Mechanisms of substitution at the COX group

Kivinen, Antti

doi:10.1002/9780470771273.ch6

Cited by 17 publications

(7 citation statements)

References 164 publications

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“…Spontaneous solvolyses of acyl halides do not fit readily into the concepts of the S N 1−S N 2 duality of mechanism developed for reactions at alkyl centers, or of the addition−elimination mechanism of deacylation. , Substituent effects, which are typically described by the value of ρ from the Hammett equation, vary in both sign and magnitude, depending on substituents, leaving groups, and the reaction medium. Solvents play a variety of roles, e.g., as nucleophiles, as general bases, and by interacting with developing ionic centers.…”

mentioning

confidence: 99%

Micellar Charge Effects upon Hydrolyses of Substituted Benzoyl Chlorides. Their Relation to Mechanism

et al. 2000

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Micellar rate effects on hydrolyses of substituted benzoyl chlorides, 1, depend on headgroup charge and electron donation or withdrawal by substituents. Micellized sodium dodecyl sulfate, SDS, inhibits hydrolyses, and first-order rate constants in the micellar pseudophase, k′M, decrease, relative to those in water, k′W, over a range of ca. 10, but in cetyl trimethylammonium chloride, CTACl, k′M/k′W > 1 for hydrolyses of 1,3,5-(NO2)2 and 1, 4-NO2, and decreases steeply with electron-donating substituents in the following sequence: 1,4-Cl ≈ 4-Br > 4-H > 4-Me > 4-OMe, over a range of >10 3 . Cetyl trimethylammonium bromide and mesylate behave like CTACl. Fits to the Hammett equation give F ≈ 1 in SDS and F ≈ 4 in CTACl. Anionic micelles have higher interfacial polarities than cationic micelles, but micellar and solvent effects do not correspond because over a range of solvents, H2O to H2O-MeCN, 1:1 w/w plots of log k′W against σ go through minima with positive F for 1, 3,5-(NO2)2, and 4-NO2 and negative for the other substrates. The micellar effects correspond to differing extents of bond-making and -breaking in the transition state. Values of k + /k -(rate constants in CTACl and SDS) decrease strongly with increasing electron donation by substituents. Micellar rate effects in hydrolyses of benzyl bromide and 4-methoxybenzyl chloride are similar to those with the benzoyl chlorides. Although data were analyzed by a pseudophase treatment, application of transition state theory and reported micellar surface potentials allows estimation of local charge at the reaction center for hydrolyses of the benzoyl chlorides.There is extensive evidence on the ability of aqueous micelles and other association colloids to influence reaction rates and equilibria, and concentration, or depletion, of reactants in the interfacial region have major effects on rates of bimolecular reactions. 1 However, this region differs from water as a reaction medium, 2-4 which can affect rates of spontaneous reaction. The effects depend on the transfer of substrate from water to micelles, the reaction mechanism, and properties of the interfacial region, e.g., local charge, and polarity and water content, which are lower than in water. Spontaneous reactions that are accelerated by decreases in solvent polarity, e.g., anionic decarboxylation and dephosphorylation, are micellar-accelerated, and most spontaneous hydrolyses that are accelerated by increases in solvent polarity are micellar-inhibited. 1d,f,g,4-6 Comparisons of kinetic solvent and micellar effects on spontaneous hydrolyses provide evidence on the structures of interfacial regions, especially with regard to changes in the headgroups. This kinetic evidence complements physical evidence and that from the use of spectral, or other, probes. 2,3 The polarities of the interfacial regions can be compared with those of bulk solvents in terms of E T (30) or effective dielectric constant, which agrees with independent evidence that these regions are partially depleted in water. 3 Hydrolysis of met...

