Kinetics and mechanism of aminolysis of phenyl acetates and phenyl trimethylacetates in dimethyl sulfoxide

Koh, Han Joong; Kim, Kyung Sik; Lee, Byung Choon; Lee, Ikchoon

doi:10.1039/p29960001353

Cited by 18 publications

(19 citation statements)

References 19 publications

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“…However, this is not necessarily true for the aminolysis of phenolic esters in polar media. 12 Our experimental data do not provide much information on the relationship between first-and second-order pathways of the reaction. We can only refer to the fact that for a less reactive ester (formate) the routes are closely competitive (Table 2).…”

mentioning

confidence: 93%

Kinetics and mechanism of aminolysis of aliphatic esters in aprotic solvents

Talvik¹,

Tuulmets²,

Vaino³

1999

J. Phys. Org. Chem.

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Kinetic studies were carried out on the aminolysis reactions of substituted aliphatic esters in a variety of aprotic solvents. The reaction rate is strongly affected by inductive and steric effects of substituents in the acyl group, rising more than 10 4 -fold from cyanoacetate to trifluoroacetate. The quantitative treatment of solvent effects revealed a rate decrease by the polarity and p-basicity of the solvents, and also an accelerating effect of the polarizability of solvents. Cyclic transition states were assumed for both the first and second-order (in amine) reactions.

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mentioning

confidence: 93%

Kinetics and mechanism of aminolysis of aliphatic esters in aprotic solvents

Talvik¹,

Tuulmets²,

Vaino³

1999

J. Phys. Org. Chem.

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“…The slope value (ρ lg ) of the Hammett plot is quite small, which is again indicative of a stepwise mechanism with rate‐limiting attack of the nucleophile 10, 19, 27, 45. Contrarily, larger ρ lg values are obtained when rate‐limiting expulsion of the leaving group is involved 46–48. Generally, for most of the reactions of acyl compounds, a low magnitude in β and ρ values have always been attributed to the rate‐limiting attack of the nucleophiles 2, 15, 49–57.…”

Section: Resultsmentioning

confidence: 96%

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Rajarathnam

Babu

Nadar

2001

Int J of Chemical Kinetics

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The ammonolysis of several substituted phenyl thiolacetates is kinetically studied in aqueous medium, 18 • C, ionic strength 0.1 M (KCl). By following the leaving groups spectrophotometrically (λ max = 260-410 nm), under excess free ammonia, pseudo-first-order rate coefficients (k obs ) are obtained. The plots of (k obs − k H ) against free ammonia concentration are linear at constant pH. The macroscopic nucleophilic substitution rate coefficients (k N ) are obtained as the slopes of these plots and found to be pH-independent for all the thiolesters. The Brönsted-type plot (log k N against pK a of leaving groups) and the Hammett plot (log k N against σ values of substituents) obtained for the title reactions of thiolesters are linear with slope values of β lg = −0.34 and ρ = 0.74 respectively. From the magnitude of these values, experimental data, the kinetic law, and the analysis of products, it is deduced that the ammonolysis of thiolesters proceeds through a simple bimolecular nucleophilic substitution pathway with a zwitterionic tetrahedral addition intermediate (T ± ), whereby its formation is rate-determining (k 1 step). Comparison of this reaction of thiolesters with a similar reaction of analogue oxyesters shows a mechanistic difference. Further, for thiolesters there is a rate enhancement with larger k N values. The change in mechanism and enhanced reactivity observed by substitution of the oxygen atom by sulphur atom on the phenyl moiety are discussed in detail.

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“…[24][25][26][27][28][29][30] The transformation of T AE in reaction products may occur by action of a second amine molecule of an external base, with formation of T À , a very reactive anionic intermediate that quickly decomposes to amide. If the T AE concentration is small and constant within time (stationary state), then the reaction rate is determined by [Equation (3)].…”

Section: Resultsmentioning

confidence: 99%

Kinetic Investigation of the Condensation Reaction of Activated Ester–Amides Containing Oligo(oxyethylene) Segments

Solaro

Talamelli

Carbonaro

et al. 2003

Macro Chemistry & Physics

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The kinetics of polycondensation of activated ester–amides, namely pentachlorophenyl α‐amino‐ω‐oligo(ethyleneglycol)succinate hydrochlorides (PSPnNH) having a degree of oligomerization n = 1–3, were investigated in solution in dichloromethane in the presence of excess triethylamine. The large extinction coefficient of the pentachlorophenate formed during the reaction allowed the use of the stopped flow technique. Experimental data resulted in agreement with the existence of concurrent first‐ and second‐order processes, attributable to the intramolecular cyclization and intermolecular polycondensation reactions, respectively. The relative incidence of the cyclization reaction decreased on increasing the monomer concentration and on decreasing the number of oxyethylene units in the monomer. These hypotheses were confirmed by SEC, TLC, FT‐IR, and NMR characterization of the reaction products. The kinetics of PSP3NH are in very good agreement with the predictions of both the collision theory and the condensation theory of linear systems at equilibrium. However, the behavior of shorter chain monomers was opposite to that of the theoretical one, demonstrating that other parameters, such as steric hindrance and solvent interactions, must be taken into proper account. The reported findings clearly evidenced that polymerization of the investigated ester‐amides must be performed in bulk in order to suppress the cyclization reaction and to obtain high‐molecular‐weight polymers.

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Kinetics and mechanism of aminolysis of phenyl acetates and phenyl trimethylacetates in dimethyl sulfoxide

Cited by 18 publications

References 19 publications

Kinetics and mechanism of aminolysis of aliphatic esters in aprotic solvents

Kinetics and mechanism of aminolysis of aliphatic esters in aprotic solvents

Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

Kinetic Investigation of the Condensation Reaction of Activated Ester–Amides Containing Oligo(oxyethylene) Segments

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