Quantitative study of solvent effects on the Menshutkin reaction between 1,4-diazabicyclo[2.2.2]octane and 2-chloroethylbenzene, 2-bromoethylbenzene, and 2-iodoethylbenzene. Part 2. Mixed solvents

Auriel, Michel; Hoffmann, Edmond de

doi:10.1039/p29790000325

Cited by 8 publications

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“…Higher molecular masses of the polymers that were attained when acetonitrile was replaced with nitromethane should probably be attrib uted to a marked acidity of the methyl group of nitromethane; as a consequence, the electrophilic catalysis of the alkylation of oxazoline occurs. A simi lar increase in the rate constant of alkylation (by a fac tor of 2) was observed for the reaction of quarterniza tion of amines when acetonitrile was replaced with nitromethane [20], an effect that was rationalized by the proton donor properties of nitromethane.…”

Section: Resultsmentioning

confidence: 90%

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

2012

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The cationic polymerization of 2 oxazolines is a simple and suitable approach to the incorporation of polyethyleneimine into copolymers of various struc tures. After the biocompatibility of poly(2 alkyl 2 oxazolines) was discovered [1], the interest in poly mers of this type increased appreciably. In addition, aqueous solutions of a number of poly(2 alkyl 2 oxazolines) possess lower critical solution tempera tures, a circumstance that makes it possible to create new types of thermoresponsive materials on their basis [2].Poly(2 isopropyl 2 oxazoline) is one of the best studied thermosensitive polymers. In aqueous solu tions below the LCST (~40°С), the amide groups of this polymer are heavily hydrated; as a result, macro molecules turn out to be hydrophilized. Above the LCST, the degree of hydration decreases and intramo lecular hydrogen bonds form between amide frag ments. Owing to transition to the globular conforma tion, macromolecules become hydrophobic and the polymer loses the ability to dissolve in water [3].The incorporation of fragments able to efficiently bind inorganic ions and organic compounds into poly mers is a new strategy to designing supramolecular colloid structures and thus allows modeling of pro cesses occurring in living nature [4]. It was shown that the transition from linear to star shaped macromole cules significantly improves the capability of polymers for molecular recognition [5]. As is known [6], calix arenes are substances that can form complexes with low molecular mass compounds and metal ions that are capable of molecular recognition and formation of supramolecular structures. In our opinion, star shaped polymers with the central calixarene core and thermoresponsive poly(2 isopropyl 2 oxazoline) arms may be used as molecular containers for low molecu lar mass compounds and metal ions; moreover, they serve as elements of thermoresponsive colloid systems.There are two main approaches to the synthesis of star shaped macromolecules. In the first case, arms are synthesized separately and then are bound by poly functional crosslinking agents. In the second case, arms grow on a multicentered initiator. This variant was found to be efficient for the synthesis of star shaped polymers based on calixarenes, especially when living ionic or controlled radical polymerization is used. For example, initiators based on calix[8]arene and tetraethylresorcinarene were employed to imple ment the living cationic polymerization of isobutylene [7,8] and 2 methyloxazoline [9], respectively. Con trolled radical polymerization, primarily atom trans fer radical polymerization (ATRP), is also in wide use for the synthesis of star shaped polymers with calix(resorcinarene)arene cores and arms that are polystyrene [10,11], polyacrylate [11,12], or poly methacrylate [13] moieties. Therefore, the approach based on the use of the macrocyclic polyfunctional initiator for the cationic polymerization of 2 isopro pyl 2 oxazoline was selected for the synthesis of star shaped polymers with octa tert butylcalix[8]arene cores...

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Section: Resultsmentioning

confidence: 90%

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

2012

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“…The conventional TST expression cannot account for nonidealities such as high pressure and solvent effects, which are clearly important to the Menshutkin reaction. − Kramers extended the theory by modeling a chemical reaction as a classical particle of mass, m , moving in a one-dimensional asymmetric double-well potential U ( x ). , The remaining degrees of freedom of the surrounding molecules were incorporated as a heat bath at temperature T , which influences the reaction coordinate through a fluctuating force ξ( t ) (Brownian motion) and a damping force − mγx ̇, where γ represents a constant damping rate (friction). For moderate-to-strong friction, he obtained the following result for the rate constant: where ω b 2 is related to the curvature of the potential at the position of the transition state. , The term κ is called the transmission coefficient.…”

Section: Resultsmentioning

confidence: 99%

“…Of the many reactions of interest, the Menshutkin S N 2 reaction is notable for its use in the study of solvent and medium effects on chemical reactivity. − This special class of S N 2 reactions involves the alkylation of a formally sp 2 or sp 3 hybridized nitrogen atom where Nu and L represent the nucleophile (amine) and leaving group, respectively. The nucleophilic attack occurs on the opposite side of the substrate (RL) relative to the leaving group, resulting in the typical S N 2 transition state consisting of a 5-coordinated carbon atom .…”

