Influence of pH of an aqueous-organic solvent on the kinetics of N-acylation of α-amino acids with benzoic acid esters

Kuritsyn, L. V.; Sadovnikov, A. I.; Khripkova, L. N.; Калинина, Н. В.; Shcherbakova, Yu. S.

doi:10.1134/s1070363206010105

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“…Analogous sequence is observed in the reactions of esters with α-amino acids [8][9][10][11]. Reactivity of mononitro derivatives is significantly lower than that of dinitro ones.…”

Section: Kuritsyn Et Al 886mentioning

confidence: 84%

“…Kinetic studies of acylation of aliphatic amines and α-amino acids with non-substituted phenyl benzoates in water-organic media carried out under different c + /c a ratio [8][9][10][11] persuaded us that hydrolysis may be completely suppressed only under the condition of c + /c a ≥ 4. That is why in the kinetic experiments the above-mentioned ratio was maintained equal to 4.…”

Section: Kuritsyn Et Al 886mentioning

confidence: 99%

“…Specific feature of aminolysis of esters in water-containing media is the possibility of parallel proceeding of hydrolysis. The most important factor affecting the rate of aminolysis and hydrolysis is the pH of medium [8][9][10][11]. Note that adequate attention to the consideration of these factors rather scarce [6,7].…”

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confidence: 99%

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Kinetics of acylation of cyclohexylamine with substituted phenyl benzoates

et al. 2012

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Kinetics of acylation of cyclohexylamine with nitro-substituted phenyl benzoates is studied in water solutions of 2-propanol and dioxane. By means of RHF/6-31G* method quantum-chemical simulation of ester molecules and of cyclohexylamine solvatocomplexes was carried out. On the basis of correlation of rate constants and LUMO energies of esters and population of 2p z -orbitals of carbon atom of the acyl group a conclusion on the orbital control of the reactions was made.An interest to the products of acylation of amines is caused by their wide use as polymers, dyes, surfactants, biologically active compounds, and drugs of wide spectrum of action. Optimization of conditions of the industrial synthesis of these substances requires performing kinetic studies and establishing quantitative dependences of rate constants of the abovementioned processes on the structure of reagents and the effect of medium. In the series of studies kinetics is explored and the mechanisms are established of the reactions of aromatic and aliphatic amines with different acylating agents, among them with the carboxylic acid esters in the aprotic non-polar media. Kinetic data on the aminolysis of esters in water and some water-organic solvents are also mentioned [1][2][3][4][5][6][7].In the course of years we study the acyl transfer reactions with the participation of different amines (aromatic, aliphatic including α-amino acids, and mixed). Aroyl and sulfonyl chlorides and also phenyl carboxylates were used as acylating agents. Specific feature of aminolysis of esters in water-containing media is the possibility of parallel proceeding of hydrolysis. The most important factor affecting the rate of aminolysis and hydrolysis is the pH of medium [8][9][10][11]. Note that adequate attention to the consideration of these factors rather scarce [6,7]. We have developed procedures permitting strict accounting for the effect of pH and hydrolysis of acylating agents while calculation of acylation rate constants. Together with these studies quantum-chemical simulation of the reaction mechanisms and state of reagents in solution [12] was carried out. The aim of these studies is the investigation of structure of acylating agents like 2-,3-, and 4-nitrophenyl I-III; 2,4-, 2,5-, and 2,6-dinitrophenyl IV-VI, and 2,4,6-trinitrophenyl VII benzoates on the kinetics of their reaction with cyclohexyl amine. Binary mixtures of water (molar fraction 0.73) with 2-propanol (i-PrOH) and dioxane (Diox) were used as solvents.Reaction of cyclohexylamine with esters under the conditions of kinetic experiments (pH 8.8) proceeds according to Eqs. (1)-(4) where R 1 is mono-, di-or trinitrosubstituted phenyl, k ac , k(H 2 O), and k OH -are rate constants of the processes (1)-(3). fast According to the Eqs. (1)-(4) the rate of change in the concentration of ester (c es ) in the kinetic experiment is described by Eqs. (5), (6).-(dc ef )/(dτ) = k ac с а с ef + k(H 2 O)c(H 2 O)c ef + k OH -с OH -с ef = k obs c ef ,k obs = k ac с а + k(H 2 O)c(H 2 O) + k OH -c OH -.

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“…Analogous sequence is observed in the reactions of esters with α-amino acids [8][9][10][11]. Reactivity of mononitro derivatives is significantly lower than that of dinitro ones.…”

Section: Kuritsyn Et Al 886mentioning

confidence: 84%

Section: Kuritsyn Et Al 886mentioning

confidence: 99%