Aryloxide Ions Research Articles

METHODS FOR SYNTHESIS OF POLYETHERIMIDES

The review summarizes and systematizes the currently known data on the synthesis of polyetherimides. Polyetherimides are a promising class of high-quality polymeric materials with a valua-ble set of properties that can be directed to the appropriate design of the polymer chain. Thus, to obtain polyetherimide with a lower glass transition temperature, as much as possible of ether bonds are introduced into the macromolecule, as well as m-phenylene fragments that increase the flexibility of the polymer chain. Polyetherimides of this structure are amorphous and soluble in a number of amide solvents and chlorinated hydrocarbons. Three main methods for the preparation of polyetherimide are discussed in detail: high-temperature polycondensation by nucleophilic substitution in solution, polycondensation in a melt, and production of polyetherimide directly during extrusion. The most promising method for today is the method of high-temperature polycondensation in solution by the reaction of nucleophilic aromatic substitution. As a halogen-containing monomer, chlorine or fluorophthalic anhydrides are used in the synthesis. The reaction of diamines with chlorophthalic anhydride proceeds at lower rates in comparison with the fluorine-containing analog. However, the use of fluorophthalic anhydride proved to be inexpedient from the economic point of view. The economic availability of the corresponding nitrosubstituted phthalic derivatives and high rates of displacement of nitro groups with the help of aryl oxide ions allow to product the commercially avail-able polymers. As solvents, aprotic dipolar (dimethylsulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, etc.), nonpolar organic (o-dichlorobenzene, methylene chloride, etc.) and phenolic solvents can be used. However, the increasing attention of researchers is attracted to the synthesis in the environment of o-dichlorobenzene.

Frustrated Lewis Pair-Like Reactivity of Rare-Earth Metal Complexes: 1,4-Addition Reactions and Polymerizations of Conjugated Polar Alkenes.

Three rare-earth aryloxide ion pairs {[L1REOAr]+ /[B(C6 F5 )4 ]- ; L1=CH3 C(2,6-iPr2 C6 H3 N)CHC(CH3 )(NCH2 CH2 PPh2 ); RE=Sc, Y, Lu; Ar=2,6-tBu2 C6 H3 } were reported that feature rare-earth/phosphorus (RE/P) combinations exhibiting frustrated Lewis pair (FLP)-like 1,4-addition reactions towards conjugated carbonyl substrates (e.g., enone, ynone, and acrylic substrates). Furthermore, these RE/P complexes were found to be effective catalysts for the polymerization of conjugated polar alkene monomers. Mechanistic studies revealed that the rare-earth metal-catalyzed polymerizations were initiated by new FLP-type 1,4-additions rather than traditional and ubiquitous covalent RE-E (E=H, C, N, etc.) bond insertion or single-electron transfer.

Theoretical Study on the Mechanism and Regioselectivity of the Macromolecular Substitution Reactions of [NPCl2]n with Bifunctional Nucleophiles by a Combination of Quantum Mechanical and Molecular Dynamics Calculations

A combination of molecular dynamics simulations and quantum chemistry calculations affords a good understanding of the reaction between [NPCl2]n and the bifunctional nucleophile aminophenol HO−C6H4−NH2 in THF solution and in the presence of alkali carbonates. This reaction is regiospecific at room temperature favoring the attack by the NH2 group, and only at higher temperatures the attack by the OH is activated. It is also explained why the reaction of HO−C6H4−NH2 with {[NP(O2C12H8)]1−x[NPCl2]x}n and Cs2CO3 at reflux proceeds exclusively by the OH giving aryloxyphosphazenes with terminal NH2 substituents. Molecular dynamics simulations have been performed on model systems consisting on [NPCl2]n chains surrounded by aminophenol molecules or ions obtained by deprotonation of either the OH or NH2 groups. Quantum mechanics calculations consisted in density functional theory (DFT) computation of the reaction mechanism of aminophenol with the phosphoranimine (NH2)Cl2P(=NH) as a simple model for the NPCl2 phosphazene units, using B3LYP approximation with 6-31G(d). Our results provide evidence to support that the macromolecular substitution reactions of poly(dichlorophosphazene) with aryloxide ions are diffusion controlled and governed by the atomic charges, while the reaction with amino-arenes are directed by hydrogen interactions between the NH2 hydrogens and the phosphazene nitrogen atoms that initiate a lower activation energy stepwise mechanism competing with a concerted mechanism. The combined methodology employed in this work seems to be useful to address the regiochemistry of the macromolecular substitution on polyphosphazenes with heterobifunctional nucleophiles which is a central issue in the design of polymers with predetermined chemical composition and structure.

