Counterion and solvent effects on the anionic polymerization of β-butyrolactone initiated with acetic acid salts

The comparative studies on the anionic polymerization of β-butyrolactone (BL) initiated with various salts of acetic acid have revealed strong sensitivity of the reaction rate on solvent polarity (benzene, THF, DMSO) and size of counterion. It was found that the polymerization rate in THF depends on the size of counterion and the type of macrocyclic ligand; it decreases in the following order: K⁺/Kryptofix® 222 ≈TBA⁺ > K⁺/18C6 > Na⁺/18C6 > Na⁺/15C5 > K⁺. It was also shown that the anionic polymerization of BL initiated with carboxylic acid salts depends strongly on the solvent polarity. In the polymerization initiated by acetate anions with a large counterion, the high-polar solvent as DMSO affects unfavorably the reaction rate, however, when a small counterion is applied, the opposite tendency is observed.     

The structure of the ion pairs of the carbanion of indene with alkali metal cations

NMR spectra have been measured of the Li⁺, Na⁺ and K⁺ ion pairs of the indenyl carbanion in 1,2-dimethoxyethane and tetrahydrofuran as a function of temperature. The changes of the chemical shifts are explained in terms of the detailed structure of the ion pairs. The results in both solvents strongly suggest that in indenyl-Li⁺ the counterion is predominantly located over the six-membered ring. In THF the preferred position of the cations Na⁺ and K⁺ in the contact ion pairs seems to be the five-membered ring.     

Syntheses of amphiphilic block copolymers. Block copolymers of methacrylic acid and p-N,N-dimethylaminostyrene

Amphiphilic block copolymers consisting of methacrylic acid (MA) sequences and p-N,N-dimethylaminostyrene (DMS) sequences were prepared by living anionic polymerization. DMS was polymerized by lithium naphthalene in tetrahydrofuran to yield a living polymer solution, to which trimethylsilyl methacrylate (TMSM) was added to allow the block copolymerization. The conversion of TMSM was dependent on the countercation, i.e., with Na⁺ as counterion, no quantitative conversion was reached owing to premature termination, whereas with Li⁺ the conversion was quantitative. The role of the counterion was discussed in some detail in connection with self-termination by the backbiting mechanism. The trimethylsilyl ester groups in the block copolymer were quantitatively hydrolyzed by treatment with aqueous methanol at room temperature, yielding MA sequences. The block copolymer of MA and DMS exhibited micellar properties in an aqueous solution.     

Ambident anion chemistry: The reaction of sterically-hindered phenolate anions with 1H-pyrrole-2,5-diones

The reaction of N-phenylmaleimide, 4a , with sodium 2,6-di-t-butylphenolate, 5a , in dimethylsulfoxide (DMSO) resulted a complex oligomeric mixture. The dimer 8 was isolated from the reaction of the N-alkyl-maleimide 4b with 5a in DMSO. The reaction of 4a with 5a in tetrahydrofuran (THF), which is an aprotic solvent that is known to promote ion pairing, resulted in the isolation of a low yield of 6a . The reaction of 4a with 5a in the hydrogen-bonding solvent t-butyl alcohol gave 6a in slightly higher yield. The N-alkylpyrrolidine-2,5-diones 6c-f were obtained by the reaction of the maleimides 4c-e with the corresponding sodium phenolate 5a-b in t-butyl alcohol reaction medium. The isolated yield of product increased with the size of the N-alkyl substituent of the maleimide. Surprisingly, the reaction of the 2,6-dimethylphenolate 5c with 4d led to the isolation of the dimer 10 with the formation of a quaternary carbon atom. The yield of 6a was observed to counterion dependent, increasing in the order Na⁺ < Li⁺ < MgBr⁺ in t-butyl alcohol. The bismaleimides 12 and 14 were obtained by the reaction of either 11 or 13 with 5d in THF.     

