77637-90-2Relevant academic research and scientific papers
A new, mild, general and efficient route to aryl ethyl carbonates in solvent-free conditions promoted by magnesium perchlorate
Bartoli, Giuseppe,Bosco, Marcella,Carlone, Armando,Locatelli, Manuela,Marcantoni, Enrico,Melchiorre, Paolo,Palazzi, Paolo,Sambri, Letizia
, p. 4429 - 4434 (2007/10/03)
A new, general and mild method for the direct synthesis of aryl and alkyl ethyl carbonates promoted by a Lewis acid is reported. The reaction proceeds smoothly with diethyl dicarbonate in the presence of Mg(ClO4) 2, a specific activator of 1,3-dicarbonyl compounds, and shows general applicability. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.
Concerted mechanisms of the reactions of ethyl S-aryl thiocarbonates with substituted phenoxide ions
Castro,Paves,Santos
, p. 2310 - 2313 (2007/10/03)
The reactions of 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6- trinitrophenyl O-ethyl thiolcarbonates with substituted phenoxide ions are subjected to a kinetic study in water, 25.0 °C, ionic strength 0.2 M (KCl). By following the reactions spectrophotometrically, pseudo-first-order rate coefficients (k(obsd)) are found under excess of the nucleophile. Plots of k(obsd) vs phenoxide anion concentration at constant pH are linear, with the slope (k(N)) independent of pH. The Bronsted-type plots (log k(N) vs pK(a) of the phenols) are linear with slopes β = 0.92, 0.77, and 0.61 for the reactions of the 4-nitrophenyl, 2,4-dinitrophenyl, and 2,4,6-trinitrophenyl derivatives, respectively. For these reactions, a concerted mechanism is proposed since the slope values are similar to those found in the concerted phenolysis of aryl acetates; the slope magnitudes are not consistent with a stepwise mechanism where the formation of a tetrahedral intermediate is rate limiting. Our results are in line with the finding that the reactions of the 2,4-dinitrophenyl and 2,4,6-trinitrophenyl derivatives with secondary alicyclic amines in water are concerted. In contrast, the reactions of the same substrates with pyridines are stepwise, which means that substitution of a pyridine moiety in a tetrahedral intermediate with a benzenethio group by a phenoxy group destabilizes the intermediate.
Effect of Nucleophile Basicity on Intramolecular Nucleophilic Aminolysis Reactions of Carbonate Diesters
Fife, Thomas H.,Hutchins, J. E. C.
, p. 4194 - 4199 (2007/10/02)
The rates of phenol release from para-substituted phenyl 2-pyridylethyl carbonates have been measured in H2O at 25 deg C (μ 0.5 M).The pH-rate constant profiles are sigmoidal, showing participation by the pyridine neutral base species.The D2O solvent isotope effect is nearly unity, indicating that participation is by a nucleophilic reaction.The Hammett ρ value for intramolecular pyridine assisted phenol release is +2.2, and the fit is better with ?- than with ?, indicating considerable C-O bond breaking in the transition state.The effective molarity of the neighboring pyridine of p-nitrophenyl 2-pyridylethyl carbonate is 81 M in comparison with pyridine acting as a bimolecular catalyst in the hydrolysis of ethyl p-nitrophenyl carbonate.Intramolecular nucleophilic attack is 217 times more favorable when a five-membered ring is formed with phenyl 2-pyridylmethyl carbonate than in the case of phenyl 2-pyridylethyl carbonate where the reaction proceeds via a six-membered ring.The effective molarity of neighboring pyridine in the 2-pyridylmethyl series is 2x103 M.Sigmoidal pH-rate constant profiles were also obtained with neighboring imidazole, N,N-dimethylamino, and N-methylpiperidine nucleophiles.Values of the limiting rate constants (kB) are similar in spite of pKapp values which vary from 3.9 to 10.The effective molarity of the dimethylamino group of p-nitrophenyl N,N-dimethylaminopropyl carbonate is only 32 M in comparison to reaction of triethylamine with ethyl p-nitrophenyl carbonate.On the other hand, the effective molarity of the dimethylamino group of p-nitrophenyl o-(N,N-dimethylamino)phenyl carbonate (pKapp=3.9) is > 105 M.The most efficient intramolecular nucleophiles in reactions of p-nitrophenyl carbonate diesters are those of low pKa.In contrast, with analogous carboxylate esters the converse is the case, even though the rate constants for bimolecular aminolysuis of p-nitrophenyl acetate and ethyl p-nitrophenyl carbonate are closely similar.These results may indicate that C-N bond formation is not complete in the transition states of the intramolecular reactions.