Kinetics of the Reactions of [p-Nitrophenoxy(phenyl)carbene]pentacarbonylchromium(0) with Aryloxide Ions, Hydroxide Ion, and Water in Aqueous Acetonitrile. Concerted or Stepwise?

The main question addressed in this paper is whether the nucleophilic substitution of the p-nitrophenoxy group in (CO)5Cr=C(OC6H4-4-NO2)Ph (1-NO2) by a series of substituted phenoxide ions is concerted or stepwise. Rate constants, kArO, for these substitution reactions were determined in 50% MeCN-50% water (v/v) at 25 degrees C. A Brønsted plot of log kArO versus pKa(ArOH) s consistent with a stepwise mechanism. This contrasts with reactions of aryl oxide ions with p-nitrophenyl acetate and with similar acyl transfers which are concerted. The reason for the contrast is that the tetrahedral intermediates formed in the reactions of 1-NO2 are much more stable than those in acyl transfers and the intrinsic barriers to their decomposition are higher than for the ester reactions. The points on the Brønsted plots for which pKa(ArOH) > or = pKa(PNP) define a straight line with beta(nuc) = -0.39, suggesting that bond formation has made very little progress at the transition state and that partial desolvation of the nucleophile is part of the activation process. The hydrolysis of 1-NO2 and of the unsubstituted analogue (1-H) has also been studied over a wide pH range, providing rate constants for nucleophilic attack by hydroxide ion (kOH), by water (kH2O), and by general base-catalyzed reaction with water (kB). Furthermore, kH2O values were obtained for the hydrolysis of (CO)5Cr=C(OC6H4X)Ph (1-X) as a byproduct of the reactions of 1-NO2 with aryl oxide ions. Structure-reactivity relationships for these reactions are discussed in terms of inductive, pi-donor, and steric effects.

Bis(dialkylamide)hydrogen Dibromobromate Precursors of Hypobromite Ion in Reactions with Nerve and Blister Agent Simulants

Hypobromite ion, BrO(-), is an effective alpha-nucleophile that reacts rapidly with activated phosphorus(V) and sulfonate esters. The parent acid rapidly oxidizes organic sulfides and aryloxide ions. At pH 10-11 BrO(-) and HOBr coexist in water and are potentially useful as decontaminants of chlorosulfide blister agents and the phosphonyl nerve agents. Bis(dialkylamide)hydrogen dibromobromates are well characterized, stable, solids which rapidly form HOBr-BrO(-) in mildly alkaline water. Reactions of 4-nitrophenyl diethyl phosphate and phosphonate, which are simulants of the phosphonofluoridate nerve agents, and of 4-nitrophenyl tosylate, with BrO(-) are rapid (t(1/2) = 60-700 s) with 0.1 M BrO(-), under conditions in which oxidations of organic sulfides are too fast to be followed by conventional methods.

Role of peroxophosphate intermediates in reactions of tris(4-nitrophenyl) phosphate and phenyl phosphoro-chloridate with alkaline hydrogen peroxide

Reaction of alkaline hydrogen peroxide with tris(4-nitrophenyl) phosphate generates ca 1.5 equiv. of 4-nitrophenol per mole of substrate with no evidence of build-up of an intermediate, and reaction of bis(4-nitrophenyl) phosphate anion is too slow to give a product. The initially formed bis(4-nitrophenyl) peroxophosphate is assumed to decompose to the phosphate ester by reaction with H2O2 or to eliminate 4-nitrophenoxide ion with the formation of a transient cyclic peroxophosphate. Reaction of phenyl phosphorochloridate anion with HO2− does not give phenoxide ion by this intramolecular reaction. Semi-empirical and ab initio simulations indicate that elimination of aryloxide ion from an aryl peroxophosphate should generate a cyclic rather than an open-chain peroxophosphate. Copyright © 2001 John Wiley & Sons, Ltd.