Polymérisation anionique des diènes. IV. Contribution aux etudes des mécanismes de propagation stéréospécifique des isoprène et butadiène par les organo-alcalins

By taking into account different possible interactions between the living end, the counterion and the nature of the solvent used on the one hand, and the influence of the temperature on the kinetics and the microstructures of polydienes on the other hand, it has been possible to suggest some new explanations concerning the mechanisms of the anionic propagation of butadiene and isoprene. In hydrocarbon media, the stereospecificity of the 1,4 propagation initiated by lithium should be considered as the consequence of the coordination of the counterion by both of the two bonds of the diene molécule. The stereospecificity of the vinyl propagation by the same counterion in dioxane solvent should be the consequence of the competition between the (Li⁺, dioxane) and (Li⁺, diene) coordination complexations. In this case, the Li⁺ counterion should only be coordinated by only one of the two double bonds of the diene molecule. With isoprene, the π-electron donation should originate mainly from the C₃?C₄ double bond. The decrease of the stereospecificity is due to the increasing size of the alkali counterion and the separation or the dissociation of the growing ion-pairs.     

Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair SN2 Reaction of and CH3Cl

We have computationally studied the bimolecular nucleophilic substitution (S_N2) reactions of M_nNH₂⁽ⁿ⁻¹⁾ + CH₃Cl (M⁺ = Li⁺, Na⁺, K⁺, and MgCl⁺; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M⁺ and of solvation on the reaction profile and the stereochemical preference, that is, backside (S_N2-b) versus frontside attack (S_N2-f). The results were compared to the corresponding ion-pair S_N2 reactions involving F⁻ and OH⁻ nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in S_N2 reactivity along the nucleophiles F⁻, OH⁻, and , including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.     

Counterion mixing effects on the conformational transitions of polyelectrolytes. II. Counterion binding as measured by NMR spectroscopy of alkali metal poly(acrylate)s

Bound states of counterions during the coil‐globule transition of poly(acrylic acid) in water/organic solvent mixtures were investigated by NMR spectroscopy of alkali metal cations (Li⁺, Na⁺, Cs⁺). Accompanying the transition, the line widths of the respective NMR peaks significantly increased with increasing the organic solvent composition in the medium. Although this line width broadening suggests that some specific counterion binding with desolvation is involved with the coil‐globule transition, the most marked broadening was observed in higher organic solvent compositions than those of the coil‐globule transition region detected by the viscometry. Namely, the specific counterion binding with desolvation proceeds even after the polymer chain collapsed. This means in turn that such a strong counterion binding is not a prerequisite for the coil‐globule transition, at least at the stage of the onset. For the Li⁺/Cs⁺ mixed counterion system in 60 vol % DMSO, where our previous conductivity data suggested that the specific counterion binding occurred only for Cs⁺ during the coil‐globule transition induced on mixing with Li⁺, a significant increase in the line width was also observed only for Cs⁺. The coincidence between the conductivity and the NMR results for the Li⁺/Cs⁺ mixed counterion system strongly supports a working hypothesis, “size‐fitting effect,” that has been proposed to determine the counterion specificity observed for the conformational transitions of polyelectrolytes. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2132–2139, 2009     

Charge density-dependent coil–globule transition of alkali metal polycarboxylates in aqueous organic solvent mixtures

The effects of polymer charge density on the counterion-specific and solvent-specific coil–globule transition of polycarboxylates were investigated for alkali metal salts of poly(styrene-alt-maleic acid) (PSaltMA) and poly(acrylic acid) (PAA) in aqueous organic solvent mixtures. The order of the transition region, namely, the counterion specificity for the transition in, e.g., aqueous dimethyl sulfoxide (DMSO), was the same for both polyelectrolytes, Na⁺?>?K⁺?>?Cs⁺?>?Li⁺, while the discrepancy of the transition region between Na⁺ and Li⁺ systems was appreciably narrower for PSaltMA (approximately 20 vol%) than that of PAA (approximately 29 vol%). Such diminished counterion specificity for the former was ascribed to the nonuniform charge array. Namely, PSaltMA has two kinds of nearest charge arrays, one is the shorter spacing between the maleic acid carboxyl groups and the other is the longer one via one styrene group. Thus, the former may be favorable for binding of the smaller counterion (i.e., Li⁺) and the latter for the larger one (Cs⁺). Such a “size-fitting effect” for the counterion binding was in fact further confirmed with variously neutralized PAAs. For example, the counterion specificity in aqueous DMSO of PAA40 that was neutralized to 40 % was Cs⁺?>?K⁺?>?Na⁺?>?Li⁺, showing that the largest counterion becomes most favorable in inducing the transition with increasing average charge spacing. In fact, the nuclear magnetic resonance line width measurement for ¹³³Cs suggested that the counterion binding strength of the large counterion for PAA increases with decreasing charge density from 100 to 40 % neutralization.     