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confidence: 99%

Micellar Charge Effects upon Hydrolyses of Substituted Benzoyl Chlorides. Their Relation to Mechanism

et al. 2000

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“…This fact reflects the existence of some type of intermediate in the reaction pathway, where the tertiary amine (pyridine) catalysed the reaction due to the formation of an acylpyridinium complex which undergoes a fast aminolysis. The mechanism has been previously reported for a variety of acyl halides reactions [28][29][30].…”

Section: Factors Affecting Synthesis Of Aromatic Polyamides 597mentioning

confidence: 63%

Monomer Reactivity and Steric Factors affecting the Synthesis of Aromatic Polyamides

Muñoz

Lozano

Campa

et al. 2007

High Performance Polymers

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A series of aromatic polyamides were synthesized by activation of aromatic diamines through a newly improved synthetic method. The polymers described herein were prepared by direct polycon-densation of isophthaloyl chloride (IPC) with silylated aromatic diamines prepared in situ by addition of chloro(trimethyl)silane (CTMS). Moreover, the same polycondensation reaction was carried out in a medium containing pyridine, to investigate the effect of the base as a promoter. The reactions were studied for diamines of different reactivity to demonstrate the feasibility of this synthetic method in polycondensation reactions. An interesting behavior was observed for sterically hindered, and therefore less reactive diamine, 4,4'-methylene-bis(2,6-dimethylaniline). The two activation methods here employed afforded readily polyamides having an inherent viscosity of 2.54 dL g-1 for the most reactive diamine (1a), when CTMS was used as the activating agent, and polyamides having an inherent viscosity of 0.65 dL g-1 for the sterically hindered diamine (1e), using the pair CTMS/Py as the activating agent. The experimental work was supported by calculations of the electronic parameters of the aromatic diamines, using quantum mechanical methods (DFT). Overall, this highly efficient one-pot method provides advantages through an easy handling and simple procedure.

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“…As shown in Figure 5B, as a function of time, the intensity of ν C=O of RCOF decreased, and that of ν C=O of C 5 H 11 CO 2 H (1 722 cm −1 ) increased, probably due to the reaction with CHM and/or with adventitious water. Although it is known that acyl fluorides have lower reactivity, relative to other acyl halides, e.g., in acyl‐transfer‐,67, 68 and Friedel‐Crafts reactions,69 it is safe to assume that at least a part of the product is formed by reaction with RCOF.…”

Section: Resultsmentioning

confidence: 99%

Successful Application of an Ionic Liquid Carrying the Fluoride Counter‐ion in Biomacromolecular Chemistry: Microwave‐Assisted Acylation of Cellulose in the Presence of 1‐Allyl‐3‐methylimidazolium Fluoride/DMSO Mixtures

Casarano

Seoud

2013

Macromolecular Bioscience

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The use of ionic liquids with fluoride anion (IL-F) is challenging because of side reactions. Neat 1-allyl-3-methylimidazolium fluoride (AlMeImF) is used as a solvent in microwave-assisted acylation of cellulose. The results are disappointing due to side reactions in the IL proper, and F(-) -mediated hydrolysis of the produced ester. A dramatic improvement is observed, when AlMeImF/DMSO mixture is employed. The results are comparable to those obtained when pure 1-allyl-3-methylimidazolium chloride is employed. FTIR spectroscopy shows that dissolving a carboxylic acid anhydride in IL-F leads to the formation of acyl fluoride. Thus ILs are far from being "spectator" solvents. The new approach (use of IL-F/DMSO) is attractive because of its efficiency, low cost, and applicability to the derivatization of any polymer.

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Mechanisms of substitution at the COX group

Cited by 17 publications

References 164 publications

Micellar Charge Effects upon Hydrolyses of Substituted Benzoyl Chlorides. Their Relation to Mechanism

Micellar Charge Effects upon Hydrolyses of Substituted Benzoyl Chlorides. Their Relation to Mechanism

Monomer Reactivity and Steric Factors affecting the Synthesis of Aromatic Polyamides

Successful Application of an Ionic Liquid Carrying the Fluoride Counter‐ion in Biomacromolecular Chemistry: Microwave‐Assisted Acylation of Cellulose in the Presence of 1‐Allyl‐3‐methylimidazolium Fluoride/DMSO Mixtures

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