Reactivity and selectivity control in the substitution reactions of nitro group and fluorine in 3‐R‐5‐nitrobenzotrifluorides with aryloxide and arylthioxide ions

Reactivity and selectivity control in the substitution reactions of nitro group and fluorine in 3‐R‐5‐nitrobenzotrifluorides with aryloxide and arylthioxide ions

Kinetics of the reaction of 2‐chloro‐3‐nitro‐ and 2‐chloro‐5‐nitropyridines with aryloxide ions in methanol

Kinetics of the reaction of 2‐chloro‐3‐nitro‐ and 2‐chloro‐5‐nitropyridines with aryloxide ions in methanol

Kinetics of the reaction of 2-chloro-3-nitro- and 2-chloro-5-nitropyridines with aryloxide ions in methanol

The kinetics of the reaction of 2-chloro-3-nitropyridine (ortho-like) and 2-chloro-5-nitropyridine (para-like) with a series of aryloxide ions were studied in methanol at different temperatures. Plots of ΔH≠ versus ΔS≠ for both reactions gave good straight lines with isokinetic temperatures of 168 and 195 °C. Good linear relationships were obtained from the plots of log k2 against σ° values with relatively large negative ρ values indicating the formation of Meisenheimer σ-complex intermediates. Plots of log k2 against pKa values gave good straight lines indicating that the reactions show an appreciable degree of bond formation in the transition state. An addition–elimination mechanism is suggested. Copyright © 1999 John Wiley & Sons, Ltd.

Reactivity of phenolic nucleophiles towards nitroso compounds. Part 2.1 Reaction with alkyl nitrites (O-nitroso compounds)

Second-order rate constants, k, have been measured for the reaction of substituted phenolate ions with alkyl nitrites in aqueous solution at 25 °C. The final products of this reaction were identified as aromatic C-nitroso compounds and/or NO2–. Nitrosation of the phenolate ion yields ca. 90% of the p-nitroso product. However, methylation of the activated position of the ring (as in 4-methylphenol) does not result in the decrease in the overall reaction rate that would be expected. The reactivity of all the phenolate ions studied correlates well with their basicity, with the Hammett σ– constant and with their reactivity in other reactions in which they are known to act as O-nucleophiles. All these facts suggest that the reaction of aryloxide ions with alkyl nitrites always occurs through the oxygen atom to yield an unstable O-nitroso compound. This intermediate is likely to undergo an internal rearrangement of the NO group to give the corresponding C-nitroso product, competing with homolysis of the O–NO bond to yield nitric oxide. Oxidation of NO in the presence of O2 gives N2O3, which could act as a nitrosating agent towards ArO–. Hydrolysis of N2O3 in basic media accounts for the presence of the nitrite ion as one of the products.

Kinetics of Proton Transfer from Benzoylnitromethane and 1,2-Diphenyl-2-nitroethanone to Various Bases. Resonance, Inductive, Solvation, Steric, and Transition State Hydrogen-Bonding Effects on Intrinsic Rate Constants.