Copolymerization reactivities and conductivities of some living polymers of p-substituted styrenes

A kinetic study in tetrahydrofuran of the addition of 1,1-diphenylethylene on para-substituted styrylcarbanions (with Cs⁺ as counterion) has given the reactivities of free ions and ion-pairs. For both species, the addition rate constant increased in the following sequence for the substituent of the phenyl ring: pH < p-CH₃ <p-CH₃O. It was also shown that in the same solvent, the dissociation constants of the polystyryl ion-pairs decreased with the electron-donating power of the substituent.     

Conversion of diaryliodonium salts to aryl fluorides

The preparation of aryl fluorides by the reaction of diaryliodonium salts with KF is discussed. Generally, best results were obtained when the salt Ar₂I⁺X^? was heated with KF in the absence of solvent. The counterion, X^?, must be non-nucleophilic.     

Solvent‐ and counterion‐specific swelling behavior of poly(acrylic acid) gels

The collapse of alkali metal poly(acrylate) (PAAM) gels was investigated for various water/organic solvent mixture systems: methanol (MeOH), ethanol (EtOH), 2‐propanol (2PrOH), t‐butanol (tBuOH), dimethyl sulfoxide (DMSO), acetonitrile (AcN), acetone, tetrahydrofuran (THF), and dioxane. In order to ascertain the counterion specificity in the swelling behavior, four kinds of alkali metal counterions were used: Li⁺, Na⁺, K⁺, and Cs⁺. Remarkable solvent and counterion specificities were observed for every counterion species and every solvent system, respectively. For example, in aqueous EtOH the dielectric constants (D_cr) at which collapse occurred were in the order PAACs < PAALi < PAAK < PAANa. On the other hand, the D_cr at which PAALi gel collapsed increased in the order tBuOH < dioxane < THF < MeOH < 2PrOH < EtOH < acetone < AcN < DMSO, where the D_cr ranged from about 39 to about 67. This was in contrast to our previous observation for a partially quaternized poly(4‐vinyl pyridine) (P4VP) gel, which collapsed in a much narrower D_cr region in similar mixed solvents. The present solvent‐ and counterion‐specific collapses are discussed on the basis of solvent properties such as the dielectric constant and Gutmann's donor number and acceptor number of a pure solvent. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2791–2800, 2000     

The Roles of Counterion and Water in a Stereoselective Cysteine‐Catalyzed Rauhut–Currier Reaction: A Challenge for Computational Chemistry

The stereoselective Rauhut–Currier (RC) reaction catalyzed by a cysteine derivative has been explored computationally with density functional theory (M06‐2X). Both methanethiol and a chiral cysteine derivative were studied as nucleophiles. The complete reaction pathway involves rate‐determining elimination of the thiol catalyst from the Michael addition product. The stereoselective Rauhut–Currier reaction, catalyzed by a cysteine derivative as a nucleophile, has also been studied in detail. This reaction was experimentally found to be extremely sensitive to the reaction conditions, such as the number of water equivalents and the effect of potassium counterion. The E1cB process for catalyst elimination has been explored computationally for the eight possible stereoisomers. The effect of explicit water solvation and the presence of counterion (either K⁺ or Na⁺) has been studied for the lowest energy enantiomer pair (1S, 2R, 3S)/(1R, 2S, 3R).     