Section: Introductionmentioning

confidence: 99%

“…The nucleophilic attack occurs on the opposite side of the substrate (RL) relative to the leaving group, resulting in the typical S N 2 transition state consisting of a 5-coordinated carbon atom . Since the reaction involves the formation of ionic products from neutral reactants, it is heavily influenced by the nature of the solvent, and large increases in the reaction rate have been observed with increases in solvent polarity and polarizability. − …”

Section: Introductionmentioning

confidence: 99%

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Enhanced Menshutkin S_N2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement

et al. 2020

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A significant enhancement in the Menshutkin S N 2 reaction between 1-methylimidazole (MeIm) and methyl thiocyanate (MeSCN) is observed when the reaction is confined in the nanoscale silica pores of MCM41 and SBA15. The experiments in the silica pores are conducted without the surrounding bulk reaction mixture. The influences of temperature, pore radius, and surface chemistry on the kinetics of the confined reaction are analyzed with time-dependent infrared spectroscopy, molecular dynamics simulations, and ab initio calculations. The rate constant of the pseudofirst order reaction increases with decreasing pore size, and the activation energy is found to decrease by 5.6 kJ/mol in the smallest pore studied (2.8 nm) relative to the bulk reaction. The rate constant dependence on pore size is accurately described by a twostate model in which molecules within the 4.6 Å interfacial layer experience a 2.4-fold rate constant increase relative to those reacting at the bulk rate further away from the interface. The removal of polar silanol groups from the silica surface via passivation with trimethylsilyl chloride results in bulk-like kinetics despite a reduction in the pore diameter, demonstrating the role of silanols as catalytic sites. Electronic structure calculations of the energy profile on a model silica surface confirm that silanol groups, particularly those of the vicinal type, can reduce the activation energy and reaction endothermicity through the donation of hydrogen bonds to the reactant, transition state, and product complexes.

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“…50,54 The Menshutkin reaction is also a characteristic example for studying the effect of solvation on reactions 53 since it displays pronounced solvent effects on activation barriers. 54,56,57 Experimental studies have shown a decrease in the activation energy depending on the polarity of the solvent. The experimentally reported activation barrier for Pyr+MeBr in methanol is 22.5 kcal/mol which is 3.1 and 5.1 kcal/mol lower compared with apolar cyclohexane and di-n-butyl ether.…”

Section: Introductionmentioning

confidence: 99%

Solvent Effects on the Menshutkin Reaction

Turan¹,

Brickel²,

Meuwly³

2021

Preprint

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The Menshutkin reaction is a methyl transfer reaction relevant in fields ranging from biochemistry to chemical synthesis. In the present work, energetics and solvent distributions for NH 3 +MeCl and Pyr+MeBr reactions were investigated in the gas-phase, in water, methanol, acetonitrile, benzene, and in cyclohexane by means of reactive molecular dynamics simulations. For polar solvents (water, methanol, and acetonitrile) and benzene, strong to moderate catalytic effect for both reactions is found whereas apolar and bulky cyclohexane interacts weakly with the solute and does not show pronounced barrier reduction. Calculated barrier heights for the Pyr+MeBr reaction in acetonitrile and cyclohexane are 23.2 and 28.1 kcal/mol compared with experimentally measured barriers of 22.5 and 27.6 kcal/mol, respectively. The 2-dimensional solvent distributions change considerably between reactant and TS but comparatively little between TS and product conformations of the solute. The simulations also suggest that as the system approaches the transition state, correlated solvent motions that destabilize the solvent-solvent interactions are required to surmount the barrier. Finally, the average solvent-solvent interaction energies in the reactant, TS, and product state geometries are correlated with changes in the solvent structure around the solute.

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Quantitative study of solvent effects on the Menshutkin reaction between 1,4-diazabicyclo[2.2.2]octane and 2-chloroethylbenzene, 2-bromoethylbenzene, and 2-iodoethylbenzene. Part 2. Mixed solvents

Cited by 8 publications

References 0 publications

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

Enhanced Menshutkin S_N2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement

Solvent Effects on the Menshutkin Reaction

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Quantitative study of solvent effects on the Menshutkin reaction between 1,4-diazabicyclo[2.2.2]octane and 2-chloroethylbenzene, 2-bromoethylbenzene, and 2-iodoethylbenzene. Part 2. Mixed solvents

Cited by 8 publications

References 0 publications

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazolines) based on octa-tert-butylcalix[8]arene

Enhanced Menshutkin SN2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement

Solvent Effects on the Menshutkin Reaction

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Enhanced Menshutkin S_N2 Reactivity in Mesoporous Silica: The Influence of Surface Catalysis and Confinement