The replacement of a hydrogen in nitromethane and in phenylnitromethane by the PhCO group has a strong acidifying effect, i.e., PhCOCH(2)NO(2), 5, is 5.8, 6.6, and 8.6 pK(a) units more acidic than CH(3)NO(2) in water, 50% DMSO-50% water (v/v), and 90% DMSO-10% water (v/v), respectively, and PhCOCH(Ph)NO(2), 6, is 2.0, 3.0, and 3.2 pK(a) units more acidic than PhCH(2)NO(2) in the same solvents. A major focus of this paper is an attempt to sort out the relative contributions of resonance, inductive/field, and solvation effects that lead to the increased acidities. To this end rate constants for the reversible deprotonation of 5 by secondary alicyclic amines in water, 50% DMSO-50% water (v/v), and 90% DMSO-10% water (v/v) and for the reversible deprotonation of 6 by secondary alicyclic amines, carboxylate ions, thiolate ions, and aryloxide ions in water, by secondary alicyclic and primary aliphatic amines in 50% DMSO, and by secondary alicyclic anions in 90% DMSO were determined. From Brønsted plots based on these data the intrinsic rate constants (k(o)) for the reactions of 5 and 6 with the various buffer families were obtained and compared with previously determined k(o) values for the deprotonation of CH(3)NO(2) and PhCH(2)NO(2), respectively. An analysis of the changes in k(o) induced by the introduction of the PhCO group, coupled with a comparison of solvent transfer activity coefficients for the transfer of the anions (5(-) and 6(-)) from water to 50% and 90% DMSO with those for CH(2)=NO(2)(-) and PhCH=NO(2)(-), respectively, indicates a substantial increase in the resonance stabilization of 5(-) relative to CH(2)=NO(2)(-) and a corresponding sharp drop in the solvational stabilization by hydrogen bonding from water; the effects on 6(-) are qualitatively similar but quantitatively much smaller. Our study also shows that the intrinsic rate constant for proton transfer from 6 to thiolate ions is higher than for proton transfer to aryl oxide ions and amines. This result indicates that, in contrast to most other proton-transfer reactions, hydrogen-bonding stabilization of the transition state for deprotonation of 6 is not an important factor.

Ambident reactivity of aryloxide ions towards the super-electrophile, 4,6-dinitrobenzofuroxan. Kinetics, thermodynamics and stereoelectronic factors on regioselectivity

Reactions of the aryloxide ions, phenoxide (PhO-) and 3,5-di-tert-butylphenoxide (3,5-DTBPhO-), with the super-electrophilic heteroaromatic substrate, 4,6-dinitrobenzofuroxan (DNBF, 1), have been examined by 400 MHz 1H NMR spectroscopy in acetronitrile–dimethoxyethane ([2H3]MeCN∶[2H10]DME 1∶1, v/v) as a function of varying temperature (-40 to 23 °C) and in dimethyl sulfoxide ([2H6]DMSO) at room temperature. We herein report the first observation and full characterization of the O-bonded σ-adduct (DNBF·OPh-, 3a) formed by attack of PhO-, acting as an O-nucleophile, at the C-7 super-electrophilic site of 1. No C-5 adduct was seen in the initial spectrum (-40 °C, [2H3]MeCN∶[2H10]DME) or in subsequent monitoring of the reaction. These results suggest that PhO- displays K7T7 regioselectivity towards DNBF wherein attack at the C-7 site is favoured by both kinetics and thermodynamics, comparable to the behaviour shown by PhO- towards 2,4,6-trinitroanisole where the C-1 adduct is the product of both kinetic and thermodynamic control (i.e. K1T1 regioselectivity). Upon warming the reaction mixture to ambient, the C-7 O-adduct, DNBF·OPh-, 3a, gives way to the more stable C-7 C-bonded σ-adducts (DNBF·ortho-PhOH- adduct, 4, and DNBF·para-PhOH- adduct, 5, in a ratio of ca. 1∶6). The C-7 hydroxide adduct, DNBF·OH-, 2a, and phenol are detected at this temperature. The C-adducts, 4 and 5, are the sole PhO- adducts previously observed in the DNBF–PhO- reaction system (in [2H6]DMSO at room temperature). When C-attachment is precluded by steric hindrance, as in the reaction of 1 with 3,5-DTBPhO-, the C-7 DNBF·OPhDTB- adduct, 3b, is observed by 1H NMR spectroscopy even in [2H6]DMSO under ambient conditions. The results of the kinetics and thermodynamics of aryloxide adduct formation with DNBF, including the ambident reactivity found, are discussed with regard to stereoelectronic stabilization in the adducts and with comparison to relevant 4-nitrobenzofuroxan (NBF), 2-(nitroaryl)-4,6-dinitrobenzotriazole 1-oxides (2-Ar-4,6-DNBT) systems and to the normal electrophile, 1,3,5-trinitrobenzene (TNB).