Stereoselective synthesis of substituted piperazines

The treatment of allylarylamines with mercury(II) acetate in tetrahydrofuran followed by a double decomposition reaction with potassium bromide leads to trans-2,5-bis(bromomercuriomethyl)-1,4-diarylpiperazines (2). The stereochemistry of the reaction products has been elucidated by an ¹H-nmr spectroscopic study of the trans-2,5-dimethyl-1,4-diarylpiperazines (3) obtained by sodium borohydride reduction of 2 in alkaline media. The course of the reaction strongly depends on the steric demand of the groups attached to either the allylic group or the ortho-position in the aromatic ring of the starting amine (1).     

Synthesis of Functionalized 1‐Benzamido‐1,4‐dihydropyridines via a One‐Pot Two‐Step Four‐Component Reaction

The one‐pot four‐component reaction of benzohydrazide, acetylenedicarboxylate, aromatic aldehydes and malononitrile in ethanol with triethylamine as base catalyst afforded functionalized 1‐benzamido‐1,4‐dihydropyridines in satisfactory yields. Under similar conditions, picolinohydrazide or nicotinohydrazide can also be successfully utilized in the reactions to give corresponding functionalized 1,4‐dihydropyridines. ¹H NMR data indicated that an equilibrium of cis/trans‐conformations exist in 1‐benzamido‐1,4‐dihydropyridines.     

Novel route to poly(p‐phenylene vinylene) polymers

Poly(p‐phenylene vinylene) (PPV), poly(2,5‐dioctyl‐p‐phenylene vinylene) (PDOPPV), and poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylene vinylene] (MEHPPV) were synthesized by a liquid–solid two‐phase reaction. The liquid phase was tetrahydrofuran containing 1,4‐bis(bromomethyl)benzene, 1,4‐bis(chloromethyl)‐2,5‐dioctylbenzene, or 1,4‐bis(chloromethyl)‐2‐methoxyl‐5‐(2′‐ethylhexyloxy)benzene as the monomer and a certain amount of tetrabutylammonium bromide as a phase‐transfer catalyst. The solid phase consisted of potassium hydroxide particles with diameters smaller than 2 mm. The experimental results demonstrated that the reaction conversions of PPV and PDOPPV were fairly high (～65%), but the conversion of MEHPPV was only 45%. Moreover, gelation was found in the polymerization processes. As a result, PPV was insoluble and PDOPPV and MEHPPV were partially soluble in the usual organic solvents, such as tetrahydrofuran and chloroform. Soluble PDOPPV and MEHPPV were obtained with chloromethylbenzene or bromomethylbenzene as a retardant regent. The molar mass of soluble PDOPPV was measured to be 2 × 10⁴ g mol^?1, and that of MEHPPV was 6 × 10⁴ g mol^?1. A thin, compact film of MEHPPV was formed via spin coating, and it emitted a yellow light. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 449–455, 2003     

Kinetics and mechanism of the anionic polymerization of cyclohexadienes initiated by naphthalene radical anions and dianions

The anionic polymerization of 1.3-cyclohexadiene (1.3-CHD) was investigated in temperatures that ranged from 25 to ?77°C. Initiation by lithium naphthalene (N^?·,Li⁺) in tetrahydrofuran at ?20°C yields polymers with fairly narrow molecular weight distribution. The M?_w of these polymers so prepared is ca. 20,000. Polymerization of 1.3-CHD conducted at room temperature is accompanied by the dehydrogenation and disproportionation of the monomer, especially when N^?·,K⁺ acts as initiator. Oligomers are formed when hexamethylphosphoramide is used as a solvent. The mechanism of the initiation of the polymerization of 1.3-CHD by N^?·,Li⁺ was elucidated and the rate constants at ?20°C in tetrahydrofuran of the elementary reactions were determined. It was established that the dianions formed by disproportionation of N^?·,Li⁺ act as effective initiators for 1.3-CHD. The adducts formed constitute the cyclohexanyl and naphthyl carbanionic groups. The former carbanions (λ_max ～ 275 nm) propagate the polymerization. The initially formed dimeric adducts are stabilized by the separation of the carbanionic end groups by the additional monomer units. Chain transfer to the monomer limits the growth of the polymers. The isomerization of the cyclohexadienyl anions, formed as result of chain transfer, may be followed by the elimination of lithium hydride. The latter reaction represents a termination step. Addition of 1.4-CHD to the reaction mixture enhances the chain transfer and the termination.     

