)phenol (BrPADAP, ClPADAP) and their complexation equilibria with zinc(II) ions

1982 ◽  
Vol 47 (10) ◽  
pp. 2676-2691 ◽  
Author(s):  
Miroslav Macka ◽  
Vlastimil Kubáň
Keyword(s):  
Equilibrium Constants ◽  
Spectrophotometric Study ◽  
Graphical Analysis ◽  
Alkaline Media ◽  
Acid Base ◽  
Ethanol Medium ◽  
Triton X ◽  
Mixed Water ◽  
Derivatives Of

The optical and acid-base characteristics of BrPADAP and ClPADAP were studied in mixed water-ethanol and water-DMF media and in 10% ethanol medium in the presence of cationic, anionic and nonionic tensides. The composition, optical characteristics, molar absorption coefficients and equilibrium constants of the ML and ML2 complexes with zinc(II) ions were found by graphical analysis and numerical interpretation of the absorbance curves by the modified SQUAD-G program. Optimal conditions were found for the spectrophotometric determination of Zn(II) in the presence of 0.1% Triton X-100 or 1% Brij 35 in alkaline media with pH = 6.5-10. BrPADAP and ClPADAP are the most sensitive reagents (ε = 1.3-1.6 . 105 mmol-1 cm2 at 557 and 560 nm, respectively) for the determination of zinc with high colour contrast of the reaction (Δλ = 104 nm) and selectivity similar to that for the other N-heterocyclic azodyes (PAN, PAR, etc.).

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