Concerted displacement mechanisms at trigonal carbon: the aminolysis of 4-aryloxy-2,6-dimethoxy-1,3,5-triazines

4-Aryloxy-1,3,5-triazines undergo bimolecular nucleophilic displacement reactions with amines and pyridines to yield the 4-substituted triazine and aryloxide ion. Rate constants in aqueous solution for the bimolecular reaction of morpholine and 4-dimethylaminopyridine with the title ethers obey the Hammett σ equations with Hammett ρlg values 1.65 and 0.82, respectively. Comparison of the ρlg values with the Hammett ρeq for the equilibrium constants indicates that build-up of effective charge on the departing ether oxygen in the transition structure is less than half of that for complete bond fission. Rate constants for the reaction of substituted pyridines with the 4-nitro- and 3,4-dinitro-phenyl ethers obey Bronsted equations with exponents βnuc of 0.68 and 1.06, respectively. The build-up of effective charge in bond formation is greater than half of that expected for complete bond formation. Variation in βnuc and ρlg as a function of leaving group and nucleophile structure, respectively, is consistent with substantial coupling between bond forming and bond breaking. The ratio of the Leffler exponents in the pyridinolysis reactions, αnuc/αlg, is greater than unity, consistent with an imbalance between bond fission and bond formation and indicating an accumulation of negative charge in the heteroaromatic nucleus in the transition structure 29% of that expected for adduct formation.

Kinetics and Mechanism of Aminolysis of Phenyl Acetates in Aqueous Solutions of Poly(ethylenimine).

Second-order rate constants (k(n)) for the aminolysis of some phenyl acetates with poly(ethylenimine) (PEI) were obtained in a pH range 4.36-11.20 at 25 degrees C in 1 M KCl. Linear Bronsted-type plots (log k(n) vs pK(N) of PEI) were found for less reactive esters 2-nitrophenyl acetate, 4-acetoxy-3-chlorobenzoic acid, and 4-acetoxybenzenesulfonate with slopes of 0.92, 0.99, and 0.82, respectively. Curved plots were obtained for 3-acetoxy-2,6-dinitrobenzoic acid and 4-acetoxy-3-nitrobenzenesulfonate, which are consistent with a stepwise reaction. The most likely mechanism involves the existence of a tetrahedral intermediate (T(+/-)) and a change in the rate-determining step from its breakdown to its formation when the basicity of the polyamine increases. A semiempirical equation was used to calculate the values of limiting slopes of the plots (0.9 and 0.1 for both esters) and pK(N) at the center of the curvature of the plots (pK(N degrees ) = 7.94 and 9.02, respectively). The values of pK(N degrees ) are lower than those estimated for the aminolysis of the same esters with simple monomeric amines (pK(n degrees ) > 11) because of a better leaving ability of the aryl oxide ion from the tetrahedral intermediate when amino groups of PEI instead of simple amines are involved. Estimation of the pK's of the reactive intermediates and of the microscopic rate constants for the proton transfer from T(+/-) to PEI or from PEIH(+) to T(+/-) indicates that either base or acid catalysis is unimportant in the aminolysis of these esters by PEI.

Stepwise versus Concerted Mechanisms at Trigonal Carbon: Transfer of the 1,3,5-Triazinyl Group between Aryl Oxide Ions in Aqueous Solution

Displacements of 4-nitrophenolate ions from 2-(4-nitrophenoxy)-4,6-dimethoxy-1,3,5-triazine by substituted phenolate ions in aqueous solution obey a linear Bronsted-type equation, log k(Aro) = 0.951pK(a) - 10.98, over a range of pK(a) values greater than and less than the pK(a) of the leaving phenol. The absence of curvature is consistent with a mechanism involving a single transition state. This conclusion is supported by the existence of cross-correlation effects (p(xy) = 0.0561) on beta(nuc) of the pK(a) of the leaving group and on beta(1g) of the pK(a) of the nucleophile on beta(1g). The value of beta(eq), the Bronsted selectivity for transfer of the triazinyl function between phenolate ions, is calculated from the Bronsted data to be 1.48. The identity reaction of 3,4-dinitrophenolate ion with the (3,3-dinitrophenoxy)triazine is calculated to have a Kreevoy-Albery tau value of 1.04, indicating that in this case changes in effective charge on entering and leaving ligands are approximately balanced.