Theoretical study on the solvent effect of the nitrosyl cation (NO+) generating reaction

Nitrosyl cation (NO⁺) generating reaction HONO + H⁺ → NO⁺ + H₂O has been theoretically investigated by B3LYP and high‐electron‐correlation QCISD methods with 6‐31G (d,p) basis set. The solvent effects on the geometries, reaction path properties, energies, thermodynamic, and kinetic characters in four solvents (benzene, tetrahydrofuran, acetonitrile, and water) have been calculated using self‐consistent reaction field (SCRF) approach with the polarizable continuum model (PCM). The results show that the activation energy barriers and the relative energies of the products are decreased with increase of the polarities of the solvents, and the reaction is favored in polar solvents thermodynamically and kinetically. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Controlled stereochemistry of polyamides derived from cis/trans‐1,4‐cyclohexanedicarboxylic acid

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4‐cyclohexanedicarboxylic acid (1,4‐CHDA) residue, or a mixture of both. The influence of the synthetic route of 1,4‐CHDA containing polyamides on the obtained cis–trans ratio of the incorporated 1,4‐CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis–trans ratio of the 1,4‐CHDA residue during synthesis, whereas synthesis at elevated pressure and temperature caused isomerization. The content and cis–trans ratio of 1,4‐CHDA in the copolyamides were determined by solution ¹³C NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4‐CHDA resulted in an increase in T_m, even for low molar precentages of 1,4‐CHDA. This phenomenon points to isomorphous crystallization of both the 12.6 and 12.CHDA repeating units. The mps of the synthesized polyamides were independent of the initial cis–trans ratio of 1,4‐CHDA, provided that the samples were annealed at 300 °C before DSC analysis. The polyamides exhibited a different melting pattern depending on the 1,4‐CHDA content. At a low a 1,4‐CHDA content a net exothermic recrystallization occurred during melting, whereas at higher contents of 1,4‐CHDA this recrystallization occurs to a lesser extent, and two separate melting areas are observed. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 833–840, 2001     

Mechanism of Nitrogen-Containing Cyclic Polymerization

Abstract

The comprehensive polymerization mechanism of the nitrogen-containing cycles 1-azobicyclo (3,1,0)-hexane (ABH), conidine, quinuclidine, and triethylenediamine under the action of quaternary ammonium salts, ammonium salts, and BF₃ complex with conidine is studied. Polymerization is of the living polymers type, and the active centers of monomer polymerization are ions and ion pairs: the activity of the latter is comparable to and exceeds that of the free ions. The effects of the nature of the counterion, cation, and medium polarity on the reaction rate are investigated. The polymerization rate is found to depend on the nature of the counterion in the polymerization of ion pairs, but not to depend on the counterion in the polymerization of free ions. The reaction rate is proportional to the counterion size in the polymerization of ion pairs. In the case of conidine K₊ = 0.2, K_±(Cl^?) = 0.28, K_±(Br^?) = 0.36, K_±(I^?) = 0.51, and K_±(ClO₄ ^?) = 0.62 (liter)/(mole)(min). The heats of nitrogen-cyclic polymerization are measured and correlated with the activation energy.     

Two-directional synthesis of the non-adjacent bis(tetrahydrofuran) core of cis-sylvaticin

Synthesis of the C₂-symmetric, non-adjacent bis(tetrahydrofuran) core of cis-sylvaticin in seven steps and 24% overall yield from (2R,3S)-1,2-epoxy-4-penten-3-ol is reported. A strategy involving assembly of the central 1,4-diol unit by silicon-tethered ring-closing metathesis and subsequent two-directional functionalization, including establishment of the cis/threo stereochemical relationships of the tetrahydrofuran rings by Sharpless asymmetric dihydroxylation/S_N2 cyclization, is employed.