Cleavage rates for radiolysis‐produced radical anions of naphthylmethyl phenyl ethers and naphthyl benzyl ethers

AbstractCleavage reactions of α‐ and β‐naphthylmethyl phenyl ethers and of α‐ and β‐naphthyl benzyl ethers were studied by pulse radilysis. Transient spectra indicate that reactions occur via electron capture followed by cleavage of the resultant radical anions to give arylmethyl radicals and aryloxide ions. Product studies of extensively irradiated samples are consistent with this scheme and show patterns which are informative for radiation studies in general. The reactions were studied in several solvents. The behavior of transient spectra obtained in acetonitrile for these ethers shows clearly that radical anions of the naphthylmethyl ethers cleave more rapidly than do the radical anions of the naphthyl benzyl ethers.

Ambident reactivity of aryloxide ions towards 1,3,5‐trinitrobenzene, low‐temperature characterization of the elusive Oxygen‐bonded σ‐complexes by 1H and 13C NMR spectroscopy

AbstractThe ambident reactivity of phenoxide ion towards 1,3,5‐trinitrobenzene (TNB) was re‐examined by means of a novel reaction system(CD3CN–glyme‐d10) which allows the investigation of species formed at low temperatures (−40°C), contrasting with previous studies in dimethyl sulfoxide (DMSO) at ambient temperature. The new method coupled with 400 MHz NMR spectroscopy has allowed the definitive observation of both O‐ and C‐bonded phenoxide σ‐complex adducts for the first time, confirming the formation of the former through kinetic control and of the latter through thermodynamic control. The corresponding O‐bonded σ‐adduct in the TNB–mesitoxide system (whereC‐bonded σ‐adduct formation is not possible but where there is competing nitro group displacement) has also been characterized by 1H and 13C NBR. Another O‐bonded aryloxide adduct characterized is that from the reaction of TNB with3,5‐di‐tert‐butylphenoxide; in this system there is also competing NO2 displacement. Stereoelectronic factors in the O‐bonded σ‐adducts and aryl ethers are discussed.

S RN1C-arylation of potassium aryloxides by arylazo phenyl or tert- butyl sulfides in DMSO

Aryloxide ions (Ar'O -) behave as C-nucleophiles towards diazosulfides (ArN=NSR; R = Ph, Bu t) leading to unsymmetrical hydroxybiaryls (ArAr'OH) via C-C coupling. The reaction is particularly suited for the synthesis of terms which contain electron-withdrawing groups on the Ar moiety. The S RN1 mechanism is proposed on the grounds of experimental evidences.

Structure and reactivity of lithium and sodium aryloxides in dimethylformamide. Ions, ion pairs, and ion triplets

Reactivity and u.v. spectra of aryloxide ions in dimethylformamide are affected by the addition of either Li+ and Na+ ions in a way that suggests the occurrence of ion triplets M+A–M+ in addition to free ions and ion pairs.

Solvolytic elimination and hydrolysis promoted by an aromatic hydroxy group. Part 1. The reaction of 2,6-dibromo-4-dibromomethylphenol and of 2,6-dibromo-4-bromomethylene-cyclohexa-2,5-dienone with water in 95% 1,4-dioxane

The reaction of 2,6-dibromo-4-dibromomethylphenol with water to give the quinone methide, 2,6-dibromo-4-bromomethylenecyclohexa-2,5-dienone, together with 2,6-dibromo-4-hydroxybenzaldehyde has been studied in 95% 1,4-dioxane. U.v. spectroscopy has been used to study the kinetic form of the reaction. At very low acidities, rapid conversion into the quinone methide occurs through the aryl oxide ion, and is followed by addition and replacement to give the aldehyde. At acidities greater than 10–3M, reaction of the un-ionised phenol is dominant and follows a conventional SN1 pathway through a mesomeric carbocationic intermediate. Subsequent loss of a proton from this intermediate to give the quinone methide is competitive with its capture by the solvent (to give in several steps the related aldehyde) and by bromide ion (to give starting material).The mass-law constant for capture of the carbocation by bromide ion is very large (ca. 104 in this solvent), so that relatively small concentrations of hydrogen bromide convert the quinone methide back into the dibromomethylphenol by 1,6-addition. Solvent kinetic isotope effects on the individual reaction stages are reported. The rate of solvolysis of the phenol is much greater than would be predicted by the use of conventional linear free-energy parameters.